From 5f6c927e1a68f9495ee147653493b835450aa134 Mon Sep 17 00:00:00 2001
From: peter <peter@jetbrains.com>
Date: Sun, 28 Oct 2012 21:01:04 +0100
Subject: [PATCH] highlight not-null == null as always false (IDEA-88777)

---
 .../dataFlow/DfaMemoryStateImpl.java            | 17 +++++++++++++----
 .../dataFlow/fixture/EqualsNotNull.java         |  5 ++++-
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/java/java-impl/src/com/intellij/codeInspection/dataFlow/DfaMemoryStateImpl.java b/java/java-impl/src/com/intellij/codeInspection/dataFlow/DfaMemoryStateImpl.java
index d39fe8ee47a5..7ba70d51f555 100644
--- a/java/java-impl/src/com/intellij/codeInspection/dataFlow/DfaMemoryStateImpl.java
+++ b/java/java-impl/src/com/intellij/codeInspection/dataFlow/DfaMemoryStateImpl.java
@@ -612,10 +612,8 @@ public class DfaMemoryStateImpl implements DfaMemoryState {
       return true;
     }
 
-    if (dfaRight == myFactory.getConstFactory().getNull() && dfaLeft instanceof DfaVariableValue) {
-      final DfaVariableState varState = getVariableState((DfaVariableValue)dfaLeft);
-      if (varState.isNotNull()) return isNegated;
-      varState.setNullable(!isNegated);
+    if (isNull(dfaRight) && compareVariableWithNull(dfaLeft) || isNull(dfaLeft) && compareVariableWithNull(dfaRight)) {
+      return isNegated;
     }
 
     if (dfaLeft instanceof DfaUnknownValue || dfaRight instanceof DfaUnknownValue) return true;
@@ -623,6 +621,17 @@ public class DfaMemoryStateImpl implements DfaMemoryState {
     return applyEquivalenceRelation(dfaRelation, dfaLeft, dfaRight);
   }
 
+  private boolean compareVariableWithNull(DfaValue val) {
+    if (val instanceof DfaVariableValue) {
+      DfaVariableValue dfaVar = (DfaVariableValue)val;
+      if (isNotNull(dfaVar)) {
+        return true;
+      }
+      getVariableState(dfaVar).setNullable(true);
+    }
+    return false;
+  }
+
   private boolean applyEquivalenceRelation(DfaRelationValue dfaRelation, DfaValue dfaLeft, DfaValue dfaRight) {
     boolean isNegated = dfaRelation.isNonEquality();
     if (!isNegated && !dfaRelation.isEquality()) {
diff --git a/java/java-tests/testData/inspection/dataFlow/fixture/EqualsNotNull.java b/java/java-tests/testData/inspection/dataFlow/fixture/EqualsNotNull.java
index 4b6277ad93aa..0459c905a130 100644
--- a/java/java-tests/testData/inspection/dataFlow/fixture/EqualsNotNull.java
+++ b/java/java-tests/testData/inspection/dataFlow/fixture/EqualsNotNull.java
@@ -62,7 +62,10 @@ public class Main {
     if (val != null) {
       return val;
     }
-    if (defVal == val) {
+    if (<warning descr="Condition 'defVal == val' is always 'false'">defVal == val</warning>) {
+      return val;
+    }
+    if (<warning descr="Condition 'val == defVal' is always 'false'">val == defVal</warning>) {
       return val;
     }
     if (defVal.equals(val)) {