PY-17828 Fixed: Wrong signature inspection false positive for __prepare__ method of metaclasses

Add __prepare__ to type's skeletons

python/helpers/python-skeletons/builtins.py

@@ -361,6 +361,14 @@ class type(object):
         """
         return False
 
+    @staticmethod
+    def __prepare__(metacls, name, bases):
+        """Used to create the namespace for the class statement.
+
+        :rtype: dict[str, unknown]
+        """
+        return {}
+
 
 class enumerate(object):
     """enumerate object."""

python/testData/inspections/PyMethodOverridingInspection/DunderPrepare.py

@@ -0,0 +1,16 @@
+class MyType1(type):
+    @staticmethod
+    def __prepare__<warning descr="Signature of method 'MyType1.__prepare__()' does not match signature of base method in class 'type'">(metacls, name)</warning>:
+        return {}
+
+
+class MyType2(type):
+    @staticmethod
+    def __prepare__(metacls, name, bases):
+        return {}
+
+
+class MyType3(type):
+    @staticmethod
+    def __prepare__(metacls, name, bases, **kwargs):
+        return {}

python/testSrc/com/jetbrains/python/Py3MethodOverridingInspectionTest.java

@@ -0,0 +1,43 @@
+/*
+ * 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.
+ * 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.jetbrains.python;
+
+import com.intellij.testFramework.LightProjectDescriptor;
+import com.jetbrains.python.fixtures.PyTestCase;
+import com.jetbrains.python.inspections.PyMethodOverridingInspection;
+import com.jetbrains.python.psi.LanguageLevel;
+import org.jetbrains.annotations.Nullable;
+
+public class Py3MethodOverridingInspectionTest extends PyTestCase {
+  private static final String TEST_DIRECTORY = "inspections/PyMethodOverridingInspection/";
+
+  @Nullable
+  @Override
+  protected LightProjectDescriptor getProjectDescriptor() {
+    return ourPy3Descriptor;
+  }
+
+  // PY-17828
+  public void testDunderPrepare() {
+    runWithLanguageLevel(LanguageLevel.PYTHON30, this::doTest);
+  }
+
+  private void doTest() {
+    myFixture.configureByFile(TEST_DIRECTORY + getTestName(false) + ".py");
+    myFixture.enableInspections(PyMethodOverridingInspection.class);
+    myFixture.checkHighlighting(true, false, false);
+  }
+}