highlight: don't include scope in ScopeEnd events

When there are embedded documents, multiple scopes can start or
end at the same position. Previously, there was no guarantee that
the ScopeEnd events would always occur in the reverse order of the
ScopeStart events. The easiest way to avoid exposing inconsistency
is to not surface the scopes being ended.

cli/src/highlight.rs

@@ -209,7 +209,7 @@ pub fn ansi(
             HighlightEvent::ScopeStart(s) => {
                 scope_stack.push(s);
             }
-            HighlightEvent::ScopeEnd(_) => {
+            HighlightEvent::ScopeEnd => {
                 scope_stack.pop();
             }
         }

cli/src/tests/highlight_test.rs

@@ -162,8 +162,7 @@ fn to_token_vector<'a>(
     )? {
         match event {
             HighlightEvent::ScopeStart(s) => scopes.push(s),
-            HighlightEvent::ScopeEnd(s) => {
-                assert_eq!(*scopes.last().unwrap(), s);
+            HighlightEvent::ScopeEnd => {
                 scopes.pop();
             }
             HighlightEvent::Source(s) => {

highlight/src/lib.rs

@@ -96,7 +96,7 @@ where
 pub enum HighlightEvent<'a> {
     Source(&'a str),
     ScopeStart(Scope),
-    ScopeEnd(Scope),
+    ScopeEnd,
 }
 
 #[derive(Debug, Deserialize)]
@@ -565,10 +565,7 @@ where
                 .parse(self.source, None)
                 .expect("Failed to parse");
             let layer = Layer::new(self.source, tree, property_sheet, ranges);
-            match self
-                .layers
-                .binary_search_by_key(&(layer.offset(), 1), |l| (l.offset(), 0))
-            {
+            match self.layers.binary_search_by(|l| l.cmp(&layer)) {
                 Ok(i) | Err(i) => self.layers.insert(i, layer),
             };
         }
@@ -625,7 +622,7 @@ impl<'a, T: Fn(&str) -> Option<(Language, &'a PropertySheet<Properties>)>> Itera
                 }
 
                 scope_event = if self.layers[0].at_node_end {
-                    Some(HighlightEvent::ScopeEnd(scope))
+                    Some(HighlightEvent::ScopeEnd)
                 } else {
                     Some(HighlightEvent::ScopeStart(scope))
                 };
@@ -638,7 +635,7 @@ impl<'a, T: Fn(&str) -> Option<(Language, &'a PropertySheet<Properties>)>> Itera
             // to re-sort the layers. If the cursor is already at the end of its syntax tree,
             // remove it.
             if self.layers[0].advance() {
-                self.layers.sort_unstable_by_key(|layer| layer.offset());
+                self.layers.sort_unstable_by(|a, b| a.cmp(&b));
             } else {
                 self.layers.remove(0);
             }
@@ -676,6 +673,15 @@ impl<'a> Layer<'a> {
         }
     }
 
+    fn cmp(&self, other: &Layer) -> cmp::Ordering {
+        // Events are ordered primarily by their position in the document. But if
+        // one scope starts at a given position and another scope ends at that
+        // same position, return the scope end event before the scope start event.
+        self.offset()
+            .cmp(&other.offset())
+            .then_with(|| other.at_node_end.cmp(&self.at_node_end))
+    }
+
     fn offset(&self) -> usize {
         if self.at_node_end {
             self.cursor.node().end_byte()
@@ -770,8 +776,8 @@ where
                 scopes.push(s);
                 renderer.start_scope(s);
             }
-            HighlightEvent::ScopeEnd(s) => {
-                assert_eq!(scopes.pop(), Some(s));
+            HighlightEvent::ScopeEnd => {
+                scopes.pop();
                 renderer.end_scope();
             }
             HighlightEvent::Source(src) => {