Refactor flattening logic for highlighted syntax ranges

Author: ltentrup

crates/ra_ide/src/syntax_highlighting.rs

@@ -31,6 +31,80 @@ pub struct HighlightedRange {
     pub binding_hash: Option<u64>,
 }
 
+#[derive(Debug)]
+struct HighlightedRangeStack {
+    stack: Vec<Vec<HighlightedRange>>,
+}
+
+/// We use a stack to implement the flattening logic for the highlighted
+/// syntax ranges.
+impl HighlightedRangeStack {
+    fn new() -> Self {
+        Self { stack: vec![Vec::new()] }
+    }
+
+    fn push(&mut self) {
+        self.stack.push(Vec::new());
+    }
+
+    /// Flattens the highlighted ranges.
+    ///
+    /// For example `#[cfg(feature = "foo")]` contains the nested ranges:
+    /// 1) parent-range: Attribute [0, 23)
+    /// 2) child-range: String [16, 21)
+    ///
+    /// The following code implements the flattening, for our example this results to:
+    /// `[Attribute [0, 16), String [16, 21), Attribute [21, 23)]`
+    fn pop(&mut self) {
+        let children = self.stack.pop().unwrap();
+        let prev = self.stack.last_mut().unwrap();
+        let needs_flattening = !children.is_empty()
+            && !prev.is_empty()
+            && children.first().unwrap().range.is_subrange(&prev.last().unwrap().range);
+        if !needs_flattening {
+            prev.extend(children);
+        } else {
+            let mut parent = prev.pop().unwrap();
+            for ele in children {
+                assert!(ele.range.is_subrange(&parent.range));
+                let mut cloned = parent.clone();
+                parent.range = TextRange::from_to(parent.range.start(), ele.range.start());
+                cloned.range = TextRange::from_to(ele.range.end(), cloned.range.end());
+                if !parent.range.is_empty() {
+                    prev.push(parent);
+                }
+                prev.push(ele);
+                parent = cloned;
+            }
+            if !parent.range.is_empty() {
+                prev.push(parent);
+            }
+        }
+    }
+
+    fn add(&mut self, range: HighlightedRange) {
+        self.stack
+            .last_mut()
+            .expect("during DFS traversal, the stack must not be empty")
+            .push(range)
+    }
+
+    fn flattened(mut self) -> Vec<HighlightedRange> {
+        assert_eq!(
+            self.stack.len(),
+            1,
+            "after DFS traversal, the stack should only contain a single element"
+        );
+        let res = self.stack.pop().unwrap();
+        // Check that ranges are sorted and disjoint
+        assert!(res
+            .iter()
+            .zip(res.iter().skip(1))
+            .all(|(left, right)| left.range.end() <= right.range.start()));
+        res
+    }
+}
+
 pub(crate) fn highlight(
     db: &RootDatabase,
     file_id: FileId,
@@ -57,52 +131,17 @@ pub(crate) fn highlight(
     let mut bindings_shadow_count: FxHashMap<Name, u32> = FxHashMap::default();
     // We use a stack for the DFS traversal below.
     // When we leave a node, the we use it to flatten the highlighted ranges.
-    let mut res: Vec<Vec<HighlightedRange>> = vec![Vec::new()];
+    let mut stack = HighlightedRangeStack::new();
 
     let mut current_macro_call: Option<ast::MacroCall> = None;
 
     // Walk all nodes, keeping track of whether we are inside a macro or not.
     // If in macro, expand it first and highlight the expanded code.
     for event in root.preorder_with_tokens() {
         match &event {
-            WalkEvent::Enter(_) => res.push(Vec::new()),
-            WalkEvent::Leave(_) => {
-                /* Flattens the highlighted ranges.
-                 *
-                 * For example `#[cfg(feature = "foo")]` contains the nested ranges:
-                 * 1) parent-range: Attribute [0, 23)
-                 * 2) child-range: String [16, 21)
-                 *
-                 * The following code implements the flattening, for our example this results to:
-                 * `[Attribute [0, 16), String [16, 21), Attribute [21, 23)]`
-                 */
-                let children = res.pop().unwrap();
-                let prev = res.last_mut().unwrap();
-                let needs_flattening = !children.is_empty()
-                    && !prev.is_empty()
-                    && children.first().unwrap().range.is_subrange(&prev.last().unwrap().range);
-                if !needs_flattening {
-                    prev.extend(children);
-                } else {
-                    let mut parent = prev.pop().unwrap();
-                    for ele in children {
-                        assert!(ele.range.is_subrange(&parent.range));
-                        let mut cloned = parent.clone();
-                        parent.range = TextRange::from_to(parent.range.start(), ele.range.start());
-                        cloned.range = TextRange::from_to(ele.range.end(), cloned.range.end());
-                        if !parent.range.is_empty() {
-                            prev.push(parent);
-                        }
-                        prev.push(ele);
-                        parent = cloned;
-                    }
-                    if !parent.range.is_empty() {
-                        prev.push(parent);
-                    }
-                }
-            }
+            WalkEvent::Enter(_) => stack.push(),
+            WalkEvent::Leave(_) => stack.pop(),
         };
-        let current = res.last_mut().expect("during DFS traversal, the stack must not be empty");
 
         let event_range = match &event {
             WalkEvent::Enter(it) => it.text_range(),
@@ -119,7 +158,7 @@ pub(crate) fn highlight(
             WalkEvent::Enter(Some(mc)) => {
                 current_macro_call = Some(mc.clone());
                 if let Some(range) = macro_call_range(&mc) {
-                    current.push(HighlightedRange {
+                    stack.add(HighlightedRange {
                         range,
                         highlight: HighlightTag::Macro.into(),
                         binding_hash: None,
@@ -161,27 +200,19 @@ pub(crate) fn highlight(
 
         if let Some(token) = element.as_token().cloned().and_then(ast::RawString::cast) {
             let expanded = element_to_highlight.as_token().unwrap().clone();
-            if highlight_injection(current, &sema, token, expanded).is_some() {
+            if highlight_injection(&mut stack, &sema, token, expanded).is_some() {
                 continue;
             }
         }
 
         if let Some((highlight, binding_hash)) =
             highlight_element(&sema, &mut bindings_shadow_count, element_to_highlight)
         {
-            current.push(HighlightedRange { range, highlight, binding_hash });
+            stack.add(HighlightedRange { range, highlight, binding_hash });
         }
     }
 
-    assert_eq!(res.len(), 1, "after DFS traversal, the stack should only contain a single element");
-    let mut res = res.pop().unwrap();
-    res.sort_by_key(|range| range.range.start());
-    // Check that ranges are sorted and disjoint
-    assert!(res
-        .iter()
-        .zip(res.iter().skip(1))
-        .all(|(left, right)| left.range.end() <= right.range.start()));
-    res
+    stack.flattened()
 }
 
 fn macro_call_range(macro_call: &ast::MacroCall) -> Option<TextRange> {
@@ -358,7 +389,7 @@ fn highlight_name_by_syntax(name: ast::Name) -> Highlight {
 }
 
 fn highlight_injection(
-    acc: &mut Vec<HighlightedRange>,
+    acc: &mut HighlightedRangeStack,
     sema: &Semantics<RootDatabase>,
     literal: ast::RawString,
     expanded: SyntaxToken,
@@ -373,7 +404,7 @@ fn highlight_injection(
     let (analysis, tmp_file_id) = Analysis::from_single_file(value);
 
     if let Some(range) = literal.open_quote_text_range() {
-        acc.push(HighlightedRange {
+        acc.add(HighlightedRange {
             range,
             highlight: HighlightTag::StringLiteral.into(),
             binding_hash: None,
@@ -383,12 +414,12 @@ fn highlight_injection(
     for mut h in analysis.highlight(tmp_file_id).unwrap() {
         if let Some(r) = literal.map_range_up(h.range) {
             h.range = r;
-            acc.push(h)
+            acc.add(h)
         }
     }
 
     if let Some(range) = literal.close_quote_text_range() {
-        acc.push(HighlightedRange {
+        acc.add(HighlightedRange {
             range,
             highlight: HighlightTag::StringLiteral.into(),
             binding_hash: None,