Add support for turning mdast to hast

4 files changed, 1986 insertions, 245 deletions

diff --git a/tests/test_utils/hast.rs b/tests/test_utils/hast.rs
new file mode 100644
index 0000000..4adf0ca
--- /dev/null
+++ b/tests/test_utils/hast.rs
@@ -0,0 +1,279 @@
+#![allow(dead_code)]
+
+// ^-- fix later
+
+extern crate alloc;
+extern crate micromark;
+use alloc::{
+    fmt,
+    string::{String, ToString},
+    vec::Vec,
+};
+use micromark::{mdast::AttributeContent, unist::Position};
+
+/// Nodes.
+#[derive(Clone, PartialEq)]
+pub enum Node {
+    /// Root.
+    Root(Root),
+    /// Element.
+    Element(Element),
+    /// Document type.
+    Doctype(Doctype),
+    /// Comment.
+    Comment(Comment),
+    /// Text.
+    Text(Text),
+
+    // MDX being passed through.
+    /// MDX: JSX element.
+    MdxJsxElement(MdxJsxElement),
+    /// MDX.js ESM.
+    MdxjsEsm(MdxjsEsm),
+    // MDX: expression.
+    MdxExpression(MdxExpression),
+}
+
+impl fmt::Debug for Node {
+    // Debug the wrapped struct.
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Node::Root(x) => write!(f, "{:?}", x),
+            Node::Element(x) => write!(f, "{:?}", x),
+            Node::Doctype(x) => write!(f, "{:?}", x),
+            Node::Comment(x) => write!(f, "{:?}", x),
+            Node::Text(x) => write!(f, "{:?}", x),
+            Node::MdxJsxElement(x) => write!(f, "{:?}", x),
+            Node::MdxExpression(x) => write!(f, "{:?}", x),
+            Node::MdxjsEsm(x) => write!(f, "{:?}", x),
+        }
+    }
+}
+
+fn children_to_string(children: &[Node]) -> String {
+    children.iter().map(ToString::to_string).collect()
+}
+
+impl ToString for Node {
+    fn to_string(&self) -> String {
+        match self {
+            // Parents.
+            Node::Root(x) => children_to_string(&x.children),
+            Node::Element(x) => children_to_string(&x.children),
+            Node::MdxJsxElement(x) => children_to_string(&x.children),
+            // Literals.
+            Node::Comment(x) => x.value.clone(),
+            Node::Text(x) => x.value.clone(),
+            Node::MdxExpression(x) => x.value.clone(),
+            Node::MdxjsEsm(x) => x.value.clone(),
+            // Voids.
+            Node::Doctype(_) => "".to_string(),
+        }
+    }
+}
+
+impl Node {
+    #[must_use]
+    pub fn children(&self) -> Option<&Vec<Node>> {
+        match self {
+            // Parent.
+            Node::Root(x) => Some(&x.children),
+            Node::Element(x) => Some(&x.children),
+            Node::MdxJsxElement(x) => Some(&x.children),
+            // Non-parent.
+            _ => None,
+        }
+    }
+
+    pub fn children_mut(&mut self) -> Option<&mut Vec<Node>> {
+        match self {
+            // Parent.
+            Node::Root(x) => Some(&mut x.children),
+            Node::Element(x) => Some(&mut x.children),
+            Node::MdxJsxElement(x) => Some(&mut x.children),
+            // Non-parent.
+            _ => None,
+        }
+    }
+
+    pub fn position(&self) -> Option<&Position> {
+        match self {
+            Node::Root(x) => x.position.as_ref(),
+            Node::Element(x) => x.position.as_ref(),
+            Node::Doctype(x) => x.position.as_ref(),
+            Node::Comment(x) => x.position.as_ref(),
+            Node::Text(x) => x.position.as_ref(),
+            Node::MdxJsxElement(x) => x.position.as_ref(),
+            Node::MdxExpression(x) => x.position.as_ref(),
+            Node::MdxjsEsm(x) => x.position.as_ref(),
+        }
+    }
+
+    pub fn position_mut(&mut self) -> Option<&mut Position> {
+        match self {
+            Node::Root(x) => x.position.as_mut(),
+            Node::Element(x) => x.position.as_mut(),
+            Node::Doctype(x) => x.position.as_mut(),
+            Node::Comment(x) => x.position.as_mut(),
+            Node::Text(x) => x.position.as_mut(),
+            Node::MdxJsxElement(x) => x.position.as_mut(),
+            Node::MdxExpression(x) => x.position.as_mut(),
+            Node::MdxjsEsm(x) => x.position.as_mut(),
+        }
+    }
+
+    pub fn position_set(&mut self, position: Option<Position>) {
+        match self {
+            Node::Root(x) => x.position = position,
+            Node::Element(x) => x.position = position,
+            Node::Doctype(x) => x.position = position,
+            Node::Comment(x) => x.position = position,
+            Node::Text(x) => x.position = position,
+            Node::MdxJsxElement(x) => x.position = position,
+            Node::MdxExpression(x) => x.position = position,
+            Node::MdxjsEsm(x) => x.position = position,
+        }
+    }
+}
+
+/// Document.
+///
+/// ```html
+/// > | a
+///     ^
+/// ```
+#[derive(Clone, Debug, PartialEq)]
+pub struct Root {
+    // Parent.
+    /// Content model.
+    pub children: Vec<Node>,
+    /// Positional info.
+    pub position: Option<Position>,
+}
+
+/// Document type.
+///
+/// ```html
+/// > | <!doctype html>
+///     ^^^^^^^^^^^^^^^
+/// ```
+// To do: clone.
+#[derive(Clone, Debug, PartialEq)]
+pub struct Element {
+    pub tag_name: String,
+    pub properties: Vec<(String, PropertyValue)>,
+    // Parent.
+    pub children: Vec<Node>,
+    /// Positional info.
+    pub position: Option<Position>,
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum PropertyItem {
+    Number(f32),
+    String(String),
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum PropertyValue {
+    Number(f32),
+    Boolean(bool),
+    String(String),
+    CommaSeparated(Vec<PropertyItem>),
+    SpaceSeparated(Vec<PropertyItem>),
+}
+
+/// Document type.
+///
+/// ```html
+/// > | <!doctype html>
+///     ^^^^^^^^^^^^^^^
+/// ```
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct Doctype {
+    // Void.
+    /// Positional info.
+    pub position: Option<Position>,
+}
+
+/// Comment.
+///
+/// ```html
+/// > | <!-- a -->
+///     ^^^^^^^^^^
+/// ```
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct Comment {
+    // Text.
+    /// Content model.
+    pub value: String,
+    /// Positional info.
+    pub position: Option<Position>,
+}
+
+/// Text.
+///
+/// ```html
+/// > | a
+///     ^
+/// ```
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct Text {
+    // Text.
+    /// Content model.
+    pub value: String,
+    /// Positional info.
+    pub position: Option<Position>,
+}
+
+/// MDX: JSX element.
+///
+/// ```markdown
+/// > | <a />
+///     ^^^^^
+/// ```
+#[derive(Clone, Debug, PartialEq)]
+pub struct MdxJsxElement {
+    // Parent.
+    /// Content model.
+    pub children: Vec<Node>,
+    /// Positional info.
+    pub position: Option<Position>,
+    // JSX element.
+    /// Name.
+    ///
+    /// Fragments have no name.
+    pub name: Option<String>,
+    /// Attributes.
+    pub attributes: Vec<AttributeContent>,
+}
+
+/// MDX: expression.
+///
+/// ```markdown
+/// > | {a}
+///     ^^^
+/// ```
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct MdxExpression {
+    // Literal.
+    /// Content model.
+    pub value: String,
+    /// Positional info.
+    pub position: Option<Position>,
+}
+
+/// MDX: ESM.
+///
+/// ```markdown
+/// > | import a from 'b'
+///     ^^^^^^^^^^^^^^^^^
+/// ```
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct MdxjsEsm {
+    // Literal.
+    /// Content model.
+    pub value: String,
+    /// Positional info.
+    pub position: Option<Position>,
+}
diff --git a/tests/test_utils/mod.rs b/tests/test_utils/mod.rs
index 10b9643..111118f 100644
--- a/tests/test_utils/mod.rs
+++ b/tests/test_utils/mod.rs
@@ -1,245 +1,3 @@
-extern crate micromark;
-extern crate swc_common;
-extern crate swc_ecma_ast;
-extern crate swc_ecma_parser;
-use micromark::{MdxExpressionKind, MdxSignal};
-use swc_common::{source_map::Pos, BytePos, FileName, SourceFile, Spanned};
-use swc_ecma_ast::{EsVersion, Expr, Module};
-use swc_ecma_parser::{
-    error::Error as SwcError, parse_file_as_expr, parse_file_as_module, EsConfig, Syntax,
-};
-
-/// Parse ESM in MDX with SWC.
-pub fn parse_esm(value: &str) -> MdxSignal {
-    let (file, syntax, version) = create_config(value.to_string());
-    let mut errors = vec![];
-    let result = parse_file_as_module(&file, syntax, version, None, &mut errors);
-
-    match result {
-        Err(error) => swc_error_to_signal(&error, value.len(), 0, "esm"),
-        Ok(tree) => {
-            if errors.is_empty() {
-                check_esm_ast(tree)
-            } else {
-                if errors.len() > 1 {
-                    println!("parse_esm: todo: multiple errors? {:?}", errors);
-                }
-                swc_error_to_signal(&errors[0], value.len(), 0, "esm")
-            }
-        }
-    }
-}
-
-/// Parse expressions in MDX with SWC.
-pub fn parse_expression(value: &str, kind: MdxExpressionKind) -> MdxSignal {
-    // Empty expressions are OK.
-    if matches!(kind, MdxExpressionKind::Expression)
-        && matches!(whitespace_and_comments(0, value), MdxSignal::Ok)
-    {
-        return MdxSignal::Ok;
-    }
-
-    // For attribute expression, a spread is needed, for which we have to prefix
-    // and suffix the input.
-    // See `check_expression_ast` for how the AST is verified.
-    let (prefix, suffix) = if matches!(kind, MdxExpressionKind::AttributeExpression) {
-        ("({", "})")
-    } else {
-        ("", "")
-    };
-
-    let (file, syntax, version) = create_config(format!("{}{}{}", prefix, value, suffix));
-    let mut errors = vec![];
-    let result = parse_file_as_expr(&file, syntax, version, None, &mut errors);
-
-    match result {
-        Err(error) => swc_error_to_signal(&error, value.len(), prefix.len(), "expression"),
-        Ok(tree) => {
-            if errors.is_empty() {
-                let place = fix_swc_position(tree.span().hi.to_usize(), prefix.len());
-                let result = check_expression_ast(tree, kind);
-                if matches!(result, MdxSignal::Ok) {
-                    whitespace_and_comments(place, value)
-                } else {
-                    result
-                }
-            } else {
-                if errors.len() > 1 {
-                    unreachable!("parse_expression: todo: multiple errors? {:?}", errors);
-                }
-                swc_error_to_signal(&errors[0], value.len(), prefix.len(), "expression")
-            }
-        }
-    }
-}
-
-/// Check that the resulting AST of ESM is OK.
-///
-/// This checks that only module declarations (import/exports) are used, not
-/// statements.
-fn check_esm_ast(tree: Module) -> MdxSignal {
-    let mut index = 0;
-    while index < tree.body.len() {
-        let node = &tree.body[index];
-
-        if !node.is_module_decl() {
-            let place = fix_swc_position(node.span().hi.to_usize(), 0);
-            return MdxSignal::Error(
-                "Unexpected statement in code: only import/exports are supported".to_string(),
-                place,
-            );
-        }
-
-        index += 1;
-    }
-
-    MdxSignal::Ok
-}
-
-/// Check that the resulting AST of an expressions is OK.
-///
-/// This checks that attribute expressions are the expected spread.
-fn check_expression_ast(tree: Box<Expr>, kind: MdxExpressionKind) -> MdxSignal {
-    if matches!(kind, MdxExpressionKind::AttributeExpression)
-        && tree
-            .unwrap_parens()
-            .as_object()
-            .and_then(|object| {
-                if object.props.len() == 1 {
-                    object.props[0].as_spread()
-                } else {
-                    None
-                }
-            })
-            .is_none()
-    {
-        MdxSignal::Error(
-            "Expected a single spread value, such as `...x`".to_string(),
-            0,
-        )
-    } else {
-        MdxSignal::Ok
-    }
-}
-
-/// Turn an SWC error into an `MdxSignal`.
-///
-/// * If the error happens at `value_len`, yields `MdxSignal::Eof`
-/// * Else, yields `MdxSignal::Error`.
-fn swc_error_to_signal(
-    error: &SwcError,
-    value_len: usize,
-    prefix_len: usize,
-    name: &str,
-) -> MdxSignal {
-    let message = error.kind().msg().to_string();
-    let place = fix_swc_position(error.span().hi.to_usize(), prefix_len);
-    let message = format!("Could not parse {} with swc: {}", name, message);
-
-    if place >= value_len {
-        MdxSignal::Eof(message)
-    } else {
-        MdxSignal::Error(message, place)
-    }
-}
-
-/// Move past JavaScript whitespace (well, actually ASCII whitespace) and
-/// comments.
-///
-/// This is needed because for expressions, we use an API that parses up to
-/// a valid expression, but there may be more expressions after it, which we
-/// don’t alow.
-fn whitespace_and_comments(mut index: usize, value: &str) -> MdxSignal {
-    let bytes = value.as_bytes();
-    let len = bytes.len();
-    let mut in_multiline = false;
-    let mut in_line = false;
-
-    while index < len {
-        // In a multiline comment: `/* a */`.
-        if in_multiline {
-            if index + 1 < len && bytes[index] == b'*' && bytes[index + 1] == b'/' {
-                index += 1;
-                in_multiline = false;
-            }
-        }
-        // In a line comment: `// a`.
-        else if in_line {
-            if index + 1 < len && bytes[index] == b'\r' && bytes[index + 1] == b'\n' {
-                index += 1;
-                in_line = false;
-            } else if bytes[index] == b'\r' || bytes[index] == b'\n' {
-                in_line = false;
-            }
-        }
-        // Not in a comment, opening a multiline comment: `/* a */`.
-        else if index + 1 < len && bytes[index] == b'/' && bytes[index + 1] == b'*' {
-            index += 1;
-            in_multiline = true;
-        }
-        // Not in a comment, opening a line comment: `// a`.
-        else if index + 1 < len && bytes[index] == b'/' && bytes[index + 1] == b'/' {
-            index += 1;
-            in_line = true;
-        }
-        // Outside comment, whitespace.
-        else if bytes[index].is_ascii_whitespace() {
-            // Fine!
-        }
-        // Outside comment, not whitespace.
-        else {
-            return MdxSignal::Error(
-                "Could not parse expression with swc: Unexpected content after expression"
-                    .to_string(),
-                index,
-            );
-        }
-
-        index += 1;
-    }
-
-    if in_multiline {
-        MdxSignal::Error(
-            "Could not parse expression with swc: Unexpected unclosed multiline comment, expected closing: `*/`".to_string(),
-            index,
-        )
-    } else if in_line {
-        // EOF instead of EOL is specifically not allowed, because that would
-        // mean the closing brace is on the commented-out line
-        MdxSignal::Error(
-            "Could not parse expression with swc: Unexpected unclosed line comment, expected line ending: `\\n`".to_string(),
-            index,
-        )
-    } else {
-        MdxSignal::Ok
-    }
-}
-
-/// Create configuration for SWC, shared between ESM and expressions.
-///
-/// This enables modern JavaScript (ES2022) + JSX.
-fn create_config(source: String) -> (SourceFile, Syntax, EsVersion) {
-    (
-        // File.
-        SourceFile::new(
-            FileName::Anon,
-            false,
-            FileName::Anon,
-            source,
-            BytePos::from_usize(1),
-        ),
-        // Syntax.
-        Syntax::Es(EsConfig {
-            jsx: true,
-            ..EsConfig::default()
-        }),
-        // Version.
-        EsVersion::Es2022,
-    )
-}
-
-/// Turn an SWC byte position from a resulting AST to an offset in the original
-/// input string.
-fn fix_swc_position(index: usize, prefix_len: usize) -> usize {
-    index - 1 - prefix_len
-}
+pub mod hast;
+pub mod swc;
+pub mod to_hast;
diff --git a/tests/test_utils/swc.rs b/tests/test_utils/swc.rs
new file mode 100644
index 0000000..f455674
--- /dev/null
+++ b/tests/test_utils/swc.rs
@@ -0,0 +1,247 @@
+extern crate micromark;
+extern crate swc_common;
+extern crate swc_ecma_ast;
+extern crate swc_ecma_parser;
+use micromark::{MdxExpressionKind, MdxSignal};
+use swc_common::{source_map::Pos, BytePos, FileName, SourceFile, Spanned};
+use swc_ecma_ast::{EsVersion, Expr, Module};
+use swc_ecma_parser::{
+    error::Error as SwcError, parse_file_as_expr, parse_file_as_module, EsConfig, Syntax,
+};
+
+/// Parse ESM in MDX with SWC.
+#[allow(dead_code)]
+pub fn parse_esm(value: &str) -> MdxSignal {
+    let (file, syntax, version) = create_config(value.to_string());
+    let mut errors = vec![];
+    let result = parse_file_as_module(&file, syntax, version, None, &mut errors);
+
+    match result {
+        Err(error) => swc_error_to_signal(&error, value.len(), 0, "esm"),
+        Ok(tree) => {
+            if errors.is_empty() {
+                check_esm_ast(&tree)
+            } else {
+                if errors.len() > 1 {
+                    println!("parse_esm: todo: multiple errors? {:?}", errors);
+                }
+                swc_error_to_signal(&errors[0], value.len(), 0, "esm")
+            }
+        }
+    }
+}
+
+/// Parse expressions in MDX with SWC.
+#[allow(dead_code)]
+pub fn parse_expression(value: &str, kind: &MdxExpressionKind) -> MdxSignal {
+    // Empty expressions are OK.
+    if matches!(kind, MdxExpressionKind::Expression)
+        && matches!(whitespace_and_comments(0, value), MdxSignal::Ok)
+    {
+        return MdxSignal::Ok;
+    }
+
+    // For attribute expression, a spread is needed, for which we have to prefix
+    // and suffix the input.
+    // See `check_expression_ast` for how the AST is verified.
+    let (prefix, suffix) = if matches!(kind, MdxExpressionKind::AttributeExpression) {
+        ("({", "})")
+    } else {
+        ("", "")
+    };
+
+    let (file, syntax, version) = create_config(format!("{}{}{}", prefix, value, suffix));
+    let mut errors = vec![];
+    let result = parse_file_as_expr(&file, syntax, version, None, &mut errors);
+
+    match result {
+        Err(error) => swc_error_to_signal(&error, value.len(), prefix.len(), "expression"),
+        Ok(tree) => {
+            if errors.is_empty() {
+                let place = fix_swc_position(tree.span().hi.to_usize(), prefix.len());
+                let result = check_expression_ast(&tree, kind);
+                if matches!(result, MdxSignal::Ok) {
+                    whitespace_and_comments(place, value)
+                } else {
+                    result
+                }
+            } else {
+                if errors.len() > 1 {
+                    unreachable!("parse_expression: todo: multiple errors? {:?}", errors);
+                }
+                swc_error_to_signal(&errors[0], value.len(), prefix.len(), "expression")
+            }
+        }
+    }
+}
+
+/// Check that the resulting AST of ESM is OK.
+///
+/// This checks that only module declarations (import/exports) are used, not
+/// statements.
+fn check_esm_ast(tree: &Module) -> MdxSignal {
+    let mut index = 0;
+    while index < tree.body.len() {
+        let node = &tree.body[index];
+
+        if !node.is_module_decl() {
+            let place = fix_swc_position(node.span().hi.to_usize(), 0);
+            return MdxSignal::Error(
+                "Unexpected statement in code: only import/exports are supported".to_string(),
+                place,
+            );
+        }
+
+        index += 1;
+    }
+
+    MdxSignal::Ok
+}
+
+/// Check that the resulting AST of an expressions is OK.
+///
+/// This checks that attribute expressions are the expected spread.
+fn check_expression_ast(tree: &Expr, kind: &MdxExpressionKind) -> MdxSignal {
+    if matches!(kind, MdxExpressionKind::AttributeExpression)
+        && tree
+            .unwrap_parens()
+            .as_object()
+            .and_then(|object| {
+                if object.props.len() == 1 {
+                    object.props[0].as_spread()
+                } else {
+                    None
+                }
+            })
+            .is_none()
+    {
+        MdxSignal::Error(
+            "Expected a single spread value, such as `...x`".to_string(),
+            0,
+        )
+    } else {
+        MdxSignal::Ok
+    }
+}
+
+/// Turn an SWC error into an `MdxSignal`.
+///
+/// * If the error happens at `value_len`, yields `MdxSignal::Eof`
+/// * Else, yields `MdxSignal::Error`.
+fn swc_error_to_signal(
+    error: &SwcError,
+    value_len: usize,
+    prefix_len: usize,
+    name: &str,
+) -> MdxSignal {
+    let message = error.kind().msg().to_string();
+    let place = fix_swc_position(error.span().hi.to_usize(), prefix_len);
+    let message = format!("Could not parse {} with swc: {}", name, message);
+
+    if place >= value_len {
+        MdxSignal::Eof(message)
+    } else {
+        MdxSignal::Error(message, place)
+    }
+}
+
+/// Move past JavaScript whitespace (well, actually ASCII whitespace) and
+/// comments.
+///
+/// This is needed because for expressions, we use an API that parses up to
+/// a valid expression, but there may be more expressions after it, which we
+/// don’t alow.
+fn whitespace_and_comments(mut index: usize, value: &str) -> MdxSignal {
+    let bytes = value.as_bytes();
+    let len = bytes.len();
+    let mut in_multiline = false;
+    let mut in_line = false;
+
+    while index < len {
+        // In a multiline comment: `/* a */`.
+        if in_multiline {
+            if index + 1 < len && bytes[index] == b'*' && bytes[index + 1] == b'/' {
+                index += 1;
+                in_multiline = false;
+            }
+        }
+        // In a line comment: `// a`.
+        else if in_line {
+            if index + 1 < len && bytes[index] == b'\r' && bytes[index + 1] == b'\n' {
+                index += 1;
+                in_line = false;
+            } else if bytes[index] == b'\r' || bytes[index] == b'\n' {
+                in_line = false;
+            }
+        }
+        // Not in a comment, opening a multiline comment: `/* a */`.
+        else if index + 1 < len && bytes[index] == b'/' && bytes[index + 1] == b'*' {
+            index += 1;
+            in_multiline = true;
+        }
+        // Not in a comment, opening a line comment: `// a`.
+        else if index + 1 < len && bytes[index] == b'/' && bytes[index + 1] == b'/' {
+            index += 1;
+            in_line = true;
+        }
+        // Outside comment, whitespace.
+        else if bytes[index].is_ascii_whitespace() {
+            // Fine!
+        }
+        // Outside comment, not whitespace.
+        else {
+            return MdxSignal::Error(
+                "Could not parse expression with swc: Unexpected content after expression"
+                    .to_string(),
+                index,
+            );
+        }
+
+        index += 1;
+    }
+
+    if in_multiline {
+        MdxSignal::Error(
+            "Could not parse expression with swc: Unexpected unclosed multiline comment, expected closing: `*/`".to_string(),
+            index,
+        )
+    } else if in_line {
+        // EOF instead of EOL is specifically not allowed, because that would
+        // mean the closing brace is on the commented-out line
+        MdxSignal::Error(
+            "Could not parse expression with swc: Unexpected unclosed line comment, expected line ending: `\\n`".to_string(),
+            index,
+        )
+    } else {
+        MdxSignal::Ok
+    }
+}
+
+/// Create configuration for SWC, shared between ESM and expressions.
+///
+/// This enables modern JavaScript (ES2022) + JSX.
+fn create_config(source: String) -> (SourceFile, Syntax, EsVersion) {
+    (
+        // File.
+        SourceFile::new(
+            FileName::Anon,
+            false,
+            FileName::Anon,
+            source,
+            BytePos::from_usize(1),
+        ),
+        // Syntax.
+        Syntax::Es(EsConfig {
+            jsx: true,
+            ..EsConfig::default()
+        }),
+        // Version.
+        EsVersion::Es2022,
+    )
+}
+
+/// Turn an SWC byte position from a resulting AST to an offset in the original
+/// input string.
+fn fix_swc_position(index: usize, prefix_len: usize) -> usize {
+    index - 1 - prefix_len
+}
diff --git a/tests/test_utils/to_hast.rs b/tests/test_utils/to_hast.rs
new file mode 100644
index 0000000..821931c
--- /dev/null
+++ b/tests/test_utils/to_hast.rs
@@ -0,0 +1,1457 @@
+use crate::test_utils::hast;
+use micromark::{mdast, sanitize_, unist::Position};
+
+// Options?
+// - dangerous: raw? No
+// - clobberPrefix / footnoteLabel / footnoteLabelTagName / footnoteLabelProperties / footnoteBacklabel? Later
+
+#[derive(Debug)]
+struct State {
+    definitions: Vec<(String, String, Option<String>)>,
+    footnote_definitions: Vec<(String, Vec<hast::Node>)>,
+    footnote_calls: Vec<(String, usize)>,
+}
+
+#[derive(Debug)]
+enum Result {
+    Fragment(Vec<hast::Node>),
+    Node(hast::Node),
+    None,
+}
+
+#[allow(dead_code)]
+pub fn to_hast(mdast: &mdast::Node) -> hast::Node {
+    let mut definitions = vec![];
+
+    // Collect definitions.
+    // Calls take info from their definition.
+    // Calls can come come before definitions.
+    // Footnote calls can also come before footnote definitions, but those
+    // calls *do not* take info from their definitions, so we don’t care
+    // about footnotes here.
+    visit(mdast, |node| {
+        if let mdast::Node::Definition(definition) = node {
+            definitions.push((
+                definition.identifier.clone(),
+                definition.url.clone(),
+                definition.title.clone(),
+            ));
+        }
+    });
+
+    // - footnoteById: Record<string, Node>
+    // - footnoteOrder: Vec<string>
+    // - footnoteCounts: Record<string, usize>
+
+    let (result, mut state) = one(
+        mdast,
+        None,
+        State {
+            definitions,
+            footnote_definitions: vec![],
+            footnote_calls: vec![],
+        },
+    );
+
+    if state.footnote_calls.is_empty() {
+        if let Result::Node(node) = result {
+            return node;
+        }
+    }
+
+    // We either have to generate a footer, or we don’t have a single node.
+    // So we need a root.
+    let mut root = hast::Root {
+        children: vec![],
+        position: None,
+    };
+
+    match result {
+        Result::Fragment(children) => root.children = children,
+        Result::Node(node) => {
+            if let hast::Node::Root(existing) = node {
+                root = existing;
+            } else {
+                root.children.push(node);
+            }
+        }
+        Result::None => {}
+    }
+
+    if !state.footnote_calls.is_empty() {
+        let mut items = vec![];
+
+        let mut index = 0;
+        while index < state.footnote_calls.len() {
+            let (id, count) = &state.footnote_calls[index];
+            let safe_id = sanitize_(&id.to_lowercase());
+
+            // Find definition: we’ll always find it.
+            let mut definition_index = 0;
+            while definition_index < state.footnote_definitions.len() {
+                if &state.footnote_definitions[definition_index].0 == id {
+                    break;
+                }
+                definition_index += 1;
+            }
+            debug_assert_ne!(
+                definition_index,
+                state.footnote_definitions.len(),
+                "expected definition"
+            );
+
+            // We’ll find each used definition once, so we can split off to take the content.
+            let mut content = state.footnote_definitions[definition_index].1.split_off(0);
+
+            let mut reference_index = 0;
+            let mut backreferences = vec![];
+            while reference_index < *count {
+                let mut backref_children = vec![hast::Node::Text(hast::Text {
+                    value: "↩".into(),
+                    position: None,
+                })];
+
+                if reference_index != 0 {
+                    backreferences.push(hast::Node::Text(hast::Text {
+                        value: " ".into(),
+                        position: None,
+                    }));
+
+                    backref_children.push(hast::Node::Element(hast::Element {
+                        tag_name: "sup".into(),
+                        properties: vec![],
+                        children: vec![hast::Node::Text(hast::Text {
+                            value: (reference_index + 1).to_string(),
+                            position: None,
+                        })],
+                        position: None,
+                    }));
+                }
+
+                backreferences.push(hast::Node::Element(hast::Element {
+                    tag_name: "a".into(),
+                    properties: vec![
+                        (
+                            "href".into(),
+                            hast::PropertyValue::String(format!(
+                                "#fnref-{}{}",
+                                safe_id,
+                                if reference_index == 0 {
+                                    "".into()
+                                } else {
+                                    format!("-{}", &(reference_index + 1).to_string())
+                                }
+                            )),
+                        ),
+                        (
+                            "dataFootnoteBackref".into(),
+                            hast::PropertyValue::Boolean(true),
+                        ),
+                        (
+                            "ariaLabel".into(),
+                            hast::PropertyValue::String("Back to content".into()),
+                        ),
+                        (
+                            "className".into(),
+                            hast::PropertyValue::SpaceSeparated(vec![hast::PropertyItem::String(
+                                "data-footnote-backref".into(),
+                            )]),
+                        ),
+                    ],
+                    children: backref_children,
+                    position: None,
+                }));
+
+                reference_index += 1;
+            }
+
+            let mut backreference_opt = Some(backreferences);
+
+            if let Some(hast::Node::Element(tail_element)) = content.last_mut() {
+                if tail_element.tag_name == "p" {
+                    if let Some(hast::Node::Text(text)) = tail_element.children.last_mut() {
+                        text.value.push(' ');
+                    } else {
+                        tail_element.children.push(hast::Node::Text(hast::Text {
+                            value: " ".into(),
+                            position: None,
+                        }));
+                    }
+
+                    tail_element
+                        .children
+                        .append(&mut backreference_opt.take().unwrap());
+                }
+            }
+
+            // No paragraph, just push them.
+            if let Some(mut backreference) = backreference_opt {
+                content.append(&mut backreference);
+            }
+
+            items.push(hast::Node::Element(hast::Element {
+                tag_name: "li".into(),
+                // To do: support clobber prefix.
+                properties: vec![(
+                    "id".into(),
+                    hast::PropertyValue::String(format!("#fn-{}", safe_id)),
+                )],
+                children: wrap(content, true),
+                position: None,
+            }));
+            index += 1;
+        }
+
+        root.children.push(hast::Node::Text(hast::Text {
+            value: "\n".into(),
+            position: None,
+        }));
+        root.children.push(hast::Node::Element(hast::Element {
+            tag_name: "section".into(),
+            properties: vec![
+                ("dataFootnotes".into(), hast::PropertyValue::Boolean(true)),
+                (
+                    "className".into(),
+                    hast::PropertyValue::SpaceSeparated(vec![hast::PropertyItem::String(
+                        "footnotes".into(),
+                    )]),
+                ),
+            ],
+            children: vec![
+                hast::Node::Element(hast::Element {
+                    tag_name: "h2".into(),
+                    properties: vec![
+                        (
+                            "id".into(),
+                            hast::PropertyValue::String("footnote-label".into()),
+                        ),
+                        (
+                            "className".into(),
+                            hast::PropertyValue::SpaceSeparated(vec![hast::PropertyItem::String(
+                                "sr-only".into(),
+                            )]),
+                        ),
+                    ],
+                    children: vec![hast::Node::Text(hast::Text {
+                        value: "Footnotes".into(),
+                        position: None,
+                    })],
+                    position: None,
+                }),
+                hast::Node::Text(hast::Text {
+                    value: "\n".into(),
+                    position: None,
+                }),
+                hast::Node::Element(hast::Element {
+                    tag_name: "ol".into(),
+                    properties: vec![],
+                    children: wrap(items, true),
+                    position: None,
+                }),
+                hast::Node::Text(hast::Text {
+                    value: "\n".into(),
+                    position: None,
+                }),
+            ],
+            position: None,
+        }));
+        root.children.push(hast::Node::Text(hast::Text {
+            value: "\n".into(),
+            position: None,
+        }));
+    }
+
+    hast::Node::Root(root)
+}
+
+fn one(node: &mdast::Node, parent: Option<&mdast::Node>, state: State) -> (Result, State) {
+    match node {
+        mdast::Node::BlockQuote(_) => transform_block_quote(node, state),
+        mdast::Node::Break(_) => transform_break(node, state),
+        mdast::Node::Code(_) => transform_code(node, state),
+        mdast::Node::Delete(_) => transform_delete(node, state),
+        mdast::Node::Emphasis(_) => transform_emphasis(node, state),
+        mdast::Node::FootnoteDefinition(_) => transform_footnote_definition(node, state),
+        mdast::Node::FootnoteReference(_) => transform_footnote_reference(node, state),
+        mdast::Node::Heading(_) => transform_heading(node, state),
+        mdast::Node::Image(_) => transform_image(node, state),
+        mdast::Node::ImageReference(_) => transform_image_reference(node, state),
+        mdast::Node::InlineCode(_) => transform_inline_code(node, state),
+        mdast::Node::InlineMath(_) => transform_inline_math(node, state),
+        mdast::Node::Link(_) => transform_link(node, state),
+        mdast::Node::LinkReference(_) => transform_link_reference(node, state),
+        mdast::Node::ListItem(_) => transform_list_item(node, parent, state),
+        mdast::Node::List(_) => transform_list(node, state),
+        mdast::Node::Math(_) => transform_math(node, state),
+        mdast::Node::MdxFlowExpression(_) | mdast::Node::MdxTextExpression(_) => {
+            transform_mdx_expression(node, state)
+        }
+        mdast::Node::MdxJsxFlowElement(_) | mdast::Node::MdxJsxTextElement(_) => {
+            transform_mdx_jsx_element(node, state)
+        }
+        mdast::Node::MdxjsEsm(_) => transform_mdxjs_esm(node, state),
+        mdast::Node::Paragraph(_) => transform_paragraph(node, state),
+        mdast::Node::Root(_) => transform_root(node, state),
+        mdast::Node::Strong(_) => transform_strong(node, state),
+        // Note: this is only called here if there is a single cell passed, not when one is found in a table.
+        mdast::Node::TableCell(_) => {
+            transform_table_cell(node, false, mdast::AlignKind::None, state)
+        }
+        // Note: this is only called here if there is a single row passed, not when one is found in a table.
+        mdast::Node::TableRow(_) => transform_table_row(node, false, None, state),
+        mdast::Node::Table(_) => transform_table(node, state),
+        mdast::Node::Text(_) => transform_text(node, state),
+        mdast::Node::ThematicBreak(_) => transform_thematic_break(node, state),
+        // Ignore.
+        // Idea: support `Raw` nodes for HTML, optionally?
+        mdast::Node::Definition(_)
+        | mdast::Node::Html(_)
+        | mdast::Node::Yaml(_)
+        | mdast::Node::Toml(_) => (Result::None, state),
+    }
+}
+
+/// [`BlockQuote`][mdast::BlockQuote].
+fn transform_block_quote(node: &mdast::Node, state: State) -> (Result, State) {
+    let (children, state) = all(node, state);
+    (
+        Result::Node(augment_node(
+            node,
+            hast::Node::Element(hast::Element {
+                tag_name: "blockquote".into(),
+                properties: vec![],
+                children: wrap(children, true),
+                position: None,
+            }),
+        )),
+        state,
+    )
+}
+
+/// [`Break`][mdast::Break].
+fn transform_break(node: &mdast::Node, state: State) -> (Result, State) {
+    (
+        Result::Fragment(vec![
+            augment_node(
+                node,
+                hast::Node::Element(hast::Element {
+                    tag_name: "br".into(),
+                    properties: vec![],
+                    children: vec![],
+                    position: None,
+                }),
+            ),
+            hast::Node::Text(hast::Text {
+                value: "\n".into(),
+                position: None,
+            }),
+        ]),
+        state,
+    )
+}
+
+/// [`Code`][mdast::Code].
+fn transform_code(node: &mdast::Node, state: State) -> (Result, State) {
+    if let mdast::Node::Code(code) = node {
+        let mut value = code.value.clone();
+        value.push('\n');
+        let mut properties = vec![];
+
+        if let Some(lang) = code.lang.as_ref() {
+            let mut value = "language-".to_string();
+            value.push_str(lang);
+            let value = hast::PropertyItem::String(value);
+            properties.push((
+                "className".into(),
+                hast::PropertyValue::SpaceSeparated(vec![value]),
+            ));
+        }
+
+        // To do: option to persist `meta`?
+
+        (
+            Result::Node(augment_node(
+                node,
+                hast::Node::Element(hast::Element {
+                    tag_name: "pre".into(),
+                    properties: vec![],
+                    children: vec![augment_node(
+                        node,
+                        hast::Node::Element(hast::Element {
+                            tag_name: "code".into(),
+                            properties,
+                            children: vec![hast::Node::Text(hast::Text {
+                                value,
+                                position: None,
+                            })],
+                            position: None,
+                        }),
+                    )],
+                    position: None,
+                }),
+            )),
+            state,
+        )
+    } else {
+        unreachable!("expected `Code`")
+    }
+}
+
+/// [`Delete`][mdast::Delete].
+fn transform_delete(node: &mdast::Node, state: State) -> (Result, State) {
+    let (children, state) = all(node, state);
+    (
+        Result::Node(augment_node(
+            node,
+            hast::Node::Element(hast::Element {
+                tag_name: "del".into(),
+                properties: vec![],
+                children,
+                position: None,
+            }),
+        )),
+        state,
+    )
+}
+
+/// [`Emphasis`][mdast::Emphasis].
+fn transform_emphasis(node: &mdast::Node, state: State) -> (Result, State) {
+    let (children, state) = all(node, state);
+    (
+        Result::Node(augment_node(
+            node,
+            hast::Node::Element(hast::Element {
+                tag_name: "em".into(),
+                properties: vec![],
+                children,
+                position: None,
+            }),
+        )),
+        state,
+    )
+}
+
+/// [`FootnoteDefinition`][mdast::FootnoteDefinition].
+fn transform_footnote_definition(node: &mdast::Node, mut state: State) -> (Result, State) {
+    if let mdast::Node::FootnoteDefinition(definition) = node {
+        let result = all(node, state);
+        let children = result.0;
+        state = result.1;
+        // Set aside.
+        state
+            .footnote_definitions
+            .push((definition.identifier.clone(), children));
+        (Result::None, state)
+    } else {
+        unreachable!("expected `FootnoteDefinition`")
+    }
+}
+
+/// [`FootnoteReference`][mdast::FootnoteReference].
+fn transform_footnote_reference(node: &mdast::Node, mut state: State) -> (Result, State) {
+    if let mdast::Node::FootnoteReference(reference) = node {
+        let safe_id = sanitize_(&reference.identifier.to_lowercase());
+        let mut call_index = 0;
+
+        // See if this has been called before.
+        while call_index < state.footnote_calls.len() {
+            if state.footnote_calls[call_index].0 == reference.identifier {
+                break;
+            }
+            call_index += 1;
+        }
+
+        // New.
+        if call_index == state.footnote_calls.len() {
+            state.footnote_calls.push((reference.identifier.clone(), 0));
+        }
+
+        // Increment.
+        state.footnote_calls[call_index].1 += 1;
+
+        let reuse_counter = state.footnote_calls[call_index].1;
+
+        (
+            Result::Node(augment_node(
+                node,
+                hast::Node::Element(hast::Element {
+                    tag_name: "sup".into(),
+                    properties: vec![],
+                    children: vec![hast::Node::Element(hast::Element {
+                        tag_name: "a".into(),
+                        // To do: support clobber prefix.
+                        properties: vec![
+                            (
+                                "href".into(),
+                                hast::PropertyValue::String(format!("#fn-{}", safe_id)),
+                            ),
+                            (
+                                "id".into(),
+                                hast::PropertyValue::String(format!(
+                                    "fnref-{}{}",
+                                    safe_id,
+                                    if reuse_counter > 1 {
+                                        format!("-{}", reuse_counter)
+                                    } else {
+                                        "".into()
+                                    }
+                                )),
+                            ),
+                            ("dataFootnoteRef".into(), hast::PropertyValue::Boolean(true)),
+                            (
+                                "ariaDescribedBy".into(),
+                                hast::PropertyValue::String("footnote-label".into()),
+                            ),
+                        ],
+                        children: vec![hast::Node::Text(hast::Text {
+                            value: (call_index + 1).to_string(),
+                            position: None,
+                        })],
+                        position: None,
+                    })],
+                    position: None,
+                }),
+            )),
+            state,
+        )
+    } else {
+        unreachable!("expected `FootnoteReference`")
+    }
+}
+
+/// [`Heading`][mdast::Heading].
+fn transform_heading(node: &mdast::Node, state: State) -> (Result, State) {
+    if let mdast::Node::Heading(heading) = node {
+        let (children, state) = all(node, state);
+        let tag_name = format!("h{}", heading.depth);
+        (
+            Result::Node(augment_node(
+                node,
+                hast::Node::Element(hast::Element {
+                    tag_name,
+                    properties: vec![],
+                    children,
+                    position: None,
+                }),
+            )),
+            state,
+        )
+    } else {
+        unreachable!("expected `Heading`")
+    }
+}
+
+/// [`Image`][mdast::Image].
+fn transform_image(node: &mdast::Node, state: State) -> (Result, State) {
+    if let mdast::Node::Image(image) = node {
+        let mut properties = vec![];
+
+        properties.push((
+            "src".into(),
+            hast::PropertyValue::String(sanitize_(&image.url)),
+        ));
+
+        properties.push(("alt".into(), hast::PropertyValue::String(image.alt.clone())));
+
+        if let Some(value) = image.title.as_ref() {
+            properties.push(("title".into(), hast::PropertyValue::String(value.into())));
+        }
+
+        (
+            Result::Node(augment_node(
+                node,
+                hast::Node::Element(hast::Element {
+                    tag_name: "img".into(),
+                    properties,
+                    children: vec![],
+                    position: None,
+                }),
+            )),
+            state,
+        )
+    } else {
+        unreachable!("expected `Image`")
+    }
+}
+
+/// [`ImageReference`][mdast::ImageReference].
+fn transform_image_reference(node: &mdast::Node, state: State) -> (Result, State) {
+    if let mdast::Node::ImageReference(reference) = node {
+        let mut properties = vec![];
+
+        let definition = state
+            .definitions
+            .iter()
+            .find(|d| d.0 == reference.identifier);
+
+        // To do: revert when undefined? <https://github.com/syntax-tree/mdast-util-to-hast/blob/c393d0a60941d8936135e05a5cc78734d87578ba/lib/revert.js>
+        let (_, url, title) =
+            definition.expect("expected reference to have a corresponding definition");
+
+        properties.push(("src".into(), hast::PropertyValue::String(sanitize_(url))));
+
+        properties.push((
+            "alt".into(),
+            hast::PropertyValue::String(reference.alt.clone()),
+        ));
+
+        if let Some(value) = title {
+            properties.push(("title".into(), hast::PropertyValue::String(value.into())));
+        }
+
+        (
+            Result::Node(augment_node(
+                node,
+                hast::Node::Element(hast::Element {
+                    tag_name: "img".into(),
+                    properties,
+                    children: vec![],
+                    position: None,
+                }),
+            )),
+            state,
+        )
+    } else {
+        unreachable!("expected `ImageReference`")
+    }
+}
+
+/// [`InlineCode`][mdast::InlineCode].
+fn transform_inline_code(node: &mdast::Node, state: State) -> (Result, State) {
+    if let mdast::Node::InlineCode(code) = node {
+        (
+            Result::Node(augment_node(
+                node,
+                hast::Node::Element(hast::Element {
+                    tag_name: "code".into(),
+                    properties: vec![],
+                    children: vec![hast::Node::Text(hast::Text {
+                        value: replace_eols_with_spaces(&code.value),
+                        position: None,
+                    })],
+                    position: None,
+                }),
+            )),
+            state,
+        )
+    } else {
+        unreachable!("expected `InlineCode`")
+    }
+}
+
+/// [`InlineMath`][mdast::InlineMath].
+fn transform_inline_math(node: &mdast::Node, state: State) -> (Result, State) {
+    if let mdast::Node::InlineMath(math) = node {
+        (
+            Result::Node(augment_node(
+                node,
+                hast::Node::Element(hast::Element {
+                    tag_name: "code".into(),
+                    properties: vec![(
+                        "className".into(),
+                        hast::PropertyValue::SpaceSeparated(vec![
+                            hast::PropertyItem::String("language-math".into()),
+                            hast::PropertyItem::String("math-inline".into()),
+                        ]),
+                    )],
+                    children: vec![hast::Node::Text(hast::Text {
+                        value: replace_eols_with_spaces(&math.value),
+                        position: None,
+                    })],
+                    position: None,
+                }),
+            )),
+            state,
+        )
+    } else {
+        unreachable!("expected `InlineMath`")
+    }
+}
+
+/// [`Link`][mdast::Link].
+fn transform_link(node: &mdast::Node, state: State) -> (Result, State) {
+    if let mdast::Node::Link(link) = node {
+        let mut properties = vec![];
+
+        properties.push((
+            "href".into(),
+            hast::PropertyValue::String(sanitize_(&link.url)),
+        ));
+
+        if let Some(value) = link.title.as_ref() {
+            properties.push(("title".into(), hast::PropertyValue::String(value.into())));
+        }
+
+        let (children, state) = all(node, state);
+        (
+            Result::Node(augment_node(
+                node,
+                hast::Node::Element(hast::Element {
+                    tag_name: "a".into(),
+                    properties,
+                    children,
+                    position: None,
+                }),
+            )),
+            state,
+        )
+    } else {
+        unreachable!("expected `Link`")
+    }
+}
+
+/// [`LinkReference`][mdast::LinkReference].
+fn transform_link_reference(node: &mdast::Node, state: State) -> (Result, State) {
+    if let mdast::Node::LinkReference(reference) = node {
+        let mut properties = vec![];
+
+        let definition = state
+            .definitions
+            .iter()
+            .find(|d| d.0 == reference.identifier);
+
+        // To do: revert when undefined? <https://github.com/syntax-tree/mdast-util-to-hast/blob/c393d0a60941d8936135e05a5cc78734d87578ba/lib/revert.js>
+        let (_, url, title) =
+            definition.expect("expected reference to have a corresponding definition");
+
+        properties.push(("href".into(), hast::PropertyValue::String(sanitize_(url))));
+
+        if let Some(value) = title {
+            properties.push(("title".into(), hast::PropertyValue::String(value.into())));
+        }
+
+        let (children, state) = all(node, state);
+        (
+            Result::Node(augment_node(
+                node,
+                hast::Node::Element(hast::Element {
+                    tag_name: "a".into(),
+                    properties,
+                    children,
+                    position: None,
+                }),
+            )),
+            state,
+        )
+    } else {
+        unreachable!("expected `LinkReference`")
+    }
+}
+
+/// [`ListItem`][mdast::ListItem].
+fn transform_list_item(
+    node: &mdast::Node,
+    parent: Option<&mdast::Node>,
+    state: State,
+) -> (Result, State) {
+    if let mdast::Node::ListItem(item) = node {
+        let (mut children, state) = all(node, state);
+        let mut loose = list_item_loose(node);
+
+        if let Some(parent) = parent {
+            if matches!(parent, mdast::Node::List(_)) {
+                loose = list_loose(parent);
+            }
+        };
+
+        let mut properties = vec![];
+
+        // Inject a checkbox.
+        if let Some(checked) = item.checked {
+            // According to github-markdown-css, this class hides bullet.
+            // See: <https://github.com/sindresorhus/github-markdown-css>.
+            properties.push((
+                "className".into(),
+                hast::PropertyValue::SpaceSeparated(vec![hast::PropertyItem::String(
+                    "task-list-item".into(),
+                )]),
+            ));
+
+            let mut input = Some(hast::Node::Element(hast::Element {
+                tag_name: "input".into(),
+                properties: vec![
+                    (
+                        "type".into(),
+                        hast::PropertyValue::String("checkbox".into()),
+                    ),
+                    ("checked".into(), hast::PropertyValue::Boolean(checked)),
+                    ("disabled".into(), hast::PropertyValue::Boolean(true)),
+                ],
+                children: vec![],
+                position: None,
+            }));
+
+            if let Some(hast::Node::Element(x)) = children.first_mut() {
+                if x.tag_name == "p" {
+                    if !x.children.is_empty() {
+                        x.children.insert(
+                            0,
+                            hast::Node::Text(hast::Text {
+                                value: " ".into(),
+                                position: None,
+                            }),
+                        );
+                    }
+
+                    x.children.insert(0, input.take().unwrap());
+                }
+            }
+
+            // If the input wasn‘t injected yet, inject a paragraph.
+            if let Some(input) = input {
+                children.insert(
+                    0,
+                    hast::Node::Element(hast::Element {
+                        tag_name: "p".into(),
+                        properties: vec![],
+                        children: vec![input],
+                        position: None,
+                    }),
+                );
+            }
+        }
+
+        children.reverse();
+        let mut result = vec![];
+        let mut head = true;
+        let empty = children.is_empty();
+        let mut tail_p = false;
+
+        while let Some(child) = children.pop() {
+            let mut is_p = false;
+            if let hast::Node::Element(el) = &child {
+                if el.tag_name == "p" {
+                    is_p = true;
+                }
+            }
+
+            // Add eols before nodes, except if this is a tight, first paragraph.
+            if loose || !head || !is_p {
+                result.push(hast::Node::Text(hast::Text {
+                    value: "\n".into(),
+                    position: None,
+                }));
+            }
+
+            if is_p && !loose {
+                // Unwrap the paragraph.
+                if let hast::Node::Element(mut el) = child {
+                    result.append(&mut el.children);
+                }
+            } else {
+                result.push(child);
+            }
+
+            head = false;
+            tail_p = is_p;
+        }
+
+        // Add eol after last node, except if it is tight or a paragraph.
+        if !empty && (loose || !tail_p) {
+            result.push(hast::Node::Text(hast::Text {
+                value: "\n".into(),
+                position: None,
+            }));
+        }
+
+        (
+            Result::Node(augment_node(
+                node,
+                hast::Node::Element(hast::Element {
+                    tag_name: "li".into(),
+                    properties,
+                    children: result,
+                    position: None,
+                }),
+            )),
+            state,
+        )
+    } else {
+        unreachable!("expected `ListItem`")
+    }
+}
+
+/// [`List`][mdast::List].
+fn transform_list(node: &mdast::Node, state: State) -> (Result, State) {
+    if let mdast::Node::List(list) = node {
+        let mut contains_task_list = false;
+        let mut index = 0;
+
+        while index < list.children.len() {
+            if let mdast::Node::ListItem(item) = &list.children[index] {
+                if item.checked.is_some() {
+                    contains_task_list = true;
+                }
+            }
+
+            index += 1;
+        }
+
+        let (children, state) = all(node, state);
+        let mut properties = vec![];
+        let tag_name = if list.ordered {
+            "ol".into()
+        } else {
+            "ul".into()
+        };
+
+        // Add start.
+        if let Some(start) = list.start {
+            if list.ordered && start != 1 {
+                properties.push(("start".into(), hast::PropertyValue::Number(start.into())));
+            }
+        }
+
+        // Like GitHub, add a class for custom styling.
+        if contains_task_list {
+            properties.push((
+                "className".into(),
+                hast::PropertyValue::SpaceSeparated(vec![hast::PropertyItem::String(
+                    "contains-task-list".into(),
+                )]),
+            ));
+        }
+
+        (
+            Result::Node(augment_node(
+                node,
+                hast::Node::Element(hast::Element {
+                    tag_name,
+                    properties,
+                    children: wrap(children, true),
+                    position: None,
+                }),
+            )),
+            state,
+        )
+    } else {
+        unreachable!("expected `List`")
+    }
+}
+
+/// [`Math`][mdast::Math].
+fn transform_math(node: &mdast::Node, state: State) -> (Result, State) {
+    if let mdast::Node::Math(math) = node {
+        let mut value = math.value.clone();
+        value.push('\n');
+
+        // To do: option to persist `meta`?
+
+        (
+            Result::Node(augment_node(
+                node,
+                hast::Node::Element(hast::Element {
+                    tag_name: "pre".into(),
+                    properties: vec![],
+                    children: vec![augment_node(
+                        node,
+                        hast::Node::Element(hast::Element {
+                            tag_name: "code".into(),
+                            properties: vec![(
+                                "className".into(),
+                                hast::PropertyValue::SpaceSeparated(vec![
+                                    hast::PropertyItem::String("language-math".into()),
+                                    hast::PropertyItem::String("math-display".into()),
+                                ]),
+                            )],
+                            children: vec![hast::Node::Text(hast::Text {
+                                value,
+                                position: None,
+                            })],
+                            position: None,
+                        }),
+                    )],
+                    position: None,
+                }),
+            )),
+            state,
+        )
+    } else {
+        unreachable!("expected `Math`")
+    }
+}
+
+/// [`MdxFlowExpression`][mdast::MdxFlowExpression],[`MdxTextExpression`][mdast::MdxTextExpression].
+fn transform_mdx_expression(node: &mdast::Node, state: State) -> (Result, State) {
+    (
+        Result::Node(augment_node(
+            node,
+            hast::Node::MdxExpression(hast::MdxExpression {
+                value: node.to_string(),
+                position: None,
+            }),
+        )),
+        state,
+    )
+}
+
+/// [`MdxJsxFlowElement`][mdast::MdxJsxFlowElement],[`MdxJsxTextElement`][mdast::MdxJsxTextElement].
+fn transform_mdx_jsx_element(node: &mdast::Node, state: State) -> (Result, State) {
+    let (children, state) = all(node, state);
+
+    let (name, attributes) = match node {
+        mdast::Node::MdxJsxFlowElement(n) => (&n.name, &n.attributes),
+        mdast::Node::MdxJsxTextElement(n) => (&n.name, &n.attributes),
+        _ => unreachable!("expected mdx jsx element"),
+    };
+
+    (
+        Result::Node(augment_node(
+            node,
+            hast::Node::MdxJsxElement(hast::MdxJsxElement {
+                name: name.clone(),
+                attributes: attributes.clone(),
+                children,
+                position: None,
+            }),
+        )),
+        state,
+    )
+}
+
+/// [`MdxjsEsm`][mdast::MdxjsEsm].
+fn transform_mdxjs_esm(node: &mdast::Node, state: State) -> (Result, State) {
+    (
+        Result::Node(augment_node(
+            node,
+            hast::Node::MdxjsEsm(hast::MdxjsEsm {
+                value: node.to_string(),
+                position: None,
+            }),
+        )),
+        state,
+    )
+}
+
+/// [`Paragraph`][mdast::Paragraph].
+fn transform_paragraph(node: &mdast::Node, state: State) -> (Result, State) {
+    let (children, state) = all(node, state);
+    (
+        Result::Node(augment_node(
+            node,
+            hast::Node::Element(hast::Element {
+                tag_name: "p".into(),
+                properties: vec![],
+                children,
+                position: None,
+            }),
+        )),
+        state,
+    )
+}
+
+/// [`Root`][mdast::Root].
+fn transform_root(node: &mdast::Node, state: State) -> (Result, State) {
+    let (children, state) = all(node, state);
+    (
+        Result::Node(augment_node(
+            node,
+            hast::Node::Root(hast::Root {
+                children: wrap(children, false),
+                position: None,
+            }),
+        )),
+        state,
+    )
+}
+
+/// [`Strong`][mdast::Strong].
+fn transform_strong(node: &mdast::Node, state: State) -> (Result, State) {
+    let (children, state) = all(node, state);
+    (
+        Result::Node(augment_node(
+            node,
+            hast::Node::Element(hast::Element {
+                tag_name: "strong".into(),
+                properties: vec![],
+                children,
+                position: None,
+            }),
+        )),
+        state,
+    )
+}
+
+/// [`TableCell`][mdast::TableCell].
+fn transform_table_cell(
+    node: &mdast::Node,
+    head: bool,
+    align: mdast::AlignKind,
+    state: State,
+) -> (Result, State) {
+    let (children, state) = all(node, state);
+    // To do: option to generate a `style` instead?
+    let align_value = match align {
+        mdast::AlignKind::None => None,
+        mdast::AlignKind::Left => Some("left"),
+        mdast::AlignKind::Right => Some("right"),
+        mdast::AlignKind::Center => Some("center"),
+    };
+
+    let mut properties = vec![];
+
+    if let Some(value) = align_value {
+        properties.push(("align".into(), hast::PropertyValue::String(value.into())));
+    }
+
+    (
+        Result::Node(augment_node(
+            node,
+            hast::Node::Element(hast::Element {
+                tag_name: if head { "th".into() } else { "td".into() },
+                properties,
+                children,
+                position: None,
+            }),
+        )),
+        state,
+    )
+}
+
+/// [`TableRow`][mdast::TableRow].
+fn transform_table_row(
+    node: &mdast::Node,
+    head: bool,
+    align: Option<&[mdast::AlignKind]>,
+    mut state: State,
+) -> (Result, State) {
+    if let mdast::Node::TableRow(row) = node {
+        let mut children = vec![];
+        let mut index = 0;
+        #[allow(clippy::redundant_closure_for_method_calls)]
+        let len = align.map_or(row.children.len(), |d| d.len());
+        let empty_cell = mdast::Node::TableCell(mdast::TableCell {
+            children: vec![],
+            position: None,
+        });
+
+        while index < len {
+            let align_value = align
+                .and_then(|d| d.get(index))
+                .unwrap_or(&mdast::AlignKind::None);
+
+            let child = row.children.get(index).unwrap_or(&empty_cell);
+            let tuple = transform_table_cell(child, head, *align_value, state);
+            append_result(&mut children, tuple.0);
+            state = tuple.1;
+            index += 1;
+        }
+
+        (
+            Result::Node(augment_node(
+                node,
+                hast::Node::Element(hast::Element {
+                    tag_name: "tr".into(),
+                    properties: vec![],
+                    children: wrap(children, true),
+                    position: None,
+                }),
+            )),
+            state,
+        )
+    } else {
+        unreachable!("expected `TableRow`")
+    }
+}
+
+/// [`Table`][mdast::Table].
+fn transform_table(node: &mdast::Node, mut state: State) -> (Result, State) {
+    if let mdast::Node::Table(table) = node {
+        let mut rows = vec![];
+        // let body = hast::Element {
+        //     tag_name: "tbody".into(),
+        //     properties: vec![],
+        //     children: vec![],
+        //     position: None,
+        // };
+        let mut index = 0;
+
+        while index < table.children.len() {
+            let tuple = transform_table_row(
+                &table.children[index],
+                index == 0,
+                Some(&table.align),
+                state,
+            );
+            append_result(&mut rows, tuple.0);
+            state = tuple.1;
+            index += 1;
+        }
+
+        let body_rows = rows.split_off(1);
+        let head_row = rows.pop();
+        let mut children = vec![];
+
+        if let Some(row) = head_row {
+            let position = row.position().cloned();
+            children.push(hast::Node::Element(hast::Element {
+                tag_name: "thead".into(),
+                properties: vec![],
+                children: wrap(vec![row], true),
+                position,
+            }));
+        }
+
+        if !body_rows.is_empty() {
+            let mut position = None;
+
+            if let Some(position_start) = body_rows.first().and_then(hast::Node::position) {
+                if let Some(position_end) = body_rows.last().and_then(hast::Node::position) {
+                    position = Some(Position {
+                        start: position_start.start.clone(),
+                        end: position_end.end.clone(),
+                    });
+                }
+            }
+
+            children.push(hast::Node::Element(hast::Element {
+                tag_name: "tbody".into(),
+                properties: vec![],
+                children: wrap(body_rows, true),
+                position,
+            }));
+        }
+
+        (
+            Result::Node(augment_node(
+                node,
+                hast::Node::Element(hast::Element {
+                    tag_name: "table".into(),
+                    properties: vec![],
+                    children: wrap(children, true),
+                    position: None,
+                }),
+            )),
+            state,
+        )
+    } else {
+        unreachable!("expected `Table`")
+    }
+}
+
+/// [`Text`][mdast::Text].
+fn transform_text(node: &mdast::Node, state: State) -> (Result, State) {
+    (
+        Result::Node(augment_node(
+            node,
+            hast::Node::Text(hast::Text {
+                value: node.to_string(),
+                position: None,
+            }),
+        )),
+        state,
+    )
+}
+
+/// [`ThematicBreak`][mdast::ThematicBreak].
+fn transform_thematic_break(node: &mdast::Node, state: State) -> (Result, State) {
+    (
+        Result::Node(augment_node(
+            node,
+            hast::Node::Element(hast::Element {
+                tag_name: "hr".into(),
+                properties: vec![],
+                children: vec![],
+                position: None,
+            }),
+        )),
+        state,
+    )
+}
+
+// Transform children of `parent`.
+fn all(parent: &mdast::Node, mut state: State) -> (Vec<hast::Node>, State) {
+    let mut result = vec![];
+    if let Some(children) = parent.children() {
+        let mut index = 0;
+        while index < children.len() {
+            let child = &children[index];
+            let tuple = one(child, Some(parent), state);
+            append_result(&mut result, tuple.0);
+            state = tuple.1;
+            index += 1;
+        }
+    }
+
+    (result, state)
+}
+
+/// Wrap `nodes` with line feeds between each entry.
+/// Optionally adds line feeds at the start and end.
+fn wrap(mut nodes: Vec<hast::Node>, loose: bool) -> Vec<hast::Node> {
+    let mut result = vec![];
+    let was_empty = nodes.is_empty();
+    let mut head = true;
+
+    nodes.reverse();
+
+    if loose {
+        result.push(hast::Node::Text(hast::Text {
+            value: "\n".into(),
+            position: None,
+        }));
+    }
+
+    while let Some(item) = nodes.pop() {
+        // Inject when there’s more:
+        if !head {
+            result.push(hast::Node::Text(hast::Text {
+                value: "\n".into(),
+                position: None,
+            }));
+        }
+        head = false;
+        result.push(item);
+    }
+
+    if loose && !was_empty {
+        result.push(hast::Node::Text(hast::Text {
+            value: "\n".into(),
+            position: None,
+        }));
+    }
+
+    result
+}
+
+/// Patch a position from the node `left` onto `right`.
+fn augment_node(left: &mdast::Node, right: hast::Node) -> hast::Node {
+    if let Some(position) = left.position() {
+        augment_position(position, right)
+    } else {
+        right
+    }
+}
+
+/// Patch a position from `left` onto `right`.
+fn augment_position(left: &Position, mut right: hast::Node) -> hast::Node {
+    right.position_set(Some(left.clone()));
+    right
+}
+
+/// Visit.
+fn visit<Visitor>(node: &mdast::Node, visitor: Visitor)
+where
+    Visitor: FnMut(&mdast::Node),
+{
+    visit_impl(node, visitor);
+}
+
+/// Visit, mutably.
+// Probably useful later:
+#[allow(dead_code)]
+fn visit_mut<Visitor>(node: &mut mdast::Node, visitor: Visitor)
+where
+    Visitor: FnMut(&mut mdast::Node),
+{
+    visit_mut_impl(node, visitor);
+}
+
+/// Internal implementation to visit.
+fn visit_impl<Visitor>(node: &mdast::Node, mut visitor: Visitor) -> Visitor
+where
+    Visitor: FnMut(&mdast::Node),
+{
+    visitor(node);
+
+    if let Some(children) = node.children() {
+        let mut index = 0;
+        while index < children.len() {
+            let child = &children[index];
+            visitor = visit_impl(child, visitor);
+            index += 1;
+        }
+    }
+
+    visitor
+}
+
+/// Internal implementation to visit, mutably.
+fn visit_mut_impl<Visitor>(node: &mut mdast::Node, mut visitor: Visitor) -> Visitor
+where
+    Visitor: FnMut(&mut mdast::Node),
+{
+    visitor(node);
+
+    if let Some(children) = node.children_mut() {
+        let mut index = 0;
+        while let Some(child) = children.get_mut(index) {
+            visitor = visit_mut_impl(child, visitor);
+            index += 1;
+        }
+    }
+
+    visitor
+}
+
+// To do: trim arounds breaks: <https://github.com/syntax-tree/mdast-util-to-hast/blob/c393d0a/lib/traverse.js>.
+/// Append an (optional, variadic) result.
+fn append_result(list: &mut Vec<hast::Node>, result: Result) {
+    match result {
+        Result::Fragment(mut fragment) => list.append(&mut fragment),
+        Result::Node(node) => list.push(node),
+        Result::None => {}
+    };
+}
+
+/// Replace line endings (CR, LF, CRLF) with spaces.
+///
+/// Used for inline code and inline math.
+fn replace_eols_with_spaces(value: &str) -> String {
+    // It’ll grow a bit small for each CR+LF.
+    let mut result = String::with_capacity(value.len());
+    let bytes = value.as_bytes();
+    let mut index = 0;
+    let mut start = 0;
+
+    while index < bytes.len() {
+        let byte = bytes[index];
+
+        if byte == b'\r' || byte == b'\n' {
+            result.push_str(&value[start..index]);
+            result.push(' ');
+
+            if index + 1 < bytes.len() && byte == b'\r' && bytes[index + 1] == b'\n' {
+                index += 1;
+            }
+
+            start = index + 1;
+        }
+
+        index += 1;
+    }
+
+    result.push_str(&value[start..]);
+
+    result
+}
+
+/// Check if a list is loose.
+fn list_loose(node: &mdast::Node) -> bool {
+    if let mdast::Node::List(list) = node {
+        if list.spread {
+            return true;
+        }
+
+        if let Some(children) = node.children() {
+            let mut index = 0;
+            while index < children.len() {
+                if list_item_loose(&children[index]) {
+                    return true;
+                }
+                index += 1;
+            }
+        }
+    }
+
+    false
+}
+
+/// Check if a list item is loose.
+fn list_item_loose(node: &mdast::Node) -> bool {
+    if let mdast::Node::ListItem(item) = node {
+        item.spread
+    } else {
+        false
+    }
+}