PY-19492 Fixed: Magic method parameter value is flagged as unused but cannot be removed because it's required by Python

Update PyUnusedLocalInspectionVisitor to ignore builtin method parameters (except __init__)

python/src/com/jetbrains/python/inspections/PyUnusedLocalInspectionVisitor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2014 JetBrains s.r.o.
+ * Copyright 2000-2016 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.
@@ -25,7 +25,6 @@ import com.intellij.openapi.extensions.Extensions;
 import com.intellij.openapi.project.Project;
 import com.intellij.psi.PsiElement;
 import com.intellij.psi.util.PsiTreeUtil;
-import com.intellij.util.Function;
 import com.jetbrains.python.PyBundle;
 import com.jetbrains.python.PyNames;
 import com.jetbrains.python.codeInsight.controlflow.ControlFlowCache;
@@ -131,6 +130,9 @@ public class PyUnusedLocalInspectionVisitor extends PyInspectionVisitor {
         if (PyAugAssignmentStatementNavigator.getStatementByTarget(element) != null) {
           continue;
         }
+        if (parameterInMethodWithFixedSignature(owner, element)) {
+          continue;
+        }
         if (!myUsedElements.contains(element)) {
           myUnusedElements.add(element);
         }
@@ -138,6 +140,19 @@ public class PyUnusedLocalInspectionVisitor extends PyInspectionVisitor {
     }
   }
 
+  private static boolean parameterInMethodWithFixedSignature(@NotNull ScopeOwner owner, @NotNull PsiElement element) {
+    if (owner instanceof PyFunction && element instanceof PyParameter) {
+      final PyFunction function = (PyFunction)owner;
+      final String functionName = function.getName();
+
+      return !PyNames.INIT.equals(functionName) &&
+             function.getContainingClass() != null &&
+             PyNames.getBuiltinMethods(LanguageLevel.forElement(function)).containsKey(functionName);
+    }
+
+    return false;
+  }
+
   private void collectUsedReads(final ScopeOwner owner) {
     final Instruction[] instructions = ControlFlowCache.getControlFlow(owner).getInstructions();
     for (int i = 0; i < instructions.length; i++) {

python/testData/inspections/PyUnusedLocalVariableInspection/test.py

@@ -320,3 +320,12 @@ def test_unused_empty_init_parameter():
 # PY-14429
 def test_used_local_augmented_assignment(x, y):
     x += y
+
+
+# PY-19492
+class A:
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        print(exc_type)
+
+    def __eq__(self, other):
+        return False