stubtest: do not treat py files as source for mypy definitions (#12889)

Authored by @KotlinIsland

Co-authored-by: KotlinIsland <kotlinisland@users.noreply.github.com>

Author: hauntsaninja

mypy/stubtest.py

@@ -1301,7 +1301,8 @@ def build_stubs(modules: List[str], options: Options, find_submodules: bool = Fa
 
 def get_stub(module: str) -> Optional[nodes.MypyFile]:
     """Returns a stub object for the given module, if we've built one."""
-    return _all_stubs.get(module)
+    stub = _all_stubs.get(module)
+    return stub if stub and stub.is_stub else None
 
 
 def get_typeshed_stdlib_modules(

mypy/test/teststubtest.py

@@ -1201,6 +1201,18 @@ def test_missing_stubs(self) -> None:
             "Found 1 error (checked 1 module)\n"
         )
 
+    def test_missing_only_stubs(self) -> None:
+        with use_tmp_dir(TEST_MODULE_NAME):
+            with open(f"{TEST_MODULE_NAME}.py", "w") as f:
+                f.write("a = 1")
+            output = io.StringIO()
+            with contextlib.redirect_stdout(output):
+                test_stubs(parse_options([TEST_MODULE_NAME]))
+            assert (
+                f"error: {TEST_MODULE_NAME} failed to find stubs"
+                in remove_color_code(output.getvalue())
+            )
+
     def test_get_typeshed_stdlib_modules(self) -> None:
         stdlib = mypy.stubtest.get_typeshed_stdlib_modules(None, (3, 6))
         assert "builtins" in stdlib