return lambda folding in some cases where anonymous->lambda conversion is anyway impossible

java/java-psi-impl/src/com/intellij/codeInsight/folding/impl/JavaFoldingBuilderBase.java

@@ -807,7 +807,7 @@ public abstract class JavaFoldingBuilderBase extends CustomFoldingBuilder implem
         if (argumentList != null && argumentList.getExpressions().length == 0) {
           final PsiMethod[] methods = anonymousClass.getMethods();
           PsiClass baseClass = anonymousClass.getBaseClassType().resolve();
-          if (hasOnlyOneLambdaMethod(anonymousClass, !quick) && seemsLikeLambda(baseClass) && !PsiUtil.isLanguageLevel8OrHigher(anonymousClass)) {
+          if (hasOnlyOneLambdaMethod(anonymousClass, !quick) && seemsLikeLambda(baseClass)) {
             final PsiMethod method = methods[0];
             final PsiCodeBlock body = method.getBody();
             if (body != null) {
@@ -841,6 +841,8 @@ public abstract class JavaFoldingBuilderBase extends CustomFoldingBuilder implem
               String type = quick ? "" : getOptionalLambdaType(anonymousClass, expression);
               String methodName = quick || !isImplementingLambdaMethod(baseClass) ? method.getName() : "";
 
+              if (StringUtil.isEmpty(methodName) && PsiUtil.isLanguageLevel8OrHigher(anonymousClass)) return false;
+
               final String params = StringUtil.join(method.getParameterList().getParameters(), new Function<PsiParameter, String>() {
                 @Override
                 public String fun(final PsiParameter psiParameter) {

java/java-tests/testSrc/com/intellij/codeInsight/folding/JavaFolding8Test.groovy

@@ -0,0 +1,86 @@
+/*
+ * 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.intellij.codeInsight.folding
+
+import com.intellij.codeInsight.folding.impl.CodeFoldingManagerImpl
+import com.intellij.codeInsight.folding.impl.JavaCodeFoldingSettingsImpl
+import com.intellij.codeInsight.folding.impl.JavaFoldingBuilder
+import com.intellij.openapi.editor.ex.FoldingModelEx
+import com.intellij.openapi.editor.impl.FoldingModelImpl
+import com.intellij.testFramework.LightProjectDescriptor
+import com.intellij.testFramework.fixtures.LightCodeInsightFixtureTestCase
+/**
+ * @author peter
+ */
+public class JavaFolding8Test extends LightCodeInsightFixtureTestCase {
+
+  def JavaCodeFoldingSettingsImpl myFoldingSettings
+  def JavaCodeFoldingSettingsImpl myFoldingStateToRestore
+
+  @Override
+  protected LightProjectDescriptor getProjectDescriptor() {
+    return JAVA_8
+  }
+
+  @Override
+  public void setUp() {
+    super.setUp()
+    myFoldingSettings = JavaCodeFoldingSettings.instance as JavaCodeFoldingSettingsImpl
+    myFoldingStateToRestore = new JavaCodeFoldingSettingsImpl()
+    myFoldingStateToRestore.loadState(myFoldingSettings)
+  }
+
+  @Override
+  protected void tearDown() {
+    myFoldingSettings.loadState(myFoldingStateToRestore)
+    super.tearDown()
+  }
+
+  public void "test no plain lambda folding where anonymous class can be real lambda but fold otherwise"() {
+    myFixture.addClass('interface Runnable2 { void run(); }')
+    myFixture.addClass('abstract class MyAction { public void run(); public void update() {} }')
+    def text = """\
+class Test {
+  void test() {
+    Runnable r = new Runnable2() {
+      public void run() {
+        System.out.println();
+      }
+    };
+    MyAction action = new MyAction() {
+      public void run() {
+        System.out.println();
+      }
+    }
+  }
+}
+"""
+    configure text
+    def foldingModel = myFixture.editor.foldingModel as FoldingModelImpl
+
+    assert foldingModel.getCollapsedRegionAtOffset(text.indexOf("MyAction(")).placeholderText == 'run() ' + JavaFoldingBuilder.rightArrow + ' { '
+    assert !foldingModel.getCollapsedRegionAtOffset(text.indexOf("Runnable2("))
+  }
+
+  private def configure(String text) {
+    myFixture.configureByText("a.java", text)
+    CodeFoldingManagerImpl.getInstance(getProject()).buildInitialFoldings(myFixture.editor);
+    def foldingModel = myFixture.editor.foldingModel as FoldingModelEx
+    foldingModel.rebuild()
+    myFixture.doHighlighting()
+  }
+
+}