From 6f1b0f18747a215e43c42973d41be5131cee93d1 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Thu, 17 Apr 2025 16:47:55 +0000
Subject: [PATCH] Don't compute name of associated item if it's an RPITIT

---
 .../errors/wrong_number_of_generic_args.rs    |  2 +-
 .../dont-probe-missing-item-name-2.rs         | 12 ++++++++++
 .../dont-probe-missing-item-name-2.stderr     | 24 +++++++++++++++++++
 3 files changed, 37 insertions(+), 1 deletion(-)
 create mode 100644 tests/ui/impl-trait/in-trait/dont-probe-missing-item-name-2.rs
 create mode 100644 tests/ui/impl-trait/in-trait/dont-probe-missing-item-name-2.stderr

diff --git a/compiler/rustc_hir_analysis/src/errors/wrong_number_of_generic_args.rs b/compiler/rustc_hir_analysis/src/errors/wrong_number_of_generic_args.rs
index 526ee30209c7d..7a9d36b6c9c94 100644
--- a/compiler/rustc_hir_analysis/src/errors/wrong_number_of_generic_args.rs
+++ b/compiler/rustc_hir_analysis/src/errors/wrong_number_of_generic_args.rs
@@ -487,6 +487,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
             items
                 .in_definition_order()
                 .filter(|item| item.is_type())
+                .filter(|item| !item.is_impl_trait_in_trait())
                 .filter(|item| {
                     !self
                         .gen_args
@@ -494,7 +495,6 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
                         .iter()
                         .any(|constraint| constraint.ident.name == item.name())
                 })
-                .filter(|item| !item.is_impl_trait_in_trait())
                 .map(|item| self.tcx.item_ident(item.def_id).to_string())
                 .collect()
         } else {
diff --git a/tests/ui/impl-trait/in-trait/dont-probe-missing-item-name-2.rs b/tests/ui/impl-trait/in-trait/dont-probe-missing-item-name-2.rs
new file mode 100644
index 0000000000000..e8329e3694d73
--- /dev/null
+++ b/tests/ui/impl-trait/in-trait/dont-probe-missing-item-name-2.rs
@@ -0,0 +1,12 @@
+trait Foo {
+    fn rpitit() -> impl Sized;
+}
+
+// Ensure that we don't try to probe the name of the RPITIT when looking for
+// fixes to suggest for the redundant generic below.
+
+fn test<T: Foo<i32, Assoc = i32>>() {}
+//~^ ERROR trait takes 0 generic arguments but 1 generic argument was supplied
+//~| ERROR associated type `Assoc` not found for `Foo`
+
+fn main() {}
diff --git a/tests/ui/impl-trait/in-trait/dont-probe-missing-item-name-2.stderr b/tests/ui/impl-trait/in-trait/dont-probe-missing-item-name-2.stderr
new file mode 100644
index 0000000000000..1058ef01f323f
--- /dev/null
+++ b/tests/ui/impl-trait/in-trait/dont-probe-missing-item-name-2.stderr
@@ -0,0 +1,24 @@
+error[E0107]: trait takes 0 generic arguments but 1 generic argument was supplied
+  --> $DIR/dont-probe-missing-item-name-2.rs:8:12
+   |
+LL | fn test<T: Foo<i32, Assoc = i32>>() {}
+   |            ^^^------------------ help: remove the unnecessary generics
+   |            |
+   |            expected 0 generic arguments
+   |
+note: trait defined here, with 0 generic parameters
+  --> $DIR/dont-probe-missing-item-name-2.rs:1:7
+   |
+LL | trait Foo {
+   |       ^^^
+
+error[E0220]: associated type `Assoc` not found for `Foo`
+  --> $DIR/dont-probe-missing-item-name-2.rs:8:21
+   |
+LL | fn test<T: Foo<i32, Assoc = i32>>() {}
+   |                     ^^^^^ associated type `Assoc` not found
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0107, E0220.
+For more information about an error, try `rustc --explain E0107`.