Do not ICE on generic type mismatch in anonymous const

Author: LeSeulArtichaut

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -1660,10 +1660,19 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         // it's a actual definition. According to the comments (e.g. in
         // librustc_typeck/check/compare_method.rs:compare_predicate_entailment) the latter
         // is relied upon by some other code. This might (or might not) need cleanup.
-        let body_owner_def_id =
+        let mut body_owner_def_id =
             self.tcx.hir().opt_local_def_id(cause.body_id).unwrap_or_else(|| {
                 self.tcx.hir().body_owner_def_id(hir::BodyId { hir_id: cause.body_id })
             });
+
+        if let hir::def::DefKind::AnonConst = self.tcx.hir().def_kind(body_owner_def_id) {
+            // #80062: we need to pass the containing function to access the generics properly
+            body_owner_def_id = self
+                .tcx
+                .hir()
+                .get_parent_did(self.tcx.hir().local_def_id_to_hir_id(body_owner_def_id));
+        }
+
         self.check_and_note_conflicting_crates(diag, terr);
         self.tcx.note_and_explain_type_err(diag, terr, cause, span, body_owner_def_id.to_def_id());
 

src/test/ui/typeck/issue-80062-mismatched-types-anon-const.rs

@@ -0,0 +1,12 @@
+// Regression test for issue #80062
+
+fn foo<Foo>() -> Foo { todo!() }
+
+fn bar<T>() {
+    let _: [u8; foo::<T>()];
+    //~^   ERROR the size for values of type `T` cannot be known at compilation time
+    //~^^  ERROR mismatched types
+    //~^^^ ERROR the size for values of type `T` cannot be known at compilation time
+}
+
+fn main() {}

src/test/ui/typeck/issue-80062-mismatched-types-anon-const.stderr

@@ -0,0 +1,41 @@
+error[E0277]: the size for values of type `T` cannot be known at compilation time
+  --> $DIR/issue-80062-mismatched-types-anon-const.rs:6:23
+   |
+LL | fn foo<Foo>() -> Foo { todo!() }
+   |        --- required by this bound in `foo`
+LL | 
+LL | fn bar<T>() {
+   |        - this type parameter needs to be `Sized`
+LL |     let _: [u8; foo::<T>()];
+   |                       ^ doesn't have a size known at compile-time
+   |
+help: consider relaxing the implicit `Sized` restriction
+   |
+LL | fn foo<Foo: ?Sized>() -> Foo { todo!() }
+   |           ^^^^^^^^
+
+error[E0308]: mismatched types
+  --> $DIR/issue-80062-mismatched-types-anon-const.rs:6:17
+   |
+LL | fn bar<T>() {
+   |        - this type parameter
+LL |     let _: [u8; foo::<T>()];
+   |                 ^^^^^^^^^^ expected `usize`, found type parameter `T`
+   |
+   = note:        expected type `usize`
+           found type parameter `T`
+
+error[E0277]: the size for values of type `T` cannot be known at compilation time
+  --> $DIR/issue-80062-mismatched-types-anon-const.rs:6:17
+   |
+LL | fn bar<T>() {
+   |        - this type parameter needs to be `Sized`
+LL |     let _: [u8; foo::<T>()];
+   |                 ^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = note: the return type of a function must have a statically known size
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0277, E0308.
+For more information about an error, try `rustc --explain E0277`.