convert abstract class to interface when constructor is empty (IDEA-164278)

plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/com/siyeh/ig/classlayout/ClassMayBeInterfaceInspection.java

@@ -111,6 +111,10 @@ public class ClassMayBeInterfaceInspection extends BaseInspection {
 
     private static void changeClassToInterface(PsiClass aClass) {
       for (PsiMethod method : aClass.getMethods()) {
+        if (isEmptyConstructor(method)) {
+          method.delete();
+          continue;
+        }
         PsiUtil.setModifierProperty(method, PsiModifier.PUBLIC, false);
         if (method.hasModifierProperty(PsiModifier.STATIC) || method.hasModifierProperty(PsiModifier.ABSTRACT)) {
           continue;
@@ -193,6 +197,16 @@ public class ClassMayBeInterfaceInspection extends BaseInspection {
     return new ClassMayBeInterfaceVisitor();
   }
 
+  private static boolean isEmptyConstructor(@NotNull PsiMethod method) {
+    if (method.isConstructor()) {
+      PsiCodeBlock body = method.getBody();
+      if (body != null && body.getStatements().length == 0 && method.getDocComment() == null) {
+        return true;
+      }
+    }
+    return false;
+  }
+
   private class ClassMayBeInterfaceVisitor extends BaseInspectionVisitor {
 
     @Override
@@ -250,6 +264,9 @@ public class ClassMayBeInterfaceInspection extends BaseInspection {
     private boolean allMethodsPublicAbstract(PsiClass aClass) {
       final PsiMethod[] methods = aClass.getMethods();
       for (final PsiMethod method : methods) {
+        if (isEmptyConstructor(method)) {
+          continue;
+        }
         if (!method.hasModifierProperty(PsiModifier.ABSTRACT) &&
             (!reportClassesWithNonAbstractMethods || !PsiUtil.isLanguageLevel8OrHigher(aClass))) {
           return false;

plugins/InspectionGadgets/test/com/siyeh/igfixes/classlayout/class_may_be_interface/DefaultConstructor.after.java

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2000-2016 JetBrains s.r.o.
+ *
+ * Licensed 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 com.siyeh.igfixes.classlayout.class_may_be_interface;
+
+interface ConvertMe {
+}

plugins/InspectionGadgets/test/com/siyeh/igfixes/classlayout/class_may_be_interface/DefaultConstructor.java

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2000-2016 JetBrains s.r.o.
+ *
+ * Licensed 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 com.siyeh.igfixes.classlayout.class_may_be_interface;
+
+abstract class <caret>ConvertMe {
+  public ConvertMe() {}
+}

plugins/InspectionGadgets/testsrc/com/siyeh/ig/fixes/classlayout/ClassMayBeInterfaceFixTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2015 JetBrains s.r.o.
+ * Copyright 2000-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -36,4 +36,7 @@ public class ClassMayBeInterfaceFixTest extends IGQuickFixesTestCase {
 
   public void testConvertMe() { doTest(); }
 
+  public void testDefaultConstructor() throws Exception {
+    doTest();
+  }
 }