redundant cast: don't highlight conditional with functional branches (IDEA-161971)

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

@@ -807,6 +807,13 @@ public class RedundantCastUtil {
         }
       }
     }
+    else if (stripParenthesisOperand instanceof PsiConditionalExpression) {
+      final PsiExpression thenExpr = PsiUtil.skipParenthesizedExprDown(((PsiConditionalExpression)stripParenthesisOperand).getThenExpression());
+      final PsiExpression elseExpr = PsiUtil.skipParenthesizedExprDown(((PsiConditionalExpression)stripParenthesisOperand).getElseExpression());
+      if (thenExpr instanceof PsiFunctionalExpression || elseExpr instanceof PsiFunctionalExpression) {
+        return true;
+      }
+    }
 
     PsiElement parent = typeCast.getParent();
     while(parent instanceof PsiParenthesizedExpression) parent = parent.getParent();

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

@@ -0,0 +1,18 @@
+import java.util.function.Function;
+
+class Main {
+  public static void main(String[] args) {
+    Test test = new Test();
+    ((Function<String, Long>)(args.length == 2 ? (<error descr="Method reference expression is not expected here">test::foo</error>) : <error descr="Method reference expression is not expected here">test::bar</error>)).apply("");
+  }
+
+  static class Test {
+    public long foo(String s) {
+      return 0;
+    }
+
+    public long bar(String s) {
+      return 0;
+    }
+  }
+}

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

@@ -84,6 +84,10 @@ public class LambdaRedundantCastTest extends LightDaemonAnalyzerTestCase {
     doTest();
   }
 
+  public void testInvalidConditional() throws Exception {
+    doTest();
+  }
+
   private void doTest() {
     doTest(BASE_PATH + "/" + getTestName(false) + ".java", true, false);
   }