Rollup merge of rust-lang#119215 - mu001999:fix/119209, r=Nilstrieb

Emits error if has bound regions

Fixes rust-lang#119209

Author: matthiaskrgr

compiler/rustc_hir_analysis/src/check/entry.rs

@@ -124,7 +124,10 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
     if let Some(term_did) = tcx.lang_items().termination() {
         let return_ty = main_fnsig.output();
         let return_ty_span = main_fn_return_type_span(tcx, main_def_id).unwrap_or(main_span);
-        let return_ty = return_ty.skip_binder();
+        let Some(return_ty) = return_ty.no_bound_vars() else {
+            tcx.sess.emit_err(errors::MainFunctionReturnTypeGeneric { span: return_ty_span });
+            return;
+        };
         let infcx = tcx.infer_ctxt().build();
         let cause = traits::ObligationCause::new(
             return_ty_span,

tests/ui/entry-point/return-ty-has-bound-vars.rs

@@ -0,0 +1,3 @@
+// issue-119209
+
+fn main<'a>(_: &'a i32) -> &'a () { &() } //~ERROR `main` function return type is not allowed to have generic parameters

tests/ui/entry-point/return-ty-has-bound-vars.stderr

@@ -0,0 +1,9 @@
+error[E0131]: `main` function return type is not allowed to have generic parameters
+  --> $DIR/return-ty-has-bound-vars.rs:3:28
+   |
+LL | fn main<'a>(_: &'a i32) -> &'a () { &() }
+   |                            ^^^^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0131`.