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improve performance of tree sitter query captures (for text object motions in particular) #4707

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Nov 11, 2022
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improve performance of tree sitter query captures (for text object motions in particular) #4707

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3c6877b
add tree sitter match limit to avoid slowdowns for larger files
pascalkuthe Nov 10, 2022
500e9e2
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pascalkuthe Nov 11, 2022
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24 changes: 24 additions & 0 deletions helix-core/src/syntax.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -354,6 +354,26 @@ impl<'a> CapturedNode<'a> {
}
}

/// The number of matches a TS cursor can at once to avoid performance problems for medium to large files.
/// Set with `set_match_limit`.
/// Using such a limit means that we loose valid captures in, so there is fundamentally a tradeoff here.
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///
///
/// Old tree sitter versions used a limit of 32 by default until this limit was removed in version `0.19.5` (must now best set manually).
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/// However, this causes performance issues for medium to large files.
/// In helix, this problem caused treesitter motions to take multiple seconds to complete in medium-sized rust files (3k loc).
/// Neovim also encountered this problem and reintroduced this limit after it was removed upstream
/// (see <https://github.com/neovim/neovim/issues/14897> and <https://github.com/neovim/neovim/pull/14915>).
/// The number used here is fundamentally a tradeoff between breaking some obscure edge cases and performance.
///
///
/// A value of 64 was chosen because neovim uses that value.
/// Neovim chose this value somewhat arbitrarily (<https://github.com/neovim/neovim/pull/18397>) adjusting it whenever issues occur in practice.
/// However this value has been in use for a long time and due to the large userbase of neovim it is probably a good choice.
/// If this limit causes problems for a grammar in the future, it could be increased.

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const TREE_SITTER_MATCH_LIMIT: u32 = 64;

impl TextObjectQuery {
/// Run the query on the given node and return sub nodes which match given
/// capture ("function.inside", "class.around", etc).
Expand Down Expand Up @@ -394,6 +414,8 @@ impl TextObjectQuery {
.iter()
.find_map(|cap| self.query.capture_index_for_name(cap))?;

cursor.set_match_limit(TREE_SITTER_MATCH_LIMIT);

let nodes = cursor
.captures(&self.query, node, RopeProvider(slice))
.filter_map(move |(mat, _)| {
Expand Down Expand Up @@ -843,6 +865,7 @@ impl Syntax {
let mut cursor = ts_parser.cursors.pop().unwrap_or_else(QueryCursor::new);
// TODO: might need to set cursor range
cursor.set_byte_range(0..usize::MAX);
cursor.set_match_limit(TREE_SITTER_MATCH_LIMIT);

let source_slice = source.slice(..);

Expand Down Expand Up @@ -1032,6 +1055,7 @@ impl Syntax {

// if reusing cursors & no range this resets to whole range
cursor_ref.set_byte_range(range.clone().unwrap_or(0..usize::MAX));
cursor_ref.set_match_limit(TREE_SITTER_MATCH_LIMIT);

let mut captures = cursor_ref
.captures(
Expand Down