rumdl_lib/rules/

md018_no_missing_space_atx.rs

/// Rule MD018: No missing space after ATX heading marker
///
/// See [docs/md018.md](../../docs/md018.md) for full documentation, configuration, and examples.
mod md018_config;

pub(super) use md018_config::MD018Config;

use crate::config::MarkdownFlavor;
use crate::lint_context::{AtxMissingSpace, LineInfo};
use crate::rule::{Fix, LintError, LintResult, LintWarning, Rule, RuleCategory, Severity};
use crate::utils::obsidian_tag::TAG_PATTERN;
use crate::utils::range_utils::{byte_to_char_count, calculate_single_line_range};
use regex::Regex;
use std::sync::LazyLock;

// Emoji and Unicode hashtag patterns
const EMOJI_HASHTAG_PATTERN_STR: &str = r"^#️⃣|^#⃣";
const UNICODE_HASHTAG_PATTERN_STR: &str = r"^#[\u{FE0F}\u{20E3}]";
static EMOJI_HASHTAG_PATTERN: LazyLock<Regex> = LazyLock::new(|| Regex::new(EMOJI_HASHTAG_PATTERN_STR).unwrap());
static UNICODE_HASHTAG_PATTERN: LazyLock<Regex> = LazyLock::new(|| Regex::new(UNICODE_HASHTAG_PATTERN_STR).unwrap());

// MagicLink issue/PR reference pattern: #123, #10, etc.
// Matches # followed by one or more digits, then either end of string,
// whitespace, or punctuation (not alphanumeric continuation)
const MAGICLINK_REF_PATTERN_STR: &str = r"^#\d+(?:\s|[^a-zA-Z0-9]|$)";
static MAGICLINK_REF_PATTERN: LazyLock<Regex> = LazyLock::new(|| Regex::new(MAGICLINK_REF_PATTERN_STR).unwrap());

#[derive(Clone)]
pub struct MD018NoMissingSpaceAtx {
    config: MD018Config,
}

impl Default for MD018NoMissingSpaceAtx {
    fn default() -> Self {
        Self::new()
    }
}

impl MD018NoMissingSpaceAtx {
    pub fn new() -> Self {
        Self {
            config: MD018Config::default(),
        }
    }

    pub fn from_config_struct(config: MD018Config) -> Self {
        Self { config }
    }

    /// Check if a line is a MagicLink-style issue/PR reference (e.g., #123, #10)
    /// Used by MkDocs flavor to skip PyMdown MagicLink patterns
    fn is_magiclink_ref(line: &str) -> bool {
        MAGICLINK_REF_PATTERN.is_match(line.trim_start())
    }

    /// Check if a line is a tag (e.g., #tagname, #project/active, #3d_printing)
    fn is_tag(line: &str) -> bool {
        TAG_PATTERN.is_match(line.trim_start())
    }

    /// Whether tag patterns should be recognized for the given flavor
    fn tags_enabled(&self, flavor: MarkdownFlavor) -> bool {
        self.config.tags_enabled(flavor)
    }

    /// Drops Unicode whitespace (NBSP, em space, ideographic space, ...) that follows the
    /// hashes. CommonMark only strips ASCII spaces and tabs, so inserting a space in front of
    /// such a character would leave it in the heading text. Text that is all whitespace is kept.
    fn without_leading_unicode_space(text: &str) -> &str {
        let rest = text.trim_start_matches(char::is_whitespace);
        if rest.is_empty() { text } else { rest }
    }

    /// Check if an ATX heading line is missing space after the marker
    fn check_atx_heading_line(&self, line: &str, flavor: MarkdownFlavor) -> Option<(usize, String)> {
        // Look for ATX marker at start of line (with optional indentation)
        let trimmed_line = line.trim_start();
        let indent = line.len() - trimmed_line.len();

        if !trimmed_line.starts_with('#') {
            return None;
        }

        // Only flag patterns at column 1 (no indentation) to match markdownlint behavior
        // Indented patterns are likely:
        // - Multi-line link continuations (e.g., "  #sig-contribex](url)")
        // - List item content
        // - Other continuation contexts
        if indent > 0 {
            return None;
        }

        // Skip emoji hashtags and Unicode hashtag patterns
        let is_emoji = EMOJI_HASHTAG_PATTERN.is_match(trimmed_line);
        let is_unicode = UNICODE_HASHTAG_PATTERN.is_match(trimmed_line);
        if is_emoji || is_unicode {
            return None;
        }

        // Count the number of hashes
        let hash_count = trimmed_line.chars().take_while(|&c| c == '#').count();
        if hash_count == 0 || hash_count > 6 {
            return None;
        }

        // Check what comes after the hashes
        let after_hashes = &trimmed_line[hash_count..];

        // Skip if what follows the hashes is an emoji modifier or variant selector
        if after_hashes
            .chars()
            .next()
            .is_some_and(|ch| matches!(ch, '\u{FE0F}' | '\u{20E3}' | '\u{FE0E}'))
        {
            return None;
        }

        // If there's content immediately after hashes (no space), it needs fixing
        if !after_hashes.is_empty() && !after_hashes.starts_with(' ') && !after_hashes.starts_with('\t') {
            // Additional checks to avoid false positives
            let content = after_hashes.trim();

            // Skip if it's just more hashes (horizontal rule)
            if content.chars().all(|c| c == '#') {
                return None;
            }

            // Skip if content is too short to be meaningful
            if content.len() < 2 {
                return None;
            }

            // Skip if it starts with emphasis markers
            if content.starts_with('*') || content.starts_with('_') {
                return None;
            }

            // MagicLink config: skip MagicLink-style issue/PR refs (#123, #10, etc.)
            // MagicLink only uses single #, so check hash_count == 1
            if self.config.magiclink && hash_count == 1 && Self::is_magiclink_ref(line) {
                return None;
            }

            // Tags mode: skip tag syntax (#tagname, #project/active, etc.)
            // Tags only use single #
            if self.tags_enabled(flavor) && hash_count == 1 && Self::is_tag(line) {
                return None;
            }

            // This looks like a malformed heading that needs a space
            let fixed = format!(
                "{}{} {}",
                " ".repeat(indent),
                "#".repeat(hash_count),
                Self::without_leading_unicode_space(after_hashes)
            );
            return Some((indent + hash_count, fixed));
        }

        None
    }

    /// Split a line the parser found missing the space after its `#`s into its
    /// marker and the text that follows it, or `None` when the line is left
    /// alone: indented (MD018 flags column 1 only, like markdownlint), an emoji
    /// or Unicode hashtag, a MagicLink reference, or a tag.
    fn missing_space_split<'a>(
        &self,
        line: &'a str,
        indent: usize,
        missing: AtxMissingSpace,
        flavor: MarkdownFlavor,
    ) -> Option<(&'a str, &'a str)> {
        if indent > 0 {
            return None;
        }
        let trimmed = &line[indent..];
        if EMOJI_HASHTAG_PATTERN.is_match(trimmed) || UNICODE_HASHTAG_PATTERN.is_match(trimmed) {
            return None;
        }
        if missing.level == 1
            && ((self.config.magiclink && Self::is_magiclink_ref(line))
                || (self.tags_enabled(flavor) && Self::is_tag(line)))
        {
            return None;
        }
        let (marker, after_marker) = trimmed.split_at_checked(usize::from(missing.level))?;
        (!after_marker.is_empty()).then_some((marker, after_marker))
    }

    /// Whether a line the parser recorded nothing for may still be a heading
    /// missing its space: an ATX-shaped line the heading pass does not reach.
    /// A setext heading's text lines are
    /// heading text, recorded only on the last of them, so they are excluded.
    fn may_be_unrecorded_missing_space(line_info: &LineInfo) -> bool {
        line_info.heading.is_none()
            && !line_info.is_setext_heading_text
            && !line_info.in_code_block
            && !line_info.in_front_matter
            && !line_info.in_html_comment
            && !line_info.in_mdx_comment
            && !line_info.is_blank
    }
}

impl Rule for MD018NoMissingSpaceAtx {
    fn native_format_policy(&self) -> Option<crate::format_proof::NativeFormatPolicy> {
        (self.config == Default::default()).then_some(crate::format_proof::NativeFormatPolicy::for_rule::<Self>(18))
    }

    fn name(&self) -> &'static str {
        "MD018"
    }

    fn description(&self) -> &'static str {
        "No space after hash in heading"
    }

    fn check(&self, ctx: &crate::lint_context::LintContext) -> LintResult {
        let mut warnings = Vec::new();

        // A quoted setext heading's text lines are heading text, not ATX candidates.
        let quoted_setext_lines: std::collections::HashSet<usize> = ctx
            .headings()
            .filter(|h| h.is_blockquote() && h.is_setext())
            .flat_map(|h| (h.first_line_num() - 1)..h.line_num)
            .collect();

        // Check every line the parser found missing the space after its `#`s
        let edges = crate::utils::blockquote::container_edges(ctx);

        let source = ctx
            .candidate_line_indices(crate::lint_context::LineCandidateKind::Hash)
            .iter()
            .map(|&index| (index, &ctx.lines[index]));

        for (line_num, line_info) in source {
            if line_info.atx_missing_space.is_none()
                && (!Self::may_be_unrecorded_missing_space(line_info)
                    || (line_info.blockquote.is_none()
                        && line_info.list_item.is_none()
                        && !line_info.content(ctx.content).trim_start().starts_with('#')))
            {
                continue;
            }
            let marker_byte = line_info.byte_offset + line_info.indent;
            if line_info.in_esm_block
                || ctx.is_in_code_span_byte(marker_byte)
                || ctx.is_in_parsed_link(marker_byte)
                || ctx.overlaps_template_code(marker_byte, marker_byte + 1)
                || ctx.is_in_html_tag(marker_byte)
                || ctx.overlaps_mdx_inline_code(marker_byte, marker_byte + 1)
                || ctx.is_in_jsx_component_tag(marker_byte)
            {
                continue;
            }
            // Skip lines inside HTML blocks, HTML comments, or PyMdown blocks
            if line_info.in_html_block
                || line_info.in_html_comment
                || line_info.in_mdx_comment
                || line_info.in_pymdown_block
            {
                continue;
            }

            if let Some(missing) = line_info.atx_missing_space {
                let line = line_info.content(ctx.content);
                if let Some((marker, after_marker)) =
                    self.missing_space_split(line, line_info.indent, missing, ctx.flavor)
                {
                    // The indent and '#' markers are ASCII, so convert the byte
                    // offset to a character column.
                    let hash_end_col = byte_to_char_count(line, line_info.indent + marker.len());
                    let (start_line, start_col, end_line, end_col) = calculate_single_line_range(
                        line_num + 1, // Convert to 1-indexed
                        hash_end_col,
                        0, // Zero-width to indicate missing space
                    );

                    warnings.push(LintWarning {
                        rule_name: Some(self.name().to_string()),
                        message: format!("No space after {marker} in heading"),
                        line: start_line,
                        column: start_col,
                        end_line,
                        end_column: end_col,
                        severity: Severity::Warning,
                        fix: Some(Fix::new(ctx.line_content_byte_range(line_num + 1), {
                            // Preserve original indentation (including tabs)
                            let original_indent = &line[..line_info.indent];
                            format!(
                                "{original_indent}{marker} {}",
                                Self::without_leading_unicode_space(after_marker)
                            )
                        })),
                    });
                }
            } else if Self::may_be_unrecorded_missing_space(line_info) {
                // Inside a blockquote the heading candidate is the quoted content,
                // and the quote prefix stays out of the reported range and the fix.
                let line = line_info.content(ctx.content);
                let (prefix_len, quoted_content) = if line_info.blockquote.is_some() {
                    if quoted_setext_lines.contains(&line_num) {
                        continue;
                    }
                    match crate::utils::blockquote::parse_blockquote_prefix(line) {
                        Some(parsed)
                            if crate::utils::blockquote::quote_markers_are_real(line)
                                && !crate::utils::blockquote::quote_markers_are_paragraph_text(
                                    ctx, &edges, line_num, line,
                                ) =>
                        {
                            (line.len() - parsed.content.len(), parsed.content)
                        }
                        _ => continue,
                    }
                } else {
                    (0, line)
                };
                // A quote opened inside a list item (`- > #Bad`) holds the candidate.
                let (prefix_len, quoted_content) = match line_info
                    .list_item
                    .as_ref()
                    .and_then(|_| crate::utils::blockquote::quote_text_start_in_items(line, prefix_len))
                {
                    Some(_) if quoted_setext_lines.contains(&line_num) => continue,
                    Some(start) => (start, &line[start..]),
                    None => (prefix_len, quoted_content),
                };
                // Check for malformed headings that weren't detected as proper headings
                if let Some((hash_end_pos, fixed_line)) = self.check_atx_heading_line(quoted_content, ctx.flavor) {
                    let hash_end_col = line[..prefix_len].chars().count() + hash_end_pos;
                    let (start_line, start_col, end_line, end_col) = calculate_single_line_range(
                        line_num + 1,     // Convert to 1-indexed
                        hash_end_col + 1, // 1-indexed column
                        0,                // Zero-width to indicate missing space
                    );

                    let fixed = format!("{}{}", &line[..prefix_len], fixed_line);
                    warnings.push(LintWarning {
                        rule_name: Some(self.name().to_string()),
                        message: "No space after hash in heading".to_string(),
                        line: start_line,
                        column: start_col,
                        end_line,
                        end_column: end_col,
                        severity: Severity::Warning,
                        fix: Some(Fix::new(ctx.line_content_byte_range(line_num + 1), fixed)),
                    });
                }
            }
        }

        Ok(warnings)
    }

    fn fixes_from_diagnostics(&self) -> bool {
        true
    }

    fn fix(&self, ctx: &crate::lint_context::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());
        crate::utils::fix_utils::apply_warning_fixes(ctx.content, &warnings)
            .map_err(crate::rule::LintError::InvalidInput)
    }

    /// Get the category of this rule for selective processing
    fn category(&self) -> RuleCategory {
        RuleCategory::Heading
    }

    /// Check if this rule should be skipped
    fn should_skip(&self, ctx: &crate::lint_context::LintContext) -> bool {
        // Fast path: check if document likely has headings
        !ctx.likely_has_headings()
    }

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

    crate::impl_rule_config_methods!(MD018Config);
}

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

    #[test]
    fn test_basic_functionality() {
        let rule = MD018NoMissingSpaceAtx::new();

        // Test with correct space
        let content = "# Heading 1\n## Heading 2\n### Heading 3";
        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();
        assert!(result.is_empty());

        // Test with missing space
        let content = "#Heading 1\n## Heading 2\n###Heading 3";
        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();
        assert_eq!(result.len(), 2); // Should flag the two headings with missing spaces
        assert_eq!(result[0].line, 1);
        assert_eq!(result[1].line, 3);
    }

    #[test]
    fn test_malformed_heading_detection() {
        let rule = MD018NoMissingSpaceAtx::new();

        // Test the check_atx_heading_line method
        assert!(
            rule.check_atx_heading_line("##Introduction", MarkdownFlavor::Standard)
                .is_some()
        );
        assert!(
            rule.check_atx_heading_line("###Background", MarkdownFlavor::Standard)
                .is_some()
        );
        assert!(
            rule.check_atx_heading_line("####Details", MarkdownFlavor::Standard)
                .is_some()
        );
        assert!(
            rule.check_atx_heading_line("#Summary", MarkdownFlavor::Standard)
                .is_some()
        );
        assert!(
            rule.check_atx_heading_line("######Conclusion", MarkdownFlavor::Standard)
                .is_some()
        );
        assert!(
            rule.check_atx_heading_line("##Table of Contents", MarkdownFlavor::Standard)
                .is_some()
        );

        // Should NOT detect these
        assert!(rule.check_atx_heading_line("###", MarkdownFlavor::Standard).is_none()); // Just hashes
        assert!(rule.check_atx_heading_line("#", MarkdownFlavor::Standard).is_none()); // Single hash
        assert!(rule.check_atx_heading_line("##a", MarkdownFlavor::Standard).is_none()); // Too short
        assert!(
            rule.check_atx_heading_line("#*emphasis", MarkdownFlavor::Standard)
                .is_none()
        ); // Emphasis marker
        assert!(
            rule.check_atx_heading_line("#######TooBig", MarkdownFlavor::Standard)
                .is_none()
        ); // More than 6 hashes
    }

    #[test]
    fn test_malformed_heading_with_context() {
        let rule = MD018NoMissingSpaceAtx::new();

        // Test with full content that includes code blocks
        let content = r#"# Test Document

##Introduction
This should be detected.

    ##CodeBlock
This should NOT be detected (indented code block).

```
##FencedCodeBlock
This should NOT be detected (fenced code block).
```

##Conclusion
This should be detected.
"#;

        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should detect malformed headings but ignore code blocks
        let detected_lines: Vec<usize> = result.iter().map(|w| w.line).collect();
        assert!(detected_lines.contains(&3)); // ##Introduction
        assert!(detected_lines.contains(&14)); // ##Conclusion (updated line number)
        assert!(!detected_lines.contains(&6)); // ##CodeBlock (should be ignored)
        assert!(!detected_lines.contains(&10)); // ##FencedCodeBlock (should be ignored)
    }

    #[test]
    fn test_malformed_heading_fix() {
        let rule = MD018NoMissingSpaceAtx::new();

        let content = r#"##Introduction
This is a test.

###Background
More content."#;

        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let fixed = rule.fix(&ctx).unwrap();

        let expected = r#"## Introduction
This is a test.

### Background
More content."#;

        assert_eq!(fixed, expected);
    }

    #[test]
    fn test_mixed_proper_and_malformed_headings() {
        let rule = MD018NoMissingSpaceAtx::new();

        let content = r#"# Proper Heading

##Malformed Heading

## Another Proper Heading

###Another Malformed

#### Proper with space
"#;

        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should only detect the malformed ones
        assert_eq!(result.len(), 2);
        let detected_lines: Vec<usize> = result.iter().map(|w| w.line).collect();
        assert!(detected_lines.contains(&3)); // ##Malformed Heading
        assert!(detected_lines.contains(&7)); // ###Another Malformed
    }

    #[test]
    fn test_css_selectors_in_html_blocks() {
        let rule = MD018NoMissingSpaceAtx::new();

        // Test CSS selectors inside <style> tags should not trigger MD018
        // This is a common pattern in Quarto/RMarkdown files
        let content = r#"# Proper Heading

<style>
#slide-1 ol li {
    margin-top: 0;
}

#special-slide ol li {
    margin-top: 2em;
}
</style>

## Another Heading
"#;

        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should not detect CSS selectors as malformed headings
        assert_eq!(
            result.len(),
            0,
            "CSS selectors in <style> blocks should not be flagged as malformed headings"
        );
    }

    #[test]
    fn test_js_code_in_script_blocks() {
        let rule = MD018NoMissingSpaceAtx::new();

        // Test that patterns like #element in <script> tags don't trigger MD018
        let content = r#"# Heading

<script>
const element = document.querySelector('#main-content');
#another-comment
</script>

## Another Heading
"#;

        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should not detect JS code as malformed headings
        assert_eq!(
            result.len(),
            0,
            "JavaScript code in <script> blocks should not be flagged as malformed headings"
        );
    }

    #[test]
    fn test_all_malformed_headings_detected() {
        let rule = MD018NoMissingSpaceAtx::new();

        // All patterns at line start should be detected as malformed headings
        // (matching markdownlint behavior)

        // Lowercase single-hash - should be detected
        assert!(
            rule.check_atx_heading_line("#hello", MarkdownFlavor::Standard)
                .is_some(),
            "#hello SHOULD be detected as malformed heading"
        );
        assert!(
            rule.check_atx_heading_line("#tag", MarkdownFlavor::Standard).is_some(),
            "#tag SHOULD be detected as malformed heading"
        );
        assert!(
            rule.check_atx_heading_line("#hashtag", MarkdownFlavor::Standard)
                .is_some(),
            "#hashtag SHOULD be detected as malformed heading"
        );
        assert!(
            rule.check_atx_heading_line("#javascript", MarkdownFlavor::Standard)
                .is_some(),
            "#javascript SHOULD be detected as malformed heading"
        );

        // Numeric patterns - should be detected (could be headings like "# 123")
        assert!(
            rule.check_atx_heading_line("#123", MarkdownFlavor::Standard).is_some(),
            "#123 SHOULD be detected as malformed heading"
        );
        assert!(
            rule.check_atx_heading_line("#12345", MarkdownFlavor::Standard)
                .is_some(),
            "#12345 SHOULD be detected as malformed heading"
        );
        assert!(
            rule.check_atx_heading_line("#29039)", MarkdownFlavor::Standard)
                .is_some(),
            "#29039) SHOULD be detected as malformed heading"
        );

        // Uppercase single-hash - should be detected
        assert!(
            rule.check_atx_heading_line("#Summary", MarkdownFlavor::Standard)
                .is_some(),
            "#Summary SHOULD be detected as malformed heading"
        );
        assert!(
            rule.check_atx_heading_line("#Introduction", MarkdownFlavor::Standard)
                .is_some(),
            "#Introduction SHOULD be detected as malformed heading"
        );
        assert!(
            rule.check_atx_heading_line("#API", MarkdownFlavor::Standard).is_some(),
            "#API SHOULD be detected as malformed heading"
        );

        // Multi-hash patterns - should be detected
        assert!(
            rule.check_atx_heading_line("##introduction", MarkdownFlavor::Standard)
                .is_some(),
            "##introduction SHOULD be detected as malformed heading"
        );
        assert!(
            rule.check_atx_heading_line("###section", MarkdownFlavor::Standard)
                .is_some(),
            "###section SHOULD be detected as malformed heading"
        );
        assert!(
            rule.check_atx_heading_line("###fer", MarkdownFlavor::Standard)
                .is_some(),
            "###fer SHOULD be detected as malformed heading"
        );
        assert!(
            rule.check_atx_heading_line("##123", MarkdownFlavor::Standard).is_some(),
            "##123 SHOULD be detected as malformed heading"
        );
    }

    #[test]
    fn test_patterns_that_should_not_be_flagged() {
        let rule = MD018NoMissingSpaceAtx::new();

        // Just hashes (horizontal rule or empty)
        assert!(rule.check_atx_heading_line("###", MarkdownFlavor::Standard).is_none());
        assert!(rule.check_atx_heading_line("#", MarkdownFlavor::Standard).is_none());

        // Content too short
        assert!(rule.check_atx_heading_line("##a", MarkdownFlavor::Standard).is_none());

        // Emphasis markers
        assert!(
            rule.check_atx_heading_line("#*emphasis", MarkdownFlavor::Standard)
                .is_none()
        );

        // More than 6 hashes
        assert!(
            rule.check_atx_heading_line("#######TooBig", MarkdownFlavor::Standard)
                .is_none()
        );

        // Proper headings with space
        assert!(
            rule.check_atx_heading_line("# Hello", MarkdownFlavor::Standard)
                .is_none()
        );
        assert!(
            rule.check_atx_heading_line("## World", MarkdownFlavor::Standard)
                .is_none()
        );
        assert!(
            rule.check_atx_heading_line("### Section", MarkdownFlavor::Standard)
                .is_none()
        );
    }

    #[test]
    fn test_inline_issue_refs_not_at_line_start() {
        let rule = MD018NoMissingSpaceAtx::new();

        // Inline patterns (not at line start) are not checked by check_atx_heading_line
        // because that function only checks lines that START with #

        // These should return None because they don't start with #
        assert!(
            rule.check_atx_heading_line("See issue #123", MarkdownFlavor::Standard)
                .is_none()
        );
        assert!(
            rule.check_atx_heading_line("Check #trending on Twitter", MarkdownFlavor::Standard)
                .is_none()
        );
        assert!(
            rule.check_atx_heading_line("- fix: issue #29039", MarkdownFlavor::Standard)
                .is_none()
        );
    }

    #[test]
    fn test_lowercase_patterns_full_check() {
        // Integration test: verify lowercase patterns are flagged through full check() flow
        let rule = MD018NoMissingSpaceAtx::new();

        let content = "#hello\n\n#world\n\n#tag";
        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        assert_eq!(result.len(), 3, "All three lowercase patterns should be flagged");
        assert_eq!(result[0].line, 1);
        assert_eq!(result[1].line, 3);
        assert_eq!(result[2].line, 5);
    }

    #[test]
    fn test_numeric_patterns_full_check() {
        // Integration test: verify numeric patterns are flagged through full check() flow
        let rule = MD018NoMissingSpaceAtx::new();

        let content = "#123\n\n#456\n\n#29039";
        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        assert_eq!(result.len(), 3, "All three numeric patterns should be flagged");
    }

    #[test]
    fn test_fix_lowercase_patterns() {
        // Verify fix() correctly handles lowercase patterns
        let rule = MD018NoMissingSpaceAtx::new();

        let content = "#hello\nSome text.\n\n#world";
        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let fixed = rule.fix(&ctx).unwrap();

        let expected = "# hello\nSome text.\n\n# world";
        assert_eq!(fixed, expected);
    }

    #[test]
    fn test_fix_numeric_patterns() {
        // Verify fix() correctly handles numeric patterns
        let rule = MD018NoMissingSpaceAtx::new();

        let content = "#123\nContent.\n\n##456";
        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let fixed = rule.fix(&ctx).unwrap();

        let expected = "# 123\nContent.\n\n## 456";
        assert_eq!(fixed, expected);
    }

    #[test]
    fn test_indented_malformed_headings() {
        // Indented patterns are skipped to match markdownlint behavior.
        // Markdownlint only flags patterns at column 1 (no indentation).
        // Indented patterns are often multi-line link continuations or list content.
        let rule = MD018NoMissingSpaceAtx::new();

        // Indented patterns should NOT be flagged (matches markdownlint)
        assert!(
            rule.check_atx_heading_line(" #hello", MarkdownFlavor::Standard)
                .is_none(),
            "1-space indented #hello should be skipped"
        );
        assert!(
            rule.check_atx_heading_line("  #hello", MarkdownFlavor::Standard)
                .is_none(),
            "2-space indented #hello should be skipped"
        );
        assert!(
            rule.check_atx_heading_line("   #hello", MarkdownFlavor::Standard)
                .is_none(),
            "3-space indented #hello should be skipped"
        );

        // 4+ spaces is a code block, not checked by this function
        // (code block detection happens at LintContext level)

        // BUT patterns at column 1 (no indentation) ARE flagged
        assert!(
            rule.check_atx_heading_line("#hello", MarkdownFlavor::Standard)
                .is_some(),
            "Non-indented #hello should be detected"
        );
    }

    #[test]
    fn test_tab_after_hash_is_valid() {
        // Tab after hash is valid (acts like space)
        let rule = MD018NoMissingSpaceAtx::new();

        assert!(
            rule.check_atx_heading_line("#\tHello", MarkdownFlavor::Standard)
                .is_none(),
            "Tab after # should be valid"
        );
        assert!(
            rule.check_atx_heading_line("##\tWorld", MarkdownFlavor::Standard)
                .is_none(),
            "Tab after ## should be valid"
        );
    }

    #[test]
    fn test_mixed_case_patterns() {
        let rule = MD018NoMissingSpaceAtx::new();

        // All should be detected regardless of case
        assert!(
            rule.check_atx_heading_line("#hELLO", MarkdownFlavor::Standard)
                .is_some()
        );
        assert!(
            rule.check_atx_heading_line("#Hello", MarkdownFlavor::Standard)
                .is_some()
        );
        assert!(
            rule.check_atx_heading_line("#HELLO", MarkdownFlavor::Standard)
                .is_some()
        );
        assert!(
            rule.check_atx_heading_line("#hello", MarkdownFlavor::Standard)
                .is_some()
        );
    }

    #[test]
    fn test_unicode_lowercase() {
        let rule = MD018NoMissingSpaceAtx::new();

        // Unicode lowercase should be detected
        assert!(
            rule.check_atx_heading_line("#über", MarkdownFlavor::Standard).is_some(),
            "Unicode lowercase #über should be detected"
        );
        assert!(
            rule.check_atx_heading_line("#café", MarkdownFlavor::Standard).is_some(),
            "Unicode lowercase #café should be detected"
        );
        assert!(
            rule.check_atx_heading_line("#日本語", MarkdownFlavor::Standard)
                .is_some(),
            "Japanese #日本語 should be detected"
        );
    }

    #[test]
    fn test_matches_markdownlint_behavior() {
        // Comprehensive test matching markdownlint's expected behavior
        let rule = MD018NoMissingSpaceAtx::new();

        let content = r#"#hello

## world

###fer

#123

#Tag
"#;

        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // markdownlint flags: #hello (line 1), ###fer (line 5), #123 (line 7), #Tag (line 9)
        // ## world is correct (has space)
        let flagged_lines: Vec<usize> = result.iter().map(|w| w.line).collect();

        assert!(flagged_lines.contains(&1), "#hello should be flagged");
        assert!(!flagged_lines.contains(&3), "## world should NOT be flagged");
        assert!(flagged_lines.contains(&5), "###fer should be flagged");
        assert!(flagged_lines.contains(&7), "#123 should be flagged");
        assert!(flagged_lines.contains(&9), "#Tag should be flagged");

        assert_eq!(result.len(), 4, "Should have exactly 4 warnings");
    }

    #[test]
    fn test_skip_frontmatter_yaml_comments() {
        // YAML comments in frontmatter should NOT be flagged as missing space in headings
        let rule = MD018NoMissingSpaceAtx::new();

        let content = r#"---
#reviewers:
#- sig-api-machinery
#another_comment: value
title: Test Document
---

# Valid heading

#invalid heading without space
"#;

        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should only flag line 10 (#invalid heading without space)
        // Lines 2-4 are YAML comments in frontmatter and should be skipped
        assert_eq!(
            result.len(),
            1,
            "Should only flag the malformed heading outside frontmatter"
        );
        assert_eq!(result[0].line, 10, "Should flag line 10");
    }

    #[test]
    fn test_skip_html_comments() {
        // Content inside HTML comments should NOT be flagged
        // This includes Jupyter cell markers like #%% in commented-out code blocks
        let rule = MD018NoMissingSpaceAtx::new();

        let content = r#"# Real Heading

Some text.

<!--
```
#%% Cell marker
import matplotlib.pyplot as plt

#%% Another cell
data = [1, 2, 3]
```
-->

More content.
"#;

        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should find no issues - the #%% markers are inside HTML comments
        assert!(
            result.is_empty(),
            "Should not flag content inside HTML comments, found {} issues",
            result.len()
        );
    }

    #[test]
    fn test_mkdocs_magiclink_skips_numeric_refs() {
        // With magiclink config enabled, should skip MagicLink-style issue/PR refs (#123, #10, etc.)
        let rule = MD018NoMissingSpaceAtx::from_config_struct(MD018Config {
            magiclink: true,
            ..Default::default()
        });

        // These numeric patterns should be SKIPPED with magiclink enabled
        assert!(
            rule.check_atx_heading_line("#10", MarkdownFlavor::Standard).is_none(),
            "#10 should be skipped with magiclink config (MagicLink issue ref)"
        );
        assert!(
            rule.check_atx_heading_line("#123", MarkdownFlavor::Standard).is_none(),
            "#123 should be skipped with magiclink config (MagicLink issue ref)"
        );
        assert!(
            rule.check_atx_heading_line("#10 discusses the issue", MarkdownFlavor::Standard)
                .is_none(),
            "#10 followed by text should be skipped with magiclink config"
        );
        assert!(
            rule.check_atx_heading_line("#37.", MarkdownFlavor::Standard).is_none(),
            "#37 followed by punctuation should be skipped with magiclink config"
        );
    }

    #[test]
    fn test_mkdocs_magiclink_still_flags_non_numeric() {
        // With magiclink config enabled, should still flag non-numeric patterns
        let rule = MD018NoMissingSpaceAtx::from_config_struct(MD018Config {
            magiclink: true,
            ..Default::default()
        });

        // Non-numeric patterns should still be flagged even with magiclink enabled
        assert!(
            rule.check_atx_heading_line("#Summary", MarkdownFlavor::Standard)
                .is_some(),
            "#Summary should still be flagged with magiclink config"
        );
        assert!(
            rule.check_atx_heading_line("#hello", MarkdownFlavor::Standard)
                .is_some(),
            "#hello should still be flagged with magiclink config"
        );
        assert!(
            rule.check_atx_heading_line("#10abc", MarkdownFlavor::Standard)
                .is_some(),
            "#10abc (mixed) should still be flagged with magiclink config"
        );
    }

    #[test]
    fn test_mkdocs_magiclink_only_single_hash() {
        // MagicLink only uses single #, so ##10 should still be flagged
        let rule = MD018NoMissingSpaceAtx::from_config_struct(MD018Config {
            magiclink: true,
            ..Default::default()
        });

        assert!(
            rule.check_atx_heading_line("##10", MarkdownFlavor::Standard).is_some(),
            "##10 should be flagged with magiclink config (only single # is MagicLink)"
        );
        assert!(
            rule.check_atx_heading_line("###123", MarkdownFlavor::Standard)
                .is_some(),
            "###123 should be flagged with magiclink config"
        );
    }

    #[test]
    fn test_standard_flavor_flags_numeric_refs() {
        // Standard flavor should still flag numeric patterns (no MagicLink awareness)
        let rule = MD018NoMissingSpaceAtx::new();

        assert!(
            rule.check_atx_heading_line("#10", MarkdownFlavor::Standard).is_some(),
            "#10 should be flagged in Standard flavor"
        );
        assert!(
            rule.check_atx_heading_line("#123", MarkdownFlavor::Standard).is_some(),
            "#123 should be flagged in Standard flavor"
        );
    }

    #[test]
    fn test_mkdocs_magiclink_full_check() {
        // Integration test: verify magiclink config skips MagicLink refs through full check() flow
        let rule = MD018NoMissingSpaceAtx::from_config_struct(MD018Config {
            magiclink: true,
            ..Default::default()
        });

        let content = r#"# PRs that are helpful for context

#10 discusses the philosophy behind the project, and #37 shows a good example.

#Summary

##Introduction
"#;

        // With magiclink enabled - should skip #10 and #37, but flag #Summary and ##Introduction
        let ctx = LintContext::new(content, MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        let flagged_lines: Vec<usize> = result.iter().map(|w| w.line).collect();
        assert!(
            !flagged_lines.contains(&3),
            "#10 should NOT be flagged with magiclink config"
        );
        assert!(
            flagged_lines.contains(&5),
            "#Summary SHOULD be flagged with magiclink config"
        );
        assert!(
            flagged_lines.contains(&7),
            "##Introduction SHOULD be flagged with magiclink config"
        );
    }

    #[test]
    fn test_mkdocs_magiclink_fix_exact_output() {
        // Verify fix() produces exact expected output with magiclink config
        let rule = MD018NoMissingSpaceAtx::from_config_struct(MD018Config {
            magiclink: true,
            ..Default::default()
        });

        let content = "#10 discusses the issue.\n\n#Summary";
        let ctx = LintContext::new(content, MarkdownFlavor::Standard, None);
        let fixed = rule.fix(&ctx).unwrap();

        // Exact expected output: #10 preserved, #Summary fixed
        let expected = "#10 discusses the issue.\n\n# Summary";
        assert_eq!(
            fixed, expected,
            "magiclink config fix should preserve MagicLink refs and fix non-numeric headings"
        );
    }

    #[test]
    fn test_mkdocs_magiclink_edge_cases() {
        // Test various edge cases for MagicLink pattern matching
        let rule = MD018NoMissingSpaceAtx::from_config_struct(MD018Config {
            magiclink: true,
            ..Default::default()
        });

        // These should all be SKIPPED with magiclink config (valid MagicLink refs)
        // Note: #1 alone is skipped due to content length < 2, not MagicLink
        let valid_refs = [
            "#10",             // Two digits
            "#999999",         // Large number
            "#10 text after",  // Space then text
            "#10\ttext after", // Tab then text
            "#10.",            // Period after
            "#10,",            // Comma after
            "#10!",            // Exclamation after
            "#10?",            // Question mark after
            "#10)",            // Close paren after
            "#10]",            // Close bracket after
            "#10;",            // Semicolon after
            "#10:",            // Colon after
        ];

        for ref_str in valid_refs {
            assert!(
                rule.check_atx_heading_line(ref_str, MarkdownFlavor::Standard).is_none(),
                "{ref_str:?} should be skipped as MagicLink ref with magiclink config"
            );
        }

        // These should still be FLAGGED with magiclink config (not valid MagicLink refs)
        let invalid_refs = [
            "#10abc",   // Alphanumeric continuation
            "#10a",     // Single alpha continuation
            "#abc10",   // Alpha prefix
            "#10ABC",   // Uppercase continuation
            "#Summary", // Pure text
            "#hello",   // Lowercase text
        ];

        for ref_str in invalid_refs {
            assert!(
                rule.check_atx_heading_line(ref_str, MarkdownFlavor::Standard).is_some(),
                "{ref_str:?} should be flagged with magiclink config (not a valid MagicLink ref)"
            );
        }
    }

    #[test]
    fn test_mkdocs_magiclink_hyphenated_continuation() {
        // Hyphenated patterns like #10-related should still be flagged
        // because they're likely malformed headings, not MagicLink refs
        let rule = MD018NoMissingSpaceAtx::from_config_struct(MD018Config {
            magiclink: true,
            ..Default::default()
        });

        // Hyphen is not alphanumeric, so #10- would match as MagicLink
        // But #10-related has alphanumeric after the hyphen
        // The regex ^#\d+(?:\s|[^a-zA-Z0-9]|$) would match #10- but not consume -related
        // So #10-related would match (the -r part is after the match)
        assert!(
            rule.check_atx_heading_line("#10-", MarkdownFlavor::Standard).is_none(),
            "#10- should be skipped with magiclink config (hyphen is non-alphanumeric terminator)"
        );
    }

    #[test]
    fn test_mkdocs_magiclink_standalone_number() {
        // #10 alone on a line (common in changelogs)
        let rule = MD018NoMissingSpaceAtx::from_config_struct(MD018Config {
            magiclink: true,
            ..Default::default()
        });

        let content = "See issue:\n\n#10\n\nFor details.";
        let ctx = LintContext::new(content, MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // #10 alone should not be flagged with magiclink config
        assert!(
            result.is_empty(),
            "Standalone #10 should not be flagged with magiclink config"
        );

        // Verify fix doesn't modify it
        let fixed = rule.fix(&ctx).unwrap();
        assert_eq!(fixed, content, "fix() should not modify standalone MagicLink ref");
    }

    #[test]
    fn test_standard_flavor_flags_all_numeric() {
        // Standard flavor should flag ALL numeric patterns (no MagicLink awareness)
        // Note: #1 is skipped because content length < 2 (existing behavior)
        let rule = MD018NoMissingSpaceAtx::new();

        let numeric_patterns = ["#10", "#123", "#999999", "#10 text"];

        for pattern in numeric_patterns {
            assert!(
                rule.check_atx_heading_line(pattern, MarkdownFlavor::Standard).is_some(),
                "{pattern:?} should be flagged in Standard flavor"
            );
        }

        // #1 is skipped due to content length < 2 rule (not MagicLink related)
        assert!(
            rule.check_atx_heading_line("#1", MarkdownFlavor::Standard).is_none(),
            "#1 should be skipped (content too short, existing behavior)"
        );
    }

    #[test]
    fn test_mkdocs_vs_standard_fix_comparison() {
        // Compare fix output between magiclink enabled and disabled
        let content = "#10 is an issue\n#Summary";
        let ctx = LintContext::new(content, MarkdownFlavor::Standard, None);

        // With magiclink: preserves #10, fixes #Summary
        let rule_magiclink = MD018NoMissingSpaceAtx::from_config_struct(MD018Config {
            magiclink: true,
            ..Default::default()
        });
        let fixed_magiclink = rule_magiclink.fix(&ctx).unwrap();
        assert_eq!(fixed_magiclink, "#10 is an issue\n# Summary");

        // Without magiclink: fixes both
        let rule_default = MD018NoMissingSpaceAtx::new();
        let fixed_default = rule_default.fix(&ctx).unwrap();
        assert_eq!(fixed_default, "# 10 is an issue\n# Summary");
    }

    // ==================== Tags config tests ====================

    #[test]
    fn test_tags_config_standard_flavor() {
        // tags = true with standard flavor should skip tag patterns
        let rule = MD018NoMissingSpaceAtx::from_config_struct(MD018Config {
            magiclink: false,
            tags: Some(true),
        });

        let content = "#tag\n\n#project/active\n\n##Introduction";
        let ctx = LintContext::new(content, MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        let flagged_lines: Vec<usize> = result.iter().map(|w| w.line).collect();
        assert!(!flagged_lines.contains(&1), "#tag should be skipped with tags = true");
        assert!(
            !flagged_lines.contains(&3),
            "#project/active should be skipped with tags = true"
        );
        assert!(flagged_lines.contains(&5), "##Introduction should still be flagged");
    }

    #[test]
    fn test_tags_config_fix_standard_flavor() {
        let rule = MD018NoMissingSpaceAtx::from_config_struct(MD018Config {
            magiclink: false,
            tags: Some(true),
        });

        let content = "#tag\n\n##Introduction";
        let ctx = LintContext::new(content, MarkdownFlavor::Standard, None);
        let fixed = rule.fix(&ctx).unwrap();
        assert_eq!(fixed, "#tag\n\n## Introduction");
    }

    #[test]
    fn test_tags_config_disabled_obsidian_flavor() {
        // tags = false with Obsidian flavor should flag tag patterns
        let rule = MD018NoMissingSpaceAtx::from_config_struct(MD018Config {
            magiclink: false,
            tags: Some(false),
        });

        let content = "#tag\n\n#project/active";
        let ctx = LintContext::new(content, MarkdownFlavor::Obsidian, None);
        let result = rule.check(&ctx).unwrap();

        assert_eq!(
            result.len(),
            2,
            "tags = false should flag tag patterns even in Obsidian"
        );
    }

    #[test]
    fn test_tags_config_default_follows_flavor() {
        // Unset tags should default based on flavor
        let rule = MD018NoMissingSpaceAtx::new(); // tags: None

        // Standard: should flag
        let content = "#tag";
        let ctx = LintContext::new(content, MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();
        assert!(!result.is_empty(), "Default standard should flag #tag");

        // Obsidian: should skip
        let ctx = LintContext::new(content, MarkdownFlavor::Obsidian, None);
        let result = rule.check(&ctx).unwrap();
        assert!(result.is_empty(), "Default Obsidian should skip #tag");
    }

    // ==================== Obsidian flavor tests ====================

    #[test]
    fn test_obsidian_tag_skips_simple_tags() {
        // Obsidian flavor should skip tag syntax (#tagname)
        let rule = MD018NoMissingSpaceAtx::new();

        // Simple tags should be SKIPPED in Obsidian flavor
        assert!(
            rule.check_atx_heading_line("#hey", MarkdownFlavor::Obsidian).is_none(),
            "#hey should be skipped in Obsidian flavor (tag syntax)"
        );
        assert!(
            rule.check_atx_heading_line("#tag", MarkdownFlavor::Obsidian).is_none(),
            "#tag should be skipped in Obsidian flavor"
        );
        assert!(
            rule.check_atx_heading_line("#hello", MarkdownFlavor::Obsidian)
                .is_none(),
            "#hello should be skipped in Obsidian flavor"
        );
        assert!(
            rule.check_atx_heading_line("#myTag", MarkdownFlavor::Obsidian)
                .is_none(),
            "#myTag should be skipped in Obsidian flavor"
        );
    }

    #[test]
    fn test_obsidian_tag_skips_complex_tags() {
        // Obsidian tags can have hyphens, underscores, numbers, and slashes
        let rule = MD018NoMissingSpaceAtx::new();

        // Complex tag patterns should be SKIPPED in Obsidian flavor
        assert!(
            rule.check_atx_heading_line("#project/active", MarkdownFlavor::Obsidian)
                .is_none(),
            "#project/active should be skipped in Obsidian flavor (nested tag)"
        );
        assert!(
            rule.check_atx_heading_line("#my-tag", MarkdownFlavor::Obsidian)
                .is_none(),
            "#my-tag should be skipped in Obsidian flavor"
        );
        assert!(
            rule.check_atx_heading_line("#my_tag", MarkdownFlavor::Obsidian)
                .is_none(),
            "#my_tag should be skipped in Obsidian flavor"
        );
        assert!(
            rule.check_atx_heading_line("#tag2023", MarkdownFlavor::Obsidian)
                .is_none(),
            "#tag2023 should be skipped in Obsidian flavor"
        );
        assert!(
            rule.check_atx_heading_line("#project/sub/task", MarkdownFlavor::Obsidian)
                .is_none(),
            "#project/sub/task should be skipped in Obsidian flavor"
        );
    }

    #[test]
    fn test_obsidian_tag_with_trailing_content() {
        // Tags followed by whitespace should still be skipped
        let rule = MD018NoMissingSpaceAtx::new();

        assert!(
            rule.check_atx_heading_line("#hey ", MarkdownFlavor::Obsidian).is_none(),
            "#hey followed by space should be skipped"
        );
        assert!(
            rule.check_atx_heading_line("#tag some text", MarkdownFlavor::Obsidian)
                .is_none(),
            "#tag followed by text should be skipped"
        );
    }

    #[test]
    fn test_obsidian_tag_still_flags_multi_hash() {
        // Obsidian tags only use single #, so ##tag should still be flagged
        let rule = MD018NoMissingSpaceAtx::new();

        assert!(
            rule.check_atx_heading_line("##tag", MarkdownFlavor::Obsidian).is_some(),
            "##tag should be flagged in Obsidian flavor (only single # is a tag)"
        );
        assert!(
            rule.check_atx_heading_line("###hello", MarkdownFlavor::Obsidian)
                .is_some(),
            "###hello should be flagged in Obsidian flavor"
        );
    }

    #[test]
    fn test_obsidian_tag_numeric_still_flagged() {
        // An Obsidian tag needs at least one non-numerical character, so an
        // all-numeric #123 is not a tag and should still be flagged
        let rule = MD018NoMissingSpaceAtx::new();

        assert!(
            rule.check_atx_heading_line("#123", MarkdownFlavor::Obsidian).is_some(),
            "#123 should be flagged in Obsidian flavor (no non-numerical character)"
        );
        assert!(
            rule.check_atx_heading_line("#10", MarkdownFlavor::Obsidian).is_some(),
            "#10 should be flagged in Obsidian flavor"
        );
    }

    #[test]
    fn test_obsidian_flavor_full_check() {
        // Integration test: verify Obsidian flavor skips tags through full check() flow
        let rule = MD018NoMissingSpaceAtx::new();

        let content = r#"# Real Heading

#hey this is a tag

#project/active also a tag

##Introduction

#123
"#;

        // Obsidian flavor - should skip #hey and #project/active, but flag ##Introduction and #123
        let ctx = LintContext::new(content, MarkdownFlavor::Obsidian, None);
        let result = rule.check(&ctx).unwrap();

        let flagged_lines: Vec<usize> = result.iter().map(|w| w.line).collect();
        assert!(
            !flagged_lines.contains(&3),
            "#hey should NOT be flagged in Obsidian flavor"
        );
        assert!(
            !flagged_lines.contains(&5),
            "#project/active should NOT be flagged in Obsidian flavor"
        );
        assert!(
            flagged_lines.contains(&7),
            "##Introduction SHOULD be flagged in Obsidian flavor"
        );
        assert!(flagged_lines.contains(&9), "#123 SHOULD be flagged in Obsidian flavor");
    }

    #[test]
    fn test_obsidian_flavor_fix_exact_output() {
        // Verify fix() produces exact expected output
        let rule = MD018NoMissingSpaceAtx::new();

        // In Obsidian flavor, all single-# patterns that look like tags are preserved
        // Only multi-hash patterns (##tag) and numeric patterns (#123) are fixed
        let content = "#hey is a tag.\n\n##Introduction";
        let ctx = LintContext::new(content, MarkdownFlavor::Obsidian, None);
        let fixed = rule.fix(&ctx).unwrap();

        // Exact expected output: #hey preserved, ##Introduction fixed
        let expected = "#hey is a tag.\n\n## Introduction";
        assert_eq!(
            fixed, expected,
            "Obsidian fix should preserve tags and fix multi-hash headings"
        );
    }

    #[test]
    fn test_standard_flavor_flags_obsidian_tags() {
        // Standard flavor should flag patterns that look like Obsidian tags
        let rule = MD018NoMissingSpaceAtx::new();

        assert!(
            rule.check_atx_heading_line("#hey", MarkdownFlavor::Standard).is_some(),
            "#hey should be flagged in Standard flavor"
        );
        assert!(
            rule.check_atx_heading_line("#tag", MarkdownFlavor::Standard).is_some(),
            "#tag should be flagged in Standard flavor"
        );
        assert!(
            rule.check_atx_heading_line("#project/active", MarkdownFlavor::Standard)
                .is_some(),
            "#project/active should be flagged in Standard flavor"
        );
    }

    #[test]
    fn test_obsidian_vs_standard_fix_comparison() {
        // Compare fix output between Obsidian and Standard flavors
        let rule = MD018NoMissingSpaceAtx::new();

        // Use a pattern that clearly shows the difference:
        // - #hey tag: single-hash, looks like Obsidian tag followed by text
        // - ##Introduction: multi-hash, clearly a malformed heading
        let content = "#hey tag\n##Introduction";

        // Obsidian: preserves #hey tag (single-hash tag syntax), fixes ##Introduction
        let ctx_obsidian = LintContext::new(content, MarkdownFlavor::Obsidian, None);
        let fixed_obsidian = rule.fix(&ctx_obsidian).unwrap();
        assert_eq!(fixed_obsidian, "#hey tag\n## Introduction");

        // Standard: fixes both (no tag awareness)
        let ctx_standard = LintContext::new(content, MarkdownFlavor::Standard, None);
        let fixed_standard = rule.fix(&ctx_standard).unwrap();
        assert_eq!(fixed_standard, "# hey tag\n## Introduction");
    }

    #[test]
    fn test_obsidian_tag_edge_cases() {
        // Test various edge cases for Obsidian tag pattern matching
        let rule = MD018NoMissingSpaceAtx::new();

        // Valid Obsidian tags - should be SKIPPED
        let valid_tags = [
            "#a",      // Minimum valid tag (also under the content length < 2 rule)
            "#tag",    // Simple tag
            "#Tag",    // Capitalized tag
            "#TAG",    // Uppercase tag
            "#my-tag", // Hyphenated tag
            "#my_tag", // Underscored tag
            "#tag123", // Tag with trailing numbers
            "#a1",     // Short tag with number
            "#日本語", // Unicode tag
            "#über",   // Unicode with umlaut
        ];

        for tag in valid_tags {
            assert!(
                rule.check_atx_heading_line(tag, MarkdownFlavor::Obsidian).is_none(),
                "{tag:?} should be skipped in Obsidian flavor (valid tag)"
            );
        }

        // Not tags - should be FLAGGED. Every one of these is all-numeric up to
        // the first character Obsidian would not accept in a tag.
        let invalid_tags = ["#123", "#1984", "#37.", "#42,"];

        for tag in invalid_tags {
            assert!(
                rule.check_atx_heading_line(tag, MarkdownFlavor::Obsidian).is_some(),
                "{tag:?} should be flagged in Obsidian flavor (no non-numerical character)"
            );
        }
    }

    #[test]
    fn test_obsidian_tag_alone_on_line() {
        // Standalone tag on a line (common in Obsidian notes)
        let rule = MD018NoMissingSpaceAtx::new();

        let content = "Some text\n\n#todo\n\nMore text.";
        let ctx = LintContext::new(content, MarkdownFlavor::Obsidian, None);
        let result = rule.check(&ctx).unwrap();

        // #todo alone should not be flagged in Obsidian flavor
        assert!(
            result.is_empty(),
            "Standalone #todo should not be flagged in Obsidian flavor"
        );

        // Verify fix doesn't modify it
        let fixed = rule.fix(&ctx).unwrap();
        assert_eq!(fixed, content, "fix() should not modify standalone Obsidian tag");
    }

    #[test]
    fn test_obsidian_deeply_nested_tags() {
        // Obsidian supports deeply nested tags with /
        let rule = MD018NoMissingSpaceAtx::new();

        let nested_tags = [
            "#a/b",
            "#a/b/c",
            "#project/2023/q1/task",
            "#work/meetings/weekly",
            "#life/health/exercise/running",
        ];

        for tag in nested_tags {
            assert!(
                rule.check_atx_heading_line(tag, MarkdownFlavor::Obsidian).is_none(),
                "{tag:?} should be skipped in Obsidian flavor (nested tag)"
            );
        }
    }

    #[test]
    fn test_obsidian_unicode_tags() {
        // Obsidian supports Unicode in tags
        let rule = MD018NoMissingSpaceAtx::new();

        let unicode_tags = [
            "#日本語", // Japanese
            "#中文",   // Chinese
            "#한국어", // Korean
            "#über",   // German umlaut
            "#café",   // French accent
            "#ñoño",   // Spanish tilde
            "#Москва", // Russian
            "#αβγ",    // Greek
        ];

        for tag in unicode_tags {
            assert!(
                rule.check_atx_heading_line(tag, MarkdownFlavor::Obsidian).is_none(),
                "{tag:?} should be skipped in Obsidian flavor (Unicode tag)"
            );
        }
    }

    #[test]
    fn test_obsidian_tags_with_special_endings() {
        // Tags followed by various punctuation
        let rule = MD018NoMissingSpaceAtx::new();

        // Tags followed by space then text should be skipped
        assert!(
            rule.check_atx_heading_line("#tag followed by text", MarkdownFlavor::Obsidian)
                .is_none(),
            "#tag followed by text should be skipped"
        );

        // Tag at end of line (no trailing space)
        let content = "#todo";
        let ctx = LintContext::new(content, MarkdownFlavor::Obsidian, None);
        let result = rule.check(&ctx).unwrap();
        assert!(result.is_empty(), "#todo at end of line should be skipped");
    }

    #[test]
    fn test_obsidian_combined_with_other_skip_contexts() {
        // Verify Obsidian tags in code blocks and HTML comments are still skipped
        let rule = MD018NoMissingSpaceAtx::new();

        // Tag inside code block (should be skipped by code block logic, not Obsidian logic)
        let content = "```\n#todo\n```";
        let ctx = LintContext::new(content, MarkdownFlavor::Obsidian, None);
        let result = rule.check(&ctx).unwrap();
        assert!(result.is_empty(), "Tag in code block should be skipped");

        // Tag inside HTML comment
        let content = "<!-- #todo -->";
        let ctx = LintContext::new(content, MarkdownFlavor::Obsidian, None);
        let result = rule.check(&ctx).unwrap();
        assert!(result.is_empty(), "Tag in HTML comment should be skipped");
    }

    #[test]
    fn test_obsidian_boundary_cases() {
        // Test boundary cases for Obsidian tag detection
        let rule = MD018NoMissingSpaceAtx::new();

        // Minimum valid tag (single char after #)
        // Note: #a alone might be skipped by content length < 2 rule
        // #ab should definitely be recognized as a tag
        assert!(
            rule.check_atx_heading_line("#ab", MarkdownFlavor::Obsidian).is_none(),
            "#ab should be skipped in Obsidian flavor"
        );

        // Tag with underscore
        assert!(
            rule.check_atx_heading_line("#my_tag", MarkdownFlavor::Obsidian)
                .is_none(),
            "#my_tag should be skipped"
        );

        // Tag with hyphen
        assert!(
            rule.check_atx_heading_line("#my-tag", MarkdownFlavor::Obsidian)
                .is_none(),
            "#my-tag should be skipped"
        );

        // Tag with mixed case
        assert!(
            rule.check_atx_heading_line("#MyTag", MarkdownFlavor::Obsidian)
                .is_none(),
            "#MyTag should be skipped"
        );

        // All caps (could be a tag or acronym)
        assert!(
            rule.check_atx_heading_line("#TODO", MarkdownFlavor::Obsidian).is_none(),
            "#TODO should be skipped in Obsidian flavor"
        );
    }

    #[test]
    fn test_obsidian_tag_may_start_with_a_digit() {
        // Obsidian requires at least one non-numerical character anywhere in the
        // tag, not a non-numerical FIRST character.
        let rule = MD018NoMissingSpaceAtx::new();

        let tags = [
            "#3d_printing",       // the reported case
            "#1tag",              // digit then letters
            "#2023-project",      // digit run then a hyphen
            "#100DaysOfCode",     // digits then mixed case
            "#1on1",              // digits on both sides of letters
            "#5S",                // single digit, single letter
            "#3/4",               // digit run then a nested-tag separator
            "#1_2",               // digit run then an underscore
            "#3🔥",               // digit run then an emoji
            "#3\u{FE0F}\u{20E3}", // keycap: digit, variation selector, enclosing mark
        ];

        for tag in tags {
            assert!(
                rule.check_atx_heading_line(tag, MarkdownFlavor::Obsidian).is_none(),
                "{tag:?} contains a non-numerical character and should be skipped as a tag"
            );
        }
    }

    #[test]
    fn test_numeric_references_are_not_tags() {
        // The counterpart of the test above: allowing a leading digit run must
        // not turn an issue reference or a numeric heading into a tag. Without
        // these, widening the pattern to any non-digit would pass unnoticed.
        let rule = MD018NoMissingSpaceAtx::new();

        let not_tags = [
            "#1984",                   // all-numeric, Obsidian's own example
            "#123",                    // all-numeric
            "#10",                     // issue reference
            "#37.",                    // issue reference ending a sentence
            "#42,",                    // issue reference in a list
            "#42)",                    // issue reference in parentheses
            "#404 Not Found",          // numeric heading
            "#10 discusses the issue", // issue reference opening a line
        ];

        for line in not_tags {
            assert!(
                rule.check_atx_heading_line(line, MarkdownFlavor::Obsidian).is_some(),
                "{line:?} has no non-numerical tag character and should stay flagged"
            );
        }
    }

    #[test]
    fn test_digit_leading_tag_survives_check_and_fix() {
        // End-to-end through the two paths a user actually hits: the Obsidian
        // flavor default, and `tags = true` on Standard flavor as reported.
        let obsidian = MD018NoMissingSpaceAtx::new();
        let standard = MD018NoMissingSpaceAtx::from_config_struct(MD018Config {
            magiclink: false,
            tags: Some(true),
        });

        // ##Heading is the positive control: it must still be flagged and fixed,
        // otherwise an untouched tag proves nothing about the fix having run.
        let content = "# Header\n\n#3d_printing\n\n##Heading\n";

        for (rule, flavor, label) in [
            (&obsidian, MarkdownFlavor::Obsidian, "obsidian flavor"),
            (&standard, MarkdownFlavor::Standard, "tags = true"),
        ] {
            let ctx = LintContext::new(content, flavor, None);
            let flagged: Vec<usize> = rule.check(&ctx).unwrap().iter().map(|w| w.line).collect();
            assert_eq!(
                flagged,
                vec![5],
                "{label}: only ##Heading should be flagged, got {flagged:?}"
            );

            let fixed = rule.fix(&ctx).unwrap();
            assert_eq!(
                fixed, "# Header\n\n#3d_printing\n\n## Heading\n",
                "{label}: fix must leave the tag alone and still fix the heading"
            );
        }
    }

    #[test]
    fn test_digit_leading_tag_is_still_flagged_without_tags_mode() {
        // Standard flavor without the option keeps treating it as a malformed
        // heading, so the fix does not leak tag awareness into other flavors.
        let rule = MD018NoMissingSpaceAtx::new();

        assert!(
            rule.check_atx_heading_line("#3d_printing", MarkdownFlavor::Standard)
                .is_some(),
            "#3d_printing should be flagged in Standard flavor (tags disabled)"
        );
    }

    fn check_and_fix(content: &str) -> (Vec<(usize, usize)>, String) {
        let rule = MD018NoMissingSpaceAtx::new();
        let ctx = LintContext::new(content, MarkdownFlavor::Standard, None);
        let warnings = rule.check(&ctx).unwrap();
        let fixed = rule.fix(&ctx).unwrap();
        (warnings.iter().map(|w| (w.line, w.column)).collect(), fixed)
    }

    #[test]
    fn test_quoted_missing_space_is_flagged_and_fixed_inside_the_quote() {
        // (input, flagged (line, column), fixed): the column is the character
        // after the hashes, the same position an unquoted `#Bad` reports.
        let cases = [
            ("> #Bad\n", vec![(1, 4)], "> # Bad\n"),
            ("> > ##Bad\n", vec![(1, 7)], "> > ## Bad\n"),
            (">#Bad\n", vec![(1, 3)], "># Bad\n"),
            ("> text\n> #Bad\n", vec![(2, 4)], "> text\n> # Bad\n"),
            ("> > #Bad\n> > text\n", vec![(1, 6)], "> > # Bad\n> > text\n"),
            ("> é #x\n> #Bad\n", vec![(2, 4)], "> é #x\n> # Bad\n"),
            ("-   text\n\n    > #Bad\n", vec![(3, 8)], "-   text\n\n    > # Bad\n"),
        ];
        for (input, flagged, fixed) in cases {
            let (got, out) = check_and_fix(input);
            assert_eq!(got, flagged, "flagged positions for {input:?}");
            assert_eq!(out, fixed, "fix for {input:?}");
        }
    }

    #[test]
    fn test_quoted_missing_space_leaves_non_candidates_alone() {
        for input in [
            "> # Good\n",
            "> #1\n",
            "> ##\n",
            "> #*emphasis\n",
            "> #\u{fe0f}\u{20e3} x\n",
            "> >  #Bad\n",
            "> text\n>     #Bad\n",
            "> ```\n> #Bad\n> ```\n",
            "> `#Bad` text\n",
            "> Title\n> ===\n",
            "> #Bad\n> ===\n",
            "> <!--\n> #Bad\n> -->\n",
            "> [text\n> #sig](url)\n",
            "> `code\n> #Bad` text\n",
            "> <a\n> #href>text</a>\n",
        ] {
            let (got, out) = check_and_fix(input);
            assert!(got.is_empty(), "{input:?} must not be flagged, got {got:?}");
            assert_eq!(out, input, "{input:?} must not change");
        }
    }

    #[test]
    fn test_quote_inside_list_item_is_checked_and_fix_keeps_the_prefix() {
        let rule = MD018NoMissingSpaceAtx::new();
        for (prefix, col) in [
            ("- > ", 6),
            ("1. > ", 7),
            ("- - > ", 8),
            ("> - > ", 8),
            ("> 1. - > ", 11),
        ] {
            let content = format!("# T\n\n{prefix}#Bad\n");
            let ctx = LintContext::new(&content, crate::config::MarkdownFlavor::Standard, None);
            let result = rule.check(&ctx).unwrap();
            assert_eq!(result.len(), 1, "{content:?}: {result:?}");
            assert_eq!((result[0].line, result[0].column), (3, col), "{content:?}");
            assert_eq!(rule.fix(&ctx).unwrap(), format!("# T\n\n{prefix}# Bad\n"));
        }
    }

    #[test]
    fn test_list_item_content_that_is_not_a_quote_heading_candidate_is_left_alone() {
        let rule = MD018NoMissingSpaceAtx::new();
        for content in [
            "# T\n\n-     > #Bad\n",
            "# T\n\n- > # Good\n",
            "# T\n\n- #Bad\n",
            "# T\n\nx\n2. > #Bad\n",
        ] {
            let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
            assert!(rule.check(&ctx).unwrap().is_empty(), "{content:?}");
        }
    }

    #[test]
    fn test_quote_in_list_item_allows_four_spaces_after_the_marker_and_spares_setext_text() {
        let rule = MD018NoMissingSpaceAtx::new();
        let content = "# T\n\n-    > #Bad\n";
        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        assert_eq!(rule.check(&ctx).unwrap().len(), 1);
        assert_eq!(rule.fix(&ctx).unwrap(), "# T\n\n-    > # Bad\n");
        // The text of a setext heading in the quote is heading text.
        let content = "# T\n\n- > #Bad\n  > ---\n";
        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        assert!(rule.check(&ctx).unwrap().is_empty());
    }

    #[test]
    fn test_quote_in_list_item_measures_a_tab_after_the_marker_at_its_tab_stop() {
        let rule = MD018NoMissingSpaceAtx::new();
        for content in [" -   > #Bad\n", " -\t> #Bad\n", " -\t > #Bad\n"] {
            let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
            assert_eq!(rule.check(&ctx).unwrap().len(), 1, "{content:?}");
        }
    }

    #[test]
    fn test_indented_quote_after_a_list_ended_by_an_unindented_quote_is_paragraph_text() {
        let rule = MD018NoMissingSpaceAtx::new();
        let content = "- item\n> text\n    > #Bad\n";
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        assert!(rule.check(&ctx).unwrap().is_empty());
    }
}