Fix Self macro and partial macro invocation parsing null check

gcc/rust/ast/rust-path.cc

@@ -167,8 +167,7 @@ Path::convert_to_simple_path (bool with_opening_scope_resolution) const
   for (const auto &segment : segments)
     {
       // return empty path if doesn't meet simple path segment requirements
-      if (segment.is_error () || segment.has_generic_args ()
-	  || segment.as_string () == "Self")
+      if (segment.is_error () || segment.has_generic_args ())
 	return SimplePath::create_empty ();
 
       // create segment and add to vector

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

@@ -11760,6 +11760,8 @@ Parser<ManagedTokenSource>::parse_stmt_or_expr ()
 	    std::unique_ptr<AST::MacroInvocation> invoc
 	      = parse_macro_invocation_partial (std::move (path),
 						std::move (outer_attrs));
+	    if (invoc == nullptr)
+	      return ExprOrStmt::create_error ();
 
 	    if (restrictions.consume_semi && maybe_skip_token (SEMICOLON))
 	      {
@@ -11771,9 +11773,12 @@ Parser<ManagedTokenSource>::parse_stmt_or_expr ()
 
 	    TokenId after_macro = lexer.peek_token ()->get_id ();
 
-	    if (invoc->get_invoc_data ().get_delim_tok_tree ().get_delim_type ()
-		  == AST::CURLY
-		&& after_macro != DOT && after_macro != QUESTION_MARK)
+	    AST::DelimType delim_type = invoc->get_invoc_data ()
+					  .get_delim_tok_tree ()
+					  .get_delim_type ();
+
+	    if (delim_type == AST::CURLY && after_macro != DOT
+		&& after_macro != QUESTION_MARK)
 	      {
 		rust_debug ("braced macro statement");
 		return ExprOrStmt (

gcc/testsuite/rust/compile/issue-3974.rs

@@ -0,0 +1,8 @@
+impl<'a, F> RunUntil<'a, F> {
+    // { dg-error "could not resolve type path" "" { target *-*-* } .-1 }
+    fn project<'pin>() -> Projection<'pin, 'a, F> {
+        // { dg-error "could not resolve type path" "" { target *-*-* } .-1 }
+        Self!()
+        // { dg-error "could not resolve macro invocation" "" { target *-*-* } .-1 }
+    }
+}