[java-dfa] IDEA-277611 Enhance enum support in Java DFA (this in enum classes support)

GitOrigin-RevId: 078ff8adc32f123e3d8a4c874a028b3fc6a257a3

java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/jvm/descriptors/ThisDescriptor.java

@@ -4,6 +4,8 @@ package com.intellij.codeInspection.dataFlow.jvm.descriptors;
 import com.intellij.codeInsight.Nullability;
 import com.intellij.codeInspection.dataFlow.Mutability;
 import com.intellij.codeInspection.dataFlow.MutationSignature;
+import com.intellij.codeInspection.dataFlow.TypeConstraint;
+import com.intellij.codeInspection.dataFlow.TypeConstraints;
 import com.intellij.codeInspection.dataFlow.types.DfType;
 import com.intellij.codeInspection.dataFlow.types.DfTypes;
 import com.intellij.codeInspection.dataFlow.value.DfaValueFactory;
@@ -81,10 +83,14 @@ public final class ThisDescriptor extends PsiVarDescriptor {
     if (context != null) {
       PsiMethod method = ObjectUtils.tryCast(context.getParent(), PsiMethod.class);
       if (method != null && myQualifier.equals(method.getContainingClass())) {
+        if (myQualifier instanceof PsiEnumConstantInitializer) {
+          PsiEnumConstant constant = ((PsiEnumConstantInitializer)myQualifier).getEnumConstant();
+          return DfTypes.referenceConstant(constant, TypeConstraints.exactClass(myQualifier));
+        }
         if (!method.isConstructor() && MutationSignature.fromMethod(method).preservesThis()) {
           return dfType.meet(Mutability.UNMODIFIABLE_VIEW.asDfType());
         }
-        else if (method.isConstructor()) {
+        if (method.isConstructor()) {
           return dfType.meet(DfTypes.LOCAL_OBJECT);
         }
       }

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

@@ -0,0 +1,9 @@
+public class ThisInEnumSubclass {
+  enum MyEnum {
+    A, B, C {
+      void test() {
+        if (<warning descr="Condition 'this == C' is always 'true'">this == C</warning>) {}
+      }
+    }
+  }
+}

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

@@ -712,4 +712,5 @@ public class DataFlowInspectionTest extends DataFlowInspectionTestCase {
   public void testTempVarsInContracts() { doTest(); }
   public void testNestedUnrolledLoopNotComplex() { doTest(); }
   public void testEnumOrdinal() { doTest(); }
+  public void testThisInEnumSubclass() { doTest(); }
 }