redundant cast: do not raise if result in bad return type in lambda expression (IDEA-138927)

java/java-psi-api/src/com/intellij/psi/util/RedundantCastUtil.java

@@ -425,10 +425,14 @@ public class RedundantCastUtil {
       PsiTypeCastExpression castExpression = computeCastExpression.fun(newReturnExpression);
       PsiExpression castOperand = castExpression.getOperand();
       if (castOperand == null) return;
-      castExpression.replace(castOperand);
+      castOperand = (PsiExpression)castExpression.replace(castOperand);
       final PsiType functionalInterfaceType = lambdaExpression.getFunctionalInterfaceType();
       if (interfaceType.equals(functionalInterfaceType)) {
-        addToResults(returnExpression);
+        final PsiType interfaceReturnType = LambdaUtil.getFunctionalInterfaceReturnType(interfaceType);
+        final PsiType castExprType = castOperand.getType();
+        if (interfaceReturnType != null && castExprType != null && interfaceReturnType.isAssignableFrom(castExprType)) {
+          addToResults(returnExpression);
+        }
       }
     }
 

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/lambda/redundantCast/PreventBadReturnTypeInReturnExpression.java

@@ -0,0 +1,7 @@
+import java.util.stream.Stream;
+
+class Test {
+  public void filterByBoolean(Stream<Object[]> stream) {
+    stream.filter(it -> (Boolean) it[0]);
+  }
+}

java/java-tests/testSrc/com/intellij/codeInsight/daemon/lambda/LambdaRedundantCastTest.java

@@ -38,6 +38,8 @@ public class LambdaRedundantCastTest extends LightDaemonAnalyzerTestCase {
   public void testSer() { doTest(); }
   public void testLambdaReturnExpressions() { doTest(); }
   public void testLambdaReturnExpressions1() { doTest(); }
+  public void testPreventBadReturnTypeInReturnExpression() { doTest(); }
+
   private void doTest() {
     doTest(BASE_PATH + "/" + getTestName(false) + ".java", true, false);
   }