PY-18958: Always use case-sensitive resolve, even on Windows (PEP 235)

python/src/com/jetbrains/python/psi/resolve/ResolveImportUtil.java

@@ -401,7 +401,8 @@ public class ResolveImportUtil {
                                                              boolean checkForPackage,
                                                              boolean withoutStubs) {
     final PsiDirectory subdir = dir.findSubdirectory(referencedName);
-    if (subdir != null && (!checkForPackage || PyUtil.isPackage(subdir, containingFile))) {
+    // VFS may be case insensitive on Windows, but resolve is always case sensitive (PEP 235, PY-18958), so we check name here
+    if (subdir != null && (!checkForPackage || PyUtil.isPackage(subdir, containingFile)) && subdir.getName().equals(referencedName)) {
       return ResolveResultList.to(subdir);
     }
 

python/testData/resolveTest/UnitTest/__init__.py

@@ -0,0 +1 @@
+ 

python/testData/resolveTest/test.py

@@ -0,0 +1,4 @@
+from unittest import TestCase
+
+
+TestCase().assertIsNotNo<caret>

python/testSrc/com/jetbrains/env/PyCaseSensitiveResolveTest.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2000-2017 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.env;
+
+import com.intellij.openapi.application.ApplicationManager;
+import com.jetbrains.python.sdkTools.SdkCreationType;
+import org.jetbrains.annotations.NotNull;
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Ensures resolve is always case-sensitive, even in Windows (see pep 235)
+ *
+ * @author Ilya.Kazakevich
+ */
+public final class PyCaseSensitiveResolveTest extends PyEnvTestCase {
+  @Test
+  public void testCaseSensitive() throws Exception {
+    runTest(new PyExecutionFixtureTestTask(null) {
+      @NotNull
+      @Override
+      protected String getTestDataPath() {
+        return super.getTestDataPath() + "/resolveTest";
+      }
+
+      @Override
+      public void runTestOn(@NotNull  final String sdkHome) throws Exception {
+        createTempSdk(sdkHome, SdkCreationType.SDK_PACKAGES_AND_SKELETONS);
+        ApplicationManager.getApplication().invokeAndWait(() -> {
+          myFixture.copyDirectoryToProject("", "");
+          myFixture.configureByFile("test.py");
+          myFixture.completeBasic();
+          Assert.assertEquals("Completion failed. Failed to resolve unittest? Case-sensitive resolve failed?",
+                              "from unittest import TestCase\n" +
+                              '\n' +
+                              '\n' +
+                              "TestCase().assertIsNotNone()",
+                              myFixture.getFile().getText());
+        });
+      }
+    }, getTestName(false));
+  }
+}