Erase type params when suggesting fully qualified path

When suggesting the use of a fully qualified path for a method call that
is ambiguous because it has multiple candidates, erase type params in
the resulting code, as they would result in an error when applied. We
replace them with `_` in the output to rely on inference. There might be
cases where this still produces slighlty incomplete suggestions, but it
otherwise produces many more errors in relatively common cases.

Fix #96292

2 files changed, 57 insertions, 0 deletions

diff --git a/src/test/ui/traits/do-not-mention-type-params-by-name-in-suggestion-issue-96292.rs b/src/test/ui/traits/do-not-mention-type-params-by-name-in-suggestion-issue-96292.rs
new file mode 100644
index 00000000000..f08025d99b5
--- /dev/null
+++ b/src/test/ui/traits/do-not-mention-type-params-by-name-in-suggestion-issue-96292.rs
@@ -0,0 +1,20 @@
+struct Thing<X>(X);
+
+trait Method<T> {
+    fn method(self) -> T;
+}
+
+impl<X> Method<i32> for Thing<X> {
+    fn method(self) -> i32 { 0 }
+}
+
+impl<X> Method<u32> for Thing<X> {
+    fn method(self) -> u32 { 0 }
+}
+
+fn main() {
+    let thing = Thing(true);
+    thing.method();
+    //~^ ERROR type annotations needed
+    //~| ERROR type annotations needed
+}
diff --git a/src/test/ui/traits/do-not-mention-type-params-by-name-in-suggestion-issue-96292.stderr b/src/test/ui/traits/do-not-mention-type-params-by-name-in-suggestion-issue-96292.stderr
new file mode 100644
index 00000000000..2e80fa89f63
--- /dev/null
+++ b/src/test/ui/traits/do-not-mention-type-params-by-name-in-suggestion-issue-96292.stderr
@@ -0,0 +1,37 @@
+error[E0282]: type annotations needed
+  --> $DIR/do-not-mention-type-params-by-name-in-suggestion-issue-96292.rs:17:11
+   |
+LL |     thing.method();
+   |     ------^^^^^^--
+   |     |     |
+   |     |     cannot infer type for type parameter `T` declared on the trait `Method`
+   |     this method call resolves to `T`
+
+error[E0283]: type annotations needed
+  --> $DIR/do-not-mention-type-params-by-name-in-suggestion-issue-96292.rs:17:11
+   |
+LL |     thing.method();
+   |     ------^^^^^^--
+   |     |     |
+   |     |     cannot infer type for type parameter `T` declared on the trait `Method`
+   |     this method call resolves to `T`
+   |
+note: multiple `impl`s satisfying `Thing<bool>: Method<_>` found
+  --> $DIR/do-not-mention-type-params-by-name-in-suggestion-issue-96292.rs:7:1
+   |
+LL | impl<X> Method<i32> for Thing<X> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | impl<X> Method<u32> for Thing<X> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: use the fully qualified path for the potential candidates
+   |
+LL |     <Thing<_> as Method<i32>>::method(thing);
+   |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+LL |     <Thing<_> as Method<u32>>::method(thing);
+   |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0282, E0283.
+For more information about an error, try `rustc --explain E0282`.