markdown_syntax/

ast.rs

//! The owned Markdown AST that [`parse()`](crate::parse()) produces and
//! `Document::to_markdown`/`to_html` consume. Every node carries a [`NodeMeta`]
//! with an optional source [`Span`]. [`Block`] and [`Inline`] are the two node
//! enums; everything else is a concrete node struct or a small enum describing
//! a node's variant.

use alloc::{string::String, sync::Arc, vec::Vec};

use crate::diagnostic::Diagnostic;
use crate::parse::Definitions;
use crate::span::Span;

/// Metadata attached to every AST node; currently just the source span.
#[derive(Clone, Debug, Default, Eq, PartialEq)]
pub struct NodeMeta {
    /// The node's source location, or `None` for hand-built nodes.
    pub span: Option<Span>,
}

impl NodeMeta {
    /// Wrap an optional [`Span`] into a [`NodeMeta`].
    pub const fn new(span: Option<Span>) -> Self {
        Self { span }
    }
}

/// The root of a document: a sequence of top-level [`Block`]s, and for a
/// parsed document the source it was parsed from.
///
/// The source is the only truth: writing a parsed document back with
/// [`Document::to_markdown`] reuses the source of every top-level block that
/// did not change. Only [`parse()`](crate::parse()) gives a document a
/// source; [`Document::without_source`] drops it, and a document without one
/// is written as canonical Markdown.
#[derive(Clone, Debug, Default, Eq, PartialEq)]
pub struct Document {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The document's top-level blocks, in source order.
    pub children: Vec<Block>,
    /// The input `parse` read, shared by clones.
    source: Option<Arc<str>>,
}

impl Document {
    /// A document holding `children` and no source.
    pub fn new(children: Vec<Block>) -> Self {
        Self {
            meta: NodeMeta::default(),
            children,
            source: None,
        }
    }

    /// The document `parse` returns: `children` read from `source`.
    pub(crate) fn parsed(meta: NodeMeta, children: Vec<Block>, source: &str) -> Self {
        Self {
            meta,
            children,
            source: Some(Arc::from(source)),
        }
    }

    /// The input this document was parsed from, or `None` for a document
    /// built by hand or returned by [`Document::without_source`].
    pub fn source(&self) -> Option<&str> {
        self.source.as_deref()
    }

    /// This document without its source; writing it gives canonical
    /// Markdown.
    #[must_use]
    pub fn without_source(mut self) -> Self {
        self.source = None;
        self
    }
}

impl From<Vec<Block>> for Document {
    fn from(children: Vec<Block>) -> Self {
        Self::new(children)
    }
}

/// Child indices from a document down to one node. A list's children are its
/// items, a table's are its rows, and a row's are its cells; every other
/// container's are its blocks.
#[derive(Clone, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct NodePath(pub Vec<usize>);

impl From<Vec<usize>> for NodePath {
    fn from(indices: Vec<usize>) -> Self {
        Self(indices)
    }
}

impl From<&[usize]> for NodePath {
    fn from(indices: &[usize]) -> Self {
        Self(indices.into())
    }
}

impl<const N: usize> From<[usize; N]> for NodePath {
    fn from(indices: [usize; N]) -> Self {
        Self(indices.into())
    }
}

/// A block-level node: the building blocks of a document's vertical structure.
#[derive(Clone, Debug, Eq, PartialEq)]
pub enum Block {
    /// A paragraph of inline content.
    Paragraph(Paragraph),
    /// An ATX heading: `# h`.
    Heading(Heading),
    /// A thematic break / horizontal rule: `---`, `***`, or `___`.
    ThematicBreak(ThematicBreak),
    /// A block quote: lines prefixed with `> `.
    BlockQuote(BlockQuote),
    /// A GFM alert / admonition: `> [!NOTE]` etc.
    Alert(Alert),
    /// A bullet or ordered list.
    List(List),
    /// A fenced (```` ``` ````) or indented code block.
    CodeBlock(CodeBlock),
    /// A raw HTML block.
    HtmlBlock(HtmlBlock),
    /// A structured raw HTML container whose interior is parsed as Markdown.
    HtmlContainer(HtmlContainer),
    /// A link reference definition: `[label]: url "title"`.
    Definition(Definition),
    /// A footnote definition: `[^id]: text`.
    FootnoteDefinition(FootnoteDefinition),
    /// A GFM pipe table.
    Table(Table),
    /// A display math block: `$$ … $$`.
    MathBlock(MathBlock),
    /// A leading frontmatter block (`---` YAML or `+++` TOML).
    Frontmatter(Frontmatter),
    /// A leaf directive: `::name[label]{attrs}`.
    LeafDirective(LeafDirective),
    /// A container directive: `:::name … :::`.
    ContainerDirective(ContainerDirective),
    /// A blank line beyond the one that separates two blocks.
    BlankLine(BlankLine),
}

/// A paragraph: a run of inline content. Source: any plain text line(s).
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Paragraph {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The paragraph's inline content.
    pub children: Vec<Inline>,
    /// The text the content was built from, by [`Paragraph::with_source`].
    pub(crate) source: Option<String>,
}

/// A heading. Source: `# Title` … `###### Title` (ATX).
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Heading {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// Heading level, 1..=6.
    pub depth: u8,
    /// The heading's inline content.
    pub children: Vec<Inline>,
    /// The text the content was built from, by [`Heading::with_source`].
    pub(crate) source: Option<String>,
}

/// A blank line the source holds beyond the one that separates two blocks:
/// K blank lines between two blocks are one separator and K − 1 of these.
/// Before a document's first block, at the start or end of a block quote,
/// alert, HTML container, or container directive, and after a document's
/// last line, each blank line is one. Source: a line holding only
/// whitespace and its containers' `>` markers.
#[derive(Clone, Debug, Default, Eq, PartialEq)]
pub struct BlankLine {
    /// Node metadata (source span): the line with its line ending.
    pub meta: NodeMeta,
}

/// A thematic break / horizontal rule. Source: `---`, `***`, or `___`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct ThematicBreak {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// Which character formed the break.
    pub marker: ThematicBreakMarker,
}

/// The character used to draw a [`ThematicBreak`].
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum ThematicBreakMarker {
    /// Dashes: `---`.
    Dash,
    /// Asterisks: `***`.
    Asterisk,
    /// Underscores: `___`.
    Underscore,
}

/// A block quote: content prefixed with `> `.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct BlockQuote {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The quoted block content.
    pub children: Vec<Block>,
}

/// A GFM alert / admonition. Source: `> [!NOTE]` followed by quoted content.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Alert {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The alert severity / type.
    pub kind: AlertKind,
    /// An optional custom title following the `[!KIND]` marker.
    pub title: Option<String>,
    /// The alert's block content.
    pub children: Vec<Block>,
}

/// The kind of a GFM [`Alert`] (the `[!KIND]` marker).
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum AlertKind {
    /// `> [!NOTE]`.
    Note,
    /// `> [!TIP]`.
    Tip,
    /// `> [!IMPORTANT]`.
    Important,
    /// `> [!WARNING]`.
    Warning,
    /// `> [!CAUTION]`.
    Caution,
}

/// A bullet or ordered list. Source: `- a` / `1. a` lines.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct List {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// `true` for an ordered list, `false` for a bullet list.
    pub ordered: bool,
    /// The marker delimiter used by the list items.
    pub delimiter: ListDelimiter,
    /// `true` if the list is tight (no blank lines between items / no `<p>`).
    pub tight: bool,
    /// The list's items.
    pub children: Vec<ListItem>,
}

/// The marker character that delimits a list's items.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum ListDelimiter {
    /// Bullet `-`.
    Dash,
    /// Bullet `*`.
    Asterisk,
    /// Bullet `+`.
    Plus,
    /// Ordered `1.`.
    Period,
    /// Ordered `1)`.
    Paren,
}

/// A single list item, optionally a GFM task-list checkbox.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct ListItem {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// Task-list state: `Some(true)` for `[x]`, `Some(false)` for `[ ]`, `None` otherwise.
    pub checked: Option<bool>,
    /// The number an ordered item is written with (`3.` => `Some(3)`), which
    /// for the first item is the list's start. `None` is written as the
    /// previous item's number plus one, or 1 for the first item; a bullet
    /// item holds `None`.
    pub number: Option<u64>,
    /// The item's block content.
    pub children: Vec<Block>,
}

/// A code block. Source: ```` ```lang … ``` ```` (fenced) or 4-space-indented lines.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct CodeBlock {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// Whether the block is fenced (and with what fence) or indented.
    pub kind: CodeBlockKind,
    /// The info string after a fence (e.g. the `rust` in ```` ```rust ````).
    pub info: Option<String>,
    /// The literal code contents.
    pub value: String,
}

/// Whether a [`CodeBlock`] is fenced or indented.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum CodeBlockKind {
    /// A fenced code block; records the fence char and its run length.
    Fenced {
        /// Which character formed the fence (backtick or tilde).
        marker: FenceMarker,
        /// The number of fence characters in the opening fence (>=3).
        length: usize,
    },
    /// A 4-space-indented code block.
    Indented,
}

/// The character used to fence a [`CodeBlock`].
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum FenceMarker {
    /// Backtick fence: ```` ``` ````.
    Backtick,
    /// Tilde fence: `~~~`.
    Tilde,
}

/// A raw HTML block: HTML emitted verbatim.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct HtmlBlock {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The literal HTML source.
    pub value: String,
}

/// A structured raw HTML container, such as `<details> ... </details>`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct HtmlContainer {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The opening HTML tag.
    pub opening: HtmlTag,
    /// The parsed container content.
    pub content: HtmlContainerContent,
    /// The closing HTML tag.
    pub closing: HtmlTag,
}

/// A raw HTML tag that bounds an [`HtmlContainer`].
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct HtmlTag {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The normalized lowercase tag name.
    pub name: String,
    /// The literal tag source, including angle brackets and attributes.
    pub raw: String,
}

/// The parsed content inside an [`HtmlContainer`].
#[derive(Clone, Debug, Eq, PartialEq)]
pub enum HtmlContainerContent {
    /// Block-level Markdown content.
    Blocks(Vec<Block>),
    /// Inline-level Markdown content.
    Inlines(Vec<Inline>),
}

/// A link reference definition. Source: `[label]: destination "title"`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Definition {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The label as written in the source (e.g. `Foo Bar`).
    pub label: String,
    /// The normalized lookup key (case-folded, whitespace-collapsed) for matching references.
    pub identifier: String,
    /// The link target URL.
    pub destination: String,
    /// How the destination was delimited (bare or `<…>`).
    pub destination_kind: LinkDestinationKind,
    /// The optional link title, with the quotes it is written in.
    pub title: Option<Title>,
}

/// A footnote definition. Source: `[^id]: footnote text`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct FootnoteDefinition {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The label as written in the source (the text after `^`).
    pub label: String,
    /// The normalized lookup key matching [`FootnoteReference`]s.
    pub identifier: String,
    /// The footnote's block content.
    pub children: Vec<Block>,
}

/// A GFM pipe table: a header row, an alignment row, then body rows. Source:
/// `| a | b |` / `|---|---|` / `| 1 | 2 |`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Table {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// Per-column alignment from the delimiter row.
    pub alignments: Vec<TableAlignment>,
    /// All rows; the first is the header row.
    pub rows: Vec<TableRow>,
}

/// The alignment of a [`Table`] column, from the `:---:` delimiter row.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum TableAlignment {
    /// No explicit alignment: `---`.
    None,
    /// Left-aligned: `:---`.
    Left,
    /// Center-aligned: `:---:`.
    Center,
    /// Right-aligned: `---:`.
    Right,
}

/// A single row of a [`Table`].
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct TableRow {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The row's cells.
    pub cells: Vec<TableCell>,
}

/// A single cell of a [`TableRow`].
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct TableCell {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The cell's inline content.
    pub children: Vec<Inline>,
    /// The text the content was built from, by [`TableCell::with_source`].
    pub(crate) source: Option<String>,
}

/// A display math block. Source: `$$ … $$`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct MathBlock {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The literal math contents (between the `$$` fences).
    pub value: String,
}

/// A leading frontmatter block. Source: `---` YAML or `+++` TOML at the top of
/// the document.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Frontmatter {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// Whether the frontmatter is YAML or TOML.
    pub kind: FrontmatterKind,
    /// The literal frontmatter contents (between the fences).
    pub value: String,
}

/// The format of a [`Frontmatter`] block.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum FrontmatterKind {
    /// YAML frontmatter, fenced by `---`.
    Yaml,
    /// TOML frontmatter, fenced by `+++`.
    Toml,
}

/// A leaf directive. Source: `::name[label]{attrs}`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct LeafDirective {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The directive name following the `::`.
    pub name: String,
    /// The optional `[label]` inline content.
    pub label: Vec<Inline>,
    /// The optional `{attrs}` attributes.
    pub attributes: Vec<DirectiveAttribute>,
    /// The text the label was built from, by [`LeafDirective::with_source`].
    pub(crate) label_source: Option<String>,
}

/// A container directive. Source: `:::name[label]{attrs}` … `:::`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct ContainerDirective {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The directive name following the `:::`.
    pub name: String,
    /// The optional `[label]` inline content.
    pub label: Vec<Inline>,
    /// The optional `{attrs}` attributes.
    pub attributes: Vec<DirectiveAttribute>,
    /// The directive's enclosed block content.
    pub children: Vec<Block>,
    /// The text the label was built from, by
    /// [`ContainerDirective::with_source`].
    pub(crate) label_source: Option<String>,
}

/// An inline-level node: the leaf and span content inside blocks.
#[derive(Clone, Debug, Eq, PartialEq)]
pub enum Inline {
    /// Literal text.
    Text(Text),
    /// A backslash escape such as `\*`.
    Escape(Escape),
    /// A character reference such as `&amp;` or `&#247;`.
    CharacterReference(CharacterReference),
    /// Emphasis: `*text*` or `_text_`.
    Emphasis(Emphasis),
    /// Strong emphasis: `**text**` or `__text__`.
    Strong(Strong),
    /// Strikethrough: `~~text~~`.
    Delete(Delete),
    /// A highlight / "mark" span: `==text==`.
    Mark(Mark),
    /// An emoji-style shortcode: `:name:`.
    Shortcode(Shortcode),
    /// An inline code span: `` `code` ``.
    Code(CodeInline),
    /// An inline link: `[text](url)`.
    Link(Link),
    /// An autolink: `<https://example.com>` or a bare literal URL or email.
    Autolink(Autolink),
    /// An inline image: `![alt](url)`.
    Image(Image),
    /// A reference link: `[text][label]`.
    LinkReference(LinkReference),
    /// A reference image: `![alt][label]`.
    ImageReference(ImageReference),
    /// Raw inline HTML such as `<span>`.
    Html(HtmlInline),
    /// A soft line break (a plain newline within a paragraph).
    SoftBreak(SoftBreak),
    /// A hard line break (`\` or two trailing spaces).
    LineBreak(LineBreak),
    /// Inline math: `$x$`.
    Math(MathInline),
    /// A footnote reference: `[^id]`.
    FootnoteReference(FootnoteReference),
    /// An inline footnote: `^[inline note]`.
    InlineFootnote(InlineFootnote),
    /// A wiki link: `[[target|label]]`.
    WikiLink(WikiLink),
    /// A text directive: `:name[label]{attrs}`.
    TextDirective(TextDirective),
    /// A tag: `#name`.
    Tag(Tag),
}

/// Literal text content.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Text {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The text value.
    pub value: String,
}

/// A backslash escape such as `\*` or `\\`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Escape {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The escaped (literal) character.
    pub value: char,
}

/// A character reference such as `&amp;` or `&#247;`. The reference as
/// written is the node's one fact; [`CharacterReference::value`] decodes it.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct CharacterReference {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The reference as written, including `&` and `;` (e.g. `&amp;`).
    pub reference: String,
}

/// Emphasis (typically italic): `*text*` or `_text_`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Emphasis {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The delimiter the span was written with.
    pub delimiter: EmphasisDelimiter,
    /// The emphasized inline content.
    pub children: Vec<Inline>,
}

/// Strong emphasis (typically bold): `**text**` or `__text__`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Strong {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The delimiter the span was written with.
    pub delimiter: EmphasisDelimiter,
    /// The strongly-emphasized inline content.
    pub children: Vec<Inline>,
}

/// The delimiter character of an [`Emphasis`] or [`Strong`] span.
#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
pub enum EmphasisDelimiter {
    /// `*text*` / `**text**`.
    #[default]
    Asterisk,
    /// `_text_` / `__text__`.
    Underscore,
}

/// Strikethrough: `~~text~~`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Delete {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The struck-through inline content.
    pub children: Vec<Inline>,
}

/// A highlight / "mark" span: `==text==`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Mark {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The highlighted inline content.
    pub children: Vec<Inline>,
}

/// An emoji shortcode: `:name:`, where `name` is a gemoji name or alias.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Shortcode {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The shortcode name between the colons (e.g. `smile` for `:smile:`).
    pub name: String,
}

/// A tag: `#` and a name, such as `#rust` or `#ai/agents`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Tag {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The name as written, without the `#`. A `/` separates levels, which
    /// the caller splits.
    pub name: String,
}

/// An inline code span: `` `code` ``. The fence and the padding spaces are
/// not recorded: the serializer chooses them from the value.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct CodeInline {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The code text, normalized as CommonMark reads it: line endings as
    /// spaces, and one space stripped from each end when both ends hold one
    /// and the text is not all spaces.
    pub value: String,
}

/// An inline link: `[text](destination "title")`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Link {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The link target URL.
    pub destination: String,
    /// How the destination was delimited (bare or `<…>`).
    pub destination_kind: LinkDestinationKind,
    /// The optional link title, with the quotes it is written in.
    pub title: Option<Title>,
    /// The link's inline content (the visible text).
    pub children: Vec<Inline>,
}

/// An autolink: `<https://example.com>`, `<a@b.c>`, or a GFM literal
/// autolink, a bare `https://…`, `www.…`, or email address. The text as
/// written is the node's one fact; [`Autolink::destination`] derives the link
/// target from it.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Autolink {
    /// Node metadata (source span). An angle-bracket autolink's span covers
    /// its brackets.
    pub meta: NodeMeta,
    /// Which autolink syntax the text is written in.
    pub form: AutolinkForm,
    /// The URL or address as written, without an angle-bracket autolink's
    /// brackets.
    pub text: String,
}

/// How an [`Autolink`] is written.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum AutolinkForm {
    /// An angle-bracket autolink: `<https://example.com>` or `<a@b.c>`.
    Angle,
    /// A GFM literal autolink: a bare `https://…`, `www.…`, or email address.
    Literal,
}

/// An inline image: `![alt](destination "title")`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Image {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The image source URL.
    pub destination: String,
    /// How the destination was delimited (bare or `<…>`).
    pub destination_kind: LinkDestinationKind,
    /// The optional image title, with the quotes it is written in.
    pub title: Option<Title>,
    /// The image's alt-text inline content.
    pub alt: Vec<Inline>,
}

/// How a link/image destination was delimited in the source.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum LinkDestinationKind {
    /// A bare destination: `(url)`.
    Bare,
    /// An angle-bracketed destination: `(<url>)`.
    Angle,
    /// No destination present: `()`.
    Omitted,
}

/// How a link/image title was quoted in the source.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum LinkTitleKind {
    /// Double-quoted: `"title"`.
    DoubleQuote,
    /// Single-quoted: `'title'`.
    SingleQuote,
    /// Parenthesized: `(title)`.
    Paren,
}

/// The title of a [`Link`], [`Image`], or [`Definition`]: its text and the
/// quotes it is written in.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Title {
    /// The title text, with its escapes and character references decoded.
    pub value: String,
    /// How the title is quoted.
    pub kind: LinkTitleKind,
}

/// A reference link: `[text][label]`, `[text][]`, or `[text]`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct LinkReference {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The normalized lookup key matching a [`Definition`].
    pub identifier: String,
    /// The label as written in the source.
    pub label: String,
    /// Whether the reference is full, collapsed, or shortcut form.
    pub kind: ReferenceKind,
    /// The link's inline content (the visible text).
    pub children: Vec<Inline>,
}

/// A reference image: `![alt][label]`, `![alt][]`, or `![alt]`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct ImageReference {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The normalized lookup key matching a [`Definition`].
    pub identifier: String,
    /// The label as written in the source.
    pub label: String,
    /// Whether the reference is full, collapsed, or shortcut form.
    pub kind: ReferenceKind,
    /// The image's alt-text inline content.
    pub alt: Vec<Inline>,
}

/// The form of a reference link/image.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum ReferenceKind {
    /// Full reference: `[text][label]`.
    Full,
    /// Collapsed reference: `[label][]`.
    Collapsed,
    /// Shortcut reference: `[label]`.
    Shortcut,
}

/// Raw inline HTML such as `<span>` or `</em>`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct HtmlInline {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The literal HTML source.
    pub value: String,
}

/// A soft line break: a plain newline within a paragraph.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct SoftBreak {
    /// Node metadata (source span).
    pub meta: NodeMeta,
}

/// A hard line break: a trailing `\` or two trailing spaces.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct LineBreak {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// Which syntax produced the break.
    pub kind: LineBreakKind,
}

/// Which syntax produced a hard [`LineBreak`].
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum LineBreakKind {
    /// A trailing backslash: `\`.
    Backslash,
    /// Two or more trailing spaces.
    Spaces,
}

/// Which syntax delimited an inline [`MathInline`] span.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum MathInlineKind {
    /// Dollar-fenced inline math (`$…$`, `$$…$$`, …); `dollars` is the fence
    /// length (>=1). Dollar math always renders inline, while a 2-dollar fence
    /// is conventionally treated as display elsewhere in the ecosystem.
    Dollar {
        /// The number of `$` characters in the fence (>=1).
        dollars: u8,
    },
    /// Math-code span: `$`…`$`.
    Code,
}

/// Inline math: `$x$`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct MathInline {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The literal math contents (between the fences).
    pub value: String,
    /// Which delimiter syntax was used.
    pub kind: MathInlineKind,
}

/// A footnote reference: `[^id]`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct FootnoteReference {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The label as written in the source (the text after `^`).
    pub label: String,
    /// The normalized lookup key matching a [`FootnoteDefinition`].
    pub identifier: String,
}

/// An inline footnote: `^[inline note]`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct InlineFootnote {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The footnote's inline content.
    pub children: Vec<Inline>,
}

/// A wiki link: `[[target|label]]`, or an embed: `![[target|label]]`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct WikiLink {
    /// Node metadata (source span). An embed's span starts at its `!`.
    pub meta: NodeMeta,
    /// The link target (page name) as written in the source, its backslash
    /// escapes and character references kept; [`WikiLink::decoded_target`]
    /// gives the text they stand for.
    pub target: String,
    /// The visible label as written in the source, its backslash escapes and
    /// character references kept; [`WikiLink::decoded_label`] gives the text
    /// they stand for. A label equal to `target` means the link is written
    /// without a `|label` part.
    pub label: String,
    /// Whether a `!` directly before the `[[` marks the link as an embed.
    pub embed: bool,
}

/// A text directive. Source: `:name[label]{attrs}`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct TextDirective {
    /// Node metadata (source span).
    pub meta: NodeMeta,
    /// The directive name following the `:`.
    pub name: String,
    /// The optional `[label]` inline content.
    pub label: Vec<Inline>,
    /// The optional `{attrs}` attributes.
    pub attributes: Vec<DirectiveAttribute>,
}

/// One attribute of a directive's `{name=value}` block.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct DirectiveAttribute {
    /// The attribute name.
    pub name: String,
    /// The attribute value, or `None` for a valueless attribute.
    pub value: Option<String>,
}

// ---------------------------------------------------------------------------
// Ergonomic accessors and a minimal construction layer.
//
// Every node carries a `meta: NodeMeta`, so `meta()`/`span()` are uniform across
// the enums and free callers from writing an exhaustive match just to read a
// span. `From`/`new` collapse the `Variant(Struct { meta, .. })` boilerplate for
// hand-built ASTs; the raw struct literals remain available for full control.
// ---------------------------------------------------------------------------

macro_rules! impl_meta_accessors {
    ($enum:ident { $($variant:ident),+ $(,)? }) => {
        impl $enum {
            /// Borrow this node's [`NodeMeta`].
            pub fn meta(&self) -> &NodeMeta {
                match self { $( $enum::$variant(node) => &node.meta, )+ }
            }

            /// This node's source span, if it carries one.
            pub fn span(&self) -> Option<Span> {
                self.meta().span
            }
        }
    };
}

macro_rules! impl_from_variants {
    ($enum:ident { $($variant:ident($ty:ty)),+ $(,)? }) => {
        $(
            impl From<$ty> for $enum {
                fn from(node: $ty) -> Self {
                    $enum::$variant(node)
                }
            }
        )+
    };
}

impl_meta_accessors!(Block {
    Paragraph,
    Heading,
    ThematicBreak,
    BlockQuote,
    Alert,
    List,
    CodeBlock,
    HtmlBlock,
    HtmlContainer,
    Definition,
    FootnoteDefinition,
    Table,
    MathBlock,
    Frontmatter,
    LeafDirective,
    ContainerDirective,
    BlankLine,
});

impl_from_variants!(Block {
    Paragraph(Paragraph), Heading(Heading), ThematicBreak(ThematicBreak),
    BlockQuote(BlockQuote), Alert(Alert), List(List),
    CodeBlock(CodeBlock), HtmlBlock(HtmlBlock), Definition(Definition),
    HtmlContainer(HtmlContainer),
    FootnoteDefinition(FootnoteDefinition), Table(Table), MathBlock(MathBlock),
    Frontmatter(Frontmatter), LeafDirective(LeafDirective), ContainerDirective(ContainerDirective),
    BlankLine(BlankLine),
});

impl_meta_accessors!(Inline {
    Text,
    Escape,
    CharacterReference,
    Emphasis,
    Strong,
    Delete,
    Mark,
    Shortcode,
    Code,
    Link,
    Autolink,
    Image,
    LinkReference,
    ImageReference,
    Html,
    SoftBreak,
    LineBreak,
    Math,
    FootnoteReference,
    InlineFootnote,
    WikiLink,
    TextDirective,
    Tag,
});

impl_from_variants!(Inline {
    Text(Text), Escape(Escape), CharacterReference(CharacterReference),
    Emphasis(Emphasis), Strong(Strong), Delete(Delete), Mark(Mark),
    Shortcode(Shortcode), Code(CodeInline), Link(Link), Autolink(Autolink), Image(Image),
    LinkReference(LinkReference), ImageReference(ImageReference), Html(HtmlInline),
    SoftBreak(SoftBreak), LineBreak(LineBreak), Math(MathInline),
    FootnoteReference(FootnoteReference), InlineFootnote(InlineFootnote), WikiLink(WikiLink),
    TextDirective(TextDirective), Tag(Tag),
});

impl Block {
    /// The blocks directly inside this block: a block quote's, an alert's, a
    /// footnote definition's, a container directive's, or an HTML container's
    /// that holds blocks; an empty slice for every other block. A list's
    /// blocks are in its items ([`ListItem::children`]), as [`NodePath`]
    /// counts them, so a walker over blocks steps into a list's items itself.
    pub fn children(&self) -> &[Block] {
        match self {
            Block::BlockQuote(n) => &n.children,
            Block::Alert(n) => &n.children,
            Block::FootnoteDefinition(n) => &n.children,
            Block::ContainerDirective(n) => &n.children,
            Block::HtmlContainer(n) => match &n.content {
                HtmlContainerContent::Blocks(blocks) => blocks,
                HtmlContainerContent::Inlines(_) => &[],
            },
            Block::Paragraph(_)
            | Block::Heading(_)
            | Block::ThematicBreak(_)
            | Block::List(_)
            | Block::CodeBlock(_)
            | Block::HtmlBlock(_)
            | Block::Definition(_)
            | Block::Table(_)
            | Block::MathBlock(_)
            | Block::Frontmatter(_)
            | Block::LeafDirective(_)
            | Block::BlankLine(_) => &[],
        }
    }
}

impl Inline {
    /// The inline subtree of this node, or an empty slice for a leaf. Covers the
    /// `alt`/`label` fields uniformly, so a generic walker never silently skips
    /// an image's alt text or a directive's label.
    pub fn children(&self) -> &[Inline] {
        match self {
            Inline::Emphasis(n) => &n.children,
            Inline::Strong(n) => &n.children,
            Inline::Delete(n) => &n.children,
            Inline::Mark(n) => &n.children,
            Inline::Link(n) => &n.children,
            Inline::Image(n) => &n.alt,
            Inline::LinkReference(n) => &n.children,
            Inline::ImageReference(n) => &n.alt,
            Inline::InlineFootnote(n) => &n.children,
            Inline::TextDirective(n) => &n.label,
            Inline::Text(_)
            | Inline::Escape(_)
            | Inline::CharacterReference(_)
            | Inline::Shortcode(_)
            | Inline::Code(_)
            | Inline::Autolink(_)
            | Inline::Html(_)
            | Inline::SoftBreak(_)
            | Inline::LineBreak(_)
            | Inline::Math(_)
            | Inline::FootnoteReference(_)
            | Inline::WikiLink(_)
            | Inline::Tag(_) => &[],
        }
    }
}

impl CharacterReference {
    /// A character reference node for `reference`, written with its `&` and
    /// `;` (e.g. `&amp;`).
    pub fn new(reference: impl Into<String>) -> Self {
        Self {
            meta: NodeMeta::default(),
            reference: reference.into(),
        }
    }

    /// The character the reference decodes to, or `None` when
    /// [`reference`](Self::reference) is not exactly one character reference.
    /// A valid document holds only references that decode.
    pub fn value(&self) -> Option<String> {
        crate::decode::decode_character_reference(&self.reference)
    }
}

impl Autolink {
    /// An autolink of `form` whose text is `text`.
    pub fn new(form: AutolinkForm, text: impl Into<String>) -> Self {
        Self {
            meta: NodeMeta::default(),
            form,
            text: text.into(),
        }
    }

    /// The link target the text writes, or `None` when the text is not
    /// exactly one autolink of its form. An angle-bracket URI links to itself
    /// and an email address to it after `mailto:`; a literal `www.` domain
    /// links to it after `http://`, a literal email address to it after
    /// `mailto:`, and any other literal autolink to itself. A valid document
    /// holds only autolinks with a destination.
    pub fn destination(&self) -> Option<String> {
        match self.form {
            AutolinkForm::Angle => crate::parse::angle_autolink_destination(&self.text),
            AutolinkForm::Literal => crate::parse::literal_autolink_destination(&self.text),
        }
    }
}

impl Title {
    /// A title holding `value`, quoted as `kind`.
    pub fn new(value: impl Into<String>, kind: LinkTitleKind) -> Self {
        Self {
            value: value.into(),
            kind,
        }
    }
}

impl Shortcode {
    /// The emoji the crate's pinned gemoji table gives this shortcode's
    /// name, or `None` for a name the table does not hold.
    pub fn glyph(&self) -> Option<&'static str> {
        crate::gemoji::glyph(&self.name)
    }
}

impl Tag {
    /// A tag named `name`, written without its `#`.
    pub fn new(name: impl Into<String>) -> Self {
        Self {
            meta: NodeMeta::default(),
            name: name.into(),
        }
    }
}

impl WikiLink {
    /// The target with its backslash escapes and character references
    /// decoded, as CommonMark decodes a link destination: `a \| b &amp; c`
    /// decodes to `a | b & c`.
    pub fn decoded_target(&self) -> String {
        crate::decode::decode_escapes_and_references(&self.target)
    }

    /// The label with its backslash escapes and character references
    /// decoded, as [`WikiLink::decoded_target`] decodes the target.
    pub fn decoded_label(&self) -> String {
        crate::decode::decode_escapes_and_references(&self.label)
    }
}

impl Text {
    /// A text node with the given string value.
    pub fn new(value: impl Into<String>) -> Self {
        Self {
            meta: NodeMeta::default(),
            value: value.into(),
        }
    }
}

impl From<&str> for Text {
    fn from(value: &str) -> Self {
        Text::new(value)
    }
}

impl From<String> for Text {
    fn from(value: String) -> Self {
        Text::new(value)
    }
}

impl Paragraph {
    /// A paragraph from any iterator of inline-convertible children.
    pub fn new<I, T>(children: I) -> Self
    where
        I: IntoIterator<Item = T>,
        T: Into<Inline>,
    {
        Self {
            meta: NodeMeta::default(),
            children: children.into_iter().map(Into::into).collect(),
            source: None,
        }
    }

    /// A paragraph whose content is `text`, read as
    /// [`parse_inline`](crate::parse_inline) reads it with `definitions`, and
    /// the diagnostics of that read. The paragraph keeps `text`, which the
    /// writer writes in place of its inlines while they are the ones `text`
    /// reads as; the spans of its inlines are offsets in `text`. Pass the
    /// definitions of the document the paragraph will be written in
    /// ([`Definitions::of`]); after they change, or for a leaf built with
    /// others, [`Document::reread_kept_sources`] reads its text again.
    pub fn with_source(text: &str, definitions: &Definitions) -> (Self, Vec<Diagnostic>) {
        let (children, diagnostics) = read_source(text, definitions);
        let paragraph = Self {
            source: Some(text.into()),
            ..Self::new(children)
        };
        (paragraph, diagnostics)
    }

    /// The text [`Paragraph::with_source`] built the paragraph from.
    pub fn source(&self) -> Option<&str> {
        self.source.as_deref()
    }
}

impl Heading {
    /// A heading of the given depth.
    pub fn new<I, T>(depth: u8, children: I) -> Self
    where
        I: IntoIterator<Item = T>,
        T: Into<Inline>,
    {
        Self {
            meta: NodeMeta::default(),
            depth,
            children: children.into_iter().map(Into::into).collect(),
            source: None,
        }
    }

    /// A heading of the given depth whose content is `text`, built as
    /// [`Paragraph::with_source`] builds a paragraph.
    pub fn with_source(
        depth: u8,
        text: &str,
        definitions: &Definitions,
    ) -> (Self, Vec<Diagnostic>) {
        let (children, diagnostics) = read_source(text, definitions);
        let heading = Self {
            source: Some(text.into()),
            ..Self::new(depth, children)
        };
        (heading, diagnostics)
    }

    /// The text [`Heading::with_source`] built the heading from.
    pub fn source(&self) -> Option<&str> {
        self.source.as_deref()
    }
}

impl TableCell {
    /// A cell from any iterator of inline-convertible children.
    pub fn new<I, T>(children: I) -> Self
    where
        I: IntoIterator<Item = T>,
        T: Into<Inline>,
    {
        Self {
            meta: NodeMeta::default(),
            children: children.into_iter().map(Into::into).collect(),
            source: None,
        }
    }

    /// A cell whose content is `text`, built as [`Paragraph::with_source`]
    /// builds a paragraph. A `|` in `text` is content: the writer escapes it.
    pub fn with_source(text: &str, definitions: &Definitions) -> (Self, Vec<Diagnostic>) {
        let (children, diagnostics) = read_source(text, definitions);
        let cell = Self {
            source: Some(text.into()),
            ..Self::new(children)
        };
        (cell, diagnostics)
    }

    /// The text [`TableCell::with_source`] built the cell from.
    pub fn source(&self) -> Option<&str> {
        self.source.as_deref()
    }
}

impl LeafDirective {
    /// A leaf directive named `name`, with no label and no attributes.
    pub fn new(name: impl Into<String>) -> Self {
        Self {
            meta: NodeMeta::default(),
            name: name.into(),
            label: Vec::new(),
            attributes: Vec::new(),
            label_source: None,
        }
    }

    /// A leaf directive named `name` whose label is `text`, built as
    /// [`Paragraph::with_source`] builds a paragraph's content.
    pub fn with_source(
        name: impl Into<String>,
        text: &str,
        definitions: &Definitions,
    ) -> (Self, Vec<Diagnostic>) {
        let (label, diagnostics) = read_source(text, definitions);
        let directive = Self {
            label,
            label_source: Some(text.into()),
            ..Self::new(name)
        };
        (directive, diagnostics)
    }

    /// The text [`LeafDirective::with_source`] built the label from.
    pub fn label_source(&self) -> Option<&str> {
        self.label_source.as_deref()
    }
}

impl ContainerDirective {
    /// A container directive named `name` holding `children`, with no label
    /// and no attributes.
    pub fn new(name: impl Into<String>, children: Vec<Block>) -> Self {
        Self {
            meta: NodeMeta::default(),
            name: name.into(),
            label: Vec::new(),
            attributes: Vec::new(),
            children,
            label_source: None,
        }
    }

    /// A container directive named `name` holding `children`, whose label
    /// is `text`, built as [`Paragraph::with_source`] builds a paragraph's
    /// content.
    pub fn with_source(
        name: impl Into<String>,
        text: &str,
        children: Vec<Block>,
        definitions: &Definitions,
    ) -> (Self, Vec<Diagnostic>) {
        let (label, diagnostics) = read_source(text, definitions);
        let directive = Self {
            label,
            label_source: Some(text.into()),
            ..Self::new(name, children)
        };
        (directive, diagnostics)
    }

    /// The text [`ContainerDirective::with_source`] built the label from.
    pub fn label_source(&self) -> Option<&str> {
        self.label_source.as_deref()
    }
}

/// The inlines `text` reads as, with the diagnostics of the read.
fn read_source(text: &str, definitions: &Definitions) -> (Vec<Inline>, Vec<Diagnostic>) {
    let output = crate::parse::parse_inline_tree(text, definitions);
    (output.inlines, output.diagnostics)
}

impl Link {
    /// An inline, bare-destination link with no title.
    pub fn new<I, T>(destination: impl Into<String>, children: I) -> Self
    where
        I: IntoIterator<Item = T>,
        T: Into<Inline>,
    {
        Self {
            meta: NodeMeta::default(),
            destination: destination.into(),
            destination_kind: LinkDestinationKind::Bare,
            title: None,
            children: children.into_iter().map(Into::into).collect(),
        }
    }
}

impl CodeInline {
    /// An inline code span holding `value`.
    pub fn new(value: impl Into<String>) -> Self {
        Self {
            meta: NodeMeta::default(),
            value: value.into(),
        }
    }
}

impl List {
    /// A tight, dash-delimited bullet list.
    pub fn new<I>(children: I) -> Self
    where
        I: IntoIterator<Item = ListItem>,
    {
        Self {
            meta: NodeMeta::default(),
            ordered: false,
            delimiter: ListDelimiter::Dash,
            tight: true,
            children: children.into_iter().collect(),
        }
    }
}

impl ListItem {
    /// An item holding `children`, with no task marker and no number.
    pub fn new<I, T>(children: I) -> Self
    where
        I: IntoIterator<Item = T>,
        T: Into<Block>,
    {
        Self {
            meta: NodeMeta::default(),
            checked: None,
            number: None,
            children: children.into_iter().map(Into::into).collect(),
        }
    }
}

impl BlankLine {
    /// A blank line.
    pub fn new() -> Self {
        Self::default()
    }
}