Reject operator as a full declaration name, closes #846

Author: hsutter

regression-tests/test-results/version

@@ -1,5 +1,5 @@
 
-cppfront compiler v0.3.0   Build 9104:1043
+cppfront compiler v0.3.0   Build 9104:1118
 Copyright(c) Herb Sutter   All rights reserved
 
 SPDX-License-Identifier: CC-BY-NC-ND-4.0

source/build.info

@@ -1 +1 @@
-"9104:1043"
+"9104:1118"

source/sema.h

@@ -1048,6 +1048,14 @@ class sema
     auto check(declaration_node const& n)
         -> bool
     {
+        if (n.has_name("operator")) {
+            errors.emplace_back(
+                n.position(),
+                "the name 'operator' is incomplete - did you mean to write an overloaded operator name like 'operator*' or 'operator++'?"
+            );
+            return false;
+        }
+
         //  An object of deduced type must have an initializer
         if (
             n.is_object()