IDEA-146122 Wrong 'can produce NPE' after comparing with enum constant

java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/DfaMemoryStateImpl.java

@@ -30,6 +30,7 @@ import com.intellij.openapi.util.Pair;
 import com.intellij.openapi.util.UnorderedPair;
 import com.intellij.openapi.util.text.StringUtil;
 import com.intellij.psi.JavaTokenType;
+import com.intellij.psi.PsiEnumConstant;
 import com.intellij.psi.PsiPrimitiveType;
 import com.intellij.psi.PsiType;
 import com.intellij.psi.util.TypeConversionUtil;
@@ -833,7 +834,9 @@ public class DfaMemoryStateImpl implements DfaMemoryState {
       for (long encodedPair : myDistinctClasses.toArray()) {
         EqClass c1 = myEqClasses.get(low(encodedPair));
         EqClass c2 = myEqClasses.get(high(encodedPair));
-        if (c1.findConstant(false) != null && c2.findConstant(false) != null) {
+        DfaConstValue const1 = (DfaConstValue)c1.findConstant(false);
+        DfaConstValue const2 = (DfaConstValue)c2.findConstant(false);
+        if (const1 != null && const2 != null && !preserveConstantDistinction(const1.getValue(), const2.getValue())) {
           myDistinctClasses.remove(encodedPair);
         }
       }
@@ -851,6 +854,11 @@ public class DfaMemoryStateImpl implements DfaMemoryState {
     return true;
   }
 
+  private static boolean preserveConstantDistinction(final Object c1, final Object c2) {
+    return c1 == null && c2 instanceof PsiEnumConstant ||
+           c2 == null && c1 instanceof PsiEnumConstant;
+  }
+
   private boolean areCompatibleConstants(int i1, int i2) {
     Double dv1 = getDoubleValue(i1);
     return dv1 != null && dv1.equals(getDoubleValue(i2));

java/java-tests/testData/inspection/dataFlow/fixture/CompareToEnumConstant.java

@@ -0,0 +1,21 @@
+import org.jetbrains.annotations.Nullable;
+
+enum MyEnum {
+  ITEM,
+  ANOTHER_ITEM,
+  LOL_ITEM;
+}
+
+@SuppressWarnings({"UseOfSystemOutOrSystemErr", "unused"})
+class Main {
+  void foo(@Nullable MyEnum myEnum) {
+    if (myEnum == null) return;
+    switch (myEnum) {
+      case ITEM:
+      case ANOTHER_ITEM:
+        System.out.println(myEnum == MyEnum.ITEM ? "item" : "another");
+        myEnum.name();
+      default:
+    }
+  }
+}

java/java-tests/testSrc/com/intellij/codeInspection/DataFlowInspectionTest.java

@@ -94,6 +94,7 @@ public class DataFlowInspectionTest extends LightCodeInsightFixtureTestCase {
   public void testEqualsEnumConstant() throws Throwable { doTest(); }
   public void testSwitchEnumConstant() { doTest(); }
   public void testEnumConstantNotNull() throws Throwable { doTest(); }
+  public void testCompareToEnumConstant() throws Throwable { doTest(); }
   public void testEqualsConstant() throws Throwable { doTest(); }
   public void testDontSaveTypeValue() { doTest(); }
   public void testFinalLoopVariableInstanceof() throws Throwable { doTest(); }