cleanup: Import tree-sitter-highlight so we can cache trees.

2 files changed, 994 insertions, 0 deletions

diff --git a/helix-core/src/language_mode.rs b/helix-core/src/language_mode.rs
new file mode 100644
index 00000000..3f104be4
--- /dev/null
+++ b/helix-core/src/language_mode.rs
@@ -0,0 +1,993 @@
+pub struct LanguageMode {
+    parser: Parser,
+}
+
+impl LanguageMode {
+    // buffer, grammar, config, grammars, sync_timeout?
+    pub fn new() -> Self {
+        unimplemented!()
+        // make a new root layer
+        // track markers of injections
+        //
+        // track scope_descriptor: a Vec of scopes for item in tree
+        //
+        // fetch grammar for parser based on language string
+        // update root layer
+    }
+
+    // fn buffer_changed -> call layer.update(range, new_text) on root layer and then all marker layers
+
+    // call this on transaction.apply() -> buffer_changed(changes)
+    //
+    // fn parse(language, old_tree, ranges)
+    //
+    // fn tree() -> Tree
+    //
+    // <!--update_for_injection(grammar)-->
+
+    // Highlighting
+    // fn highlight_iter() -> iterates over all the scopes
+    // on_tokenize
+    // on_change_highlighting
+
+    // Commenting
+    // comment_strings_for_pos
+    // is_commented
+
+    // Indentation
+    // suggested_indent_for_line_at_buffer_row
+    // suggested_indent_for_buffer_row
+    // indent_level_for_line
+
+    // TODO: Folding
+
+    // Syntax APIs
+    // get_syntax_node_containing_range ->
+    // ...
+    // get_syntax_node_at_pos
+    // buffer_range_for_scope_at_pos
+}
+
+pub struct LanguageLayer {
+    // mode
+// grammar
+// depth
+// tree: Tree,
+}
+
+impl LanguageLayer {
+    // fn highlight_iter() -> same as Mode but for this layer. Mode composits these
+    // fn buffer_changed
+    // fn update(range)
+    // fn update_injections()
+}
+
+// -- refactored from tree-sitter-highlight to be able to retain state
+// TODO: add seek() to iter
+
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::{iter, mem, ops, str, usize};
+use tree_sitter::{
+    Language, Node, Parser, Point, Query, QueryCaptures, QueryCursor, QueryError, QueryMatch,
+    Range, Tree,
+};
+
+const CANCELLATION_CHECK_INTERVAL: usize = 100;
+const BUFFER_HTML_RESERVE_CAPACITY: usize = 10 * 1024;
+const BUFFER_LINES_RESERVE_CAPACITY: usize = 1000;
+
+/// Indicates which highlight should be applied to a region of source code.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub struct Highlight(pub usize);
+
+/// Represents the reason why syntax highlighting failed.
+#[derive(Debug, PartialEq, Eq)]
+pub enum Error {
+    Cancelled,
+    InvalidLanguage,
+    Unknown,
+}
+
+/// Represents a single step in rendering a syntax-highlighted document.
+#[derive(Copy, Clone, Debug)]
+pub enum HighlightEvent {
+    Source { start: usize, end: usize },
+    HighlightStart(Highlight),
+    HighlightEnd,
+}
+
+/// Contains the data neeeded to higlight code written in a particular language.
+///
+/// This struct is immutable and can be shared between threads.
+pub struct HighlightConfiguration {
+    pub language: Language,
+    pub query: Query,
+    combined_injections_query: Option<Query>,
+    locals_pattern_index: usize,
+    highlights_pattern_index: usize,
+    highlight_indices: Vec<Option<Highlight>>,
+    non_local_variable_patterns: Vec<bool>,
+    injection_content_capture_index: Option<u32>,
+    injection_language_capture_index: Option<u32>,
+    local_scope_capture_index: Option<u32>,
+    local_def_capture_index: Option<u32>,
+    local_def_value_capture_index: Option<u32>,
+    local_ref_capture_index: Option<u32>,
+}
+
+/// Performs syntax highlighting, recognizing a given list of highlight names.
+///
+/// For the best performance `Highlighter` values should be reused between
+/// syntax highlighting calls. A separate highlighter is needed for each thread that
+/// is performing highlighting.
+pub struct Highlighter {
+    parser: Parser,
+    cursors: Vec<QueryCursor>,
+}
+
+#[derive(Debug)]
+struct LocalDef<'a> {
+    name: &'a str,
+    value_range: ops::Range<usize>,
+    highlight: Option<Highlight>,
+}
+
+#[derive(Debug)]
+struct LocalScope<'a> {
+    inherits: bool,
+    range: ops::Range<usize>,
+    local_defs: Vec<LocalDef<'a>>,
+}
+
+struct HighlightIter<'a, F>
+where
+    F: FnMut(&str) -> Option<&'a HighlightConfiguration> + 'a,
+{
+    source: &'a [u8],
+    byte_offset: usize,
+    highlighter: &'a mut Highlighter,
+    injection_callback: F,
+    cancellation_flag: Option<&'a AtomicUsize>,
+    layers: Vec<HighlightIterLayer<'a>>,
+    iter_count: usize,
+    next_event: Option<HighlightEvent>,
+    last_highlight_range: Option<(usize, usize, usize)>,
+}
+
+struct HighlightIterLayer<'a> {
+    _tree: Tree,
+    cursor: QueryCursor,
+    captures: iter::Peekable<QueryCaptures<'a, &'a [u8]>>,
+    config: &'a HighlightConfiguration,
+    highlight_end_stack: Vec<usize>,
+    scope_stack: Vec<LocalScope<'a>>,
+    ranges: Vec<Range>,
+    depth: usize,
+}
+
+impl Highlighter {
+    pub fn new() -> Self {
+        Highlighter {
+            parser: Parser::new(),
+            cursors: Vec::new(),
+        }
+    }
+
+    pub fn parser(&mut self) -> &mut Parser {
+        &mut self.parser
+    }
+
+    /// Iterate over the highlighted regions for a given slice of source code.
+    pub fn highlight<'a>(
+        &'a mut self,
+        config: &'a HighlightConfiguration,
+        source: &'a [u8],
+        cancellation_flag: Option<&'a AtomicUsize>,
+        mut injection_callback: impl FnMut(&str) -> Option<&'a HighlightConfiguration> + 'a,
+    ) -> Result<impl Iterator<Item = Result<HighlightEvent, Error>> + 'a, Error> {
+        let layers = HighlightIterLayer::new(
+            source,
+            self,
+            cancellation_flag,
+            &mut injection_callback,
+            config,
+            0,
+            vec![Range {
+                start_byte: 0,
+                end_byte: usize::MAX,
+                start_point: Point::new(0, 0),
+                end_point: Point::new(usize::MAX, usize::MAX),
+            }],
+        )?;
+        assert_ne!(layers.len(), 0);
+        let mut result = HighlightIter {
+            source,
+            byte_offset: 0,
+            injection_callback,
+            cancellation_flag,
+            highlighter: self,
+            iter_count: 0,
+            layers: layers,
+            next_event: None,
+            last_highlight_range: None,
+        };
+        result.sort_layers();
+        Ok(result)
+    }
+}
+
+impl HighlightConfiguration {
+    /// Creates a `HighlightConfiguration` for a given `Language` and set of highlighting
+    /// queries.
+    ///
+    /// # Parameters
+    ///
+    /// * `language`  - The Tree-sitter `Language` that should be used for parsing.
+    /// * `highlights_query` - A string containing tree patterns for syntax highlighting. This
+    ///   should be non-empty, otherwise no syntax highlights will be added.
+    /// * `injections_query` -  A string containing tree patterns for injecting other languages
+    ///   into the document. This can be empty if no injections are desired.
+    /// * `locals_query` - A string containing tree patterns for tracking local variable
+    ///   definitions and references. This can be empty if local variable tracking is not needed.
+    ///
+    /// Returns a `HighlightConfiguration` that can then be used with the `highlight` method.
+    pub fn new(
+        language: Language,
+        highlights_query: &str,
+        injection_query: &str,
+        locals_query: &str,
+    ) -> Result<Self, QueryError> {
+        // Concatenate the query strings, keeping track of the start offset of each section.
+        let mut query_source = String::new();
+        query_source.push_str(injection_query);
+        let locals_query_offset = query_source.len();
+        query_source.push_str(locals_query);
+        let highlights_query_offset = query_source.len();
+        query_source.push_str(highlights_query);
+
+        // Construct a single query by concatenating the three query strings, but record the
+        // range of pattern indices that belong to each individual string.
+        let mut query = Query::new(language, &query_source)?;
+        let mut locals_pattern_index = 0;
+        let mut highlights_pattern_index = 0;
+        for i in 0..(query.pattern_count()) {
+            let pattern_offset = query.start_byte_for_pattern(i);
+            if pattern_offset < highlights_query_offset {
+                if pattern_offset < highlights_query_offset {
+                    highlights_pattern_index += 1;
+                }
+                if pattern_offset < locals_query_offset {
+                    locals_pattern_index += 1;
+                }
+            }
+        }
+
+        // Construct a separate query just for dealing with the 'combined injections'.
+        // Disable the combined injection patterns in the main query.
+        let mut combined_injections_query = Query::new(language, injection_query)?;
+        let mut has_combined_queries = false;
+        for pattern_index in 0..locals_pattern_index {
+            let settings = query.property_settings(pattern_index);
+            if settings.iter().any(|s| &*s.key == "injection.combined") {
+                has_combined_queries = true;
+                query.disable_pattern(pattern_index);
+            } else {
+                combined_injections_query.disable_pattern(pattern_index);
+            }
+        }
+        let combined_injections_query = if has_combined_queries {
+            Some(combined_injections_query)
+        } else {
+            None
+        };
+
+        // Find all of the highlighting patterns that are disabled for nodes that
+        // have been identified as local variables.
+        let non_local_variable_patterns = (0..query.pattern_count())
+            .map(|i| {
+                query
+                    .property_predicates(i)
+                    .iter()
+                    .any(|(prop, positive)| !*positive && prop.key.as_ref() == "local")
+            })
+            .collect();
+
+        // Store the numeric ids for all of the special captures.
+        let mut injection_content_capture_index = None;
+        let mut injection_language_capture_index = None;
+        let mut local_def_capture_index = None;
+        let mut local_def_value_capture_index = None;
+        let mut local_ref_capture_index = None;
+        let mut local_scope_capture_index = None;
+        for (i, name) in query.capture_names().iter().enumerate() {
+            let i = Some(i as u32);
+            match name.as_str() {
+                "injection.content" => injection_content_capture_index = i,
+                "injection.language" => injection_language_capture_index = i,
+                "local.definition" => local_def_capture_index = i,
+                "local.definition-value" => local_def_value_capture_index = i,
+                "local.reference" => local_ref_capture_index = i,
+                "local.scope" => local_scope_capture_index = i,
+                _ => {}
+            }
+        }
+
+        let highlight_indices = vec![None; query.capture_names().len()];
+        Ok(HighlightConfiguration {
+            language,
+            query,
+            combined_injections_query,
+            locals_pattern_index,
+            highlights_pattern_index,
+            highlight_indices,
+            non_local_variable_patterns,
+            injection_content_capture_index,
+            injection_language_capture_index,
+            local_def_capture_index,
+            local_def_value_capture_index,
+            local_ref_capture_index,
+            local_scope_capture_index,
+        })
+    }
+
+    /// Get a slice containing all of the highlight names used in the configuration.
+    pub fn names(&self) -> &[String] {
+        self.query.capture_names()
+    }
+
+    /// Set the list of recognized highlight names.
+    ///
+    /// Tree-sitter syntax-highlighting queries specify highlights in the form of dot-separated
+    /// highlight names like `punctuation.bracket` and `function.method.builtin`. Consumers of
+    /// these queries can choose to recognize highlights with different levels of specificity.
+    /// For example, the string `function.builtin` will match against `function.method.builtin`
+    /// and `function.builtin.constructor`, but will not match `function.method`.
+    ///
+    /// When highlighting, results are returned as `Highlight` values, which contain the index
+    /// of the matched highlight this list of highlight names.
+    pub fn configure(&mut self, recognized_names: &[String]) {
+        let mut capture_parts = Vec::new();
+        self.highlight_indices.clear();
+        self.highlight_indices
+            .extend(self.query.capture_names().iter().map(move |capture_name| {
+                capture_parts.clear();
+                capture_parts.extend(capture_name.split('.'));
+
+                let mut best_index = None;
+                let mut best_match_len = 0;
+                for (i, recognized_name) in recognized_names.iter().enumerate() {
+                    let mut len = 0;
+                    let mut matches = true;
+                    for part in recognized_name.split('.') {
+                        len += 1;
+                        if !capture_parts.contains(&part) {
+                            matches = false;
+                            break;
+                        }
+                    }
+                    if matches && len > best_match_len {
+                        best_index = Some(i);
+                        best_match_len = len;
+                    }
+                }
+                best_index.map(Highlight)
+            }));
+    }
+}
+
+impl<'a> HighlightIterLayer<'a> {
+    /// Create a new 'layer' of highlighting for this document.
+    ///
+    /// In the even that the new layer contains "combined injections" (injections where multiple
+    /// disjoint ranges are parsed as one syntax tree), these will be eagerly processed and
+    /// added to the returned vector.
+    fn new<F: FnMut(&str) -> Option<&'a HighlightConfiguration> + 'a>(
+        source: &'a [u8],
+        highlighter: &mut Highlighter,
+        cancellation_flag: Option<&'a AtomicUsize>,
+        injection_callback: &mut F,
+        mut config: &'a HighlightConfiguration,
+        mut depth: usize,
+        mut ranges: Vec<Range>,
+    ) -> Result<Vec<Self>, Error> {
+        let mut result = Vec::with_capacity(1);
+        let mut queue = Vec::new();
+        loop {
+            if highlighter.parser.set_included_ranges(&ranges).is_ok() {
+                highlighter
+                    .parser
+                    .set_language(config.language)
+                    .map_err(|_| Error::InvalidLanguage)?;
+
+                unsafe { highlighter.parser.set_cancellation_flag(cancellation_flag) };
+                let tree = highlighter
+                    .parser
+                    .parse(source, None)
+                    .ok_or(Error::Cancelled)?;
+                unsafe { highlighter.parser.set_cancellation_flag(None) };
+                let mut cursor = highlighter.cursors.pop().unwrap_or(QueryCursor::new());
+
+                // Process combined injections.
+                if let Some(combined_injections_query) = &config.combined_injections_query {
+                    let mut injections_by_pattern_index =
+                        vec![(None, Vec::new(), false); combined_injections_query.pattern_count()];
+                    let matches =
+                        cursor.matches(combined_injections_query, tree.root_node(), |n: Node| {
+                            &source[n.byte_range()]
+                        });
+                    for mat in matches {
+                        let entry = &mut injections_by_pattern_index[mat.pattern_index];
+                        let (language_name, content_node, include_children) =
+                            injection_for_match(config, combined_injections_query, &mat, source);
+                        if language_name.is_some() {
+                            entry.0 = language_name;
+                        }
+                        if let Some(content_node) = content_node {
+                            entry.1.push(content_node);
+                        }
+                        entry.2 = include_children;
+                    }
+                    for (lang_name, content_nodes, includes_children) in injections_by_pattern_index
+                    {
+                        if let (Some(lang_name), false) = (lang_name, content_nodes.is_empty()) {
+                            if let Some(next_config) = (injection_callback)(lang_name) {
+                                let ranges = Self::intersect_ranges(
+                                    &ranges,
+                                    &content_nodes,
+                                    includes_children,
+                                );
+                                if !ranges.is_empty() {
+                                    queue.push((next_config, depth + 1, ranges));
+                                }
+                            }
+                        }
+                    }
+                }
+
+                // The `captures` iterator borrows the `Tree` and the `QueryCursor`, which
+                // prevents them from being moved. But both of these values are really just
+                // pointers, so it's actually ok to move them.
+                let tree_ref = unsafe { mem::transmute::<_, &'static Tree>(&tree) };
+                let cursor_ref =
+                    unsafe { mem::transmute::<_, &'static mut QueryCursor>(&mut cursor) };
+                let captures = cursor_ref
+                    .captures(&config.query, tree_ref.root_node(), move |n: Node| {
+                        &source[n.byte_range()]
+                    })
+                    .peekable();
+
+                result.push(HighlightIterLayer {
+                    highlight_end_stack: Vec::new(),
+                    scope_stack: vec![LocalScope {
+                        inherits: false,
+                        range: 0..usize::MAX,
+                        local_defs: Vec::new(),
+                    }],
+                    cursor,
+                    depth,
+                    _tree: tree,
+                    captures,
+                    config,
+                    ranges,
+                });
+            }
+
+            if queue.is_empty() {
+                break;
+            } else {
+                let (next_config, next_depth, next_ranges) = queue.remove(0);
+                config = next_config;
+                depth = next_depth;
+                ranges = next_ranges;
+            }
+        }
+
+        Ok(result)
+    }
+
+    // Compute the ranges that should be included when parsing an injection.
+    // This takes into account three things:
+    // * `parent_ranges` - The ranges must all fall within the *current* layer's ranges.
+    // * `nodes` - Every injection takes place within a set of nodes. The injection ranges
+    //   are the ranges of those nodes.
+    // * `includes_children` - For some injections, the content nodes' children should be
+    //   excluded from the nested document, so that only the content nodes' *own* content
+    //   is reparsed. For other injections, the content nodes' entire ranges should be
+    //   reparsed, including the ranges of their children.
+    fn intersect_ranges(
+        parent_ranges: &[Range],
+        nodes: &[Node],
+        includes_children: bool,
+    ) -> Vec<Range> {
+        let mut cursor = nodes[0].walk();
+        let mut result = Vec::new();
+        let mut parent_range_iter = parent_ranges.iter();
+        let mut parent_range = parent_range_iter
+            .next()
+            .expect("Layers should only be constructed with non-empty ranges vectors");
+        for node in nodes.iter() {
+            let mut preceding_range = Range {
+                start_byte: 0,
+                start_point: Point::new(0, 0),
+                end_byte: node.start_byte(),
+                end_point: node.start_position(),
+            };
+            let following_range = Range {
+                start_byte: node.end_byte(),
+                start_point: node.end_position(),
+                end_byte: usize::MAX,
+                end_point: Point::new(usize::MAX, usize::MAX),
+            };
+
+            for excluded_range in node
+                .children(&mut cursor)
+                .filter_map(|child| {
+                    if includes_children {
+                        None
+                    } else {
+                        Some(child.range())
+                    }
+                })
+                .chain([following_range].iter().cloned())
+            {
+                let mut range = Range {
+                    start_byte: preceding_range.end_byte,
+                    start_point: preceding_range.end_point,
+                    end_byte: excluded_range.start_byte,
+                    end_point: excluded_range.start_point,
+                };
+                preceding_range = excluded_range;
+
+                if range.end_byte < parent_range.start_byte {
+                    continue;
+                }
+
+                while parent_range.start_byte <= range.end_byte {
+                    if parent_range.end_byte > range.start_byte {
+                        if range.start_byte < parent_range.start_byte {
+                            range.start_byte = parent_range.start_byte;
+                            range.start_point = parent_range.start_point;
+                        }
+
+                        if parent_range.end_byte < range.end_byte {
+                            if range.start_byte < parent_range.end_byte {
+                                result.push(Range {
+                                    start_byte: range.start_byte,
+                                    start_point: range.start_point,
+                                    end_byte: parent_range.end_byte,
+                                    end_point: parent_range.end_point,
+                                });
+                            }
+                            range.start_byte = parent_range.end_byte;
+                            range.start_point = parent_range.end_point;
+                        } else {
+                            if range.start_byte < range.end_byte {
+                                result.push(range);
+                            }
+                            break;
+                        }
+                    }
+
+                    if let Some(next_range) = parent_range_iter.next() {
+                        parent_range = next_range;
+                    } else {
+                        return result;
+                    }
+                }
+            }
+        }
+        result
+    }
+
+    // First, sort scope boundaries by their byte offset in the document. At a
+    // given position, emit scope endings before scope beginnings. Finally, emit
+    // scope boundaries from deeper layers first.
+    fn sort_key(&mut self) -> Option<(usize, bool, isize)> {
+        let depth = -(self.depth as isize);
+        let next_start = self
+            .captures
+            .peek()
+            .map(|(m, i)| m.captures[*i].node.start_byte());
+        let next_end = self.highlight_end_stack.last().cloned();
+        match (next_start, next_end) {
+            (Some(start), Some(end)) => {
+                if start < end {
+                    Some((start, true, depth))
+                } else {
+                    Some((end, false, depth))
+                }
+            }
+            (Some(i), None) => Some((i, true, depth)),
+            (None, Some(j)) => Some((j, false, depth)),
+            _ => None,
+        }
+    }
+}
+
+impl<'a, F> HighlightIter<'a, F>
+where
+    F: FnMut(&str) -> Option<&'a HighlightConfiguration> + 'a,
+{
+    fn emit_event(
+        &mut self,
+        offset: usize,
+        event: Option<HighlightEvent>,
+    ) -> Option<Result<HighlightEvent, Error>> {
+        let result;
+        if self.byte_offset < offset {
+            result = Some(Ok(HighlightEvent::Source {
+                start: self.byte_offset,
+                end: offset,
+            }));
+            self.byte_offset = offset;
+            self.next_event = event;
+        } else {
+            result = event.map(Ok);
+        }
+        self.sort_layers();
+        result
+    }
+
+    fn sort_layers(&mut self) {
+        while !self.layers.is_empty() {
+            if let Some(sort_key) = self.layers[0].sort_key() {
+                let mut i = 0;
+                while i + 1 < self.layers.len() {
+                    if let Some(next_offset) = self.layers[i + 1].sort_key() {
+                        if next_offset < sort_key {
+                            i += 1;
+                            continue;
+                        }
+                    }
+                    break;
+                }
+                if i > 0 {
+                    &self.layers[0..(i + 1)].rotate_left(1);
+                }
+                break;
+            } else {
+                let layer = self.layers.remove(0);
+                self.highlighter.cursors.push(layer.cursor);
+            }
+        }
+    }
+
+    fn insert_layer(&mut self, mut layer: HighlightIterLayer<'a>) {
+        if let Some(sort_key) = layer.sort_key() {
+            let mut i = 1;
+            while i < self.layers.len() {
+                if let Some(sort_key_i) = self.layers[i].sort_key() {
+                    if sort_key_i > sort_key {
+                        self.layers.insert(i, layer);
+                        return;
+                    }
+                    i += 1;
+                } else {
+                    self.layers.remove(i);
+                }
+            }
+            self.layers.push(layer);
+        }
+    }
+}
+
+impl<'a, F> Iterator for HighlightIter<'a, F>
+where
+    F: FnMut(&str) -> Option<&'a HighlightConfiguration> + 'a,
+{
+    type Item = Result<HighlightEvent, Error>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        'main: loop {
+            // If we've already determined the next highlight boundary, just return it.
+            if let Some(e) = self.next_event.take() {
+                return Some(Ok(e));
+            }
+
+            // Periodically check for cancellation, returning `Cancelled` error if the
+            // cancellation flag was flipped.
+            if let Some(cancellation_flag) = self.cancellation_flag {
+                self.iter_count += 1;
+                if self.iter_count >= CANCELLATION_CHECK_INTERVAL {
+                    self.iter_count = 0;
+                    if cancellation_flag.load(Ordering::Relaxed) != 0 {
+                        return Some(Err(Error::Cancelled));
+                    }
+                }
+            }
+
+            // If none of the layers have any more highlight boundaries, terminate.
+            if self.layers.is_empty() {
+                return if self.byte_offset < self.source.len() {
+                    let result = Some(Ok(HighlightEvent::Source {
+                        start: self.byte_offset,
+                        end: self.source.len(),
+                    }));
+                    self.byte_offset = self.source.len();
+                    result
+                } else {
+                    None
+                };
+            }
+
+            // Get the next capture from whichever layer has the earliest highlight boundary.
+            let range;
+            let layer = &mut self.layers[0];
+            if let Some((next_match, capture_index)) = layer.captures.peek() {
+                let next_capture = next_match.captures[*capture_index];
+                range = next_capture.node.byte_range();
+
+                // If any previous highlight ends before this node starts, then before
+                // processing this capture, emit the source code up until the end of the
+                // previous highlight, and an end event for that highlight.
+                if let Some(end_byte) = layer.highlight_end_stack.last().cloned() {
+                    if end_byte <= range.start {
+                        layer.highlight_end_stack.pop();
+                        return self.emit_event(end_byte, Some(HighlightEvent::HighlightEnd));
+                    }
+                }
+            }
+            // If there are no more captures, then emit any remaining highlight end events.
+            // And if there are none of those, then just advance to the end of the document.
+            else if let Some(end_byte) = layer.highlight_end_stack.last().cloned() {
+                layer.highlight_end_stack.pop();
+                return self.emit_event(end_byte, Some(HighlightEvent::HighlightEnd));
+            } else {
+                return self.emit_event(self.source.len(), None);
+            };
+
+            let (mut match_, capture_index) = layer.captures.next().unwrap();
+            let mut capture = match_.captures[capture_index];
+
+            // If this capture represents an injection, then process the injection.
+            if match_.pattern_index < layer.config.locals_pattern_index {
+                let (language_name, content_node, include_children) =
+                    injection_for_match(&layer.config, &layer.config.query, &match_, &self.source);
+
+                // Explicitly remove this match so that none of its other captures will remain
+                // in the stream of captures.
+                match_.remove();
+
+                // If a language is found with the given name, then add a new language layer
+                // to the highlighted document.
+                if let (Some(language_name), Some(content_node)) = (language_name, content_node) {
+                    if let Some(config) = (self.injection_callback)(language_name) {
+                        let ranges = HighlightIterLayer::intersect_ranges(
+                            &self.layers[0].ranges,
+                            &[content_node],
+                            include_children,
+                        );
+                        if !ranges.is_empty() {
+                            match HighlightIterLayer::new(
+                                self.source,
+                                self.highlighter,
+                                self.cancellation_flag,
+                                &mut self.injection_callback,
+                                config,
+                                self.layers[0].depth + 1,
+                                ranges,
+                            ) {
+                                Ok(layers) => {
+                                    for layer in layers {
+                                        self.insert_layer(layer);
+                                    }
+                                }
+                                Err(e) => return Some(Err(e)),
+                            }
+                        }
+                    }
+                }
+
+                self.sort_layers();
+                continue 'main;
+            }
+
+            // Remove from the local scope stack any local scopes that have already ended.
+            while range.start > layer.scope_stack.last().unwrap().range.end {
+                layer.scope_stack.pop();
+            }
+
+            // If this capture is for tracking local variables, then process the
+            // local variable info.
+            let mut reference_highlight = None;
+            let mut definition_highlight = None;
+            while match_.pattern_index < layer.config.highlights_pattern_index {
+                // If the node represents a local scope, push a new local scope onto
+                // the scope stack.
+                if Some(capture.index) == layer.config.local_scope_capture_index {
+                    definition_highlight = None;
+                    let mut scope = LocalScope {
+                        inherits: true,
+                        range: range.clone(),
+                        local_defs: Vec::new(),
+                    };
+                    for prop in layer.config.query.property_settings(match_.pattern_index) {
+                        match prop.key.as_ref() {
+                            "local.scope-inherits" => {
+                                scope.inherits =
+                                    prop.value.as_ref().map_or(true, |r| r.as_ref() == "true");
+                            }
+                            _ => {}
+                        }
+                    }
+                    layer.scope_stack.push(scope);
+                }
+                // If the node represents a definition, add a new definition to the
+                // local scope at the top of the scope stack.
+                else if Some(capture.index) == layer.config.local_def_capture_index {
+                    reference_highlight = None;
+                    definition_highlight = None;
+                    let scope = layer.scope_stack.last_mut().unwrap();
+
+                    let mut value_range = 0..0;
+                    for capture in match_.captures {
+                        if Some(capture.index) == layer.config.local_def_value_capture_index {
+                            value_range = capture.node.byte_range();
+                        }
+                    }
+
+                    if let Ok(name) = str::from_utf8(&self.source[range.clone()]) {
+                        scope.local_defs.push(LocalDef {
+                            name,
+                            value_range,
+                            highlight: None,
+                        });
+                        definition_highlight =
+                            scope.local_defs.last_mut().map(|s| &mut s.highlight);
+                    }
+                }
+                // If the node represents a reference, then try to find the corresponding
+                // definition in the scope stack.
+                else if Some(capture.index) == layer.config.local_ref_capture_index {
+                    if definition_highlight.is_none() {
+                        definition_highlight = None;
+                        if let Ok(name) = str::from_utf8(&self.source[range.clone()]) {
+                            for scope in layer.scope_stack.iter().rev() {
+                                if let Some(highlight) =
+                                    scope.local_defs.iter().rev().find_map(|def| {
+                                        if def.name == name && range.start >= def.value_range.end {
+                                            Some(def.highlight)
+                                        } else {
+                                            None
+                                        }
+                                    })
+                                {
+                                    reference_highlight = highlight;
+                                    break;
+                                }
+                                if !scope.inherits {
+                                    break;
+                                }
+                            }
+                        }
+                    }
+                }
+
+                // Continue processing any additional matches for the same node.
+                if let Some((next_match, next_capture_index)) = layer.captures.peek() {
+                    let next_capture = next_match.captures[*next_capture_index];
+                    if next_capture.node == capture.node {
+                        capture = next_capture;
+                        match_ = layer.captures.next().unwrap().0;
+                        continue;
+                    }
+                }
+
+                self.sort_layers();
+                continue 'main;
+            }
+
+            // Otherwise, this capture must represent a highlight.
+            // If this exact range has already been highlighted by an earlier pattern, or by
+            // a different layer, then skip over this one.
+            if let Some((last_start, last_end, last_depth)) = self.last_highlight_range {
+                if range.start == last_start && range.end == last_end && layer.depth < last_depth {
+                    self.sort_layers();
+                    continue 'main;
+                }
+            }
+
+            // If the current node was found to be a local variable, then skip over any
+            // highlighting patterns that are disabled for local variables.
+            if definition_highlight.is_some() || reference_highlight.is_some() {
+                while layer.config.non_local_variable_patterns[match_.pattern_index] {
+                    if let Some((next_match, next_capture_index)) = layer.captures.peek() {
+                        let next_capture = next_match.captures[*next_capture_index];
+                        if next_capture.node == capture.node {
+                            capture = next_capture;
+                            match_ = layer.captures.next().unwrap().0;
+                            continue;
+                        }
+                    }
+
+                    self.sort_layers();
+                    continue 'main;
+                }
+            }
+
+            // Once a highlighting pattern is found for the current node, skip over
+            // any later highlighting patterns that also match this node. Captures
+            // for a given node are ordered by pattern index, so these subsequent
+            // captures are guaranteed to be for highlighting, not injections or
+            // local variables.
+            while let Some((next_match, next_capture_index)) = layer.captures.peek() {
+                let next_capture = next_match.captures[*next_capture_index];
+                if next_capture.node == capture.node {
+                    layer.captures.next();
+                } else {
+                    break;
+                }
+            }
+
+            let current_highlight = layer.config.highlight_indices[capture.index as usize];
+
+            // If this node represents a local definition, then store the current
+            // highlight value on the local scope entry representing this node.
+            if let Some(definition_highlight) = definition_highlight {
+                *definition_highlight = current_highlight;
+            }
+
+            // Emit a scope start event and push the node's end position to the stack.
+            if let Some(highlight) = reference_highlight.or(current_highlight) {
+                self.last_highlight_range = Some((range.start, range.end, layer.depth));
+                layer.highlight_end_stack.push(range.end);
+                return self
+                    .emit_event(range.start, Some(HighlightEvent::HighlightStart(highlight)));
+            }
+
+            self.sort_layers();
+        }
+    }
+}
+
+fn injection_for_match<'a>(
+    config: &HighlightConfiguration,
+    query: &'a Query,
+    query_match: &QueryMatch<'a>,
+    source: &'a [u8],
+) -> (Option<&'a str>, Option<Node<'a>>, bool) {
+    let content_capture_index = config.injection_content_capture_index;
+    let language_capture_index = config.injection_language_capture_index;
+
+    let mut language_name = None;
+    let mut content_node = None;
+    for capture in query_match.captures {
+        let index = Some(capture.index);
+        if index == language_capture_index {
+            language_name = capture.node.utf8_text(source).ok();
+        } else if index == content_capture_index {
+            content_node = Some(capture.node);
+        }
+    }
+
+    let mut include_children = false;
+    for prop in query.property_settings(query_match.pattern_index) {
+        match prop.key.as_ref() {
+            // In addition to specifying the language name via the text of a
+            // captured node, it can also be hard-coded via a `#set!` predicate
+            // that sets the injection.language key.
+            "injection.language" => {
+                if language_name.is_none() {
+                    language_name = prop.value.as_ref().map(|s| s.as_ref())
+                }
+            }
+
+            // By default, injections do not include the *children* of an
+            // `injection.content` node - only the ranges that belong to the
+            // node itself. This can be changed using a `#set!` predicate that
+            // sets the `injection.include-children` key.
+            "injection.include-children" => include_children = true,
+            _ => {}
+        }
+    }
+
+    (language_name, content_node, include_children)
+}
+
+fn shrink_and_clear<T>(vec: &mut Vec<T>, capacity: usize) {
+    if vec.len() > capacity {
+        vec.truncate(capacity);
+        vec.shrink_to_fit();
+    }
+    vec.clear();
+}
diff --git a/helix-core/src/lib.rs b/helix-core/src/lib.rs
index da00b9ae..6ab40694 100644
--- a/helix-core/src/lib.rs
+++ b/helix-core/src/lib.rs
@@ -1,6 +1,7 @@
 #![allow(unused)]
 pub mod commands;
 pub mod graphemes;
+pub mod language_mode;
 mod selection;
 pub mod state;
 mod transaction;