Don't show private module names from builtins in completion and mark them as unresolved (PY-7805)

python/src/com/jetbrains/python/psi/impl/references/PyReferenceImpl.java

@@ -307,7 +307,7 @@ public class PyReferenceImpl implements PsiReferenceEx, PsiPolyVariantReference
     if (uexpr == null) {
       // ...as a builtin symbol
       PyFile bfile = builtins_cache.getBuiltinsFile();
-      if (bfile != null) {
+      if (bfile != null && !PyUtil.isClassPrivateName(referencedName)) {
         uexpr = bfile.getElementNamed(referencedName);
         if (uexpr == null && "__builtins__".equals(referencedName)) {
           uexpr = bfile; // resolve __builtins__ reference

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

@@ -151,6 +151,9 @@ public class CompletionVariantsProcessor extends VariantsProcessor {
 
   @Override
   protected void addElement(String name, PsiElement element) {
+    if (PyUtil.isClassPrivateName(name) && !PyUtil.inSameFile(element, myContext)) {
+      return;
+    }
     myVariants.put(name, setupItem(LookupElementBuilder.create(element, name).withIcon(element.getIcon(0))));
   }
 

python/testData/completion/noUnderscoredBuiltin.after.py

@@ -0,0 +1 @@
+___Cl

python/testData/completion/noUnderscoredBuiltin.py

@@ -0,0 +1 @@
+___Cl<caret>

python/testData/inspections/PyUnresolvedReferencesInspection/underscoredBuiltin.py

@@ -0,0 +1,2 @@
+<error descr="Unresolved reference '___Classobj'">___Classobj</error>
+__debug__

python/testSrc/com/jetbrains/python/PythonCompletionTest.java

@@ -627,4 +627,9 @@ public class PythonCompletionTest extends PyTestCase {
                           "VAR = 2\n" +
                           "__all__ = ['VAR']");
   }
+
+  // PY-7805
+  public void testNoUnderscoredBuiltin() {
+    doTest();
+  }
 }

python/testSrc/com/jetbrains/python/inspections/PyUnresolvedReferencesInspectionTest.java

@@ -252,6 +252,11 @@ public class PyUnresolvedReferencesInspectionTest extends PyTestCase {
     doTest();
   }
 
+  // PY-7805
+  public void testUnderscoredBuiltin() {
+    doTest();
+  }
+
   private void doTest() {
     myFixture.configureByFile(TEST_DIRECTORY + getTestName(true) + ".py");
     myFixture.enableInspections(PyUnresolvedReferencesInspection.class);