From 3b3e89240dc3f5093a12a31341493e0df01b16c9 Mon Sep 17 00:00:00 2001
From: Chayim Refael Friedman <chayimfr@gmail.com>
Date: Tue, 6 May 2025 10:54:35 +0300
Subject: [PATCH] Don't panic on some weird code

---
 crates/hir-def/src/expr_store/lower/path.rs |  8 +++++++
 crates/hir-ty/src/tests/simple.rs           | 24 +++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/crates/hir-def/src/expr_store/lower/path.rs b/crates/hir-def/src/expr_store/lower/path.rs
index 629d1f2ada..be006c98a5 100644
--- a/crates/hir-def/src/expr_store/lower/path.rs
+++ b/crates/hir-def/src/expr_store/lower/path.rs
@@ -232,6 +232,14 @@ pub(super) fn lower_path(
             .with_borrow_mut(|map| map.extend(ast_segments.into_iter().zip(ast_segments_offset..)));
     }
 
+    if let Some(last_segment_args @ Some(GenericArgs { has_self_type: true, .. })) =
+        generic_args.last_mut()
+    {
+        // Well-formed code cannot have `<T as Trait>` without an associated item after,
+        // and this causes panics in hir-ty lowering.
+        *last_segment_args = None;
+    }
+
     let mod_path = Interned::new(ModPath::from_segments(kind, segments));
     if type_anchor.is_none() && generic_args.is_empty() {
         return Some(Path::BarePath(mod_path));
diff --git a/crates/hir-ty/src/tests/simple.rs b/crates/hir-ty/src/tests/simple.rs
index eeebe38f18..08127eeb46 100644
--- a/crates/hir-ty/src/tests/simple.rs
+++ b/crates/hir-ty/src/tests/simple.rs
@@ -3902,3 +3902,27 @@ fn main() {
         "#]],
     );
 }
+
+#[test]
+fn regression_19734() {
+    check_infer(
+        r#"
+trait Foo {
+    type Gat<'o>;
+}
+
+trait Bar {
+    fn baz() -> <Self::Xyz as Foo::Gat<'_>>;
+}
+
+fn foo<T: Bar>() {
+    T::baz();
+}
+    "#,
+        expect![[r#"
+            110..127 '{     ...z(); }': ()
+            116..122 'T::baz': fn baz<T>() -> <{unknown} as Foo>::Gat<'?>
+            116..124 'T::baz()': Foo::Gat<'?, {unknown}>
+        "#]],
+    );
+}