From 4830325a142952b69cf31c128d755e87ad5817d8 Mon Sep 17 00:00:00 2001
From: r0cky <mu001999@outlook.com>
Date: Fri, 22 Dec 2023 23:25:54 +0800
Subject: [PATCH 1/2] Emits error if has bound regions

---
 .../rustc_hir_analysis/src/check/entry.rs     |  5 ++++-
 .../entry-point/return-ty-has-bound-vars.rs   |  5 +++++
 .../return-ty-has-bound-vars.stderr           | 19 +++++++++++++++++++
 3 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 tests/ui/entry-point/return-ty-has-bound-vars.rs
 create mode 100644 tests/ui/entry-point/return-ty-has-bound-vars.stderr

diff --git a/compiler/rustc_hir_analysis/src/check/entry.rs b/compiler/rustc_hir_analysis/src/check/entry.rs
index 1d737e17e821b..a82853a13034d 100644
--- a/compiler/rustc_hir_analysis/src/check/entry.rs
+++ b/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,
diff --git a/tests/ui/entry-point/return-ty-has-bound-vars.rs b/tests/ui/entry-point/return-ty-has-bound-vars.rs
new file mode 100644
index 0000000000000..2c621e7885131
--- /dev/null
+++ b/tests/ui/entry-point/return-ty-has-bound-vars.rs
@@ -0,0 +1,5 @@
+// issue-119209
+
+type Foo<'a> = impl PartialEq; //~ERROR `impl Trait` in type aliases is unstable
+
+fn main<'a>(_: &'a i32) -> Foo<'a> {} //~ERROR `main` function return type is not allowed to have generic parameters
diff --git a/tests/ui/entry-point/return-ty-has-bound-vars.stderr b/tests/ui/entry-point/return-ty-has-bound-vars.stderr
new file mode 100644
index 0000000000000..a7aa69f9017f9
--- /dev/null
+++ b/tests/ui/entry-point/return-ty-has-bound-vars.stderr
@@ -0,0 +1,19 @@
+error[E0658]: `impl Trait` in type aliases is unstable
+  --> $DIR/return-ty-has-bound-vars.rs:3:16
+   |
+LL | type Foo<'a> = impl PartialEq;
+   |                ^^^^^^^^^^^^^^
+   |
+   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
+   = help: add `#![feature(type_alias_impl_trait)]` to the crate attributes to enable
+
+error[E0131]: `main` function return type is not allowed to have generic parameters
+  --> $DIR/return-ty-has-bound-vars.rs:5:28
+   |
+LL | fn main<'a>(_: &'a i32) -> Foo<'a> {}
+   |                            ^^^^^^^
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0131, E0658.
+For more information about an error, try `rustc --explain E0131`.

From d3f466a3a77d6d32e8e31ab9ccb61435938928a8 Mon Sep 17 00:00:00 2001
From: r0cky <mu001999@outlook.com>
Date: Sat, 23 Dec 2023 00:09:37 +0800
Subject: [PATCH 2/2] Update test

---
 .../entry-point/return-ty-has-bound-vars.rs   |  4 +---
 .../return-ty-has-bound-vars.stderr           | 20 +++++--------------
 2 files changed, 6 insertions(+), 18 deletions(-)

diff --git a/tests/ui/entry-point/return-ty-has-bound-vars.rs b/tests/ui/entry-point/return-ty-has-bound-vars.rs
index 2c621e7885131..0995ce0616092 100644
--- a/tests/ui/entry-point/return-ty-has-bound-vars.rs
+++ b/tests/ui/entry-point/return-ty-has-bound-vars.rs
@@ -1,5 +1,3 @@
 // issue-119209
 
-type Foo<'a> = impl PartialEq; //~ERROR `impl Trait` in type aliases is unstable
-
-fn main<'a>(_: &'a i32) -> Foo<'a> {} //~ERROR `main` function return type is not allowed to have generic parameters
+fn main<'a>(_: &'a i32) -> &'a () { &() } //~ERROR `main` function return type is not allowed to have generic parameters
diff --git a/tests/ui/entry-point/return-ty-has-bound-vars.stderr b/tests/ui/entry-point/return-ty-has-bound-vars.stderr
index a7aa69f9017f9..e7aab839f3171 100644
--- a/tests/ui/entry-point/return-ty-has-bound-vars.stderr
+++ b/tests/ui/entry-point/return-ty-has-bound-vars.stderr
@@ -1,19 +1,9 @@
-error[E0658]: `impl Trait` in type aliases is unstable
-  --> $DIR/return-ty-has-bound-vars.rs:3:16
-   |
-LL | type Foo<'a> = impl PartialEq;
-   |                ^^^^^^^^^^^^^^
-   |
-   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
-   = help: add `#![feature(type_alias_impl_trait)]` to the crate attributes to enable
-
 error[E0131]: `main` function return type is not allowed to have generic parameters
-  --> $DIR/return-ty-has-bound-vars.rs:5:28
+  --> $DIR/return-ty-has-bound-vars.rs:3:28
    |
-LL | fn main<'a>(_: &'a i32) -> Foo<'a> {}
-   |                            ^^^^^^^
+LL | fn main<'a>(_: &'a i32) -> &'a () { &() }
+   |                            ^^^^^^
 
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0131, E0658.
-For more information about an error, try `rustc --explain E0131`.
+For more information about this error, try `rustc --explain E0131`.