fix(parse): make template-argument-list optional

Author: JohelEGP

regression-tests/pure2-bugfix-optional-template-argument-list

@@ -0,0 +1 @@
+main: () -> int = std::plus<>(0, 0);

source/parse.h

@@ -4454,15 +4454,6 @@ class parser
             //  Remember current position, in case this < is isn't a template argument list
             auto start_pos = pos;
 
-            //  And since we'll do this in two places, factor it into a local function
-            auto back_out_template_arg_list = [&]{
-                //  Aha, this wasn't a template argument list after all,
-                //  so back out just that part and return the identifier
-                n->open_angle = source_position{};
-                n->template_args.clear();
-                pos = start_pos;
-            };
-
             n->open_angle = curr().position();
             next();
 
@@ -4477,8 +4468,7 @@ class parser
                     term.arg = std::move(i);
                 }
                 else {
-                    back_out_template_arg_list();
-                    return n;
+                    break;
                 }
                 n->template_args.push_back( std::move(term) );
             }
@@ -4492,7 +4482,11 @@ class parser
                 //      next  term.comma = curr().position();
 
             if (curr().type() != lexeme::Greater) {
-                back_out_template_arg_list();
+                //  Aha, this wasn't a template argument list after all,
+                //  so back out just that part and return the identifier
+                n->open_angle = source_position{};
+                n->template_args.clear();
+                pos = start_pos;
                 return n;
             }
             n->close_angle = curr().position();