[gcc r14-8605] gccrs: Generate error for `async` trait fucntions

[Arthur Cohen]

https://gcc.gnu.org/g:81fcf1087ccaa83088aaed8b8be9777e66d2465d

commit r14-8605-g81fcf1087ccaa83088aaed8b8be9777e66d2465d
Author: Kushal Pal <kushalpal109@gmail.com>
Date:   Sat Dec 16 20:07:23 2023 +0530

    gccrs: Generate error for `async` trait fucntions
    
    Fixes #2767
    
    gcc/rust/ChangeLog:
    
            * checks/errors/rust-ast-validation.cc (ASTValidation::visit):
            Added check for `async` function inside trait.
    
    gcc/testsuite/ChangeLog:
    
            * rust/compile/issue-2767.rs: New test.
    
    Signed-off-by: Kushal Pal <kushalpal109@gmail.com>

Diff:
---
 gcc/rust/checks/errors/rust-ast-validation.cc |  5 +++++
 gcc/testsuite/rust/compile/issue-2767.rs      | 13 +++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/gcc/rust/checks/errors/rust-ast-validation.cc b/gcc/rust/checks/errors/rust-ast-validation.cc
index cd197fc1ea7d..b50e9cdf8581 100644
--- a/gcc/rust/checks/errors/rust-ast-validation.cc
+++ b/gcc/rust/checks/errors/rust-ast-validation.cc
@@ -107,6 +107,11 @@ ASTValidation::visit (AST::Function &function)
     rust_error_at (function.get_locus (), ErrorCode::E0379,
 		   "functions in traits cannot be declared const");
 
+  // may change soon
+  if (qualifiers.is_async () && context.back () == Context::TRAIT_IMPL)
+    rust_error_at (function.get_locus (), ErrorCode::E0706,
+		   "functions in traits cannot be declared %<async%>");
+
   if (valid_context.find (context.back ()) == valid_context.end ()
       && function.has_self_param ())
     rust_error_at (
diff --git a/gcc/testsuite/rust/compile/issue-2767.rs b/gcc/testsuite/rust/compile/issue-2767.rs
new file mode 100644
index 000000000000..9e7e0f983d27
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-2767.rs
@@ -0,0 +1,13 @@
+// { dg-additional-options "-frust-edition=2018" }
+trait Foo {
+    fn f() -> u32;
+}
+
+impl Foo for u32 {
+    async fn f() -> u32 {
+        // { dg-error "functions in traits cannot be declared .async." "" { target *-*-* } .-1 }
+        22
+    }
+}
+
+fn main() {}