Issue #1530: Detect nested enums marked as static in RedundantModifier

check

src/main/java/com/puppycrawl/tools/checkstyle/checks/modifier/RedundantModifierCheck.java

@@ -31,7 +31,8 @@ import com.puppycrawl.tools.checkstyle.api.TokenTypes;
 /**
  * Checks for redundant modifiers in interface and annotation definitions.
  * Checks for non public class constructor and enum constructor redundant modifier.
- * Also checks for redundant final modifiers on methods of final classes
+ * Checks for redundant final modifiers on methods of final classes.
+ * Checks for redundant static modifiers on nested enums.
  *
  * <p>Examples:</p>
  *
@@ -74,6 +75,7 @@ import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  *
  * @author lkuehne
  * @author <a href="mailto:piotr.listkiewicz@gmail.com">liscju</a>
+ * @author Vladislav Lisetskiy
  */
 public class RedundantModifierCheck
     extends Check {
@@ -128,6 +130,9 @@ public class RedundantModifierCheck
                 checkClassConstructorModifiers(ast);
             }
         }
+        else if (ast.getType() == TokenTypes.ENUM_DEF) {
+            checkEnumDef(ast);
+        }
         else if (isInterfaceOrAnnotationMember(ast)) {
             processInterfaceOrAnnotation(ast);
         }
@@ -167,6 +172,24 @@ public class RedundantModifierCheck
         }
     }
 
+    /**
+     * Checks whether enum has proper modifiers.
+     * @param ast enum definition.
+     */
+    private void checkEnumDef(DetailAST ast) {
+        if (isInterfaceOrAnnotationMember(ast)) {
+            processInterfaceOrAnnotation(ast);
+        }
+        else if (ast.getParent() != null) {
+            final DetailAST modifiers = ast.findFirstToken(TokenTypes.MODIFIERS);
+            final DetailAST staticModifier = modifiers.findFirstToken(TokenTypes.LITERAL_STATIC);
+            if (staticModifier != null) {
+                log(staticModifier.getLineNo(), staticModifier.getColumnNo(),
+                        MSG_KEY, staticModifier.getText());
+            }
+        }
+    }
+
     /**
      * Do validation of interface of annotation.
      * @param ast token AST

src/test/java/com/puppycrawl/tools/checkstyle/checks/modifier/RedundantModifierTest.java

@@ -137,4 +137,17 @@ public class RedundantModifierTest
         int[] expected = ArrayUtils.EMPTY_INT_ARRAY;
         Assert.assertArrayEquals(expected, actual);
     }
+
+    @Test
+    public void testNestedStaticEnum() throws Exception {
+        final DefaultConfiguration checkConfig =
+                createCheckConfig(RedundantModifierCheck.class);
+        final String[] expected = {
+            "4:5: " + getCheckMessage(MSG_KEY, "static"),
+            "8:9: " + getCheckMessage(MSG_KEY, "static"),
+            "12:9: " + getCheckMessage(MSG_KEY, "static"),
+        };
+        verify(checkConfig, getPath("InputRedundantStatic"
+            + "ModifierInNestedEnum.java"), expected);
+    }
 }

src/test/resources/com/puppycrawl/tools/checkstyle/InputRedundantStaticModifierInNestedEnum.java

@@ -0,0 +1,14 @@
+package com.puppycrawl.tools.checkstyle;
+
+public class InputRedundantStaticModifierInNestedEnum {
+    static enum NestedEnumWithRedundantStatic {} // violation
+
+    enum CorrectNestedEnum {
+        VAL;
+        static enum NestedEnumWithRedundantStatic {} // violation
+    }
+    
+    interface NestedInterface {
+        static enum NestedEnumWithRedundantStatic {} // violation
+    }
+}

src/xdocs/config_modifier.xml

@@ -98,13 +98,17 @@
           Checks for redundant modifiers in:
         </p>
         <ol>
-          <li>interface and annotation definitions,</li>
-          <li>the final modifier on methods of final classes, and </li>
+          <li>Interface and annotation definitions.</li>
+          <li>Final modifier on methods of final classes.</li>
           <li>
-            inner <code>interface</code> declarations that are declared
+            Inner <code>interface</code> declarations that are declared
+            as <code>static</code>.
+          </li>
+          <li>Class constructors.</li>
+          <li>
+            Nested <code>enum</code> definitions that are declared
             as <code>static</code>.
           </li>
-          <li>class constructors</li>
         </ol>
         <p>
           Rationale: The Java Language Specification strongly
@@ -134,6 +138,10 @@
           modifier on the method of a final class is redundant.
         </p>
 
+        <p>
+          Nested <code>enum</code> types are always static by default.
+        </p>
+
         <p>
           Public modifier for constructors in non-public non-protected classes
           is always obsolete: