From 3db80a01df7e8012065eadb809fdd64542e8e760 Mon Sep 17 00:00:00 2001
From: Bas Leijdekkers <basleijdekkers@gmail.com>
Date: Mon, 18 Sep 2017 15:39:38 +0200
Subject: [PATCH] IG: a != b and b != a and other commutative binary operations
 are equivalent

---
 .../siyeh/ig/psiutils/EquivalenceChecker.java  |  9 ++++++---
 .../siyeh/ig/psiutils/ParenthesesUtils.java    | 18 ++++++++++++------
 .../DuplicateCondition.java                    |  6 ++++++
 3 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/com/siyeh/ig/psiutils/EquivalenceChecker.java b/plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/com/siyeh/ig/psiutils/EquivalenceChecker.java
index 5ceea468a41a..102287ad0aca 100644
--- a/plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/com/siyeh/ig/psiutils/EquivalenceChecker.java
+++ b/plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/com/siyeh/ig/psiutils/EquivalenceChecker.java
@@ -899,14 +899,17 @@ public class EquivalenceChecker {
     final PsiExpression right2 = binaryExpression2.getROperand();
     if (!tokenType1.equals(tokenType2)) {
       // process matches like "a < b" and "b > a"
-      DfaRelationValue.RelationType rel1 = DfaRelationValue.RelationType.fromElementType(tokenType1);
-      DfaRelationValue.RelationType rel2 = DfaRelationValue.RelationType.fromElementType(tokenType2);
+      final DfaRelationValue.RelationType rel1 = DfaRelationValue.RelationType.fromElementType(tokenType1);
+      final DfaRelationValue.RelationType rel2 = DfaRelationValue.RelationType.fromElementType(tokenType2);
       if(rel1 != null && rel2 != null && rel1.getFlipped() == rel2) {
         return expressionsAreEquivalent(new PsiExpression[] {left1, right1}, new PsiExpression[] {right2, left2});
       }
       return EXACT_MISMATCH;
     }
-    return expressionsAreEquivalent(new PsiExpression[] {left1, right1}, new PsiExpression[] {left2, right2});
+    final Match match = expressionsAreEquivalent(new PsiExpression[] {left1, right1}, new PsiExpression[] {left2, right2});
+    return match == EXACT_MISMATCH && ParenthesesUtils.isCommutativeOperation(binaryExpression1)
+           ? expressionsAreEquivalent(new PsiExpression[]{left1, right1}, new PsiExpression[]{right2, left2})
+           : match;
   }
 
   protected Match assignmentExpressionsMatch(@NotNull PsiAssignmentExpression assignmentExpression1, @NotNull PsiAssignmentExpression assignmentExpression2) {
diff --git a/plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/com/siyeh/ig/psiutils/ParenthesesUtils.java b/plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/com/siyeh/ig/psiutils/ParenthesesUtils.java
index 47193e778894..a75163717166 100644
--- a/plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/com/siyeh/ig/psiutils/ParenthesesUtils.java
+++ b/plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/com/siyeh/ig/psiutils/ParenthesesUtils.java
@@ -100,12 +100,18 @@ public class ParenthesesUtils {
   }
 
   public static boolean isCommutativeOperator(@NotNull IElementType token) {
-    return !(token.equals(JavaTokenType.MINUS) ||
-             token.equals(JavaTokenType.DIV) ||
-             token.equals(JavaTokenType.PERC) ||
-             token.equals(JavaTokenType.LTLT) ||
-             token.equals(JavaTokenType.GTGT) ||
-             token.equals(JavaTokenType.GTGTGT));
+    return token == JavaTokenType.PLUS || token == JavaTokenType.ASTERISK ||
+           token == JavaTokenType.EQEQ || token == JavaTokenType.NE ||
+           token == JavaTokenType.AND || token == JavaTokenType.OR || token == JavaTokenType.XOR;
+  }
+
+  public static boolean isCommutativeOperation(PsiPolyadicExpression expression) {
+    final IElementType tokenType = expression.getOperationTokenType();
+    if (!isCommutativeOperator(tokenType)) {
+      return false;
+    }
+    final PsiType type = expression.getType();
+    return type != null && !type.equalsToText(CommonClassNames.JAVA_LANG_STRING);
   }
 
   public static boolean isAssociativeOperation(PsiPolyadicExpression expression) {
diff --git a/plugins/InspectionGadgets/test/com/siyeh/igtest/controlflow/duplicate_condition/DuplicateCondition.java b/plugins/InspectionGadgets/test/com/siyeh/igtest/controlflow/duplicate_condition/DuplicateCondition.java
index 05e6c05c7b46..4e45dca2b621 100644
--- a/plugins/InspectionGadgets/test/com/siyeh/igtest/controlflow/duplicate_condition/DuplicateCondition.java
+++ b/plugins/InspectionGadgets/test/com/siyeh/igtest/controlflow/duplicate_condition/DuplicateCondition.java
@@ -33,6 +33,12 @@ public class DuplicateCondition {
       System.out.println("second");
       return;
     }
+    if (<warning descr="Duplicate condition 'x != y'">x != y</warning>) {
+      return;
+    }
+    if ((<warning descr="Duplicate condition '(y) != x'">(y) != x</warning>)) {
+      return;
+    }
   }
 
   public void foo()