Do not ignore import element completely if qualifier was resolved to namespace package

Consider the case when we are trying to invoke auto completion in
"import foo.bar.<caret>". Previously (mistakenly) type of
qualifier "foo.bar" was PyImportedModuleType(bar), which could not be
successfully resolved unless there is some other top-level "bar" module
under project roots. Now it's correct PyImportModuleType(foo.bar).

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

@@ -37,6 +37,13 @@ public class PyImportedModule extends LightElement implements NameDefiner {
   @NotNull private final PyFile myContainingFile;
   @NotNull private final QualifiedName myImportedPrefix;
 
+  /**
+   * @param importElement  parental import element, may be {@code null} if we're resolving {@code module} part in {@code from module import ...} statement
+   * @param containingFile file to be used as anchor e.g. to determine relative import position
+   * @param importedPrefix qualified name to resolve
+   *
+   * @see com.jetbrains.python.psi.resolve.ResolveImportUtil
+   */
   public PyImportedModule(@Nullable PyImportElement importElement, @NotNull PyFile containingFile, @NotNull QualifiedName importedPrefix) {
     super(containingFile.getManager(), PythonLanguage.getInstance());
     myImportElement = importElement;

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

@@ -36,7 +36,10 @@ import com.jetbrains.python.psi.*;
 import com.jetbrains.python.psi.impl.references.PyImportReference;
 import com.jetbrains.python.psi.impl.references.PyQualifiedReference;
 import com.jetbrains.python.psi.impl.references.PyReferenceImpl;
-import com.jetbrains.python.psi.resolve.*;
+import com.jetbrains.python.psi.resolve.ImplicitResolveResult;
+import com.jetbrains.python.psi.resolve.PyResolveContext;
+import com.jetbrains.python.psi.resolve.QualifiedResolveResult;
+import com.jetbrains.python.psi.resolve.RatedResolveResult;
 import com.jetbrains.python.psi.types.*;
 import com.jetbrains.python.refactoring.PyDefUseUtil;
 import org.jetbrains.annotations.NotNull;
@@ -382,8 +385,18 @@ public class PyReferenceExpressionImpl extends PyElementImpl implements PyRefere
       if (PyUtil.isPackage(dir, anchor)) {
         final PsiFile containingFile = anchor.getContainingFile();
         if (containingFile instanceof PyFile) {
-          final QualifiedName qualifiedName = QualifiedName.fromComponents(dir.getName());
-          final PyImportedModule module = new PyImportedModule(null, (PyFile)containingFile, qualifiedName);
+          final PyImportElement importElement = PsiTreeUtil.getParentOfType(anchor, PyImportElement.class);
+          final QualifiedName qualifiedName;
+          if (importElement != null) {
+            qualifiedName = anchor.asQualifiedName();
+          }
+          else {
+            qualifiedName = QualifiedName.fromComponents(dir.getName());
+          }
+          if (qualifiedName == null) {
+            return null;
+          }
+          final PyImportedModule module = new PyImportedModule(importElement, (PyFile)containingFile, qualifiedName);
           return new PyImportedModuleType(module);
         }
       }

python/testData/completion/importNestedQualifiedNamespacePackage/a.after.py

@@ -0,0 +1 @@
+import nspkg1.nspkg2.foo

python/testData/completion/importNestedQualifiedNamespacePackage/a.py

@@ -0,0 +1 @@
+import nspkg1.nspkg2.f<caret>

python/testSrc/com/jetbrains/python/Py3CompletionTest.java

@@ -115,4 +115,8 @@ public class Py3CompletionTest extends PyTestCase {
   public void testFromQualifiedNamespacePackageImport() {
     doMultiFileTest();
   }
+
+  public void testImportNestedQualifiedNamespacePackage() {
+    doMultiFileTest();
+  }
 }