PY-34478 Properly follow assignment chains for type aliases

We used to implicitly rely on PyTypingTypeProvider.getClassType() for this purpose
that, in turn, uses normal resolve machinery of a PyReference. But it (rightfully)
didn't work for references inside fragments created from text of alias RHS parts
as we prohibit resolving in them to avoid unstubbing of their containing files.

python/src/com/jetbrains/python/codeInsight/typing/PyTypingTypeProvider.java

@@ -828,6 +828,15 @@ public class PyTypingTypeProvider extends PyTypeProviderBase {
       if (anyType != null) {
         return anyType;
       }
+      // We perform chained resolve only for actual aliases as tryResolvingWithAliases() returns the passed-in 
+      // expression both when it's not a reference expression and when it's failed to resolve it, hence we might
+      // hit SOE for mere unresolved references in the latter case.
+      if (alias != null) {
+        final Ref<PyType> aliasedType = getAliasedType(resolved, context);
+        if (aliasedType != null) {
+          return aliasedType;
+        }
+      }
       final Ref<PyType> classType = getClassType(resolved, context.getTypeContext());
       if (classType != null) {
         return classType;
@@ -841,6 +850,14 @@ public class PyTypingTypeProvider extends PyTypeProviderBase {
     }
   }
 
+  @Nullable
+  private static Ref<PyType> getAliasedType(@NotNull PsiElement resolved, @NotNull Context context) {
+    if (resolved instanceof PyReferenceExpression && ((PyReferenceExpression)resolved).asQualifiedName() != null) {
+      return getType((PyExpression)resolved, context);
+    }
+    return null;
+  }
+
   @Nullable
   private static PyType addTypeVarAlias(@Nullable PyType type, @Nullable PyTargetExpression alias) {
     final PyGenericType typeVar = as(type, PyGenericType.class);

python/testData/types/TrivialRecursiveTypeAliasInAnotherFile/other.py

@@ -0,0 +1,2 @@
+alias2 = 'alias'
+alias = alias2

python/testData/types/TrivialTypeAliasInAnotherFile/other.py

@@ -0,0 +1 @@
+alias = str

python/testData/types/TrivialUnresolvedTypeAliasInAnotherFile/other.py

@@ -0,0 +1 @@
+alias = unresolved

python/testSrc/com/jetbrains/python/PyTypingTest.java

@@ -1424,6 +1424,30 @@ public class PyTypingTest extends PyTestCase {
                              "\n");
   }
 
+  // PY-34478
+  public void testTrivialTypeAliasInAnotherFile() {
+    doMultiFileStubAwareTest("str",
+                             "from other import alias\n" +
+                             "\n" +
+                             "expr: alias");
+  }
+
+  // PY-34478
+  public void testTrivialUnresolvedTypeAliasInAnotherFile() {
+    doMultiFileStubAwareTest("Any",
+                             "from other import alias\n" +
+                             "\n" +
+                             "expr: alias");
+  }
+
+  // PY-34478
+  public void testTrivialRecursiveTypeAliasInAnotherFile() {
+    doMultiFileStubAwareTest("Any",
+                             "from other import alias\n" +
+                             "\n" +
+                             "expr: alias");
+  }
+
   private void doTestNoInjectedText(@NotNull String text) {
     myFixture.configureByText(PythonFileType.INSTANCE, text);
     final InjectedLanguageManager languageManager = InjectedLanguageManager.getInstance(myFixture.getProject());