IDEA-86056 (Unnecessary 'null' check before 'equals()' call quick fix changes the logic)

plugins/InspectionGadgets/src/com/siyeh/ig/controlflow/SimplifiableEqualsExpressionInspection.java

@@ -13,7 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package com.siyeh.ig.style;
+package com.siyeh.ig.controlflow;
 
 import com.intellij.codeInspection.ProblemDescriptor;
 import com.intellij.openapi.project.Project;
@@ -71,7 +71,14 @@ public class SimplifiableEqualsExpressionInspection extends BaseInspection {
       if (operands.length != 2) {
         return;
       }
-      final PsiExpression operand = ParenthesesUtils.stripParentheses(operands[1]);
+      PsiExpression operand = ParenthesesUtils.stripParentheses(operands[1]);
+      if (operand instanceof PsiPrefixExpression) {
+        final PsiPrefixExpression prefixExpression = (PsiPrefixExpression)operand;
+        if (!JavaTokenType.EXCL.equals(prefixExpression.getOperationTokenType())) {
+          return;
+        }
+        operand = ParenthesesUtils.stripParentheses(prefixExpression.getOperand());
+      }
       if (!(operand instanceof PsiMethodCallExpression)) {
         return;
       }
@@ -170,7 +177,15 @@ public class SimplifiableEqualsExpressionInspection extends BaseInspection {
           return;
         }
         final PsiExpression rhs = ParenthesesUtils.stripParentheses(operands[1]);
-        if (!isEqualsConstant(rhs, variable)) {
+        if (!(rhs instanceof PsiPrefixExpression)) {
+          return;
+        }
+        final PsiPrefixExpression prefixExpression = (PsiPrefixExpression)rhs;
+        if (!JavaTokenType.EXCL.equals(prefixExpression.getOperationTokenType())) {
+          return;
+        }
+        final PsiExpression operand = ParenthesesUtils.stripParentheses(prefixExpression.getOperand());
+        if (!isEqualsConstant(operand, variable)) {
           return;
         }
         registerError(lhs);
@@ -226,8 +241,14 @@ public class SimplifiableEqualsExpressionInspection extends BaseInspection {
       if (operands.length != 2) {
         return null;
       }
-      final PsiExpression lhs = operands[0];
-      final PsiExpression rhs = operands[1];
+      final PsiExpression lhs = ParenthesesUtils.stripParentheses(operands[0]);
+      if (lhs == null) {
+        return null;
+      }
+      final PsiExpression rhs = ParenthesesUtils.stripParentheses(operands[1]);
+      if (rhs == null) {
+        return null;
+      }
       if (PsiType.NULL.equals(lhs.getType())) {
         if (!(rhs instanceof PsiReferenceExpression)) {
           return null;

plugins/InspectionGadgets/test/com/siyeh/igtest/controlflow/simplifiable_equals_expression/SimplifiableEqualsExpression.java

@@ -0,0 +1,28 @@
+package com.siyeh.igtest.controlflow.simplifiable_equals_expression;
+
+public class SimplifiableEqualsExpression {
+
+  void foo(String namespace) {
+    if (namespace != null && namespace.equals("")) {
+      return;
+    }
+  }
+
+  void bar(String namespace) {
+    if (namespace == null || !namespace.equals("")) {
+      return;
+    }
+  }
+
+  void baz(Integer i) {
+    if (i != null && i.equals(1)) {
+      return;
+    }
+  }
+
+  void boz(String namespace) {
+    if (namespace == null || namespace.equals("")) { // don't warn here
+      return;
+    }
+  }
+}

plugins/InspectionGadgets/test/com/siyeh/igtest/controlflow/simplifiable_equals_expression/expected.xml

@@ -0,0 +1,26 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<problems>
+  <problem>
+    <file>SimplifiableEqualsExpression.java</file>
+    <line>12</line>
+    <entry_point TYPE="method" FQNAME="com.siyeh.igtest.controlflow.simplifiable_equals_expression.SimplifiableEqualsExpression void bar(java.lang.String namespace)" />
+    <problem_class severity="WARNING" attribute_key="WARNING_ATTRIBUTES">Unnecessary 'null' check before 'equals()' call</problem_class>
+    <description>Unnecessary 'null' check #loc</description>
+  </problem>
+
+  <problem>
+    <file>SimplifiableEqualsExpression.java</file>
+    <line>18</line>
+    <entry_point TYPE="method" FQNAME="com.siyeh.igtest.controlflow.simplifiable_equals_expression.SimplifiableEqualsExpression void baz(java.lang.Integer i)" />
+    <problem_class severity="WARNING" attribute_key="WARNING_ATTRIBUTES">Unnecessary 'null' check before 'equals()' call</problem_class>
+    <description>Unnecessary 'null' check #loc</description>
+  </problem>
+
+  <problem>
+    <file>SimplifiableEqualsExpression.java</file>
+    <line>6</line>
+    <entry_point TYPE="method" FQNAME="com.siyeh.igtest.controlflow.simplifiable_equals_expression.SimplifiableEqualsExpression void foo(java.lang.String namespace)" />
+    <problem_class severity="WARNING" attribute_key="WARNING_ATTRIBUTES">Unnecessary 'null' check before 'equals()' call</problem_class>
+    <description>Unnecessary 'null' check #loc</description>
+  </problem>
+</problems>

plugins/InspectionGadgets/testsrc/com/siyeh/ig/controlflow/SimplifiableEqualsExpressionInspectionTest.java

@@ -0,0 +1,11 @@
+package com.siyeh.ig.controlflow;
+
+import com.siyeh.ig.IGInspectionTestCase;
+
+public class SimplifiableEqualsExpressionInspectionTest extends IGInspectionTestCase {
+
+  public void test() throws Exception {
+    doTest("com/siyeh/igtest/controlflow/simplifiable_equals_expression",
+           new SimplifiableEqualsExpressionInspection());
+  }
+}