IDEA-118774 Warning about lack of subclasses when using lambdas

plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/com/siyeh/ig/psiutils/InheritanceUtil.java

@@ -23,8 +23,10 @@ import com.intellij.psi.PsiTypeParameter;
 import com.intellij.psi.search.GlobalSearchScope;
 import com.intellij.psi.search.SearchScope;
 import com.intellij.psi.search.searches.ClassInheritorsSearch;
+import com.intellij.psi.search.searches.FunctionalExpressionSearch;
 import com.intellij.util.Processor;
 import com.intellij.util.Query;
+import org.jetbrains.annotations.NotNull;
 
 import java.util.concurrent.atomic.AtomicInteger;
 
@@ -75,8 +77,9 @@ public class InheritanceUtil {
     return result[0];
   }
 
-  public static boolean hasImplementation(PsiClass aClass) {
+  public static boolean hasImplementation(@NotNull PsiClass aClass) {
     final SearchScope scope = GlobalSearchScope.projectScope(aClass.getProject());
+    if (aClass.isInterface() && FunctionalExpressionSearch.search(aClass, scope).findFirst() != null) return true;
     final Query<PsiClass> search = ClassInheritorsSearch.search(aClass, scope, true, true);
     return !search.forEach(new Processor<PsiClass>() {
       @Override

plugins/InspectionGadgets/test/com/siyeh/igtest/inheritance/interface_never_implemented/InterfaceNeverImplemented.java

@@ -5,4 +5,14 @@ interface InterfaceWithOnlyOneDirectInheritor {}
 class Inheritor implements InterfaceWithOnlyOneDirectInheritor {}
 interface InterfaceWithTwoInheritors {}
 class Inheritor1 implements InterfaceWithTwoInheritors {}
-class Inheritor2 implements InterfaceWithTwoInheritors {}
+class Inheritor2 implements InterfaceWithTwoInheritors {}
+
+interface SAM {
+  void foo();
+}
+
+class LambdaCall {
+  {
+    SAM sam = () -> {};
+  }
+}

plugins/InspectionGadgets/testsrc/com/siyeh/ig/inheritance/InterfaceNeverImplementedInspectionTest.java

@@ -1,10 +1,29 @@
 package com.siyeh.ig.inheritance;
 
+import com.intellij.codeInspection.ex.LocalInspectionToolWrapper;
+import com.intellij.openapi.projectRoots.Sdk;
+import com.intellij.openapi.roots.LanguageLevelProjectExtension;
+import com.intellij.pom.java.LanguageLevel;
+import com.intellij.testFramework.IdeaTestUtil;
 import com.siyeh.ig.IGInspectionTestCase;
 
 public class InterfaceNeverImplementedInspectionTest extends IGInspectionTestCase {
 
   public void test() throws Exception {
-    doTest("com/siyeh/igtest/inheritance/interface_never_implemented", new InterfaceNeverImplementedInspection());
+    final LanguageLevelProjectExtension levelProjectExtension = LanguageLevelProjectExtension.getInstance(getProject());
+    final LanguageLevel level = levelProjectExtension.getLanguageLevel();
+    try {
+      levelProjectExtension.setLanguageLevel(LanguageLevel.JDK_1_8);
+      doTest("com/siyeh/igtest/inheritance/interface_never_implemented",
+             new LocalInspectionToolWrapper(new InterfaceNeverImplementedInspection()), "java 1.8");
+    }
+    finally {
+      levelProjectExtension.setLanguageLevel(level);
+    }
+  }
+
+  @Override
+  protected Sdk getTestProjectSdk() {
+    return IdeaTestUtil.getMockJdk18();
   }
 }