Rollup merge of rust-lang#109238 - spastorino:new-rpitit-12, r=compiler-errors

Fix generics mismatch errors for RPITITs on -Zlower-impl-trait-in-trait-to-assoc-ty

This PR stops reporting errors due to different count of generics on the new synthesized associated types for RPITITs. Those were already reported when we compare the function on the triat with the function on the impl.

r? `@compiler-errors`

Author: matthiaskrgr

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -1205,6 +1205,17 @@ fn compare_number_of_generics<'tcx>(
         return Ok(());
     }
 
+    // We never need to emit a separate error for RPITITs, since if an RPITIT
+    // has mismatched type or const generic arguments, then the method that it's
+    // inheriting the generics from will also have mismatched arguments, and
+    // we'll report an error for that instead. Delay a bug for safety, though.
+    if tcx.opt_rpitit_info(trait_.def_id).is_some() {
+        return Err(tcx.sess.delay_span_bug(
+            rustc_span::DUMMY_SP,
+            "errors comparing numbers of generics of trait/impl functions were not emitted",
+        ));
+    }
+
     let matchings = [
         ("type", trait_own_counts.types, impl_own_counts.types),
         ("const", trait_own_counts.consts, impl_own_counts.consts),

tests/ui/async-await/in-trait/generics-mismatch.rs

@@ -0,0 +1,15 @@
+// edition: 2021
+
+#![feature(async_fn_in_trait)]
+#![allow(incomplete_features)]
+
+trait Foo {
+    async fn foo<T>();
+}
+
+impl Foo for () {
+    async fn foo<const N: usize>() {}
+    //~^ ERROR: method `foo` has an incompatible generic parameter for trait `Foo` [E0053]
+}
+
+fn main() {}

tests/ui/async-await/in-trait/generics-mismatch.stderr

@@ -0,0 +1,16 @@
+error[E0053]: method `foo` has an incompatible generic parameter for trait `Foo`
+  --> $DIR/generics-mismatch.rs:11:18
+   |
+LL | trait Foo {
+   |       ---
+LL |     async fn foo<T>();
+   |                  - expected type parameter
+...
+LL | impl Foo for () {
+   | ---------------
+LL |     async fn foo<const N: usize>() {}
+   |                  ^^^^^^^^^^^^^^ found const parameter of type `usize`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0053`.

tests/ui/impl-trait/in-trait/generics-mismatch.stderr renamed to tests/ui/impl-trait/in-trait/generics-mismatch.current.stderr

@@ -1,5 +1,5 @@
 error[E0049]: method `bar` has 1 type parameter but its trait declaration has 0 type parameters
-  --> $DIR/generics-mismatch.rs:11:12
+  --> $DIR/generics-mismatch.rs:14:12
    |
 LL |     fn bar(&self) -> impl Sized;
    |           - expected 0 type parameters

tests/ui/impl-trait/in-trait/generics-mismatch.next.stderr

@@ -0,0 +1,12 @@
+error[E0049]: method `bar` has 1 type parameter but its trait declaration has 0 type parameters
+  --> $DIR/generics-mismatch.rs:14:12
+   |
+LL |     fn bar(&self) -> impl Sized;
+   |           - expected 0 type parameters
+...
+LL |     fn bar<T>(&self) {}
+   |            ^ found 1 type parameter
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0049`.

tests/ui/impl-trait/in-trait/generics-mismatch.rs

@@ -1,3 +1,6 @@
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
+
 #![feature(return_position_impl_trait_in_trait)]
 #![allow(incomplete_features)]