refactor(ast)!: store trivia comments in a sorted slice (#4045)

This gets rid of `TriviasMap`, introducing `SortedComments` in order to
store trivia comments in a sorted slice.

Closes: https://github.com/oxc-project/backlog/issues/38

crates/oxc_ast/src/lib.rs

@@ -42,7 +42,7 @@ pub use num_bigint::BigUint;
 pub use crate::{
     ast_builder::AstBuilder,
     ast_kind::{AstKind, AstType},
-    trivia::{Comment, CommentKind, Trivias, TriviasMap},
+    trivia::{Comment, CommentKind, SortedComments, Trivias},
     visit::{Visit, VisitMut},
 };
 

crates/oxc_ast/src/trivia.rs

@@ -1,8 +1,8 @@
 //! Trivias such as comments and irregular whitespaces
 
 use std::{
-    collections::btree_map::{BTreeMap, Range},
-    ops::{Deref, RangeBounds},
+    iter::FusedIterator,
+    ops::{Bound, Deref, RangeBounds},
     sync::Arc,
 };
 
@@ -37,15 +37,16 @@ impl CommentKind {
     }
 }
 
-pub type TriviasMap = BTreeMap<u32, Comment>;
+/// Sorted set of unique trivia comments, in ascending order by starting position.
+pub type SortedComments = Box<[(u32, Comment)]>;
 
 #[derive(Debug, Clone, Default)]
 pub struct Trivias(Arc<TriviasImpl>);
 
 #[derive(Debug, Default)]
 pub struct TriviasImpl {
-    /// Keyed by span.start
-    comments: TriviasMap,
+    /// Unique comments, ordered by increasing span-start.
+    comments: SortedComments,
 
     irregular_whitespaces: Vec<Span>,
 }
@@ -59,26 +60,124 @@ impl Deref for Trivias {
 }
 
 impl Trivias {
-    pub fn new(comments: TriviasMap, irregular_whitespaces: Vec<Span>) -> Trivias {
+    pub fn new(comments: SortedComments, irregular_whitespaces: Vec<Span>) -> Trivias {
         Self(Arc::new(TriviasImpl { comments, irregular_whitespaces }))
     }
 
     pub fn comments(&self) -> impl Iterator<Item = (CommentKind, Span)> + '_ {
         self.comments.iter().map(|(start, comment)| (comment.kind, Span::new(*start, comment.end)))
     }
 
-    pub fn comments_range<R>(&self, range: R) -> Range<'_, u32, Comment>
+    pub fn comments_range<R>(&self, range: R) -> CommentsRange<'_>
     where
         R: RangeBounds<u32>,
     {
-        self.comments.range(range)
+        CommentsRange::new(&self.comments, range.start_bound().cloned(), range.end_bound().cloned())
     }
 
     pub fn has_comments_between(&self, span: Span) -> bool {
-        self.comments.range(span.start..span.end).count() > 0
+        self.comments_range(span.start..span.end).count() > 0
     }
 
     pub fn irregular_whitespaces(&self) -> &Vec<Span> {
         &self.irregular_whitespaces
     }
 }
+
+/// Double-ended iterator over a range of comments, by starting position.
+pub struct CommentsRange<'a> {
+    comments: &'a [(u32, Comment)],
+    range: (Bound<u32>, Bound<u32>),
+    current_start: usize,
+    current_end: usize,
+}
+
+impl<'a> CommentsRange<'a> {
+    fn new(comments: &'a [(u32, Comment)], start: Bound<u32>, end: Bound<u32>) -> Self {
+        // Directly skip all comments that are already known to start
+        // outside the requested range.
+        let partition_start = {
+            let range_start = match start {
+                Bound::Unbounded => 0,
+                Bound::Included(x) => x,
+                Bound::Excluded(x) => x.saturating_add(1),
+            };
+            comments.partition_point(|(start, _)| *start < range_start)
+        };
+        let partition_end = {
+            let range_end = match end {
+                Bound::Unbounded => u32::MAX,
+                Bound::Included(x) => x,
+                Bound::Excluded(x) => x.saturating_sub(1),
+            };
+            comments.partition_point(|(start, _)| *start <= range_end)
+        };
+        Self {
+            comments,
+            range: (start, end),
+            current_start: partition_start,
+            current_end: partition_end,
+        }
+    }
+}
+
+impl<'c> Iterator for CommentsRange<'c> {
+    type Item = (&'c u32, &'c Comment);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.current_start < self.current_end {
+            for (start, comment) in &self.comments[self.current_start..self.current_end] {
+                self.current_start = self.current_start.saturating_add(1);
+                if self.range.contains(start) {
+                    return Some((start, comment));
+                }
+            }
+        }
+        None
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let max_remaining = self.current_end.saturating_sub(self.current_start);
+        (0, Some(max_remaining))
+    }
+}
+
+impl<'c> DoubleEndedIterator for CommentsRange<'c> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        if self.current_start < self.current_end {
+            for (start, comment) in self.comments[self.current_start..self.current_end].iter().rev()
+            {
+                self.current_end = self.current_end.saturating_sub(1);
+                if self.range.contains(start) {
+                    return Some((start, comment));
+                }
+            }
+        }
+        None
+    }
+}
+
+impl FusedIterator for CommentsRange<'_> {}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_comments_range() {
+        let comments: SortedComments = vec![
+            (0, Comment { end: 4, kind: CommentKind::SingleLine }),
+            (5, Comment { end: 9, kind: CommentKind::SingleLine }),
+            (10, Comment { end: 13, kind: CommentKind::SingleLine }),
+            (14, Comment { end: 17, kind: CommentKind::SingleLine }),
+            (18, Comment { end: 23, kind: CommentKind::SingleLine }),
+        ]
+        .into_boxed_slice();
+        let full_len = comments.len();
+        let trivias = Trivias::new(comments, vec![]);
+        assert_eq!(trivias.comments_range(..).count(), full_len);
+        assert_eq!(trivias.comments_range(1..).count(), full_len.saturating_sub(1));
+        assert_eq!(trivias.comments_range(..18).count(), full_len.saturating_sub(1));
+        assert_eq!(trivias.comments_range(..=18).count(), full_len);
+    }
+}

crates/oxc_parser/src/lexer/trivia_builder.rs

@@ -1,16 +1,18 @@
-use oxc_ast::{Comment, CommentKind, Trivias, TriviasMap};
+use oxc_ast::{Comment, CommentKind, SortedComments, Trivias};
 use oxc_span::Span;
 
 #[derive(Debug, Default)]
 pub struct TriviaBuilder {
-    // Duplicated comments can be added from rewind, use `BTreeMap` to ensure uniqueness
+    // NOTE(lucab): This is a set of unique comments. Duplicated
+    // comments could be generated in case of rewind; they are
+    // filtered out at insertion time.
     comments: Vec<(u32, Comment)>,
     irregular_whitespaces: Vec<Span>,
 }
 
 impl TriviaBuilder {
     pub fn build(self) -> Trivias {
-        let comments = TriviasMap::from_iter(self.comments);
+        let comments = SortedComments::from_iter(self.comments);
         Trivias::new(comments, self.irregular_whitespaces)
     }
 
@@ -26,9 +28,9 @@ impl TriviaBuilder {
 
     fn add_comment(&mut self, start: u32, comment: Comment) {
         // The comments array is an ordered vec, only add the comment if its not added before,
-        // to avoid situations where the parser needs to rewind and reinsert the comment.
-        if let Some(comment) = self.comments.last_mut() {
-            if start <= comment.0 {
+        // to avoid situations where the parser needs to rewind and tries to reinsert the comment.
+        if let Some((last_start, _)) = self.comments.last() {
+            if start <= *last_start {
                 return;
             }
         }