[java] inline method: keep side effects free single returns (IDEA-280791)

avoid generating red code though when return value won't be a valid statement on its own

GitOrigin-RevId: ad768417d454192680b8d6692d8e1037b3ee9308

java/java-impl/src/com/intellij/refactoring/util/InlineUtil.java

@@ -1,4 +1,4 @@
-// Copyright 2000-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+// Copyright 2000-2021 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package com.intellij.refactoring.util;
 
 import com.intellij.codeInsight.BlockUtils;
@@ -508,7 +508,9 @@ public final class InlineUtil {
     for (PsiReturnStatement returnStatement : returnStatements) {
       final PsiExpression returnValue = returnStatement.getReturnValue();
       if (returnValue != null) {
-        List<PsiExpression> sideEffects = SideEffectChecker.extractSideEffectExpressions(returnValue);
+        List<PsiExpression> sideEffects = !singleReturnMethod(method) || !PsiUtil.isStatement(returnValue) 
+                                          ? SideEffectChecker.extractSideEffectExpressions(returnValue) 
+                                          : Collections.singletonList(returnValue);
         CommentTracker ct = new CommentTracker();
         sideEffects.forEach(ct::markUnchanged);
         PsiStatement[] statements = StatementExtractor.generateStatements(sideEffects, returnValue);
@@ -529,6 +531,14 @@ public final class InlineUtil {
     }
   }
 
+  private static boolean singleReturnMethod(PsiMethod method) {
+    int statementCount = Objects.requireNonNull(method.getBody()).getStatementCount();
+    if (!method.hasModifierProperty(PsiModifier.STATIC) && PsiTreeUtil.getContextOfType(method, PsiClass.class) != null) { //this declaration
+      statementCount--;
+    }
+    return statementCount <= 1;
+  }
+
   public static PsiExpression inlineInitializer(PsiVariable variable, PsiExpression initializer, PsiJavaCodeReferenceElement ref) {
     Project project = variable.getProject();
     PsiElementFactory factory = JavaPsiFacade.getElementFactory(project);

java/java-tests/testData/refactoring/inlineMethod/EmptyMethod.java

@@ -0,0 +1,8 @@
+class A {
+    {
+        g();
+    }
+    int <caret>g() {
+        return new Integer(0);
+    }
+}

java/java-tests/testData/refactoring/inlineMethod/EmptyMethod.java.after

@@ -0,0 +1,5 @@
+class A {
+    {
+        new Integer(0);
+    }
+}

java/java-tests/testSrc/com/intellij/java/refactoring/inline/InlineMethodTest.java

@@ -1,18 +1,4 @@
-/*
- * Copyright 2000-2017 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.
- */
+// Copyright 2000-2021 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package com.intellij.java.refactoring.inline;
 
 import com.intellij.JavaTestUtil;
@@ -65,6 +51,7 @@ public class InlineMethodTest extends LightRefactoringTestCase {
   public void testSideEffect() { doTest(); }
 
   public void testInlineWithTry() { doTest(); }
+  public void testEmptyMethod() { doTest(); }
 
   public void testVoidWithReturn() { doTest(); }
   public void testVoidWithReturn1() { doTest(); }