overly strong type casts: ignore casts with functional expressions when expected type is not functional (IDEA-126764)

plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/com/siyeh/ig/abstraction/OverlyStrongTypeCastInspection.java

@@ -175,6 +175,9 @@ public class OverlyStrongTypeCastInspection extends BaseInspection {
       if (castTypeElement == null) {
         return;
       }
+      if (operand instanceof PsiFunctionalExpression && !LambdaUtil.isFunctionalType(expectedType)) {
+        return;
+      }
       registerError(castTypeElement, expectedType);
     }
 

plugins/InspectionGadgets/test/com/siyeh/igtest/abstraction/overly_strong_type_cast/OverlyStrongTypeCast.java

@@ -65,3 +65,9 @@ class SubClass2 extends SubClass{
     super.doSmth();
   }
 }
+
+class SAM {
+  {
+    Object runnable = (Runnable) () -> {};
+  }
+}

plugins/InspectionGadgets/testsrc/com/siyeh/ig/abstraction/OverlyStrongTypeCastInspectionTest.java

@@ -1,5 +1,6 @@
 package com.siyeh.ig.abstraction;
 
+import com.intellij.codeInspection.ex.LocalInspectionToolWrapper;
 import com.siyeh.ig.IGInspectionTestCase;
 
 public class OverlyStrongTypeCastInspectionTest extends IGInspectionTestCase {
@@ -7,6 +8,6 @@ public class OverlyStrongTypeCastInspectionTest extends IGInspectionTestCase {
   public void test() throws Exception {
     final OverlyStrongTypeCastInspection tool = new OverlyStrongTypeCastInspection();
     tool.ignoreInMatchingInstanceof = true;
-    doTest("com/siyeh/igtest/abstraction/overly_strong_type_cast", tool);
+    doTest("com/siyeh/igtest/abstraction/overly_strong_type_cast", new LocalInspectionToolWrapper(tool), "java 1.8");
   }
 }