rumdl_lib/rules/

md077_list_continuation_indent.rs

//!
//! Rule MD077: List continuation content indentation
//!
//! See [docs/md077.md](../../docs/md077.md) for full documentation, configuration, and examples.

use std::ops::ControlFlow;

use serde::{Deserialize, Serialize};

use crate::lint_context::{LineInfo, LintContext};
use crate::rule::{Fix, LintError, LintResult, LintWarning, Rule, RuleCategory, Severity};

mod md077_config;
use md077_config::MD077Config;

/// How strictly MD077 enforces continuation-line indentation.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default, Serialize, Deserialize)]
#[serde(rename_all = "kebab-case")]
pub enum ContinuationStyle {
    /// Permit any continuation indent in `[0, content_column]` (CommonMark lazy
    /// continuation). Only over-indentation and content that escapes the list
    /// after a blank line are flagged.
    #[default]
    Any,
    /// Require every continuation line to align to the item's content column.
    /// Tight under-indented lazy continuation (which `any` permits) is also
    /// flagged and snapped up to the content column.
    Aligned,
}

/// Rule MD077: List continuation content indentation
///
/// In both tight continuation (no blank line) and loose continuation (after a
/// blank line), content must not be **over-indented** beyond the item's content
/// column. Additionally, in loose continuation content must not be
/// **under-indented** below the content column (W+N rule), or it falls out of the
/// list; tight under-indent is valid CommonMark lazy continuation and is left
/// alone. Content indented to the content column + 4 or more is an indented code
/// block, not continuation, and is not flagged.
///
/// Under the MkDocs flavor, a minimum of 4 spaces is enforced for ordered list
/// items to satisfy Python-Markdown.
///
/// With `style = "aligned"`, tight under-indented continuation is additionally
/// flagged and aligned to the content column (mdformat parity).
#[derive(Clone, Default)]
pub struct MD077ListContinuationIndent {
    config: MD077Config,
}

impl MD077ListContinuationIndent {
    /// Construct the rule with an explicit continuation style. `Default`
    /// (`ContinuationStyle::Any`) preserves the historical behavior.
    pub fn new(style: ContinuationStyle) -> Self {
        Self {
            config: MD077Config { style, indent: None },
        }
    }

    pub fn from_config_struct(config: MD077Config) -> Self {
        Self { config }
    }
}

impl MD077ListContinuationIndent {
    /// Width of a GFM task checkbox prefix including its trailing space:
    /// `[ ] `, `[x] `, or `[X] ` — always exactly 4 bytes.
    const TASK_CHECKBOX_PREFIX_LEN: usize = 4;

    /// Returns true if the item line starts a GFM task list item, i.e. its
    /// content column begins with `[ ] `, `[x] `, or `[X] `. The trailing
    /// space is part of the match — `- [ ]` with no body is an empty list
    /// item, not a task.
    ///
    /// Task items have a second, conventionally-accepted continuation column
    /// at `content_col + 4` (aligned after the checkbox). MD013 reflow
    /// produces this column for wrapped task lines, so MD077 has to accept
    /// it to avoid a fix loop with MD013.
    ///
    /// `content_col` is a byte offset into `line`, not a visual column. The
    /// CommonMark list parser produces byte-offset content columns, and the
    /// checkbox prefix `[ ] ` is pure ASCII, so this byte-level comparison
    /// is correct. Leading indent mixing tabs and spaces is irrelevant here
    /// because `content_col` already points past any leading whitespace.
    fn is_task_list_item(line: &str, content_col: usize) -> bool {
        line.as_bytes()
            .get(content_col..content_col + Self::TASK_CHECKBOX_PREFIX_LEN)
            .is_some_and(|window| matches!(window, b"[ ] " | b"[x] " | b"[X] "))
    }

    /// Check if a trimmed line is a block-level construct (not list continuation).
    fn is_block_level_construct(trimmed: &str) -> bool {
        // Footnote definition: [^label]:
        if trimmed.starts_with("[^") && trimmed.contains("]:") {
            return true;
        }
        // Abbreviation definition: *[text]:
        if trimmed.starts_with("*[") && trimmed.contains("]:") {
            return true;
        }
        // Reference link definition: [label]: url
        // Must start with [ but not be a regular link, footnote, or abbreviation
        if trimmed.starts_with('[') && !trimmed.starts_with("[^") && trimmed.contains("]: ") {
            return true;
        }
        false
    }

    /// Check if a trimmed line is a fenced code block delimiter (opener or closer).
    fn is_code_fence(trimmed: &str) -> bool {
        let bytes = trimmed.as_bytes();
        if bytes.len() < 3 {
            return false;
        }
        let ch = bytes[0];
        (ch == b'`' || ch == b'~') && bytes[1] == ch && bytes[2] == ch
    }

    /// Check if a trimmed line starts with a list marker (*, -, +, or ordered).
    /// Used to avoid flagging deeply indented list items that the parser doesn't
    /// recognize as list items (e.g., with indent=8 configured in MD007).
    fn starts_with_list_marker(trimmed: &str) -> bool {
        let bytes = trimmed.as_bytes();
        match bytes.first() {
            Some(b'*' | b'-' | b'+') => bytes.get(1).is_some_and(|&b| b == b' ' || b == b'\t'),
            Some(b'0'..=b'9') => {
                let rest = trimmed.trim_start_matches(|c: char| c.is_ascii_digit());
                rest.starts_with(". ") || rest.starts_with(") ")
            }
            _ => false,
        }
    }

    /// Given the line number of a fenced code block opener, walk forward and
    /// return the line number of the matching closer. Returns the opener itself
    /// if no following line is in the code block (degenerate single-line block).
    fn find_fence_closer(ctx: &LintContext, opener_line: usize) -> usize {
        let mut closer_line = opener_line;
        for peek in (opener_line + 1)..=ctx.lines.len() {
            let Some(peek_info) = ctx.line_info(peek) else { break };
            if peek_info.in_code_block {
                closer_line = peek;
            } else {
                break;
            }
        }
        closer_line
    }

    /// Build an atomic fix that reindents a fenced code block from its opener
    /// through its matching closer.
    ///
    /// - **Opener and closer** are moved to `required` (the list item's
    ///   content column, which is what MD077 actually flagged).
    /// - **Interior lines** are *promoted* to `required` only if they sit
    ///   below it; interior content at or above `required` is left at its
    ///   original column. This preserves authored interior indentation when
    ///   possible while guaranteeing fence pairing: every non-blank line in
    ///   the block ends at column ≥ `required`, so the block stays inside
    ///   the list item's scope after the fix.
    ///
    /// Only used for the under-indent direction (`required > opener_actual`);
    /// over-indented fences are intentionally left untouched (see the
    /// over-indent pass in `check`), so there is no down-shift case to handle.
    ///
    /// Why a compound fix rather than three independent fixes? MD077 and
    /// MD031 run in the same iterative fix loop. If we only moved the
    /// delimiters, an intermediate state would have mismatched
    /// opener/closer indentation and MD031 would misread the block as
    /// unpaired, injecting stray blank lines (issue #574).
    ///
    /// Why `max(interior, required)` instead of `interior + delta`? The
    /// delta-shift version was not idempotent: if interior started below
    /// the list scope (e.g., col 0 under an opener at col 2 that needs to
    /// move to col 3), delta-shift landed interior at col 1 — still below
    /// the list scope — and the next MD077 pass would re-flag it
    /// individually and snap it to `required`. The promote-up rule reaches
    /// that end state in a single pass.
    ///
    /// Leading tabs are normalized to spaces: CommonMark expands a tab to
    /// the next column that's a multiple of 4, so simply prepending spaces
    /// before a tab would let the tab snap back and cancel the shift. We
    /// replace the whole leading-whitespace byte range with spaces.
    fn build_compound_fence_fix(
        ctx: &LintContext,
        opener_line: usize,
        closer_line: usize,
        opener_actual: usize,
        required: usize,
    ) -> Option<Fix> {
        if required <= opener_actual {
            return None;
        }
        let opener_info = ctx.line_info(opener_line)?;
        let closer_info = ctx.line_info(closer_line)?;

        let fix_start = opener_info.byte_offset;
        let fix_end = closer_info.byte_offset + closer_info.byte_len;

        let mut replacement = String::new();
        for i in opener_line..=closer_line {
            let info = ctx.line_info(i)?;
            if i > opener_line {
                replacement.push('\n');
            }
            let line = info.content(ctx.content);
            if info.is_blank {
                // Blank lines have no content to shift; preserve verbatim.
                replacement.push_str(line);
            } else {
                let new_visual = if i == opener_line || i == closer_line {
                    required
                } else {
                    info.visual_indent.max(required)
                };
                for _ in 0..new_visual {
                    replacement.push(' ');
                }
                replacement.push_str(&line[info.indent..]);
            }
        }

        Some(Fix::new(fix_start..fix_end, replacement))
    }

    /// Walk the continuation lines owned by a single list item, invoking
    /// `per_line` for each *in-scope, non-blank, non-nested, non-skipped*
    /// line with its pre-computed visual column and loose/tight state.
    ///
    /// This is the **single source of truth** for MD077's item-scope
    /// traversal: both the sibling-column pre-pass and the main check loop
    /// route through this method so their termination semantics cannot
    /// drift. The callback sees only lines the rule actually needs to
    /// reason about; it can return `ControlFlow::Break` for early exit.
    ///
    /// Termination conditions (applied before the callback fires):
    /// - Headings and horizontal rules end the item unconditionally.
    /// - After a blank line, content at or below the marker column has
    ///   escaped the item; further lines are not delivered.
    ///
    /// Skipped silently (do not fire the callback):
    /// - Blank lines (toggle `saw_blank`).
    /// - Nested list items (reset `saw_blank`, track their content column).
    /// - Lines inside any still-open nested item's scope: the walk keeps a
    ///   stack of open nested (marker, content) columns, so a continuation
    ///   of a middle nesting level defers to that level's own walk instead
    ///   of being claimed by a shallower ancestor.
    /// - Reference/footnote/abbreviation definitions and similar block
    ///   constructs that aren't list continuation.
    /// - Lines that `should_skip_line` rejects (code-block interior etc.).
    fn walk_item_continuation<F>(
        ctx: &LintContext,
        item_line: usize,
        range_end: usize,
        marker_col: usize,
        mut per_line: F,
    ) where
        F: FnMut(&ContinuationLine<'_>) -> ControlFlow<()>,
    {
        let mut saw_blank = false;
        let mut saw_nested = false;
        // Stack of open nested items as (marker_column, content_column),
        // outermost first. A single scalar is not enough: with 3+ levels a
        // continuation of a middle level sits below the innermost content
        // column but at-or-past its own level's, and must still be skipped
        // here so the owning level's walk evaluates it.
        let mut nested_stack: Vec<(usize, usize)> = Vec::new();

        for line_num in (item_line + 1)..=range_end {
            let Some(info) = ctx.line_info(line_num) else {
                continue;
            };

            let trimmed = info.content(ctx.content).trim_start();

            if Self::should_skip_line(info, trimmed) {
                continue;
            }

            if info.is_blank {
                saw_blank = true;
                continue;
            }

            if let Some(ref li) = info.list_item {
                if li.marker_column > marker_col {
                    // A sibling-or-shallower marker closes every nested item at
                    // or past its column before this one opens.
                    while nested_stack.last().is_some_and(|&(m, _)| m >= li.marker_column) {
                        nested_stack.pop();
                    }
                    nested_stack.push((li.marker_column, li.content_column));
                    // Sticky: once a nested child appears, every later line is a
                    // (lazy) continuation of the deeper item, which owns it under
                    // CommonMark. Ancestors must defer so the deepest item claims
                    // and aligns it.
                    saw_nested = true;
                } else {
                    nested_stack.clear();
                }
                saw_blank = false;
                continue;
            }

            if info.heading.is_some() || info.is_horizontal_rule {
                break;
            }

            if Self::is_block_level_construct(trimmed) {
                continue;
            }

            let col = info.visual_indent;

            // The line escapes every nested item whose content column it sits
            // below; if any nested item stays open, the line is that item's
            // continuation and its own walk owns the judgement.
            while nested_stack.last().is_some_and(|&(_, c)| c > col) {
                nested_stack.pop();
            }
            if !nested_stack.is_empty() {
                continue;
            }

            if saw_blank && col <= marker_col {
                break;
            }

            let line = ContinuationLine {
                line_num,
                info,
                trimmed,
                actual: col,
                saw_blank,
                saw_nested,
            };
            if per_line(&line).is_break() {
                break;
            }
        }
    }

    /// Whether the item's owned continuation range holds a *latent* structural
    /// construct: a list marker or table line the parser has not yet promoted to
    /// its own block, but would once an earlier continuation line is reindented.
    /// Such a promotion re-attributes the following lines to a different block
    /// (different content column) and breaks single-pass idempotency, so the
    /// caller skips the whole item when this returns true.
    ///
    /// A setext underline counts too: as a lazy continuation the parser reads a
    /// `=`/`-` run as paragraph text, but reindenting the prose line above it
    /// into the item turns the pair into a heading.
    ///
    /// Unlike [`walk_item_continuation`], this scans the full owned range and
    /// does NOT stop at a heading or horizontal rule. A heading partway through
    /// the continuation can itself be parse-unstable: an empty backtick run, for
    /// instance, is read as a setext heading, and reindenting an earlier line
    /// dissolves it and promotes a list marker that sits past it. Stopping at the
    /// heading would hide that marker from this check and let the reindent break
    /// idempotency. Lines already parsed as list items are real nested children,
    /// not latent, and are handled by the walk's `saw_nested` logic instead.
    fn item_range_has_latent_structure(ctx: &LintContext, item_line: usize, range_end: usize) -> bool {
        (item_line + 1..=range_end).any(|line_num| {
            ctx.line_info(line_num).is_some_and(|info| {
                if info.is_blank || info.list_item.is_some() {
                    return false;
                }
                let trimmed = info.content(ctx.content).trim_start();
                !Self::should_skip_line(info, trimmed)
                    && (Self::starts_with_list_marker(trimmed)
                        || crate::utils::skip_context::is_table_line(trimmed)
                        || Self::is_latent_setext_underline(ctx, line_num, trimmed))
            })
        })
    }

    /// Whether reindenting the line above this one would turn the pair into a
    /// setext heading. An underline that is a lazy continuation is paragraph
    /// text, so the parser reports no heading and the walk runs straight past it.
    ///
    /// Only paragraph text can become the heading's text line, so an underline
    /// under an ATX heading, a thematic break or another underline is latent
    /// nothing and must not hold the whole item back. The line above has to pass
    /// both readings: `is_paragraph_context` speaks for the block it sits in,
    /// which is what tells a closing code fence from the prose it looks like,
    /// and the text predicate speaks for the line's own markers, which is what
    /// tells an empty list item from the text it holds none of. A blank line
    /// needs no test of its own: blank means it holds nothing once its markers
    /// are stripped, which is the first thing the text predicate rejects.
    fn is_latent_setext_underline(ctx: &LintContext, line_num: usize, trimmed: &str) -> bool {
        crate::lint_context::is_setext_underline_content(trimmed)
            && ctx.line_info(line_num - 1).is_some_and(|prev| {
                prev.is_paragraph_context() && crate::lint_context::is_paragraph_text_line(prev.content(ctx.content))
            })
    }

    /// Scan an item's owned range and report whether any *other* continuation
    /// line in the item uses the content column or the post-checkbox column.
    ///
    /// Used exclusively for tie-breaking the auto-fix target when an
    /// over-indented line is exactly equidistant from `content_col` and
    /// `task_col`. In that case the author's intent is ambiguous, so we
    /// snap to whichever valid column *they're already using* elsewhere in
    /// the same item. When neither or both columns are in use, the caller
    /// falls back to a canonical default.
    fn sibling_column_usage(
        ctx: &LintContext,
        item_line: usize,
        range_end: usize,
        marker_col: usize,
        content_col: usize,
        task_col: usize,
    ) -> (bool, bool) {
        let mut uses_content = false;
        let mut uses_task = false;

        Self::walk_item_continuation(ctx, item_line, range_end, marker_col, |line| {
            if line.actual == content_col {
                uses_content = true;
            }
            if line.actual == task_col {
                uses_task = true;
            }
            if uses_content && uses_task {
                ControlFlow::Break(())
            } else {
                ControlFlow::Continue(())
            }
        });

        (uses_content, uses_task)
    }

    /// Compute the auto-fix target for an over-indented continuation line.
    /// Snaps to the nearer of the two valid columns (content_col / task_col)
    /// for task items, and on an exact tie uses sibling-column context to
    /// pick whichever column the author is already using elsewhere in this
    /// item. Non-task items always snap to `required`.
    fn compute_fix_target(
        actual: usize,
        required: usize,
        task_col: Option<usize>,
        uses_content_col: bool,
        uses_task_col: bool,
    ) -> usize {
        let Some(t) = task_col else { return required };
        match actual.abs_diff(t).cmp(&actual.abs_diff(required)) {
            std::cmp::Ordering::Less => t,
            std::cmp::Ordering::Greater => required,
            std::cmp::Ordering::Equal => match (uses_task_col, uses_content_col) {
                (true, false) => t,
                _ => required,
            },
        }
    }

    /// Check if a line should be skipped (inside code, HTML, frontmatter, etc.)
    ///
    /// Code block *content* is skipped, but fence opener/closer lines are not —
    /// their indentation matters for list continuation in MkDocs.
    ///
    /// Footnote-definition lines (the `[^id]:` line and its indented body) are
    /// skipped too: a footnote body that follows a list is its own block, not
    /// list continuation, so its indentation is MD068's concern, not MD077's.
    /// Treating it as continuation produced false over-indent warnings and a
    /// damaging auto-fix that reindented the body and then tripped MD068.
    fn should_skip_line(info: &crate::lint_context::LineInfo, trimmed: &str) -> bool {
        if info.in_code_block && !Self::is_code_fence(trimmed) {
            return true;
        }
        info.in_front_matter
            || info.in_footnote_definition
            || info.in_html_block
            || info.in_html_comment
            || info.in_mdx_comment
            || info.in_mkdocstrings
            || info.in_esm_block
            || info.in_math_block
            || info.in_admonition
            || info.in_content_tab
            || info.in_pymdown_block
            || info.in_definition_list
            || info.in_mkdocs_html_markdown
            || info.in_kramdown_extension_block
    }

    /// Build the warning for an over-indented continuation line. The fix is a
    /// single-line rewrite of the leading whitespace to `fix_target`.
    ///
    /// The over-indent pass never delivers fenced-code lines here (it skips
    /// anything `in_code_block`), so this builder does not need the compound
    /// fence handling that `build_under_indent_warning` uses: moving an
    /// over-indented fence's delimiters without its body would corrupt the code
    /// content, so over-indented fenced blocks are deliberately left as-is.
    fn build_over_indent_warning(
        ctx: &LintContext,
        line: &ContinuationLine<'_>,
        fix_target: usize,
        message: String,
    ) -> LintWarning {
        let line_content = line.info.content(ctx.content);
        let fix_start = line.info.byte_offset;
        let fix_end = fix_start + line.info.indent;
        LintWarning {
            rule_name: Some("MD077".to_string()),
            line: line.line_num,
            column: 1,
            end_line: line.line_num,
            end_column: line_content.chars().count() + 1,
            message,
            severity: Severity::Warning,
            fix: Some(Fix::new(fix_start..fix_end, " ".repeat(fix_target))),
        }
    }

    /// Build the warning for a loose-mode under-indented continuation line.
    /// When the line is the opener of a fenced code block, emit a compound
    /// fix that reindents opener + interior + closer atomically so MD031
    /// doesn't see a transiently-broken fence pair (see #574).
    ///
    /// Returns the warning plus, when the fix is compound, the closer
    /// line number so the caller can mark it flagged (preventing the
    /// main loop from double-flagging the closer as its own under-indent
    /// case). Keeping the "also flag this line" signal out of band keeps
    /// this function pure — it reads from `ctx` only and returns a
    /// plain value.
    fn build_under_indent_warning(
        ctx: &LintContext,
        line: &ContinuationLine<'_>,
        required: usize,
        message: String,
    ) -> UnderIndentOutcome {
        let line_content = line.info.content(ctx.content);
        let is_fence_opener = line.info.in_code_block
            && Self::is_code_fence(line.trimmed)
            && ctx.line_info(line.line_num - 1).is_none_or(|p| !p.in_code_block);

        let (fix, warn_end_line, warn_end_column, compound_closer) = if is_fence_opener {
            let closer_line = Self::find_fence_closer(ctx, line.line_num);
            let fix = Self::build_compound_fence_fix(ctx, line.line_num, closer_line, line.actual, required);
            let end_column = ctx
                .line_info(closer_line)
                .map_or(line_content.chars().count() + 1, |ci| {
                    ci.content(ctx.content).chars().count() + 1
                });
            let extra_flag = (closer_line != line.line_num).then_some(closer_line);
            (fix, closer_line, end_column, extra_flag)
        } else {
            let fix_start = line.info.byte_offset;
            let fix_end = fix_start + line.info.indent;
            let fix = Some(Fix::new(fix_start..fix_end, " ".repeat(required)));
            (fix, line.line_num, line_content.chars().count() + 1, None)
        };

        UnderIndentOutcome {
            warning: LintWarning {
                rule_name: Some("MD077".to_string()),
                line: line.line_num,
                column: 1,
                end_line: warn_end_line,
                end_column: warn_end_column,
                message,
                severity: Severity::Warning,
                fix,
            },
            also_flag_line: compound_closer,
        }
    }
}

/// A continuation line yielded by `walk_item_continuation`. Bundles the
/// per-line facts both checker branches need so helper functions don't
/// balloon their argument lists.
struct ContinuationLine<'a> {
    line_num: usize,
    info: &'a LineInfo,
    trimmed: &'a str,
    actual: usize,
    saw_blank: bool,
    /// True once a nested child item has appeared earlier in this item's scope.
    /// Subsequent lines are lazy continuation of the deeper item (which owns
    /// them under CommonMark), so an ancestor must not claim them.
    saw_nested: bool,
}

/// Result of `build_under_indent_warning`. Carries both the warning and,
/// when the fix is compound (fence opener → promote-to-required over the
/// whole block), the closer line so the caller can record it as already
/// handled. This keeps the warning builder free of external mutation.
struct UnderIndentOutcome {
    warning: LintWarning,
    also_flag_line: Option<usize>,
}

impl Rule for MD077ListContinuationIndent {
    fn name(&self) -> &'static str {
        "MD077"
    }

    fn description(&self) -> &'static str {
        "List continuation content indentation"
    }

    fn check(&self, ctx: &LintContext) -> LintResult {
        if ctx.content.is_empty() {
            return Ok(Vec::new());
        }

        let strict_indent = ctx.flavor.requires_strict_list_indent();
        let total_lines = ctx.lines.len();
        let mut warnings = Vec::new();
        let mut flagged_lines = std::collections::HashSet::new();

        // Collect all list item lines sorted, with their content_column,
        // marker_column, and — if the item is a GFM task — its post-checkbox
        // column. Precomputing task_col here (instead of re-reading line_info
        // inside the hot inner loop) keeps the per-item cost O(1).
        //
        // We need the owned range to extend past block.end_line because the
        // parser excludes under-indented continuation from the block, and
        // MD077 specifically has to evaluate those escaped lines.
        let mut items: Vec<(usize, usize, usize, Option<usize>)> = Vec::new();
        for block in &ctx.list_blocks {
            for &item_line in &block.item_lines {
                if let Some(info) = ctx.line_info(item_line)
                    && let Some(ref li) = info.list_item
                {
                    // Lists inside blockquotes are out of scope for MD077. Their
                    // content column is measured on the raw line, so it is
                    // meaningless for a lazy continuation sitting outside the
                    // quote: scoping them lets two items with different content
                    // columns each claim such a line and reindent it the other
                    // way on alternating passes.
                    if info.blockquote.is_some() {
                        continue;
                    }
                    let line = info.content(ctx.content);
                    let task_col = Self::is_task_list_item(line, li.content_column)
                        .then_some(li.content_column + Self::TASK_CHECKBOX_PREFIX_LEN);
                    items.push((item_line, li.marker_column, li.content_column, task_col));
                }
            }
        }
        items.sort_unstable();
        items.dedup_by_key(|&mut (ln, _, _, _)| ln);

        // Precompute each item's owned-range end. The range ends at the line
        // before the next item whose marker column is <= this item's (its next
        // sibling or an ancestor), or the last line if none follows.
        //
        // The direct "scan forward for the next marker_col <= mine" is O(n^2) on
        // a monotonically deepening list, where no later item ever qualifies so
        // every item scans to the end. A monotonic stack (nearest
        // smaller-or-equal marker column to the right) computes all range ends in
        // one linear pass. Walking right-to-left, pop every stacked item whose
        // marker column is strictly greater than the current one (they can never
        // be the sibling/ancestor of anything further left that is <= current),
        // leaving the nearest qualifying item on top.
        let mut range_ends = vec![total_lines; items.len()];
        let mut stack: Vec<usize> = Vec::new();
        for i in (0..items.len()).rev() {
            let marker_col = items[i].1;
            while let Some(&top) = stack.last() {
                if items[top].1 > marker_col {
                    stack.pop();
                } else {
                    break;
                }
            }
            range_ends[i] = stack.last().map_or(total_lines, |&j| items[j].0 - 1);
            stack.push(i);
        }

        // Precompute each item's required indent and owned line range so both
        // passes below scope identically.
        let scoped: Vec<(usize, usize, usize, Option<usize>, usize, usize)> = items
            .iter()
            .enumerate()
            .map(|(item_idx, &(item_line, marker_col, content_col, task_col))| {
                // A configured indent replaces the content column, but under a
                // flavor that requires strict list indentation it may only raise
                // the 4-space minimum. That minimum is a compatibility floor
                // rather than a style default: below it the renderer stops
                // treating the line as continuation, so honoring a smaller
                // configured value would make `fix` rewrite documents into a
                // form the flavor's renderer no longer reads as part of the item.
                let required = match self.config.indent {
                    Some(indent) if strict_indent => (marker_col + indent).max(4),
                    Some(indent) => marker_col + indent,
                    None if strict_indent => content_col.max(4),
                    None => content_col,
                };
                (
                    item_line,
                    marker_col,
                    content_col,
                    task_col,
                    required,
                    range_ends[item_idx],
                )
            })
            .collect();

        // Precompute which lines can ever reach the per-line continuation
        // callback. `walk_item_continuation` unconditionally skips (regardless of
        // which item owns the line) blank lines, list-item lines, headings,
        // horizontal rules, `should_skip_line` lines, and block-level constructs;
        // only the lines that survive all of those can be flagged. An item whose
        // owned range contains none of them produces no warning, so both passes
        // can skip it without walking the range at all.
        //
        // This keeps a document of purely deeply-nested list items linear: such a
        // document has no continuation prose, so every item skips its walk
        // instead of re-scanning the whole tail (which was O(n^2) in the item
        // count). Documents that do have continuation prose are unaffected - the
        // guard only ever skips items that could not have produced a warning.
        let prose_candidate_lines: Vec<usize> = (1..=total_lines)
            .filter(|&line_num| {
                let Some(info) = ctx.line_info(line_num) else {
                    return false;
                };
                let trimmed = info.content(ctx.content).trim_start();
                !Self::should_skip_line(info, trimmed)
                    && !info.is_blank
                    && info.list_item.is_none()
                    && info.heading.is_none()
                    && !info.is_horizontal_rule
                    && !Self::is_block_level_construct(trimmed)
            })
            .collect();
        // True when a continuation candidate falls in `(after_line, range_end]`,
        // i.e. the half-open range `walk_item_continuation` actually visits.
        let range_has_prose_candidate = |after_line: usize, range_end: usize| -> bool {
            let start = prose_candidate_lines.partition_point(|&l| l <= after_line);
            prose_candidate_lines.get(start).is_some_and(|&l| l <= range_end)
        };

        // Pass 1 - under-indented continuation.
        //
        // Loose under-indent (after a blank line) sits below the content column
        // and would escape the list item; it is always flagged. Tight
        // under-indent is valid CommonMark lazy continuation, so it is left
        // alone under `style = "any"`.
        //
        // Under `style = "aligned"`, tight under-indent is additionally flagged
        // and snapped up to the content column. MD077 scopes past the parser's
        // block end (to catch escaped loose content), and the parser absorbs
        // col-0 blockquotes, fences, and tables that sit tight under a list item
        // as lazy continuation. Reindenting those would change the rendered
        // structure, so the tight-aligned branch guards two ways: it skips lines
        // the parser classified in place (code, blockquote - see
        // `confirmed_structure`), and it bails on an item whose continuation
        // holds a construct the parser would re-parse once indentation changes
        // (a latent list marker, table or setext underline - see
        // `has_latent_structure`). Headings and horizontal rules already
        // terminate the walk; reference/footnote/abbreviation definitions are
        // skipped inside it. Erring toward skipping yields false negatives
        // (safe) rather than structural false positives.
        //
        // This pass runs first so that a deeply nested item claims an ambiguous
        // line - one that is under-indented for it yet over-indented for a
        // shallower ancestor - before pass 2 can mis-attribute it to the
        // ancestor as an over-indent and snap it the wrong way.
        let aligned = self.config.style == ContinuationStyle::Aligned;
        for &(item_line, marker_col, _content_col, _task_col, required, range_end) in &scoped {
            // No continuation candidate in this item's range: it cannot produce a
            // warning, so skip the walk (and the latent-structure scan) entirely.
            if !range_has_prose_candidate(item_line, range_end) {
                continue;
            }
            // "Latent structure": a line in this item's continuation that the
            // parser has NOT yet promoted to a list item or table, but that
            // would be once an earlier continuation line is reindented. Such a
            // promotion re-attributes the following lines to a different block
            // (different content column) and breaks single-pass idempotency, so
            // reindenting anything in the item is unsafe and the whole item is
            // skipped. This is a *prediction* of how the parser would re-parse
            // after a fix, which is why it stays a heuristic (markers, tables and
            // setext underlines are the constructs the parser absorbs as lazy
            // continuation rather than flagging on the line itself; code and
            // blockquotes are classified in place and handled per line below).
            // Well-formed prose continuation matches none, so this only bails
            // on pathological input (a safe false negative). Real nested items
            // never reach the callback (the walk handles them via `saw_nested`).
            let has_latent_structure = aligned && Self::item_range_has_latent_structure(ctx, item_line, range_end);
            // Which setting produced `required` decides what the message may
            // claim. The content column carries a structural consequence (below
            // it the content leaves the item) and the strict-flavor minimum
            // carries a renderer requirement, but a configured indent above
            // both is a house style, so it is reported as one.
            let from_configured_indent = self.config.indent.is_some_and(|indent| marker_col + indent == required);
            Self::walk_item_continuation(ctx, item_line, range_end, marker_col, |line| {
                let actual = line.actual;
                let under_indented = actual < required;
                let loose_escape = line.saw_blank && under_indented;
                // Don't reindent a line the parser classified in place as a code
                // block (fenced or indented) or a blockquote: these are read
                // straight from its per-line output, so the rule cannot drift
                // from how rumdl parses the document. Headings and horizontal
                // rules terminate the walk before the callback; latent list
                // markers and tables are handled by `has_latent_structure`.
                let confirmed_structure = line.info.in_code_block || line.info.blockquote.is_some();
                let aligned_tight = aligned
                    && !has_latent_structure
                    && !line.saw_blank
                    && !line.saw_nested
                    && under_indented
                    && !confirmed_structure;
                if (loose_escape || aligned_tight) && flagged_lines.insert(line.line_num) {
                    let message = if line.saw_blank {
                        if from_configured_indent {
                            format!(
                                "Content after blank line in list item needs {required} spaces of \
                                 indentation to match the configured indent (found {actual})",
                            )
                        } else if strict_indent {
                            format!(
                                "Content inside list item needs {required} spaces of indentation \
                                 for MkDocs compatibility (found {actual})",
                            )
                        } else {
                            format!(
                                "Content after blank line in list item needs {required} spaces of \
                                 indentation to remain part of the list (found {actual})",
                            )
                        }
                    } else {
                        format!("Continuation line under-indented (expected {required}, found {actual})")
                    };
                    let outcome = Self::build_under_indent_warning(ctx, line, required, message);
                    if let Some(closer_line) = outcome.also_flag_line {
                        flagged_lines.insert(closer_line);
                    }
                    warnings.push(outcome.warning);
                }
                ControlFlow::Continue(())
            });
        }

        // Pass 2 - over-indented continuation (tight or loose): prose pushed
        // past the content column is snapped back. Fenced code blocks are
        // skipped here (`!in_code_block`): an over-indented fence is cosmetic
        // (the code still renders), and reindenting only its delimiters - the
        // body is skipped by `should_skip_line` - would alter the literal code
        // content. Indented code blocks (content column + 4 or more) are also
        // `in_code_block`, so a blank line before such a body does not exempt
        // it from being recognized as code rather than over-indented prose.
        for &(item_line, marker_col, content_col, task_col, required, range_end) in &scoped {
            // No continuation candidate in this item's range: nothing to flag.
            if !range_has_prose_candidate(item_line, range_end) {
                continue;
            }
            // For task items, gather sibling-column usage once so the auto-fix
            // can tie-break equidistant over-indents toward whichever valid
            // column the author is already using.
            let (uses_content_col, uses_task_col) = match task_col {
                Some(t) => Self::sibling_column_usage(ctx, item_line, range_end, marker_col, content_col, t),
                None => (false, false),
            };

            Self::walk_item_continuation(ctx, item_line, range_end, marker_col, |line| {
                let actual = line.actual;
                if actual > required
                    && !line.info.in_code_block
                    && Some(actual) != task_col
                    && !Self::starts_with_list_marker(line.trimmed)
                    && flagged_lines.insert(line.line_num)
                {
                    let fix_target =
                        Self::compute_fix_target(actual, required, task_col, uses_content_col, uses_task_col);
                    let message = match task_col {
                        Some(t) => format!(
                            "Continuation line over-indented \
                             (expected {required} or {t}, found {actual})"
                        ),
                        None => {
                            format!("Continuation line over-indented (expected {required}, found {actual})")
                        }
                    };
                    warnings.push(Self::build_over_indent_warning(ctx, line, fix_target, message));
                }
                ControlFlow::Continue(())
            });
        }

        // The two passes emit independently, so order by position before
        // returning - callers and tests expect document order.
        warnings.sort_by_key(|w| (w.line, w.column));

        Ok(warnings)
    }

    fn fix(&self, ctx: &LintContext) -> Result<String, LintError> {
        let warnings = self.check(ctx)?;
        let warnings =
            crate::utils::fix_utils::filter_warnings_by_inline_config(warnings, ctx.inline_config(), self.name());
        if warnings.is_empty() {
            return Ok(ctx.content.to_string());
        }

        // Sort fixes by byte position descending to apply from end to start
        let mut fixes: Vec<Fix> = warnings.into_iter().filter_map(|w| w.fix).collect();
        fixes.sort_by_key(|f| std::cmp::Reverse(f.range.start));

        let mut content = ctx.content.to_string();
        for fix in fixes {
            if fix.range.start <= content.len() && fix.range.end <= content.len() {
                content.replace_range(fix.range, &fix.replacement);
            }
        }

        Ok(content)
    }

    fn category(&self) -> RuleCategory {
        RuleCategory::List
    }

    fn should_skip(&self, ctx: &crate::lint_context::LintContext) -> bool {
        ctx.content.is_empty() || ctx.list_blocks.is_empty()
    }

    fn as_any(&self) -> &dyn std::any::Any {
        self
    }

    crate::impl_rule_config_methods!(MD077Config);
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::config::MarkdownFlavor;

    fn check(content: &str) -> Vec<LintWarning> {
        let ctx = LintContext::new(content, MarkdownFlavor::Standard, None);
        let rule = MD077ListContinuationIndent::default();
        rule.check(&ctx).unwrap()
    }

    fn check_mkdocs(content: &str) -> Vec<LintWarning> {
        let ctx = LintContext::new(content, MarkdownFlavor::MkDocs, None);
        let rule = MD077ListContinuationIndent::default();
        rule.check(&ctx).unwrap()
    }

    fn fix(content: &str) -> String {
        let ctx = LintContext::new(content, MarkdownFlavor::Standard, None);
        let rule = MD077ListContinuationIndent::default();
        rule.fix(&ctx).unwrap()
    }

    fn fix_mkdocs(content: &str) -> String {
        let ctx = LintContext::new(content, MarkdownFlavor::MkDocs, None);
        let rule = MD077ListContinuationIndent::default();
        rule.fix(&ctx).unwrap()
    }

    fn aligned_rule() -> MD077ListContinuationIndent {
        MD077ListContinuationIndent::new(ContinuationStyle::Aligned)
    }

    fn check_aligned(content: &str) -> Vec<LintWarning> {
        let ctx = LintContext::new(content, MarkdownFlavor::Standard, None);
        aligned_rule().check(&ctx).unwrap()
    }

    fn check_aligned_mkdocs(content: &str) -> Vec<LintWarning> {
        let ctx = LintContext::new(content, MarkdownFlavor::MkDocs, None);
        aligned_rule().check(&ctx).unwrap()
    }

    fn fix_aligned(content: &str) -> String {
        let ctx = LintContext::new(content, MarkdownFlavor::Standard, None);
        aligned_rule().fix(&ctx).unwrap()
    }

    fn fix_aligned_quarto(content: &str) -> String {
        let ctx = LintContext::new(content, MarkdownFlavor::Quarto, None);
        aligned_rule().fix(&ctx).unwrap()
    }

    #[test]
    fn aligned_idempotent_with_latent_marker_behind_unstable_heading() {
        // Regression: an empty backtick run (`` ``\n`` ``) is parsed as a setext
        // heading. That heading used to terminate the latent-structure walk
        // before it reached the `- ` marker on the next line, so the marker was
        // not detected as latent. Reindenting the `1. ` continuation then
        // promoted `- ` to a real list item, producing a fresh under-indent
        // violation on the second pass and breaking single-pass idempotency.
        // The latent-structure scan now spans the full owned range, detects the
        // marker, and leaves the (ambiguous) item alone.
        let input = "1. \n``\n``\n- \n``";
        let once = fix_aligned_quarto(input);
        let twice = fix_aligned_quarto(&once);
        assert_eq!(once, twice, "MD077 aligned fix must be idempotent (Quarto)");
    }

    #[test]
    fn latent_underline_needs_paragraph_text_above_it() {
        // Only paragraph text can become a setext heading's text line, so an
        // underline sitting under an ATX heading or a thematic break is latent
        // nothing and must not hold the whole item back.
        for (label, content) in [
            ("ATX heading", "- item\nwrap\n# Heading\n===\n"),
            ("thematic break", "- item\nwrap\n***\n===\n"),
            ("HTML block", "- item\nwrap\n<div>\n===\n"),
        ] {
            assert_eq!(
                check_aligned(content).len(),
                1,
                "{label}: reindenting cannot make a setext heading here, so the under-indent is reportable"
            );
        }

        // A closing code fence is the case only the block flag can answer: its
        // text is indistinguishable from prose, and nothing but the block it
        // sits in says the line cannot be a setext heading's text.
        assert_eq!(
            check_aligned("- item\nwrap\n```\ncode\n```\n===\n").len(),
            2,
            "a closing fence is not paragraph text, so both under-indents are reportable"
        );

        // An empty list item is the case only the line's own markers can answer:
        // it is written inside a paragraph context and holds no text at all, and
        // an underline below it underlines nothing. A lone `-` is not this case
        // (under a paragraph it is itself an underline), so each marker carries
        // the space that opens an item holding nothing.
        for (label, content) in [
            ("empty bullet", "- item\n wrap\n > - \n ===\n"),
            ("empty ordered item", "- item\n wrap\n > 1. \n ===\n"),
            ("empty item in a nested quote", "- item\n wrap\n > > - \n ===\n"),
        ] {
            assert_eq!(
                check_aligned(content).len(),
                1,
                "{label}: an item holding no text cannot become a heading's text line"
            );
        }

        // A blank line above the underline is the same answer for the same
        // reason, and needs no test of its own in the rule: stripped of its
        // markers it holds nothing, which is what the text predicate rejects.
        for (label, content) in [
            ("bare blank line", "- item\n wrap\n\n ===\n"),
            ("blank line in a quote", "- item\n wrap\n >\n ===\n"),
            ("quoted whitespace", "- item\n wrap\n >   \n ===\n"),
        ] {
            assert_eq!(
                check_aligned(content).len(),
                2,
                "{label}: nothing above the underline can become a heading's text line"
            );
        }

        // Paired control: prose above the underline IS latent structure, because
        // reindenting the item would give the underline the content column and
        // turn the pair into a real heading.
        assert!(
            check_aligned("- item\nwrap\ntext\n===\n").is_empty(),
            "prose above the underline is latent structure, so the item is left alone"
        );
    }

    #[test]
    fn aligned_idempotent_with_lazy_continuation_out_of_a_blockquote() {
        // Regression: a lazy continuation that follows a blockquote-nested list
        // item gained one space of indent on every pass, so the formatter never
        // converged.
        let input = "- \n> *\n> a\n``";
        let once = fix_aligned(input);
        let twice = fix_aligned(&once);
        assert_eq!(once, twice, "MD077 aligned fix must be idempotent");
    }

    // ── Tight continuation (no blank line) ─────────────────────────────

    #[test]
    fn tight_lazy_continuation_zero_indent_not_flagged() {
        // Zero-indent lazy continuation is valid CommonMark
        let content = "- Item\ncontinuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn tight_continuation_correct_indent_not_flagged() {
        // Correctly indented tight continuation (aligns with content column)
        let content = "1. Item\n   continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn tight_continuation_over_indented_ordered() {
        // "1. " = 3 chars, but continuation has 4 spaces
        let content = "1. This is a list item with multiple lines.\n    The second line is over-indented.\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(warnings[0].line, 2);
        assert!(warnings[0].message.contains("over-indented"));
    }

    #[test]
    fn tight_continuation_over_indented_unordered() {
        // "- " = 2 chars, but continuation has 3 spaces
        let content = "- Item\n   over-indented\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(warnings[0].line, 2);
    }

    #[test]
    fn tight_continuation_multiple_over_indented_lines() {
        let content = "1. Item\n    line one\n    line two\n    line three\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 3);
    }

    #[test]
    fn tight_continuation_mixed_correct_and_over() {
        let content = "1. Item\n   correct\n    over-indented\n   correct again\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(warnings[0].line, 3);
    }

    #[test]
    fn tight_continuation_nested_over_indented() {
        // L2 "- " at column 2, content_column = 4. Continuation at 5 is over-indented for L2.
        let content = "- L1\n  - L2\n     over-indented continuation of L2\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(warnings[0].line, 3);
        // Must report expected=4 (L2's content_col), not expected=2 (L1's)
        assert!(warnings[0].message.contains("expected 4"));
        assert!(warnings[0].message.contains("found 5"));
    }

    #[test]
    fn tight_continuation_nested_correct_indent_not_flagged() {
        // Continuation at 4 spaces is correct for L2 (content_col=4). Must NOT be
        // flagged as over-indented relative to L1 (content_col=2).
        let content = "- L1\n  - L2\n    correctly indented continuation of L2\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn fix_tight_continuation_nested_over_indented() {
        // Fix should reduce to 4 spaces (L2's content_col), not 2 (L1's)
        let content = "- L1\n  - L2\n     over-indented continuation of L2\n";
        let fixed = fix(content);
        assert_eq!(fixed, "- L1\n  - L2\n    over-indented continuation of L2\n");
    }

    #[test]
    fn tight_continuation_under_indented_not_flagged() {
        // 2 spaces instead of 3 for "1. " — under-indented, not over-indented.
        // Valid lazy continuation in CommonMark, so not flagged.
        let content = "1. Item\n  under-indented\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn tight_continuation_tab_over_indented() {
        // A tab expands to 4 visual columns, which exceeds content_col=2 for "- "
        let content = "- Item\n\tover-indented\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
    }

    #[test]
    fn fix_tight_continuation_over_indented_ordered() {
        let content = "1. This is a list item with multiple lines.\n    The second line is over-indented.\n";
        let fixed = fix(content);
        assert_eq!(
            fixed,
            "1. This is a list item with multiple lines.\n   The second line is over-indented.\n"
        );
    }

    #[test]
    fn fix_tight_continuation_over_indented_unordered() {
        let content = "- Item\n   over-indented\n";
        let fixed = fix(content);
        assert_eq!(fixed, "- Item\n  over-indented\n");
    }

    #[test]
    fn fix_tight_continuation_multiple_lines() {
        let content = "1. Item\n    line one\n    line two\n";
        let fixed = fix(content);
        assert_eq!(fixed, "1. Item\n   line one\n   line two\n");
    }

    #[test]
    fn tight_continuation_mkdocs_4space_ordered_not_flagged() {
        // MkDocs requires max(3, 4) = 4 spaces for "1. " items.
        // 4-space tight continuation is correct, not over-indented.
        let content = "1. Item\n    continuation\n";
        assert!(check_mkdocs(content).is_empty());
    }

    #[test]
    fn tight_continuation_mkdocs_5space_ordered_flagged() {
        // 5 spaces exceeds the MkDocs required indent of 4
        let content = "1. Item\n     over-indented\n";
        let warnings = check_mkdocs(content);
        assert_eq!(warnings.len(), 1);
        assert!(warnings[0].message.contains("expected 4"));
        assert!(warnings[0].message.contains("found 5"));
    }

    #[test]
    fn fix_tight_continuation_mkdocs_over_indented() {
        let content = "1. Item\n     over-indented\n";
        let fixed = fix_mkdocs(content);
        assert_eq!(fixed, "1. Item\n    over-indented\n");
    }

    #[test]
    fn tight_continuation_deeply_indented_list_markers_not_flagged() {
        // Deeply indented list markers (e.g., indent=8 in MD007) may not be
        // recognized as list items by the parser. MD077 must not flag them.
        let content = "* Level 0\n        * Level 1\n                * Level 2\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn tight_continuation_ordered_marker_not_flagged() {
        // Indented ordered list marker should not be flagged
        let content = "- Parent\n      1. Child item\n";
        assert!(check(content).is_empty());
    }

    // ── Unordered list: correct indent after blank ────────────────────

    #[test]
    fn unordered_correct_indent_no_warning() {
        let content = "- Item\n\n  continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn unordered_partial_indent_warns() {
        // Content with some indent (above marker column) but less than
        // content_column is likely an indentation mistake.
        let content = "- Item\n\n continuation\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(warnings[0].line, 3);
        assert!(warnings[0].message.contains("2 spaces"));
        assert!(warnings[0].message.contains("found 1"));
    }

    #[test]
    fn unordered_zero_indent_is_new_paragraph() {
        // Content at 0 indent after a top-level list is a new paragraph, not
        // under-indented continuation.
        let content = "- Item\n\ncontinuation\n";
        assert!(check(content).is_empty());
    }

    // ── Ordered list: CommonMark W+N ──────────────────────────────────

    #[test]
    fn ordered_3space_correct_commonmark() {
        // "1. " is 3 chars, content_column = 3
        let content = "1. Item\n\n   continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn ordered_2space_under_indent_commonmark() {
        let content = "1. Item\n\n  continuation\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert!(warnings[0].message.contains("3 spaces"));
        assert!(warnings[0].message.contains("found 2"));
    }

    // ── Multi-digit ordered markers ───────────────────────────────────

    #[test]
    fn multi_digit_marker_correct() {
        // "10. " is 4 chars, content_column = 4
        let content = "10. Item\n\n    continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn multi_digit_marker_under_indent() {
        let content = "10. Item\n\n   continuation\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert!(warnings[0].message.contains("4 spaces"));
    }

    // ── MkDocs flavor: 4-space minimum ────────────────────────────────

    #[test]
    fn mkdocs_3space_ordered_warns() {
        // In MkDocs mode, 3-space indent on "1. " is not enough
        let content = "1. Item\n\n   continuation\n";
        let warnings = check_mkdocs(content);
        assert_eq!(warnings.len(), 1);
        assert!(warnings[0].message.contains("4 spaces"));
        assert!(warnings[0].message.contains("MkDocs"));
    }

    #[test]
    fn mkdocs_4space_ordered_no_warning() {
        let content = "1. Item\n\n    continuation\n";
        assert!(check_mkdocs(content).is_empty());
    }

    #[test]
    fn mkdocs_unordered_2space_ok() {
        // Unordered "- " has content_column = 2; max(2, 4) = 4 in mkdocs
        let content = "- Item\n\n    continuation\n";
        assert!(check_mkdocs(content).is_empty());
    }

    #[test]
    fn mkdocs_unordered_2space_warns() {
        // "- " has content_column 2; MkDocs requires max(2,4) = 4
        let content = "- Item\n\n  continuation\n";
        let warnings = check_mkdocs(content);
        assert_eq!(warnings.len(), 1);
        assert!(warnings[0].message.contains("4 spaces"));
    }

    // ── Auto-fix ──────────────────────────────────────────────────────

    #[test]
    fn fix_unordered_indent() {
        // Partial indent (above marker column, below content column) gets fixed
        let content = "- Item\n\n continuation\n";
        let fixed = fix(content);
        assert_eq!(fixed, "- Item\n\n  continuation\n");
    }

    #[test]
    fn fix_ordered_indent() {
        let content = "1. Item\n\n continuation\n";
        let fixed = fix(content);
        assert_eq!(fixed, "1. Item\n\n   continuation\n");
    }

    #[test]
    fn fix_mkdocs_indent() {
        let content = "1. Item\n\n   continuation\n";
        let fixed = fix_mkdocs(content);
        assert_eq!(fixed, "1. Item\n\n    continuation\n");
    }

    // ── Nested lists: only flag continuation, not sub-items ───────────

    #[test]
    fn nested_list_items_not_flagged() {
        let content = "- Parent\n\n  - Child\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn nested_list_zero_indent_is_new_paragraph() {
        // Content at 0 indent ends the list, not continuation
        let content = "- Parent\n  - Child\n\ncontinuation of parent\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn nested_list_partial_indent_flagged() {
        // Content with partial indent (above parent marker, below content col)
        let content = "- Parent\n  - Child\n\n continuation of parent\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert!(warnings[0].message.contains("2 spaces"));
    }

    // ── Code blocks inside items ─────────────────────────────────────

    #[test]
    fn code_block_correctly_indented_no_warning() {
        // Fence lines and content all at correct indent for "- " (content_column = 2)
        let content = "- Item\n\n  ```\n  code\n  ```\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn code_fence_under_indented_warns() {
        // Fence opener has 1-space indent, but "- " needs 2.
        // Only the opener is flagged — its compound fix also covers the
        // interior content and the matching closer (see issue #574).
        let content = "- Item\n\n ```\n code\n ```\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(warnings[0].line, 3);
    }

    #[test]
    fn code_fence_under_indented_ordered_mkdocs() {
        // Ordered list in MkDocs: "1. " needs max(3, 4) = 4 spaces
        // Fence at 3 spaces is correct for CommonMark but wrong for MkDocs
        let content = "1. Item\n\n   ```toml\n   key = \"value\"\n   ```\n";
        assert!(check(content).is_empty()); // Standard mode: 3 is fine
        let warnings = check_mkdocs(content);
        assert_eq!(warnings.len(), 1); // MkDocs: opener's compound fix covers the whole block
        assert_eq!(warnings[0].line, 3);
        assert!(warnings[0].message.contains("4 spaces"));
        assert!(warnings[0].message.contains("MkDocs"));
    }

    #[test]
    fn code_fence_tilde_under_indented() {
        let content = "- Item\n\n ~~~\n code\n ~~~\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1); // Tilde fences: single compound-fix warning on opener
        assert_eq!(warnings[0].line, 3);
    }

    // ── Multiple blank lines ──────────────────────────────────────────

    #[test]
    fn multiple_blank_lines_zero_indent_is_new_paragraph() {
        // Even with multiple blanks, 0-indent content is a new paragraph
        let content = "- Item\n\n\ncontinuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn multiple_blank_lines_partial_indent_flags() {
        let content = "- Item\n\n\n continuation\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
    }

    // ── Empty items: no continuation to check ─────────────────────────

    #[test]
    fn empty_item_no_warning() {
        let content = "- \n- Second\n";
        assert!(check(content).is_empty());
    }

    // ── Multiple items, only some under-indented ──────────────────────

    #[test]
    fn multiple_items_mixed_indent() {
        let content = "1. First\n\n   correct continuation\n\n2. Second\n\n  wrong continuation\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(warnings[0].line, 7);
    }

    // ── Task list items ───────────────────────────────────────────────

    #[test]
    fn task_list_correct_indent() {
        // "- [ ] " = content_column is typically at col 6
        let content = "- [ ] Task\n\n      continuation\n";
        assert!(check(content).is_empty());
    }

    // ── Frontmatter skipped ───────────────────────────────────────────

    #[test]
    fn frontmatter_not_flagged() {
        let content = "---\ntitle: test\n---\n\n- Item\n\n  continuation\n";
        assert!(check(content).is_empty());
    }

    // ── Fix produces valid output with multiple fixes ─────────────────

    #[test]
    fn fix_multiple_items() {
        let content = "1. First\n\n wrong1\n\n2. Second\n\n wrong2\n";
        let fixed = fix(content);
        assert_eq!(fixed, "1. First\n\n   wrong1\n\n2. Second\n\n   wrong2\n");
    }

    #[test]
    fn fix_multiline_loose_continuation_all_lines() {
        let content = "1. Item\n\n  line one\n  line two\n  line three\n";
        let fixed = fix(content);
        assert_eq!(fixed, "1. Item\n\n   line one\n   line two\n   line three\n");
    }

    // ── No false positive when content is after sibling item ──────────

    #[test]
    fn sibling_item_boundary_respected() {
        // The "continuation" after a blank belongs to "- Second", not "- First"
        let content = "- First\n- Second\n\n  continuation\n";
        assert!(check(content).is_empty());
    }

    // ── Blockquote-nested lists ────────────────────────────────────────

    #[test]
    fn blockquote_list_correct_indent_no_warning() {
        // Lists inside blockquotes: visual_indent includes the blockquote
        // prefix, so comparisons work on raw line columns.
        let content = "> - Item\n>\n>   continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn blockquote_list_under_indent_no_false_positive() {
        // Under-indented continuation inside a blockquote: visual_indent
        // starts at 0 (the `>` char) which is <= marker_col, so the scan
        // breaks and no warning is emitted. This is a known false negative
        // (not a false positive), which is the safer default.
        let content = "> - Item\n>\n> continuation\n";
        assert!(check(content).is_empty());
    }

    // ── Deep nesting (3+ levels) ──────────────────────────────────────

    #[test]
    fn deep_nesting_correct_indent() {
        let content = "- L1\n  - L2\n    - L3\n\n      continuation of L3\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn deep_nesting_under_indent() {
        // L3 starts at column 4 with "- " marker, content_column = 6
        // Continuation with 5 spaces is under-indented for L3.
        let content = "- L1\n  - L2\n    - L3\n\n     continuation of L3\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert!(warnings[0].message.contains("6 spaces"));
        assert!(warnings[0].message.contains("found 5"));
    }

    #[test]
    fn deep_nesting_middle_level_continuation_bullets() {
        // A loose continuation of the MIDDLE level (L2, content_column = 4)
        // after a deeper L3 list is valid; the L1 walk must not claim it as
        // its own over-indented continuation (issue #739).
        let content = "- L1\n  - L2\n    - L3\n\n    continuation of L2\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn deep_nesting_middle_level_continuation_ordered() {
        // Issue #739 repro: ordered lists, continuation of the level-2 item
        // (content_column = 6) after a level-3 bullet list.
        let content = "1. Level 1 item.\n1. Level 1 item:\n   1. Level 2 item.\n   1. Level 2 item.\n   1. Level 2 item:\n      - Level 3 item.\n      - Level 3 item.\n\n      Level 2 list continuation.\n1. Level 1 item.\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn deep_nesting_outermost_continuation() {
        // A loose continuation of the OUTERMOST level (L1, content_column = 2)
        // past two open nested levels escapes both and stays valid.
        let content = "- L1\n  - L2\n    - L3\n\n  continuation of L1\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn deep_nesting_between_levels_still_flagged() {
        // Col 3 sits strictly between L1's content column (2) and L2's (4):
        // the deepest applicable item (L2) claims it as loose under-indent.
        let content = "- L1\n  - L2\n    - L3\n\n   continuation\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert!(warnings[0].message.contains("4 spaces"));
        assert!(warnings[0].message.contains("found 3"));
    }

    #[test]
    fn deep_nesting_beyond_deepest_still_flagged() {
        // Col 7 exceeds even L3's content column (6): over-indent for L3.
        let content = "- L1\n  - L2\n    - L3\n\n       continuation\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert!(warnings[0].message.contains("over-indented"));
        assert!(warnings[0].message.contains("expected 6, found 7"));
    }

    #[test]
    fn four_levels_middle_continuation() {
        // Continuation of L2 (content_column = 4) after open L3 and L4 lists:
        // the walk must pop two deeper levels and still defer to L2.
        let content = "- L1\n  - L2\n    - L3\n      - L4\n\n    continuation of L2\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn nested_sibling_closes_deeper_level() {
        // L2b closes L2a's deeper L3 list; a continuation at L2b's content
        // column belongs to L2b and stays valid.
        let content = "- L1\n  - L2a\n    - L3\n  - L2b\n\n    continuation of L2b\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn deep_nesting_middle_level_continuation_fix_preserved() {
        // The valid middle-level continuation must survive fix() unchanged.
        let content = "- L1\n  - L2\n    - L3\n\n    continuation of L2\n";
        assert_eq!(fix(content), content);
    }

    // ── Tab indentation ───────────────────────────────────────────────

    #[test]
    fn loose_tab_continuation_over_indented() {
        // A tab expands to 4 visual columns, exceeding content_column = 2 for
        // "- ". Loose over-indent is flagged just like the tight tab case
        // (`tight_continuation_tab_over_indented`), and the fix normalizes the
        // tab down to the content-column indent.
        let content = "- Item\n\n\tcontinuation\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(warnings[0].line, 3);
        assert_eq!(fix(content), "- Item\n\n  continuation\n");
    }

    // ── Multiple continuation paragraphs ──────────────────────────────

    #[test]
    fn multiple_continuations_correct() {
        let content = "- Item\n\n  para 1\n\n  para 2\n\n  para 3\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn multiple_continuations_second_under_indent() {
        // First continuation is correct, second is under-indented
        let content = "- Item\n\n  para 1\n\n continuation 2\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(warnings[0].line, 5);
    }

    // ── Ordered list with `)` marker style ────────────────────────────

    #[test]
    fn ordered_paren_marker_correct() {
        // "1) " is 3 chars, content_column = 3
        let content = "1) Item\n\n   continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn ordered_paren_marker_under_indent() {
        let content = "1) Item\n\n  continuation\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert!(warnings[0].message.contains("3 spaces"));
    }

    // ── Star and plus markers ─────────────────────────────────────────

    #[test]
    fn star_marker_correct() {
        let content = "* Item\n\n  continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn star_marker_under_indent() {
        let content = "* Item\n\n continuation\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
    }

    #[test]
    fn plus_marker_correct() {
        let content = "+ Item\n\n  continuation\n";
        assert!(check(content).is_empty());
    }

    // ── Heading breaks scan ───────────────────────────────────────────

    #[test]
    fn heading_after_list_no_warning() {
        let content = "- Item\n\n# Heading\n";
        assert!(check(content).is_empty());
    }

    // ── Horizontal rule breaks scan ───────────────────────────────────

    #[test]
    fn hr_after_list_no_warning() {
        let content = "- Item\n\n---\n";
        assert!(check(content).is_empty());
    }

    // ── Reference link definitions skip ───────────────────────────────

    #[test]
    fn reference_link_def_not_flagged() {
        let content = "- Item\n\n [link]: https://example.com\n";
        assert!(check(content).is_empty());
    }

    // ── Footnote definitions skip ─────────────────────────────────────

    #[test]
    fn footnote_def_not_flagged() {
        let content = "- Item\n\n [^1]: footnote text\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn footnote_multiline_body_after_list_not_flagged() {
        // A footnote definition whose indented body follows a list must not be
        // read as over-indented list continuation. The 4-space body lines
        // belong to the footnote, not to `- This is a list.` (content col 2).
        let content = "# A list followed by a footnote\n\n\
                       Here is a paragraph.[^fn]\n\n\
                       - This is a list.\n\n\
                       [^fn]:\n\
                       \x20\x20\x20\x20Here is a footnote that spans multiple lines.\n\
                       \x20\x20\x20\x20It should thus be indented by at least four spaces.\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn fix_footnote_multiline_body_after_list_is_noop() {
        // The false positive also produced a damaging auto-fix: reindenting the
        // footnote body from 4 spaces to 2 broke the footnote (then tripped
        // MD068). The fix must leave the footnote untouched.
        let content = "# A list followed by a footnote\n\n\
                       Here is a paragraph.[^fn]\n\n\
                       - This is a list.\n\n\
                       [^fn]:\n\
                       \x20\x20\x20\x20Here is a footnote that spans multiple lines.\n\
                       \x20\x20\x20\x20It should thus be indented by at least four spaces.\n";
        assert_eq!(fix(content), content);
    }

    #[test]
    fn footnote_body_indented_past_list_content_col_not_flagged() {
        // Footnote body indented well past the list's content column (here a
        // single-space list marker would put content col at 2, body at 4) is
        // footnote content, not over-indented continuation.
        let content = "- Item\n\n[^fn]:\n    Body line one.\n    Body line two.\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn list_inside_footnote_body_continuation_not_flagged() {
        // Accepted trade-off: a list living *inside* a footnote body is skipped
        // wholesale, so MD077 does not police its continuation indentation.
        // Consistent with MD007, which also skips footnote-internal content.
        let content = "Text.[^fn]\n\n[^fn]:\n\
                       \x20\x20\x20\x20- nested item\n\
                       \x20\x20\x20\x20\x20\x20\x20over-indented continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn footnote_multiline_body_after_list_not_flagged_mkdocs() {
        // Same protection under the MkDocs flavor. The body sits at 6 spaces,
        // past MkDocs's required indent of 4 for `- `, so without skipping
        // footnote content it would be flagged as over-indented continuation.
        let content = "Here is a paragraph.[^fn]\n\n\
                       - This is a list.\n\n\
                       [^fn]:\n\
                       \x20\x20\x20\x20\x20\x20Footnote body that spans\n\
                       \x20\x20\x20\x20\x20\x20multiple indented lines.\n";
        assert!(check_mkdocs(content).is_empty());
    }

    // ── Fix preserves correct content ─────────────────────────────────

    #[test]
    fn fix_deep_nesting() {
        let content = "- L1\n  - L2\n    - L3\n\n     under-indented\n";
        let fixed = fix(content);
        assert_eq!(fixed, "- L1\n  - L2\n    - L3\n\n      under-indented\n");
    }

    #[test]
    fn fix_mkdocs_unordered() {
        // MkDocs: "- " has content_column 2, but MkDocs requires max(2,4) = 4
        let content = "- Item\n\n  continuation\n";
        let fixed = fix_mkdocs(content);
        assert_eq!(fixed, "- Item\n\n    continuation\n");
    }

    #[test]
    fn fix_code_fence_indent() {
        // Fence opener, interior, and closer all shift by the same delta so
        // the parser keeps pairing the fences and MD031 doesn't misfire.
        let content = "- Item\n\n ```\n code\n ```\n";
        let fixed = fix(content);
        assert_eq!(fixed, "- Item\n\n  ```\n  code\n  ```\n");
    }

    #[test]
    fn fix_mkdocs_code_fence_indent() {
        // MkDocs ordered list: fence at 3 spaces needs 4; interior shifts too
        let content = "1. Item\n\n   ```toml\n   key = \"val\"\n   ```\n";
        let fixed = fix_mkdocs(content);
        assert_eq!(fixed, "1. Item\n\n    ```toml\n    key = \"val\"\n    ```\n");
    }

    // ── Empty document / whitespace-only ──────────────────────────────

    #[test]
    fn empty_document_no_warning() {
        assert!(check("").is_empty());
    }

    #[test]
    fn whitespace_only_no_warning() {
        assert!(check("   \n\n  \n").is_empty());
    }

    // ── No list at all ────────────────────────────────────────────────

    #[test]
    fn no_list_no_warning() {
        let content = "# Heading\n\nSome paragraph.\n\nAnother paragraph.\n";
        assert!(check(content).is_empty());
    }

    // ── Multi-line continuation (additional coverage) ──────────────

    #[test]
    fn multiline_continuation_all_lines_flagged() {
        let content = "1. This is a list item.\n\n  This is continuation text and\n  it has multiple lines.\n  This is yet another line.\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 3);
        assert_eq!(warnings[0].line, 3);
        assert_eq!(warnings[1].line, 4);
        assert_eq!(warnings[2].line, 5);
    }

    #[test]
    fn multiline_continuation_with_frontmatter_fix() {
        let content = "---\ntitle: Heading\n---\n\nSome introductory text:\n\n1. This is a list item.\n\n  This is list continuation text and\n  it has multiple lines that aren't indented properly.\n  This is yet another line that isn't indented properly.\n1. This is a list item.\n\n  This is list continuation text and\n  it has multiple lines that aren't indented properly.\n  This is yet another line that isn't indented properly.\n";
        let fixed = fix(content);
        assert_eq!(
            fixed,
            "---\ntitle: Heading\n---\n\nSome introductory text:\n\n1. This is a list item.\n\n   This is list continuation text and\n   it has multiple lines that aren't indented properly.\n   This is yet another line that isn't indented properly.\n1. This is a list item.\n\n   This is list continuation text and\n   it has multiple lines that aren't indented properly.\n   This is yet another line that isn't indented properly.\n"
        );
    }

    #[test]
    fn multiline_continuation_correct_indent_no_warning() {
        let content = "1. Item\n\n   line one\n   line two\n   line three\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn multiline_continuation_mixed_indent() {
        let content = "1. Item\n\n   correct\n  wrong\n   correct\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(warnings[0].line, 4);
    }

    #[test]
    fn multiline_continuation_unordered() {
        let content = "- Item\n\n continuation 1\n continuation 2\n continuation 3\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 3);
        let fixed = fix(content);
        assert_eq!(
            fixed,
            "- Item\n\n  continuation 1\n  continuation 2\n  continuation 3\n"
        );
    }

    #[test]
    fn multiline_continuation_two_items_fix() {
        let content = "1. First\n\n  cont a\n  cont b\n\n2. Second\n\n  cont c\n  cont d\n";
        let fixed = fix(content);
        assert_eq!(
            fixed,
            "1. First\n\n   cont a\n   cont b\n\n2. Second\n\n   cont c\n   cont d\n"
        );
    }

    #[test]
    fn fence_fix_does_not_break_pairing_for_md031() {
        // Regression for issue #574: previously MD077 only reindented the
        // fence delimiter lines while leaving the code block's interior at
        // the old indent. Between iterations of the fix loop the parser
        // saw an opener-closer mismatch, and MD031 then injected stray
        // blank lines at the fence boundaries. MD077's compound fix must
        // now rewrite the whole block atomically so the fences stay paired.
        let content = "#### title\n\nabc\n\n\
                       1. ab\n\n\
                       \x20\x20`aabbccdd`\n\n\
                       2. cd\n\n\
                       \x20\x20`bbcc dd ee`\n\n\
                       \x20\x20```\n\
                       \x20\x20abcd\n\
                       \x20\x20ef gh\n\
                       \x20\x20```\n\n\
                       \x20\x20uu\n\n\
                       \x20\x20```\n\
                       \x20\x20cdef\n\
                       \x20\x20gh ij\n\
                       \x20\x20```\n";
        let expected = "#### title\n\nabc\n\n\
                        1. ab\n\n\
                        \x20\x20\x20`aabbccdd`\n\n\
                        2. cd\n\n\
                        \x20\x20\x20`bbcc dd ee`\n\n\
                        \x20\x20\x20```\n\
                        \x20\x20\x20abcd\n\
                        \x20\x20\x20ef gh\n\
                        \x20\x20\x20```\n\n\
                        \x20\x20\x20uu\n\n\
                        \x20\x20\x20```\n\
                        \x20\x20\x20cdef\n\
                        \x20\x20\x20gh ij\n\
                        \x20\x20\x20```\n";
        assert_eq!(fix(content), expected);
    }

    #[test]
    fn multiline_continuation_separated_by_blank() {
        let content = "1. Item\n\n  para1 line1\n  para1 line2\n\n  para2 line1\n  para2 line2\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 4);
        let fixed = fix(content);
        assert_eq!(
            fixed,
            "1. Item\n\n   para1 line1\n   para1 line2\n\n   para2 line1\n   para2 line2\n"
        );
    }

    #[test]
    fn tab_indented_fence_is_normalized_to_spaces() {
        // Leading tabs expand to the next multiple-of-4 column under
        // CommonMark, so simply prepending spaces before a tab would
        // silently no-op (the tab snaps back to column 4). The compound
        // fence fix must replace the leading whitespace with a fresh
        // (visual_indent + delta) run of spaces. A `100. ` item has
        // content_column = 5, so a tab-indented fence (visual col 4) is
        // under-indented by 1 and must end up at 5 spaces after the fix.
        let content = "100. ab\n\n\t```\n\tabcd\n\t```\n";
        let expected = "100. ab\n\n     ```\n     abcd\n     ```\n";
        assert_eq!(fix(content), expected);
    }

    // ── Loose continuation (after a blank line): over-indent ──────────
    //
    // Over-indentation is a mistake in both tight and loose continuation:
    // the body looks aligned but isn't. A blank line between the marker and
    // the body must not exempt it. The only over-indent that is intentional
    // after a blank line is an indented code block (content column + 4 or
    // more), which the parser marks `in_code_block` and the rule skips.

    #[test]
    fn loose_continuation_over_indented_flagged() {
        // "* " content column is 2; 3 spaces after a blank is over-indented
        // (the code-block threshold is content_col + 4 = 6).
        let content = "* Item\n\n   over-indented\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(warnings[0].line, 3);
        assert!(warnings[0].message.contains("over-indented"));
        assert!(warnings[0].message.contains("expected 2"));
        assert!(warnings[0].message.contains("found 3"));
    }

    #[test]
    fn loose_continuation_over_indented_multiline_mixed() {
        // Over, correct, over — only the two over-indented lines are flagged.
        let content = "* Item\n\n   over one\n  correct\n   over two\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 2);
        assert_eq!(warnings[0].line, 3);
        assert_eq!(warnings[1].line, 5);
    }

    #[test]
    fn fix_loose_continuation_over_indented() {
        let content = "* Item\n\n   over one\n  correct\n   over two\n";
        let fixed = fix(content);
        assert_eq!(fixed, "* Item\n\n  over one\n  correct\n  over two\n");
    }

    #[test]
    fn fix_tight_and_loose_items_normalized_identically() {
        // The reported document: a tight item and a loose item with the same
        // over-indented body must both normalize to the content column.
        let content = "---\ntitle: Heading\n---\n\nSome introductory text:\n\n\
                       * This is a list item.\n   This is list continuation text and\n  it has multiple lines that aren't indented properly.\n   This is yet another line that isn't indented properly.\n\n\
                       * This is a list item.\n\n   This is list continuation text and\n  it has multiple lines that aren't indented properly.\n   This is yet another line that isn't indented properly.\n";
        let expected = "---\ntitle: Heading\n---\n\nSome introductory text:\n\n\
                        * This is a list item.\n  This is list continuation text and\n  it has multiple lines that aren't indented properly.\n  This is yet another line that isn't indented properly.\n\n\
                        * This is a list item.\n\n  This is list continuation text and\n  it has multiple lines that aren't indented properly.\n  This is yet another line that isn't indented properly.\n";
        assert_eq!(fix(content), expected);
    }

    #[test]
    fn multi_paragraph_item_loose_paragraph_over_indented() {
        // A tight first paragraph and a loose second paragraph (after an
        // internal blank line) are both over-indented; both must be flagged.
        let content = "* Item.\n   tight over\n\n   loose over\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 2);
        assert_eq!(warnings[0].line, 2);
        assert_eq!(warnings[1].line, 4);
    }

    #[test]
    fn loose_indented_code_block_not_flagged() {
        // content_col = 2; a loose line at content_col + 4 (6 spaces) is a
        // CommonMark indented code block, not over-indented prose. The over-
        // indent check must never reach it (it is `in_code_block` and skipped).
        let content = "- Item\n\n      code line\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn mkdocs_loose_over_indented_flagged() {
        // MkDocs requires max(3, 4) = 4 for "1. ". A loose line at 5 spaces is
        // over-indented (code-block threshold is content_col + 4 = 7).
        let content = "1. Item\n\n     over\n";
        let warnings = check_mkdocs(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(warnings[0].line, 3);
        assert!(warnings[0].message.contains("over-indented"));
        assert!(warnings[0].message.contains("expected 4"));
        assert!(warnings[0].message.contains("found 5"));
    }

    #[test]
    fn task_list_loose_over_indented_flagged() {
        // "- [ ] " content_col = 2, task_col = 6. A loose line at 4 spaces is
        // neither valid column and below the code-block threshold (6); flagged.
        let content = "- [ ] Task\n\n    over\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(warnings[0].line, 3);
    }

    #[test]
    fn loose_over_indent_boundary_below_code_block_threshold_flagged() {
        // content_col = 2; 5 spaces (= content_col + 3) is the deepest loose
        // over-indent that is still prose. content_col + 4 (6 spaces) would be
        // an indented code block - see `loose_indented_code_block_not_flagged`.
        // This pins the boundary so a shift in the parser's threshold is caught.
        let content = "- Item\n\n     over\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(warnings[0].line, 3);
        assert!(warnings[0].message.contains("expected 2"));
        assert!(warnings[0].message.contains("found 5"));
    }

    #[test]
    fn loose_over_indent_does_not_steal_nested_under_indent() {
        // Inner content_col = 4, marker_col = 2. A loose continuation at column
        // 3 is under-indented for Inner yet over-indented for Outer (content_col
        // 2). The under-indent pass must claim it for Inner (snap *up* to 4,
        // preserving the apparent nesting), never letting the over-indent pass
        // mis-attribute it to Outer and snap it *down* to 2. This is the exact
        // ambiguity the two-pass ordering exists to resolve.
        let content = "- Outer\n  - Inner\n\n   continuation\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(warnings[0].line, 4);
        assert!(warnings[0].message.contains("4 spaces"));
        assert!(warnings[0].message.contains("found 3"));
        assert_eq!(fix(content), "- Outer\n  - Inner\n\n    continuation\n");
    }

    #[test]
    fn loose_over_indent_attributes_to_deepest_enclosing_item() {
        // Inner content_col = 4. A loose continuation at column 5 over-indents
        // Inner (the deepest item it sits within), so it is flagged against
        // Inner's column 4 - not Outer's column 2 - and snapped to 4.
        let content = "- Outer\n  - Inner\n\n     continuation\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(warnings[0].line, 4);
        assert!(warnings[0].message.contains("expected 4"));
        assert!(warnings[0].message.contains("found 5"));
        assert_eq!(fix(content), "- Outer\n  - Inner\n\n    continuation\n");
    }

    // ── Over-indented fenced code blocks are left untouched ───────────
    //
    // An over-indented fence is cosmetic: the code still renders inside the
    // list item. Reindenting only its delimiters (the body is skipped as code)
    // would change the literal code content, so the over-indent pass skips
    // anything `in_code_block`. The under-indent path still fixes fences, where
    // moving the block up is required to keep it inside the item.

    #[test]
    fn loose_over_indented_fence_not_flagged() {
        let content = "- Item\n\n   ```\n   code\n   ```\n";
        assert!(check(content).is_empty());
        assert_eq!(fix(content), content);
    }

    #[test]
    fn tight_over_indented_fence_not_flagged() {
        let content = "- Item\n   ```\n   code\n   ```\n";
        assert!(check(content).is_empty());
        assert_eq!(fix(content), content);
    }

    #[test]
    fn over_indented_tilde_fence_not_flagged() {
        let content = "- Item\n\n   ~~~\n   code\n   ~~~\n";
        assert!(check(content).is_empty());
        assert_eq!(fix(content), content);
    }

    #[test]
    fn fence_like_code_content_inside_fenced_block_not_flagged() {
        // A ``` line that is the *body* of a ~~~ block must not be treated as
        // over-indented continuation; rewriting it would corrupt code content.
        let content = "- Item\n\n  ~~~\n   ```\n  ~~~\n";
        assert!(check(content).is_empty());
        assert_eq!(fix(content), content);
    }

    #[test]
    fn unterminated_over_indented_fence_not_flagged() {
        // No closing fence: the last code line must not be mistaken for a
        // closer and snapped to the content column.
        let content = "- Item\n\n   ```\n   code1\n     code2deeper\n";
        assert!(check(content).is_empty());
        assert_eq!(fix(content), content);
    }

    // ── GFM task list items: post-checkbox continuation column ───────
    //
    // MD013's reflow indents wrapped task-list lines at `content_col + 4`
    // (the column after the checkbox). MD077 must accept that column for
    // both tight and loose continuation, for every marker flavour, so the
    // two rules don't fight over well-formed task items (issue #579).

    #[test]
    fn task_list_tight_continuation_post_checkbox_reproducer_579() {
        // Exact reproducer from the bug report: content wraps to the
        // post-checkbox column (6) with no blank line.
        let content = "- [ ] Lorem ipsum dolor sit amet, consectetur adipiscing\n      tempor incididunt ut labore.\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn task_list_tight_continuation_dash_unchecked() {
        let content = "- [ ] Task\n      continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn task_list_tight_continuation_dash_checked_lower() {
        let content = "- [x] Task\n      continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn task_list_tight_continuation_dash_checked_upper() {
        let content = "- [X] Task\n      continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn task_list_tight_continuation_star_marker() {
        let content = "* [ ] Task\n      continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn task_list_tight_continuation_plus_marker() {
        let content = "+ [ ] Task\n      continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn task_list_tight_continuation_content_column_still_valid() {
        // Column 2 is the CommonMark-canonical indent for "- " and remains
        // valid for task items too.
        let content = "- [ ] Task\n  continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn task_list_tight_continuation_between_columns_still_flagged() {
        // Column 4 matches neither content_col (2) nor post-checkbox (6).
        // A genuine indentation mistake — must remain flagged.
        let content = "- [ ] Task\n    continuation\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        // Task items advertise both valid columns to the user.
        assert!(warnings[0].message.contains("expected 2 or 6"));
        assert!(warnings[0].message.contains("found 4"));
    }

    #[test]
    fn task_list_tight_continuation_overshoot_still_flagged() {
        // Column 7 overshoots the post-checkbox column. Genuine mistake.
        let content = "- [ ] Task\n       continuation\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert!(warnings[0].message.contains("expected 2 or 6"));
        assert!(warnings[0].message.contains("found 7"));
    }

    // ── Task-list fix output: snap to nearer valid column ────────────

    #[test]
    fn fix_task_list_overshoot_snaps_to_task_col() {
        // Col 7 is 1 away from post-checkbox (6), 5 away from content (2).
        // Snap to 6 — the author's intent was almost certainly the
        // post-checkbox alignment, not the content column.
        let content = "- [ ] Task\n       continuation\n";
        let fixed = fix(content);
        assert_eq!(fixed, "- [ ] Task\n      continuation\n");
    }

    #[test]
    fn fix_task_list_col_5_snaps_to_task_col() {
        // Col 5 is 1 away from post-checkbox (6), 3 away from content (2).
        let content = "- [ ] Task\n     continuation\n";
        let fixed = fix(content);
        assert_eq!(fixed, "- [ ] Task\n      continuation\n");
    }

    #[test]
    fn fix_task_list_col_3_snaps_to_content_col() {
        // Col 3 is 1 away from content (2), 3 away from post-checkbox (6).
        let content = "- [ ] Task\n   continuation\n";
        let fixed = fix(content);
        assert_eq!(fixed, "- [ ] Task\n  continuation\n");
    }

    #[test]
    fn fix_task_list_col_4_ties_to_content_col() {
        // Col 4 is equidistant (±2) from both columns. Tie breaks to the
        // CommonMark-canonical content column — that's the default indent
        // MD077 would produce for a non-task item, so prefer it when the
        // author's intent is ambiguous.
        let content = "- [ ] Task\n    continuation\n";
        let fixed = fix(content);
        assert_eq!(fixed, "- [ ] Task\n  continuation\n");
    }

    #[test]
    fn fix_task_list_ordered_overshoot_snaps_to_task_col() {
        // "1. [ ] " → content_col = 3, post-checkbox = 7.
        // Col 8 is nearer to 7.
        let content = "1. [ ] Task\n        continuation\n";
        let fixed = fix(content);
        assert_eq!(fixed, "1. [ ] Task\n       continuation\n");
    }

    #[test]
    fn fix_task_list_ordered_under_overshoot_snaps_to_content_col() {
        // "1. [ ] " → content_col = 3, post-checkbox = 7.
        // Col 4 is nearer to 3.
        let content = "1. [ ] Task\n    continuation\n";
        let fixed = fix(content);
        assert_eq!(fixed, "1. [ ] Task\n   continuation\n");
    }

    #[test]
    fn task_list_tight_continuation_ordered_single_digit() {
        // "1. [ ] " → content_col = 3, post-checkbox = 7
        let content = "1. [ ] Task\n       continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn task_list_tight_continuation_ordered_multi_digit() {
        // "10. [ ] " → content_col = 4, post-checkbox = 8
        let content = "10. [ ] Task\n        continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn task_list_tight_continuation_nested_dash() {
        // Nested "  - [ ] " at marker_col=2 → content_col=4, post-checkbox=8
        let content = "- Parent\n  - [ ] Nested task\n        continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn task_list_loose_continuation_post_checkbox_column_not_flagged() {
        // Loose continuation (blank line) at col 6 is also valid. This
        // already passed before the fix, but pin the intent: the 6-space
        // indent is accepted because it's the task-alignment column, not
        // because the under-indent check happens to let it through.
        let content = "- [ ] Task\n\n      continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn task_list_empty_body_is_not_a_task() {
        // "- [ ]" with nothing after is an empty regular list item, not a
        // task. Column 4 continuation has no task alignment to justify it
        // and must still be flagged as over-indented. (Col 6 would turn
        // the continuation into an indented code block inside the item,
        // which is a different code path.)
        let content = "- [ ]\n    continuation\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert!(warnings[0].message.contains("found 4"));
    }

    #[test]
    fn task_list_malformed_checkbox_is_not_a_task() {
        // `[~] ` is not a GFM checkbox; only `[ ] `, `[x] `, `[X] ` count.
        let content = "- [~] Not a task\n      continuation\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
    }

    // ── MkDocs flavor × task checkbox ─────────────────────────────────
    //
    // MkDocs strict-indent and task alignment interact: required_min is
    // max(content_col, 4), and post-checkbox is content_col + 4. Both are
    // independently valid; values between them are flagged.

    #[test]
    fn task_list_mkdocs_unordered_required_min_valid() {
        // "- [ ]" MkDocs: required_min = max(2, 4) = 4, post-checkbox = 6.
        let content = "- [ ] Task\n    continuation\n";
        assert!(check_mkdocs(content).is_empty());
    }

    #[test]
    fn task_list_mkdocs_unordered_post_checkbox_valid() {
        let content = "- [ ] Task\n      continuation\n";
        assert!(check_mkdocs(content).is_empty());
    }

    #[test]
    fn task_list_mkdocs_unordered_between_flagged() {
        // Column 5 is between required_min=4 and post-checkbox=6.
        let content = "- [ ] Task\n     continuation\n";
        let warnings = check_mkdocs(content);
        assert_eq!(warnings.len(), 1);
    }

    #[test]
    fn task_list_mkdocs_ordered_both_columns_valid() {
        // "1. [ ]" MkDocs: required_min = max(3, 4) = 4, post-checkbox = 7.
        let at_4 = "1. [ ] Task\n    continuation\n";
        assert!(check_mkdocs(at_4).is_empty());
        let at_7 = "1. [ ] Task\n       continuation\n";
        assert!(check_mkdocs(at_7).is_empty());
    }

    #[test]
    fn task_list_mkdocs_ordered_between_flagged() {
        // Column 5 and 6 are between required_min=4 and post-checkbox=7.
        let at_5 = "1. [ ] Task\n     continuation\n";
        assert_eq!(check_mkdocs(at_5).len(), 1);
        let at_6 = "1. [ ] Task\n      continuation\n";
        assert_eq!(check_mkdocs(at_6).len(), 1);
    }

    // ── Context-aware tie-break ──────────────────────────────────────
    //
    // When a flagged line is exactly equidistant from `content_col` and
    // `task_col`, the author's intent is ambiguous. Before picking a
    // canonical default, look at whether other continuation lines in the
    // same item already use one of the valid columns — if so, snap to the
    // column they're using so the fix preserves the author's visible
    // convention.

    #[test]
    fn fix_task_list_tie_sibling_at_task_col_snaps_to_task_col() {
        // Col 4 is equidistant from content_col (2) and task_col (6).
        // A valid sibling at col 6 proves the author is aligning under the
        // checkbox, so the tie resolves to col 6.
        let content = "- [ ] Task\n      aligned continuation\n    tied continuation\n";
        let fixed = fix(content);
        assert_eq!(
            fixed,
            "- [ ] Task\n      aligned continuation\n      tied continuation\n"
        );
    }

    #[test]
    fn fix_task_list_tie_sibling_at_content_col_snaps_to_content_col() {
        // Valid sibling at col 2 proves the author is aligning to the
        // content column, so the col-4 tie resolves to col 2.
        let content = "- [ ] Task\n  aligned continuation\n    tied continuation\n";
        let fixed = fix(content);
        assert_eq!(fixed, "- [ ] Task\n  aligned continuation\n  tied continuation\n");
    }

    #[test]
    fn fix_task_list_tie_both_siblings_snaps_to_content_col() {
        // When siblings exist at both valid columns, the author's pattern
        // is self-contradictory. Fall back to the CommonMark-canonical
        // content column.
        let content = "- [ ] Task\n  at content col\n      at task col\n    tied continuation\n";
        let fixed = fix(content);
        assert_eq!(
            fixed,
            "- [ ] Task\n  at content col\n      at task col\n  tied continuation\n"
        );
    }

    #[test]
    fn fix_task_list_tie_sees_task_col_through_tight_lazy_continuation() {
        // CommonMark allows tight lazy continuation at col ≤ marker_col
        // (zero-indent continuation) inside a list item. The pre-pass
        // must MIRROR the main check loop's termination semantics: in
        // tight mode (no preceding blank) col ≤ marker_col is NOT a
        // termination signal — the lazy line still belongs to the item.
        //
        // This test pins that mirroring: a `lazy` line at col 0 is
        // followed by a legitimate task-col sibling at col 6, then a
        // tied col-4 line. If the pre-pass terminated eagerly at the
        // lazy line, the task-col sibling would be missed and the tied
        // line would fall back to content column. With correct
        // mirroring, the task-col sibling is seen and the tie resolves
        // to col 6.
        let content = concat!("- [ ] Task\n", "lazy\n", "      aligned at task col\n", "    tied\n",);
        let fixed = fix(content);
        assert!(
            fixed.contains("\n      tied\n"),
            "tied line should snap to col 6 (task col) because a task-col \
             sibling is visible past the tight lazy-continuation line; got:\n{fixed}"
        );
    }

    // ── Tab-indented task continuation ───────────────────────────────
    //
    // Leading tabs expand to the next column that's a multiple of 4 under
    // CommonMark. The fix replaces the leading whitespace bytes wholesale,
    // turning tabs into space-indented output.

    #[test]
    fn task_list_tab_indented_continuation_flagged() {
        // Two tabs → visual col 8, which overshoots both valid columns
        // for `- [ ] ` (content_col=2, task_col=6).
        let content = "- [ ] Task\n\t\twrap\n";
        let warnings = check(content);
        assert_eq!(warnings.len(), 1);
        assert!(warnings[0].message.contains("expected 2 or 6"));
        assert!(warnings[0].message.contains("found 8"));
    }

    #[test]
    fn fix_task_list_tab_indented_snaps_to_task_col() {
        // abs_diff(8, 6) = 2 < abs_diff(8, 2) = 6 → snap to task_col (6).
        let content = "- [ ] Task\n\t\twrap\n";
        let fixed = fix(content);
        assert_eq!(fixed, "- [ ] Task\n      wrap\n");
    }

    #[test]
    fn fix_task_list_single_tab_equidistant_snaps_to_content_col() {
        // One tab → visual col 4, equidistant from content_col (2) and
        // task_col (6). No siblings → tie-break to content_col.
        let content = "- [ ] Task\n\twrap\n";
        let fixed = fix(content);
        assert_eq!(fixed, "- [ ] Task\n  wrap\n");
    }

    // ── Blockquote × task-list ───────────────────────────────────────
    //
    // Blockquote-nested lists are a known limitation on MD077: the list
    // parser doesn't always expose them with the same column semantics as
    // top-level lists, and the rule prefers a false-negative default to
    // avoid spurious warnings inside blockquotes (see
    // `blockquote_list_under_indent_no_false_positive`). These tests pin
    // the current behavior so any future change is intentional.

    #[test]
    fn task_list_blockquote_post_checkbox_not_flagged() {
        // Post-checkbox alignment inside a blockquote — accepted as valid.
        let content = "> - [ ] Task\n>       continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn task_list_blockquote_between_cols_documented_limitation() {
        // Col-4-equivalent inside a blockquote is silently accepted — a
        // known MD077 limitation on blockquote-nested lists, not a task-
        // list-specific choice. Pinning the current behavior.
        let content = "> - [ ] Task\n>     continuation\n";
        assert!(check(content).is_empty());
    }

    #[test]
    fn task_list_blockquote_overshoot_documented_limitation() {
        // Overshoot inside a blockquote — same known limitation.
        let content = "> - [ ] Task\n>        continuation\n";
        assert!(check(content).is_empty());
    }

    // ── MkDocs × task × fix output ───────────────────────────────────
    //
    // MkDocs strict-indent raises `required` to max(content_col, 4) while
    // task_col stays at content_col + 4. The snap logic operates on the
    // raised required, not on the underlying content_col.

    #[test]
    fn fix_task_list_mkdocs_unordered_overshoot_snaps_to_task_col() {
        // `- [ ]` MkDocs: required=4, task_col=6. Col 7 → abs_diff(7,6)=1
        // < abs_diff(7,4)=3. Snap to task_col.
        let content = "- [ ] Task\n       continuation\n";
        let fixed = fix_mkdocs(content);
        assert_eq!(fixed, "- [ ] Task\n      continuation\n");
    }

    #[test]
    fn fix_task_list_mkdocs_unordered_tie_snaps_to_required() {
        // `- [ ]` MkDocs: required=4, task_col=6. Col 5 → abs_diff(5,6)=1
        // == abs_diff(5,4)=1. Tie with no siblings → required (4).
        let content = "- [ ] Task\n     continuation\n";
        let fixed = fix_mkdocs(content);
        assert_eq!(fixed, "- [ ] Task\n    continuation\n");
    }

    #[test]
    fn fix_task_list_mkdocs_ordered_overshoot_snaps_to_task_col() {
        // `1. [ ]` MkDocs: required=4, task_col=7. Col 8 → abs_diff(8,7)=1
        // < abs_diff(8,4)=4. Snap to task_col.
        let content = "1. [ ] Task\n        continuation\n";
        let fixed = fix_mkdocs(content);
        assert_eq!(fixed, "1. [ ] Task\n       continuation\n");
    }

    #[test]
    fn fix_task_list_mkdocs_ordered_near_required_snaps_to_required() {
        // `1. [ ]` MkDocs: required=4, task_col=7. Col 5 → abs_diff(5,7)=2
        // > abs_diff(5,4)=1. Snap to required (4). `1. [ ] Task\n     wrap`
        // has actual=5 which is over `required=4` so it's flagged in
        // strict mode, while in standard mode it falls under the lazy-
        // continuation window and isn't flagged at all.
        let content = "1. [ ] Task\n     continuation\n";
        let fixed = fix_mkdocs(content);
        assert_eq!(fixed, "1. [ ] Task\n    continuation\n");
    }

    #[test]
    fn fix_task_list_mkdocs_ordered_between_cols_snaps_to_task_col() {
        // `1. [ ]` MkDocs: required=4, task_col=7. Col 6 → abs_diff(6,7)=1
        // < abs_diff(6,4)=2. Snap to task_col (7).
        let content = "1. [ ] Task\n      continuation\n";
        let fixed = fix_mkdocs(content);
        assert_eq!(fixed, "1. [ ] Task\n       continuation\n");
    }

    // ── Fix idempotency (property test) ──────────────────────────────
    //
    // A fix pass on already-fixed content must produce the same content
    // — otherwise MD077 would oscillate on repeated invocations. This is
    // the core property that issue #579 was about (MD077 vs. MD013 fix
    // loop), and the integration test covers the MD013 interaction. The
    // property tests below pin the *internal* idempotency of MD077's own
    // fix, so any future change that introduces oscillation fails fast.

    fn assert_idempotent(content: &str) {
        let once = fix(content);
        let twice = fix(&once);
        assert_eq!(once, twice, "MD077 fix was not idempotent on input: {content:?}");
    }

    fn assert_idempotent_mkdocs(content: &str) {
        let once = fix_mkdocs(content);
        let twice = fix_mkdocs(&once);
        assert_eq!(
            once, twice,
            "MD077 (MkDocs) fix was not idempotent on input: {content:?}"
        );
    }

    #[test]
    fn idempotent_task_list_between_cols() {
        assert_idempotent("- [ ] Task\n    continuation\n");
    }

    #[test]
    fn idempotent_task_list_overshoot() {
        assert_idempotent("- [ ] Task\n       continuation\n");
    }

    #[test]
    fn idempotent_task_list_under_post_checkbox() {
        assert_idempotent("- [ ] Task\n   continuation\n");
    }

    #[test]
    fn idempotent_task_list_near_post_checkbox() {
        assert_idempotent("- [ ] Task\n     continuation\n");
    }

    #[test]
    fn idempotent_task_list_tab_overshoot() {
        assert_idempotent("- [ ] Task\n\t\twrap\n");
    }

    #[test]
    fn idempotent_task_list_single_tab() {
        assert_idempotent("- [ ] Task\n\twrap\n");
    }

    #[test]
    fn idempotent_task_list_ordered_overshoot() {
        assert_idempotent("1. [ ] Task\n        continuation\n");
    }

    #[test]
    fn idempotent_task_list_ordered_under() {
        assert_idempotent("1. [ ] Task\n    continuation\n");
    }

    #[test]
    fn idempotent_task_list_tie_with_sibling_at_task_col() {
        assert_idempotent("- [ ] Task\n      aligned\n    tied\n");
    }

    #[test]
    fn idempotent_task_list_tie_with_sibling_at_content_col() {
        assert_idempotent("- [ ] Task\n  aligned\n    tied\n");
    }

    #[test]
    fn idempotent_task_list_mkdocs_unordered_overshoot() {
        assert_idempotent_mkdocs("- [ ] Task\n       continuation\n");
    }

    #[test]
    fn idempotent_task_list_mkdocs_unordered_tie() {
        assert_idempotent_mkdocs("- [ ] Task\n     continuation\n");
    }

    #[test]
    fn idempotent_task_list_mkdocs_ordered_overshoot() {
        assert_idempotent_mkdocs("1. [ ] Task\n        continuation\n");
    }

    #[test]
    fn idempotent_task_list_mkdocs_ordered_between() {
        assert_idempotent_mkdocs("1. [ ] Task\n      continuation\n");
    }

    #[test]
    fn idempotent_task_list_reproducer_579() {
        // The exact reproducer from issue #579 already has correct indent
        // (col 6 = post-checkbox), so idempotency is trivially true. Pin
        // it anyway as a smoke test against future regressions.
        assert_idempotent(
            "- [ ] Lorem ipsum dolor sit amet, consectetur adipiscing\n      tempor incididunt ut labore.\n",
        );
    }

    #[test]
    fn idempotent_non_task_list_still_holds() {
        // Non-task items never enter the task_col code path; sanity-check
        // that idempotency is preserved for them too.
        assert_idempotent("1. Item\n    over-indented\n");
        assert_idempotent("- Item\n\n continuation\n");
    }

    // ── Non-task idempotency: loose-mode under-indent ────────────────
    //
    // When a blank line precedes the continuation (loose mode),
    // under-indented content is flagged and fixed up to the content
    // column. Idempotency pins that one pass of the fix is sufficient.

    #[test]
    fn idempotent_non_task_loose_under_indent_ordered() {
        // 1. Item → content col 3; "  x" is 2 spaces, under content col.
        assert_idempotent("1. Item\n\n  continuation\n");
    }

    #[test]
    fn idempotent_non_task_loose_under_indent_multi_digit() {
        // 10. Item → content col 4; single-space continuation needs 4.
        assert_idempotent("10. Item\n\n continuation\n");
    }

    #[test]
    fn idempotent_non_task_tight_over_indent_ordered() {
        // Tight-mode over-indent: 5 spaces where content col is 3.
        assert_idempotent("1. Item\n     over-indented\n");
    }

    // ── Non-task idempotency: fenced code block compound fix ─────────
    //
    // A fence opener that needs re-indenting is repaired by the
    // compound-fence fix which shifts opener + interior + closer
    // together. Idempotency pins that the compound fix settles in one
    // pass and does not oscillate between runs.

    #[test]
    fn idempotent_non_task_fence_ordered_loose() {
        // 1. Item → content col 3; fence at col 2 needs to shift to 3.
        assert_idempotent("1. Item\n\n  ```rust\n  let x = 1;\n  ```\n");
    }

    #[test]
    fn idempotent_non_task_fence_tilde_under_indent() {
        // Tilde fences use the same compound-fix path as backtick fences.
        // Interior below the list scope (col 0 here, required col 3) must
        // be promoted up in the same pass as the fence delimiters —
        // otherwise a second pass would flag the interior individually
        // and defeat idempotency.
        assert_idempotent("1. Item\n\n  ~~~\nplain text\n  ~~~\n");
    }

    #[test]
    fn idempotent_non_task_fence_interior_above_required() {
        // Interior already above the required column must not be pushed
        // further up by the compound fix — authored interior indentation
        // is preserved when it doesn't threaten fence pairing.
        assert_idempotent("1. Item\n\n  ```\n    deeply indented code\n  ```\n");
    }

    #[test]
    fn fence_fix_promotes_interior_below_scope_in_single_pass() {
        // Concrete behavioral check, not just idempotency:
        // interior at col 0 with opener at col 2, required 3, must land
        // at col 3 (same as opener) so fence pairing is preserved.
        let content = "1. Item\n\n  ```\ncode\n  ```\n";
        let fixed = fix(content);
        assert_eq!(fixed, "1. Item\n\n   ```\n   code\n   ```\n");
    }

    #[test]
    fn fence_fix_preserves_interior_above_required() {
        // Opener at col 2 → col 3 (required). Interior at col 4 stays at
        // col 4 (above required, no need to push it).
        let content = "1. Item\n\n  ```\n    code\n  ```\n";
        let fixed = fix(content);
        assert_eq!(fixed, "1. Item\n\n   ```\n    code\n   ```\n");
    }

    // ── Non-task idempotency: MkDocs strict-indent ───────────────────
    //
    // Under MkDocs flavor, continuation requires max(content_col, 4),
    // which can force a fix even when CommonMark would accept the
    // content. Pin idempotency for the non-task path there too.

    #[test]
    fn idempotent_non_task_mkdocs_ordered_at_3_spaces() {
        // CommonMark-valid (3 spaces) but MkDocs demands 4 → fix runs.
        assert_idempotent_mkdocs("1. Item\n\n   continuation\n");
    }

    #[test]
    fn idempotent_non_task_mkdocs_unordered_at_2_spaces() {
        // "- Item" → content col 2, but MkDocs raises the floor to 4.
        assert_idempotent_mkdocs("- Item\n\n  continuation\n");
    }

    #[test]
    fn idempotent_non_task_mkdocs_fence_compound() {
        // MkDocs non-task fence: opener/interior/closer shift together.
        assert_idempotent_mkdocs("1. Item\n\n   ```toml\n   k = 1\n   ```\n");
    }

    // ── style = "aligned" ──────────────────────────────────────────────

    #[test]
    fn aligned_tight_zero_indent_continuation_flagged() {
        // The core #682 case: a tight 0-indent lazy continuation is valid
        // CommonMark (and accepted by `any`), but `aligned` requires it to sit
        // at the content column.
        let content = "- this is a long line\nthat continues on a second line\n";
        let warnings = check_aligned(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(warnings[0].line, 2);
        assert_eq!(
            fix_aligned(content),
            "- this is a long line\n  that continues on a second line\n"
        );
    }

    #[test]
    fn aligned_full_issue_example_made_consistent() {
        // The full #682 example: every continuation line is snapped to the
        // content column, producing the consistent result the reporter wants.
        let content = "- this is a long line\n\
                       that continues on a second line\n\
                       - this is another long line\n\
                       \x20\x20that continues on the next line\n\
                       - yet again a long line\n\
                       and still inconsistently spaced\n\
                       \x20\x20and even worse\n";
        let expected = "- this is a long line\n\
                        \x20\x20that continues on a second line\n\
                        - this is another long line\n\
                        \x20\x20that continues on the next line\n\
                        - yet again a long line\n\
                        \x20\x20and still inconsistently spaced\n\
                        \x20\x20and even worse\n";
        assert_eq!(fix_aligned(content), expected);
        // And the fix is a fixpoint.
        assert_eq!(fix_aligned(expected), expected);
    }

    #[test]
    fn aligned_already_aligned_not_flagged() {
        let content = "- item\n  continuation at content column\n";
        assert!(check_aligned(content).is_empty());
    }

    #[test]
    fn aligned_tight_partial_indent_flagged() {
        // 1 space under "- " (content col 2): tight partial under-indent.
        let content = "- item\n continuation\n";
        let warnings = check_aligned(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(fix_aligned(content), "- item\n  continuation\n");
    }

    #[test]
    fn aligned_post_blank_zero_indent_still_new_paragraph() {
        // After a blank line, 0-indent content is a NEW paragraph that has left
        // the list - aligned mode must not reindent it back into the item.
        let content = "- item\n\nnew paragraph\n";
        assert!(check_aligned(content).is_empty());
        assert_eq!(fix_aligned(content), content);
    }

    // ── aligned: structural blocks must NOT be pulled into the list ────

    #[test]
    fn aligned_top_level_blockquote_after_list_untouched() {
        // A blockquote tight after a list item is a list-breaking separator,
        // not continuation. `in_list_block` is false for it, so aligned mode
        // must leave it alone (no reindent into the item).
        let content = "- item\n> quote\n";
        assert!(check_aligned(content).is_empty());
        assert_eq!(fix_aligned(content), content);
    }

    #[test]
    fn aligned_top_level_fence_after_list_untouched() {
        let content = "- item\n```\ncode\n```\n";
        assert!(check_aligned(content).is_empty());
        assert_eq!(fix_aligned(content), content);
    }

    #[test]
    fn aligned_top_level_table_after_list_untouched() {
        let content = "- item\n| a | b |\n|---|---|\n| 1 | 2 |\n";
        assert!(check_aligned(content).is_empty());
        assert_eq!(fix_aligned(content), content);
    }

    // ── aligned: nested lists ──────────────────────────────────────────

    #[test]
    fn aligned_nested_tight_lazy_continuation_aligns_to_inner() {
        // A tight lazy continuation after a nested item is, per CommonMark,
        // continuation of the innermost open item, so it aligns to the inner
        // item's content column (4), not the outer's (2). The outer item must
        // defer to the inner one.
        let content = "- Outer\n  - Inner\ncontinuation\n";
        let warnings = check_aligned(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(fix_aligned(content), "- Outer\n  - Inner\n    continuation\n");
    }

    #[test]
    fn aligned_nested_continuation_already_aligned_not_flagged() {
        let content = "- L1\n  - L2\n    cont of L2 at 4\n";
        assert!(check_aligned(content).is_empty());
    }

    #[test]
    fn aligned_nested_idempotent() {
        let content = "- Outer\n  - Inner\ncontinuation\n";
        let once = fix_aligned(content);
        assert_eq!(fix_aligned(&once), once);
    }

    #[test]
    fn aligned_three_level_nesting_aligns_to_innermost() {
        // The saw_nested cascade defers through every level, so the tight lazy
        // line aligns to L3's content column (6), the innermost open item.
        let content = "- L1\n  - L2\n    - L3\ncont\n";
        assert_eq!(fix_aligned(content), "- L1\n  - L2\n    - L3\n      cont\n");
    }

    #[test]
    fn aligned_continuation_after_sibling_owned_by_last_item() {
        // Tight lazy continuation after the second sibling belongs to that
        // sibling (no nesting), so it aligns to its content column (2).
        let content = "- a\n- b\nlazy\n";
        assert_eq!(fix_aligned(content), "- a\n- b\n  lazy\n");
    }

    #[test]
    fn aligned_multi_digit_ordered_marker_aligns_to_content_column() {
        let content = "10. Item\nwrap\n";
        assert_eq!(fix_aligned(content), "10. Item\n    wrap\n");
    }

    #[test]
    fn aligned_latent_setext_underline_is_left_alone() {
        // The underline is a lazy continuation, so the whole item renders as one
        // paragraph and no heading exists. Reindenting `Text` into the item would
        // promote the pair to a setext heading, changing the rendered structure,
        // so the item is skipped.
        let content = "- item\nText\n===\n";
        assert!(check_aligned(content).is_empty());
        assert_eq!(fix_aligned(content), content);
    }

    #[test]
    fn aligned_reindents_prose_that_only_looks_like_an_underline() {
        // Positive control for the guard above: `= = =` has internal spaces, so
        // it is not an underline and cannot be promoted. The item is reindented.
        let content = "- item\nText\n= = =\n";
        assert_eq!(fix_aligned(content), "- item\n  Text\n  = = =\n");
    }

    #[test]
    fn aligned_latent_marker_in_continuation_is_idempotent() {
        // Regression (fuzzer-found): a list-marker-looking line ("2. ") that the
        // parser absorbs as lazy continuation can be promoted to a real list
        // item once an earlier continuation line is reindented, re-attributing
        // later lines and breaking single-pass idempotency. Such items are not
        // reindented at all.
        let content = "# \n- \n``\n2. \n![]()";
        let once = fix_aligned(content);
        assert_eq!(fix_aligned(&once), once, "fix must be idempotent in one pass");
        assert_eq!(once, content, "item with a latent marker is left untouched");
    }

    #[test]
    fn aligned_latent_table_in_continuation_is_idempotent() {
        // Regression (fuzzer-found): a table-looking line that the parser
        // absorbs as lazy continuation (so it is NOT yet `in_table_block`) can
        // be promoted to a real table once an earlier line is reindented. Like
        // a latent marker, this re-parses the block, so the item is left alone.
        let content = "- \n![`]()\n|  | ` |\n| --- | --- |";
        let once = fix_aligned(content);
        assert_eq!(fix_aligned(&once), once, "fix must be idempotent in one pass");
        assert_eq!(once, content, "item with a latent table is left untouched");
    }

    #[test]
    fn aligned_blockquote_nested_list_not_touched() {
        // Lists inside blockquotes are a documented MD077 limitation (the scan
        // breaks at the blockquote prefix). Aligned inherits that conservative
        // no-false-positive behavior.
        let content = "> - item\n> wrap\n";
        assert!(check_aligned(content).is_empty());
        assert_eq!(fix_aligned(content), content);
    }

    // ── aligned: GFM task list items ───────────────────────────────────

    #[test]
    fn aligned_task_post_checkbox_column_accepted() {
        // Continuation aligned to the post-checkbox column (content_col + 4 = 6)
        // stays valid so aligned mode doesn't fight MD013 reflow.
        let content = "- [ ] Task\n      wrap\n";
        assert!(check_aligned(content).is_empty());
        assert_eq!(fix_aligned(content), content);
    }

    #[test]
    fn aligned_task_under_indent_snaps_to_content_column() {
        let content = "- [ ] Task\nwrap\n";
        let warnings = check_aligned(content);
        assert_eq!(warnings.len(), 1);
        assert_eq!(fix_aligned(content), "- [ ] Task\n  wrap\n");
    }

    // ── aligned: MkDocs flavor ─────────────────────────────────────────

    #[test]
    fn aligned_mkdocs_tight_under_indent_snaps_to_four() {
        // MkDocs raises the required indent to max(content_col, 4) = 4 for "- ".
        let content = "- item\nwrap\n";
        let warnings = check_aligned_mkdocs(content);
        assert_eq!(warnings.len(), 1);
        let ctx = LintContext::new(content, MarkdownFlavor::MkDocs, None);
        assert_eq!(aligned_rule().fix(&ctx).unwrap(), "- item\n    wrap\n");
    }

    // ── any (default) regression: tight lazy continuation untouched ────

    #[test]
    fn any_default_does_not_flag_tight_lazy_continuation() {
        // The default style must preserve CommonMark lazy continuation.
        let content = "- item\nwrapped at zero indent\n";
        assert!(check(content).is_empty());
        assert_eq!(fix(content), content);
    }

    #[test]
    fn from_config_aligned_enables_tight_flagging() {
        // End-to-end: `[MD077] style = "aligned"` wires through from_config.
        let mut config = crate::config::Config::default();
        let mut rule_config = crate::config::RuleConfig::default();
        rule_config
            .values
            .insert("style".to_string(), toml::Value::String("aligned".to_string()));
        config.rules.insert("MD077".to_string(), rule_config);

        let rule = MD077ListContinuationIndent::from_config(&config);
        let ctx = LintContext::new("- item\nwrap\n", MarkdownFlavor::Standard, None);
        assert_eq!(rule.check(&ctx).unwrap().len(), 1);
    }

    #[test]
    fn from_config_default_is_any() {
        // No config -> default `any` -> tight lazy continuation untouched.
        let config = crate::config::Config::default();
        let rule = MD077ListContinuationIndent::from_config(&config);
        let ctx = LintContext::new("- item\nwrap\n", MarkdownFlavor::Standard, None);
        assert!(rule.check(&ctx).unwrap().is_empty());
    }

    #[test]
    fn from_config_indent_sets_fixed_requirement() {
        // End-to-end: `[MD077] indent = 4` wires through from_config and
        // requires continuation content to sit 4 spaces past the marker.
        let mut config = crate::config::Config::default();
        let mut rule_config = crate::config::RuleConfig::default();
        rule_config.values.insert("indent".to_string(), toml::Value::Integer(4));
        config.rules.insert("MD077".to_string(), rule_config);

        let rule = MD077ListContinuationIndent::from_config(&config);

        // "- item\n    wrap\n" -> continuation at 4 spaces: accepted.
        let ok_ctx = LintContext::new("- item\n    wrap\n", MarkdownFlavor::Standard, None);
        assert!(rule.check(&ok_ctx).unwrap().is_empty());
        assert_eq!(rule.fix(&ok_ctx).unwrap(), "- item\n    wrap\n");

        // "- item\n\n  wrap\n" -> continuation at 2 spaces after a blank line:
        // flagged as under-indented (would escape the list item).
        let bad_ctx = LintContext::new("- item\n\n  wrap\n", MarkdownFlavor::Standard, None);
        let warnings = rule.check(&bad_ctx).unwrap();
        assert_eq!(warnings.len(), 1);
        assert!(warnings[0].message.contains("needs 4 spaces"));
    }

    #[test]
    fn from_config_indent_applies_per_nested_marker() {
        // With a fixed indent, each item's requirement is its own marker
        // column plus the configured indent (nested item marker at 2 -> 6).
        let mut config = crate::config::Config::default();
        let mut rule_config = crate::config::RuleConfig::default();
        rule_config.values.insert("indent".to_string(), toml::Value::Integer(4));
        config.rules.insert("MD077".to_string(), rule_config);

        let rule = MD077ListContinuationIndent::from_config(&config);
        let ctx = LintContext::new("- a\n  - b\n      wrap\n", MarkdownFlavor::Standard, None);
        let warnings = rule.check(&ctx).unwrap();
        assert!(
            warnings.is_empty(),
            "continuation at 6 spaces should pass: {warnings:?}"
        );
    }

    /// A rule configured through the real `[MD077]` config path.
    fn rule_with(settings: &[(&str, toml::Value)]) -> Box<dyn Rule> {
        let mut config = crate::config::Config::default();
        let mut rule_config = crate::config::RuleConfig::default();
        for (key, value) in settings {
            rule_config.values.insert((*key).to_string(), value.clone());
        }
        config.rules.insert("MD077".to_string(), rule_config);
        MD077ListContinuationIndent::from_config(&config)
    }

    #[test]
    fn configured_indent_cannot_lower_the_strict_flavor_minimum() {
        // The MkDocs 4-space minimum is what the renderer needs to read a line
        // as part of the item, so `indent = 2` may not pull it down to 2 - that
        // would have `fix` rewrite a rendering document into a broken one.
        let rule = rule_with(&[("indent", toml::Value::Integer(2))]);

        let two = LintContext::new("- item\n\n  wrap\n", MarkdownFlavor::MkDocs, None);
        let warnings = rule.check(&two).unwrap();
        assert_eq!(warnings.len(), 1, "2 spaces is below the MkDocs minimum: {warnings:?}");
        assert!(
            warnings[0].message.contains("needs 4 spaces") && warnings[0].message.contains("MkDocs"),
            "the requirement comes from MkDocs, so the message must say so: {}",
            warnings[0].message
        );
        assert_eq!(rule.fix(&two).unwrap(), "- item\n\n    wrap\n");

        // Control: a document already at the minimum is left alone.
        let four = LintContext::new("- item\n\n    wrap\n", MarkdownFlavor::MkDocs, None);
        assert!(rule.check(&four).unwrap().is_empty());

        // Control: the clamp is scoped to the strict flavor. Under the standard
        // flavor the same setting means exactly what it says, and 4 is then an
        // over-indent to be snapped back to 2.
        let standard = LintContext::new("- item\n\n    wrap\n", MarkdownFlavor::Standard, None);
        assert_eq!(rule.check(&standard).unwrap().len(), 1);
        assert_eq!(rule.fix(&standard).unwrap(), "- item\n\n  wrap\n");
    }

    #[test]
    fn configured_indent_can_raise_the_strict_flavor_minimum() {
        // The clamp is a floor, not a fixed value: above 4 the configured indent
        // still governs under the MkDocs flavor.
        let rule = rule_with(&[("indent", toml::Value::Integer(6))]);
        let ctx = LintContext::new("- item\n\n    wrap\n", MarkdownFlavor::MkDocs, None);
        let warnings = rule.check(&ctx).unwrap();
        assert_eq!(warnings.len(), 1);
        assert!(
            warnings[0].message.contains("needs 6 spaces"),
            "configured 6 must win over the 4-space floor: {}",
            warnings[0].message
        );
        assert_eq!(rule.fix(&ctx).unwrap(), "- item\n\n      wrap\n");
    }

    #[test]
    fn configured_indent_message_does_not_claim_a_structural_consequence() {
        // Two spaces under a `- ` marker keeps the content in the list item, so
        // a message blaming list membership would be false. The requirement is
        // the configured one and the message has to say which.
        let rule = rule_with(&[("indent", toml::Value::Integer(4))]);
        let ctx = LintContext::new("- item\n\n  wrap\n", MarkdownFlavor::Standard, None);
        let warnings = rule.check(&ctx).unwrap();
        assert_eq!(warnings.len(), 1);
        assert!(
            warnings[0].message.contains("match the configured indent"),
            "expected the configured-indent wording, got: {}",
            warnings[0].message
        );
        assert!(
            !warnings[0].message.contains("remain part of the list"),
            "the content does remain part of the list here: {}",
            warnings[0].message
        );

        // Control: the default rule reports the same document as clean, which is
        // what makes the structural claim wrong above.
        assert!(check("- item\n\n  wrap\n").is_empty());

        // Control: content that really would escape the item still gets the
        // structural message, so the wording was narrowed and not replaced.
        let escaping = check("- item\n\n wrap\n");
        assert_eq!(escaping.len(), 1);
        assert!(
            escaping[0].message.contains("remain part of the list"),
            "unconfigured under-indent keeps its structural message, got: {}",
            escaping[0].message
        );
    }

    #[test]
    fn configured_indent_leaves_tight_lazy_continuation_to_style() {
        // `indent` sets what the requirement is; `style` decides which lines are
        // measured against it. A tight continuation is CommonMark lazy
        // continuation, so `any` accepts it however the requirement was derived.
        let any = rule_with(&[("indent", toml::Value::Integer(4))]);
        let ctx = LintContext::new("- item\n  wrap\n", MarkdownFlavor::Standard, None);
        assert!(
            any.check(&ctx).unwrap().is_empty(),
            "style = any accepts tight lazy continuation"
        );

        let aligned = rule_with(&[
            ("indent", toml::Value::Integer(4)),
            ("style", toml::Value::String("aligned".to_string())),
        ]);
        let warnings = aligned.check(&ctx).unwrap();
        assert_eq!(warnings.len(), 1, "style = aligned raises it: {warnings:?}");
        assert!(warnings[0].message.contains("expected 4"));
        assert_eq!(aligned.fix(&ctx).unwrap(), "- item\n    wrap\n");
    }

    #[test]
    fn aligned_tight_underindented_fence_inside_item_left_alone() {
        // A fenced block is a structural construct; aligned mode does not
        // reindent it (the `in_code_block` guard), so a tight under-indented
        // fence is a no-op rather than a risky delimiter-only rewrite.
        let content = "- item\n ```\n code\n ```\n";
        assert!(check_aligned(content).is_empty());
        assert_eq!(fix_aligned(content), content);
    }

    #[test]
    fn aligned_task_under_indent_fix_is_idempotent() {
        let content = "- [ ] Task\nwrap\n";
        let once = fix_aligned(content);
        assert_eq!(fix_aligned(&once), once);
    }

    #[test]
    fn aligned_partial_indent_fix_is_idempotent() {
        let content = "- item\n continuation\n";
        let once = fix_aligned(content);
        assert_eq!(fix_aligned(&once), once);
    }
}