PY-31299 Fix resolution of built-in classes' names in PyPsiFacade

Additionally, I extracted tests on PyPsiFacade implementation into a dedicated
test case.

python/psi-api/src/com/jetbrains/python/psi/PyPsiFacade.java

@@ -64,6 +64,10 @@ public abstract class PyPsiFacade {
   /**
    * Retrieve a top-level class by its qualified name. The name provided is supposed to be <em>fully qualified absolute name</em>
    * of the class, neither relative to the containing file of the anchor element, nor dependent on its imports.
+   * <p>
+   * The only exception to the rule above are built-in classes as it's too cumbersome to explicitly specify "__builtin__" or "builtins"
+   * prefix for them each time, and, overall, it's rather intuitive that these classes can be found solely by their short names.
+   * <p>
    * The anchor element is needed only to detect the corresponding module and its SDK.
    *
    * @param qName  qualified name of the required class

python/src/com/jetbrains/python/psi/impl/PyPsiFacadeImpl.java

@@ -91,12 +91,18 @@ public class PyPsiFacadeImpl extends PyPsiFacade {
   @Nullable
   @Override
   public final PyClass createClassByQName(@NotNull final String qName, @NotNull final PsiElement anchor) {
+    final QualifiedName qualifiedName = QualifiedName.fromDottedString(qName);
+    // Only built-in classes can be found by their unqualified names.
+    if (qualifiedName.getComponentCount() == 1) {
+      return PyBuiltinCache.getInstance(anchor).getClass(qName);
+    }
+
     final Module module = ModuleUtilCore.findModuleForPsiElement(ObjectUtils.notNull(anchor.getContainingFile(), anchor));
     if (module == null) return null;
     // Don't use PyResolveImportUtil.fromFoothold here as setting foothold file is going to affect resolve results
     // particularly if the anchor element happens to be in the same file as the target class.
     final PyQualifiedNameResolveContext resolveContext = PyResolveImportUtil.fromModule(module).copyWithMembers();
-    return StreamEx.of(resolveQualifiedName(QualifiedName.fromDottedString(qName), resolveContext))
+    return StreamEx.of(resolveQualifiedName(qualifiedName, resolveContext))
       .select(PyClass.class)
       .findFirst()
       .orElse(null);

python/testSrc/com/jetbrains/python/PyMultiFileResolveTest.java

@@ -496,8 +496,8 @@ public class PyMultiFileResolveTest extends PyMultiFileResolveTestCase {
       final List<PsiElement> elements = PyUtil.multiResolveTopPriority((PsiPolyVariantReference)ref);
       assertEquals(2, elements.size());
       final Set<String> parentNames = elements.stream()
-                                              .filter(e -> e instanceof PyFile)
-                                              .map(e -> ((PyFile)e).getVirtualFile().getParent().getName()).collect(Collectors.toSet());
+        .filter(e -> e instanceof PyFile)
+        .map(e -> ((PyFile)e).getVirtualFile().getParent().getName()).collect(Collectors.toSet());
       assertContainsElements(parentNames, "root", "ext");
     });
   }
@@ -588,13 +588,4 @@ public class PyMultiFileResolveTest extends PyMultiFileResolveTestCase {
   public void testIncompleteFromImport() {
     assertUnresolved();
   }
-
-  public void testCreateClassByQNameDoesntDependOnExistingImports() {
-    prepareTestDirectory();
-    runWithSourceRoots(Collections.singletonList(myFixture.findFileInTempDir("src")), () -> {
-      myFixture.configureByFile("src/" + getTestName(false) + ".py");
-      final PyPsiFacade facade = PyPsiFacade.getInstance(myFixture.getProject());
-      assertNotNull(facade.createClassByQName("foo.bar.MyClass", myFixture.getFile()));
-    });
-  }
 }

python/testSrc/com/jetbrains/python/PyPsiFacadeTest.java

@@ -0,0 +1,34 @@
+// Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+package com.jetbrains.python;
+
+import com.intellij.psi.PsiFile;
+import com.jetbrains.python.fixtures.PyTestCase;
+import com.jetbrains.python.psi.PyClass;
+import com.jetbrains.python.psi.PyPsiFacade;
+import com.jetbrains.python.psi.impl.PyBuiltinCache;
+
+import java.util.Collections;
+
+public class PyPsiFacadeTest extends PyTestCase {
+  public void testCreateClassByQNameDoesntDependOnExistingImports() {
+    myFixture.copyDirectoryToProject(getTestName(true), "");
+    runWithSourceRoots(Collections.singletonList(myFixture.findFileInTempDir("src")), () -> {
+      myFixture.configureByFile("src/" + getTestName(false) + ".py");
+      final PyPsiFacade facade = PyPsiFacade.getInstance(myFixture.getProject());
+      assertNotNull(facade.createClassByQName("foo.bar.MyClass", myFixture.getFile()));
+    });
+  }
+
+  public void testCreateClassByQNameCanResolveUnqualifiedNamesOfBuiltinClasses() {
+    final PsiFile file = myFixture.configureByText("a.py", "");
+    final PyPsiFacade facade = PyPsiFacade.getInstance(myFixture.getProject());
+    final PyClass builtinInt = facade.createClassByQName("int", file);
+    assertNotNull(builtinInt);
+    assertTrue(PyBuiltinCache.getInstance(file).isBuiltin(builtinInt));
+  }
+
+  @Override
+  protected String getTestDataPath() {
+    return super.getTestDataPath() + "/psiFacade/";
+  }
+}