gccrs: Allow const and async specifiers in functions

We need to account for const specifiers in async parsing as const
can be used in the syntax before the async keyword.

gcc/rust/ChangeLog:

	* parse/rust-parse-impl.h (Parser::parse_vis_item): Allow parsing async
	items in const.
	(Parser::parse_async_item): Account for const offset during async
	lookahead.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/gcc/rust/parse/rust-parse-impl.h b/gcc/rust/parse/rust-parse-impl.h
index a1ad4f1..acceec3 100644
--- a/gcc/rust/parse/rust-parse-impl.h
+++ b/gcc/rust/parse/rust-parse-impl.h
@@ -1383,6 +1383,8 @@ Parser<ManagedTokenSource>::parse_vis_item (AST::AttrVec outer_attrs)
 	  return parse_const_item (std::move (vis), std::move (outer_attrs));
 	case UNSAFE:
 	case EXTERN_KW:
+	case ASYNC:
+	  return parse_async_item (std::move (vis), std::move (outer_attrs));
 	case FN_KW:
 	  return parse_function (std::move (vis), std::move (outer_attrs));
 	default:
@@ -1445,7 +1447,9 @@ std::unique_ptr<AST::Function>
 Parser<ManagedTokenSource>::parse_async_item (AST::Visibility vis,
 					      AST::AttrVec outer_attrs)
 {
-  const_TokenPtr t = lexer.peek_token ();
+  auto offset = (lexer.peek_token ()->get_id () == CONST) ? 1 : 0;
+  const_TokenPtr t = lexer.peek_token (offset);
+
   if (Session::get_instance ().options.get_edition ()
       == CompileOptions::Edition::E2015)
     {
@@ -1456,7 +1460,7 @@ Parser<ManagedTokenSource>::parse_async_item (AST::Visibility vis,
 		     "to use %<async fn%>, switch to Rust 2018 or later"));
     }
 
-  t = lexer.peek_token (1);
+  t = lexer.peek_token (offset + 1);
 
   switch (t->get_id ())
     {