From 8fa454d7aa9d295d3434e0150b996fa724c4b3e3 Mon Sep 17 00:00:00 2001
From: Shoyu Vanilla <modulo641@gmail.com>
Date: Mon, 5 Aug 2024 00:06:29 +0900
Subject: [PATCH] fix: Insert a generic arg for `impl Trait` when lowering
 generic args

---
 crates/hir-def/src/path/lower.rs      |  5 +++++
 crates/hir-ty/src/tests/regression.rs | 19 +++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/crates/hir-def/src/path/lower.rs b/crates/hir-def/src/path/lower.rs
index 7c39773aa6..70918a9358 100644
--- a/crates/hir-def/src/path/lower.rs
+++ b/crates/hir-def/src/path/lower.rs
@@ -194,6 +194,11 @@ pub(super) fn lower_generic_args(
         match generic_arg {
             ast::GenericArg::TypeArg(type_arg) => {
                 let type_ref = TypeRef::from_ast_opt(lower_ctx, type_arg.ty());
+                type_ref.walk(&mut |tr| {
+                    if let TypeRef::ImplTrait(bounds) = tr {
+                        lower_ctx.update_impl_traits_bounds(bounds.clone());
+                    }
+                });
                 args.push(GenericArg::Type(type_ref));
             }
             ast::GenericArg::AssocTypeArg(assoc_type_arg) => {
diff --git a/crates/hir-ty/src/tests/regression.rs b/crates/hir-ty/src/tests/regression.rs
index ac2dfea101..2819838612 100644
--- a/crates/hir-ty/src/tests/regression.rs
+++ b/crates/hir-ty/src/tests/regression.rs
@@ -2122,3 +2122,22 @@ fn test() {
 "#,
     )
 }
+
+#[test]
+fn issue_17191() {
+    check_types(
+        r#"
+trait A {
+    type Item;
+}
+
+trait B<T> {}
+
+fn foo<T: B<impl A>>() {}
+
+fn test() {
+    let f = foo;
+      //^ fn foo<{unknown}>()
+}"#,
+    );
+}