From 7f299c4f6c3aac04fe0b6ae91f1d8afef40cc536 Mon Sep 17 00:00:00 2001
From: Andreas Dangel <andreas.dangel@pmd-code.org>
Date: Fri, 4 Dec 2020 18:21:11 +0100
Subject: [PATCH] [java] CompareObjectsWithEquals: only allow this with equals
 (#2934)

---
 pmd-java/src/main/resources/category/java/errorprone.xml | 5 ++++-
 .../rule/errorprone/xml/CompareObjectsWithEquals.xml     | 9 +++++++--
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/pmd-java/src/main/resources/category/java/errorprone.xml b/pmd-java/src/main/resources/category/java/errorprone.xml
index 2e02d7e2f3..ae48bb363b 100644
--- a/pmd-java/src/main/resources/category/java/errorprone.xml
+++ b/pmd-java/src/main/resources/category/java/errorprone.xml
@@ -1114,7 +1114,10 @@ Use equals() to compare object references; avoid comparing them with ==.
         [not(pmd-java:typeIs('java.lang.Enum'))]
         [not(pmd-java:typeIs('java.lang.Class'))]) = 2
     ]
-    [not(PrimaryExpression[PrimaryPrefix/@ThisModifier = true()][not(PrimarySuffix)])]
+    [not(PrimaryExpression[PrimaryPrefix/@ThisModifier = true()]
+                          [not(PrimarySuffix)]
+                          [ancestor::MethodDeclaration[@Name = 'equals']])
+    ]
 ]]>
                 </value>
             </property>
diff --git a/pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/errorprone/xml/CompareObjectsWithEquals.xml b/pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/errorprone/xml/CompareObjectsWithEquals.xml
index 3a4b2dc453..893433e2e4 100644
--- a/pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/errorprone/xml/CompareObjectsWithEquals.xml
+++ b/pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/errorprone/xml/CompareObjectsWithEquals.xml
@@ -294,7 +294,8 @@ public class ClassWithFields {
 
     <test-code>
         <description>#2934 this and class should be ignored</description>
-        <expected-problems>0</expected-problems>
+        <expected-problems>1</expected-problems>
+        <expected-linenumbers>16</expected-linenumbers>
         <code><![CDATA[
 package net.sourceforge.pmd.lang.java.rule.errorprone.compareobjectswithequals;
 
@@ -302,13 +303,17 @@ public class ClassWithFields {
     private Object a;
     private Object b;
 
-    void test(Object o) {
+    public boolean equals(Object o) {
         if (this == o) { } // should be allowed, since this is a often used pattern in Object::equals.
         // comparing class instances is ok
         if (o.getClass() == a.getClass()) { }
         if (this.getClass() == this.a.getClass()) { }
         if (Object.class == a.getClass()) { }
     }
+
+    void test(Object o) {
+        if (this == o) { } // this is not allowed here, only in equals
+    }
 }
         ]]></code>
     </test-code>