Rollup merge of #139981 - compiler-errors:name-2, r=nnethercote

Don't compute name of associated item if it's an RPITIT

Another simple fix for an RPITIT name ICE.

Fixes https://github.com/rust-lang/rust/issues/139941
Fixes #140084

r? nnethercote

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() {}

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`.

tests/ui/impl-trait/in-trait/dont-probe-missing-item-name-3.rs

@@ -0,0 +1,11 @@
+trait Trait {
+    fn method() -> impl Sized;
+}
+
+// Ensure that we don't try to probe the name of the RPITIT when looking for
+// fixes to suggest for the missing associated type's trait path below.
+
+fn foo() -> i32::Assoc {}
+//~^ ERROR ambiguous associated type
+
+fn main() {}

tests/ui/impl-trait/in-trait/dont-probe-missing-item-name-3.stderr

@@ -0,0 +1,15 @@
+error[E0223]: ambiguous associated type
+  --> $DIR/dont-probe-missing-item-name-3.rs:8:13
+   |
+LL | fn foo() -> i32::Assoc {}
+   |             ^^^^^^^^^^
+   |
+help: if there were a trait named `Example` with associated type `Assoc` implemented for `i32`, you could use the fully-qualified path
+   |
+LL - fn foo() -> i32::Assoc {}
+LL + fn foo() -> <i32 as Example>::Assoc {}
+   |
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0223`.