2 files changed, 45 insertions, 3 deletions

diff --git a/crates/ide/src/syntax_highlighting/highlight.rs b/crates/ide/src/syntax_highlighting/highlight.rs
index 8dd5d801b..8cc877c1c 100644
--- a/crates/ide/src/syntax_highlighting/highlight.rs
+++ b/crates/ide/src/syntax_highlighting/highlight.rs
@@ -358,8 +358,18 @@ fn highlight_def(db: &RootDatabase, def: Definition) -> Highlight {
             hir::ModuleDef::Trait(_) => HlTag::Symbol(SymbolKind::Trait),
             hir::ModuleDef::TypeAlias(type_) => {
                 let mut h = Highlight::new(HlTag::Symbol(SymbolKind::TypeAlias));
-                if type_.as_assoc_item(db).is_some() {
-                    h |= HlMod::Associated
+                if let Some(item) = type_.as_assoc_item(db) {
+                    h |= HlMod::Associated;
+                    match item.container(db) {
+                        AssocItemContainer::Impl(i) => {
+                            if i.trait_(db).is_some() {
+                                h |= HlMod::Trait;
+                            }
+                        }
+                        AssocItemContainer::Trait(_t) => {
+                            h |= HlMod::Trait;
+                        }
+                    }
                 }
                 return h;
             }
diff --git a/crates/ide/src/syntax_highlighting/tests.rs b/crates/ide/src/syntax_highlighting/tests.rs
index 1b02857ec..933cfa6f3 100644
--- a/crates/ide/src/syntax_highlighting/tests.rs
+++ b/crates/ide/src/syntax_highlighting/tests.rs
@@ -1,6 +1,8 @@
+use std::time::Instant;
+
 use expect_test::{expect_file, ExpectFile};
 use ide_db::SymbolKind;
-use test_utils::{bench, bench_fixture, skip_slow_tests};
+use test_utils::{bench, bench_fixture, skip_slow_tests, AssertLinear};
 
 use crate::{fixture, FileRange, HlTag, TextRange};
 
@@ -258,6 +260,36 @@ fn benchmark_syntax_highlighting_long_struct() {
 }
 
 #[test]
+fn syntax_highlighting_not_quadratic() {
+    if skip_slow_tests() {
+        return;
+    }
+
+    let mut al = AssertLinear::default();
+    while al.next_round() {
+        for i in 6..=10 {
+            let n = 1 << i;
+
+            let fixture = bench_fixture::big_struct_n(n);
+            let (analysis, file_id) = fixture::file(&fixture);
+
+            let time = Instant::now();
+
+            let hash = analysis
+                .highlight(file_id)
+                .unwrap()
+                .iter()
+                .filter(|it| it.highlight.tag == HlTag::Symbol(SymbolKind::Struct))
+                .count();
+            assert!(hash > n as usize);
+
+            let elapsed = time.elapsed();
+            al.sample(n as f64, elapsed.as_millis() as f64);
+        }
+    }
+}
+
+#[test]
 fn benchmark_syntax_highlighting_parser() {
     if skip_slow_tests() {
         return;