From ca5da73932d54e98fd57a7d7c2e964cd89a87d0e Mon Sep 17 00:00:00 2001
From: Tagir Valeev <Tagir.Valeev@jetbrains.com>
Date: Mon, 11 Jan 2021 11:02:58 +0700
Subject: [PATCH] [java-dfa] Do not report variable is already assigned to this
 value for final field assignments (IDEA-258765)

GitOrigin-RevId: 0820f165cacbde79ced969d1ca8f1ba5910c99d6
---
 .../dataFlow/DataFlowInspectionBase.java      | 26 ++++++++++++-------
 .../dataFlow/fixture/RedundantAssignment.java |  9 +++++++
 2 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/DataFlowInspectionBase.java b/java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/DataFlowInspectionBase.java
index 6e70179e7f86..83bee52049cd 100644
--- a/java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/DataFlowInspectionBase.java
+++ b/java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/DataFlowInspectionBase.java
@@ -528,16 +528,22 @@ public abstract class DataFlowInspectionBase extends AbstractBaseJavaLocalInspec
       if (context instanceof PsiForStatement && PsiTreeUtil.isAncestor(((PsiForStatement)context).getInitialization(), expr, true)) {
         return;
       }
-      if (context instanceof PsiClassInitializer && expr instanceof PsiReferenceExpression) {
-        if (assignment != null) {
-          Object constValue = ExpressionUtils.computeConstantExpression(assignment.getRExpression());
-          if (constValue == PsiTypesUtil.getDefaultValue(expr.getType())) {
-            PsiReferenceExpression ref = (PsiReferenceExpression)expr;
-            PsiElement target = ref.resolve();
-            if (target instanceof PsiField &&
-                (((PsiField)target).hasModifierProperty(PsiModifier.STATIC) || ExpressionUtil.isEffectivelyUnqualified(ref)) &&
-                ((PsiField)target).getContainingClass() == ((PsiClassInitializer)context).getContainingClass()) {
-              return;
+      if (expr instanceof PsiReferenceExpression) {
+        PsiReferenceExpression ref = (PsiReferenceExpression)expr;
+        PsiField field = tryCast(ref.resolve(), PsiField.class);
+        if (field != null) {
+          // Final field assignment: even if redundant according to DFA model (e.g. this.field = null),
+          // it's necessary due to language semantics
+          if (field.hasModifierProperty(PsiModifier.FINAL)) return;
+          if (context instanceof PsiClassInitializer) {
+            if (assignment != null) {
+              Object constValue = ExpressionUtils.computeConstantExpression(assignment.getRExpression());
+              if (constValue == PsiTypesUtil.getDefaultValue(expr.getType())) {
+                if ((field.hasModifierProperty(PsiModifier.STATIC) || ExpressionUtil.isEffectivelyUnqualified(ref)) &&
+                    field.getContainingClass() == ((PsiClassInitializer)context).getContainingClass()) {
+                  return;
+                }
+              }
             }
           }
         }
diff --git a/java/java-tests/testData/inspection/dataFlow/fixture/RedundantAssignment.java b/java/java-tests/testData/inspection/dataFlow/fixture/RedundantAssignment.java
index 29677c1e0cbf..3f702ab8d438 100644
--- a/java/java-tests/testData/inspection/dataFlow/fixture/RedundantAssignment.java
+++ b/java/java-tests/testData/inspection/dataFlow/fixture/RedundantAssignment.java
@@ -76,3 +76,12 @@ class TestConstant {
     x = NONE;
   }
 }
+// IDEA-258765
+interface Intersection {
+  interface I { }
+  final class A { }
+  class Data<T extends A & I> {
+    final T value;
+    private Data(T value) { this.value = value; }
+  }
+}
\ No newline at end of file