GROOVY-8066: protected fields should be disallowed in traits (closes groovy#482)

Author: paulk-asert

src/main/org/codehaus/groovy/transform/trait/TraitASTTransformation.java

@@ -386,6 +386,12 @@ private static boolean methodNeedsReplacement(ClassNode classNode, MethodNode m)
 
 
     private void processField(final FieldNode field, final MethodNode initializer, final MethodNode staticInitializer, final ClassNode fieldHelper, final ClassNode trait, final Set<String> knownFields) {
+        if (field.isProtected()) {
+            unit.addError(new SyntaxException("Cannot have protected field in a trait (" + trait.getName() + "#" + field.getName() + ")",
+                    field.getLineNumber(), field.getColumnNumber()));
+            return;
+        }
+
         Expression initialExpression = field.getInitialExpression();
         MethodNode selectedMethod = field.isStatic()?staticInitializer:initializer;
         if (initialExpression != null && !field.isFinal()) {

src/test/groovy/bugs/Groovy8066Bug.groovy

@@ -0,0 +1,33 @@
+/*
+ *  Licensed to the Apache Software Foundation (ASF) under one
+ *  or more contributor license agreements.  See the NOTICE file
+ *  distributed with this work for additional information
+ *  regarding copyright ownership.  The ASF licenses this file
+ *  to you under the Apache License, Version 2.0 (the
+ *  "License"); you may not use this file except in compliance
+ *  with the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing,
+ *  software distributed under the License is distributed on an
+ *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ *  KIND, either express or implied.  See the License for the
+ *  specific language governing permissions and limitations
+ *  under the License.
+ */
+package groovy.bugs
+
+import gls.CompilableTestSupport
+
+class Groovy8066Bug extends CompilableTestSupport {
+    void testTraitWithProtectedFieldShouldGiveCompileError() {
+        def message = shouldNotCompile """
+            trait Foo {
+                protected String bar
+            }
+            class Baz implements Foo { }
+        """
+        assert message.contains('Cannot have protected field in a trait')
+    }
+}