Parse normal functions with self parameter correctly

Fixes #2812

gcc/rust/ChangeLog:

	* parse/rust-parse-impl.h (Parser::parse_function):
	Skip token if its a COMMA.

gcc/testsuite/ChangeLog:

	* rust/compile/issue-2812.rs: New test.

Signed-off-by: Kushal Pal <kushalpal109@gmail.com>

Author: braw-lee

gcc/rust/parse/rust-parse-impl.h

@@ -2946,8 +2946,8 @@ Parser<ManagedTokenSource>::parse_function (AST::Visibility vis,
       && initial_param.error () != ParseSelfError::NOT_SELF)
     return nullptr;
 
-  if (initial_param.has_value ())
-    skip_token (COMMA);
+  if (initial_param.has_value () && lexer.peek_token ()->get_id () == COMMA)
+    skip_token ();
 
   // parse function parameters (only if next token isn't right paren)
   std::vector<std::unique_ptr<AST::Param>> function_params;

gcc/testsuite/rust/compile/issue-2812.rs

@@ -0,0 +1,4 @@
+// { dg-additional-options "-frust-compile-until=astvalidation" }
+fn foo_1(&self);
+fn foo_1(&mut self);
+fn foo_1(self);