new "'equals()' called on itself" inspection

plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/META-INF/InspectionGadgets.xml

@@ -202,6 +202,10 @@
                      key="equals.between.inconvertible.types.display.name" groupBundle="messages.InspectionsBundle"
                      groupKey="group.names.probable.bugs" enabledByDefault="true" level="WARNING"
                      implementationClass="com.siyeh.ig.bugs.EqualsBetweenInconvertibleTypesInspection"/>
+    <localInspection language="JAVA" shortName="EqualsWithItself" bundle="com.siyeh.InspectionGadgetsBundle"
+                     key="equals.with.itself.display.name" groupBundle="messages.InspectionsBundle"
+                     groupKey="group.names.probable.bugs" enabledByDefault="true" level="WARNING"
+                     implementationClass="com.siyeh.ig.bugs.EqualsWithItselfInspection"/>
     <localInspection language="JAVA" suppressId="NonFinalFieldReferenceInEquals" shortName="EqualsUsesNonFinalVariable"
                      bundle="com.siyeh.InspectionGadgetsBundle" key="non.final.field.in.equals.display.name"
                      groupBundle="messages.InspectionsBundle" groupKey="group.names.probable.bugs" enabledByDefault="false" level="WARNING"

plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/com/siyeh/InspectionGadgetsBundle.properties

@@ -2101,3 +2101,5 @@ assignment.to.lambda.parameter.problem.descriptor=Assignment to lambda parameter
 class.with.only.private.constructors.display.name=Class with only 'private' constructors should be declared 'final'
 class.with.only.private.constructors.problem.descriptor=Class <code>#ref</code> with only 'private' constructors should be declared 'final'
 property.value.set.to.itself.display.name=Property value set to itself
+equals.with.itself.display.name='equals()' called on itself
+equals.with.itself.problem.descriptor=Identical qualifier and argument to <code>#ref()</code> call

plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/com/siyeh/ig/bugs/EqualsWithItselfInspection.java

@@ -0,0 +1,75 @@
+/*
+ * Copyright 2000-2014 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.siyeh.ig.bugs;
+
+import com.intellij.psi.PsiExpression;
+import com.intellij.psi.PsiExpressionList;
+import com.intellij.psi.PsiMethodCallExpression;
+import com.intellij.psi.PsiReferenceExpression;
+import com.siyeh.InspectionGadgetsBundle;import com.siyeh.ig.BaseInspection;
+import com.siyeh.ig.BaseInspectionVisitor;
+import com.siyeh.ig.psiutils.EquivalenceChecker;
+import com.siyeh.ig.psiutils.MethodCallUtils;
+import com.siyeh.ig.psiutils.SideEffectChecker;
+import org.jetbrains.annotations.Nls;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * @author Bas Leijdekkers
+ */
+public class EqualsWithItselfInspection extends BaseInspection {
+  @Nls
+  @NotNull
+  @Override
+  public String getDisplayName() {
+    return InspectionGadgetsBundle.message("equals.with.itself.display.name");
+  }
+
+  @NotNull
+  @Override
+  protected String buildErrorString(Object... infos) {
+    return InspectionGadgetsBundle.message("equals.with.itself.problem.descriptor");
+  }
+
+  @Override
+  public BaseInspectionVisitor buildVisitor() {
+    return new EqualsWithIfSelfVisitor();
+  }
+
+  private static class EqualsWithIfSelfVisitor extends BaseInspectionVisitor {
+
+    @Override
+    public void visitMethodCallExpression(PsiMethodCallExpression expression) {
+      super.visitMethodCallExpression(expression);
+      if (!MethodCallUtils.isEqualsCall(expression)) {
+        return;
+      }
+      final PsiReferenceExpression methodExpression = expression.getMethodExpression();
+      final PsiExpression qualifier = methodExpression.getQualifierExpression();
+      if (qualifier == null) {
+        return;
+      }
+      final PsiExpressionList argumentList = expression.getArgumentList();
+      final PsiExpression[] arguments = argumentList.getExpressions();
+      final PsiExpression argument = arguments[0];
+      if (!EquivalenceChecker.expressionsAreEquivalent(qualifier, argument) ||
+          SideEffectChecker.mayHaveSideEffects(qualifier)) {
+        return;
+      }
+      registerMethodCallError(expression);
+    }
+  }
+}

plugins/InspectionGadgets/src/inspectionDescriptions/EqualsWithItself.html

@@ -0,0 +1,10 @@
+<html>
+<body>
+Reports call to <b>equals()</b> were an object is compared for equality with itself.
+This means that the argument and the qualifier to the call are identical.
+In this case <b>equals()</b> will always return <b>true</b>.
+<!-- tooltip end -->
+<p>
+<small>New in 14</small>
+</body>
+</html>

plugins/InspectionGadgets/test/com/siyeh/igtest/bugs/equals_with_itself/EqualsWithItself.java

@@ -0,0 +1,23 @@
+class EqualsWithItself {
+
+  boolean foo(Object o) {
+    return o.<warning descr="Identical qualifier and argument to 'equals()' call">equals</warning>(((o)));
+  }
+
+  boolean withGetter() {
+    return getValue().<warning descr="Identical qualifier and argument to 'equals()' call">equals</warning>(getValue());
+  }
+
+  boolean withMethodCall() {
+    return build().equals(build());
+  }
+
+  private Integer value = 1;
+  public Integer getValue() {
+    return value;
+  }
+
+  public Object build() {
+    return new Object();
+  }
+}

plugins/InspectionGadgets/testsrc/com/siyeh/ig/bugs/EqualsWithItselfInspectionTest.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2000-2014 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.siyeh.ig.bugs;
+
+import com.intellij.codeInspection.InspectionProfileEntry;
+import com.siyeh.ig.LightInspectionTestCase;
+import org.jetbrains.annotations.Nullable;
+
+/**
+ * @author Bas Leijdekkers
+ */
+public class EqualsWithItselfInspectionTest extends LightInspectionTestCase {
+
+  public void testEqualsWithItSelf() { doTest(); }
+
+  @Nullable
+  @Override
+  protected InspectionProfileEntry getInspection() {
+    return new EqualsWithItselfInspection();
+  }
+}