Fix resolution of ParamSpec in circular dependencies

What's happening here?
1. We load module `bar`, by requesting it from the loader.
1. Before resolving types, we need to load its dependencies. So we load module `foo`.
1. We'd like to load `foo`'s dependencies, but that's `bar` and that's a circle, so we start resolving types in `foo`.
1. When resolving external types we create alias an `foo.bar`, copying the unresolved signature from `bar.bar`.
1. When resolving local types, `_P` is not resolvable within `foo`.
1. We run `visitors.AdjustTypeParameters`, which seems to require local type resolution, and runs afterwards. It declares `_P` in `foo`. Now `_P.args` would be resolvable but we already finished resolving local types and we don't do it again.
1. We resolve types in `bar`, validate `bar`'s AST and return.
1. We load module `foo`, by requesting it from the loader.
1. It's cached. We just need to validate it. We realize that types aren't resolved, yet, e.g. `_P.args`. We used to do only external type resolution again, which did not resolve ParamSpec, and we eventually bailed. This change also adds local type resolution again, which does resolve ParamSpec.

PiperOrigin-RevId: 684443947

pytype/load_pytd.py

@@ -737,6 +737,11 @@ def finish_and_verify_ast(self, mod_ast):
               self._modules[k].ast
           )
         mod_ast = self._resolve_external_types(mod_ast)
+        # Circular imports can leave type params (e.g. ParamSpecArgs)
+        # unresolved. External type parameters are added to the AST in
+        # visitors.AdjustTypeParameters, after resolving local types. But those
+        # are needed to resolve e.g. `_P.args` references.
+        mod_ast = self._resolver.resolve_local_types(mod_ast)
         self._resolver.verify(mod_ast)
     return mod_ast
 

pytype/load_pytd_test.py

@@ -280,6 +280,43 @@ class Popen: ...
           )
       )
 
+  def test_circular_dependency_with_type_param(self):
+    with test_utils.Tempdir() as d:
+      d.create_file(
+          "bar.pyi",
+          """
+          from typing import Callable, ParamSpec
+
+          from foo import Foo
+
+          _P = ParamSpec("_P")
+
+          class Bar:
+            foo: Foo | None
+          def bar(obj: Callable[_P, None], /, *args: _P.args, **kwargs: _P.kwargs) -> Bar: ...
+          """,
+      )
+      d.create_file(
+          "foo.pyi",
+          """
+          from bar import bar as _bar
+
+          class Foo: ...
+          bar = _bar
+          """,
+      )
+      loader = load_pytd.Loader(
+          config.Options.create(
+              module_name="base",
+              python_version=self.python_version,
+              pythonpath=d.path,
+          )
+      )
+      bar = loader.import_name("bar")
+      foo = loader.import_name("foo")
+      self.assertTrue(bar.Lookup("bar.bar"))
+      self.assertTrue(foo.Lookup("foo.bar"))
+
   def test_cache(self):
     with test_utils.Tempdir() as d:
       d.create_file("foo.pyi", "def get_bar() -> bar.Bar: ...")