More detailed checking of type objects in stubtest (#18251)

This uses `checkmember.type_object_type` and context to produce better
types of type objects.

Author: tungol

mypy/stubtest.py

@@ -34,6 +34,9 @@
 from typing_extensions import get_origin, is_typeddict
 
 import mypy.build
+import mypy.checkexpr
+import mypy.checkmember
+import mypy.erasetype
 import mypy.modulefinder
 import mypy.nodes
 import mypy.state
@@ -792,7 +795,11 @@ def _verify_arg_default_value(
                 "has a default value but stub parameter does not"
             )
         else:
-            runtime_type = get_mypy_type_of_runtime_value(runtime_arg.default)
+            type_context = stub_arg.variable.type
+            runtime_type = get_mypy_type_of_runtime_value(
+                runtime_arg.default, type_context=type_context
+            )
+
             # Fallback to the type annotation type if var type is missing. The type annotation
             # is an UnboundType, but I don't know enough to know what the pros and cons here are.
             # UnboundTypes have ugly question marks following them, so default to var type.
@@ -1247,7 +1254,7 @@ def verify_var(
     ):
         yield Error(object_path, "is read-only at runtime but not in the stub", stub, runtime)
 
-    runtime_type = get_mypy_type_of_runtime_value(runtime)
+    runtime_type = get_mypy_type_of_runtime_value(runtime, type_context=stub.type)
     if (
         runtime_type is not None
         and stub.type is not None
@@ -1832,7 +1839,18 @@ def is_subtype_helper(left: mypy.types.Type, right: mypy.types.Type) -> bool:
         return mypy.subtypes.is_subtype(left, right)
 
 
-def get_mypy_type_of_runtime_value(runtime: Any) -> mypy.types.Type | None:
+def get_mypy_node_for_name(module: str, type_name: str) -> mypy.nodes.SymbolNode | None:
+    stub = get_stub(module)
+    if stub is None:
+        return None
+    if type_name not in stub.names:
+        return None
+    return stub.names[type_name].node
+
+
+def get_mypy_type_of_runtime_value(
+    runtime: Any, type_context: mypy.types.Type | None = None
+) -> mypy.types.Type | None:
     """Returns a mypy type object representing the type of ``runtime``.
 
     Returns None if we can't find something that works.
@@ -1893,14 +1911,45 @@ def anytype() -> mypy.types.AnyType:
             is_ellipsis_args=True,
         )
 
-    # Try and look up a stub for the runtime object
-    stub = get_stub(type(runtime).__module__)
-    if stub is None:
-        return None
-    type_name = type(runtime).__name__
-    if type_name not in stub.names:
+    skip_type_object_type = False
+    if type_context:
+        # Don't attempt to process the type object when context is generic
+        # This is related to issue #3737
+        type_context = mypy.types.get_proper_type(type_context)
+        # Callable types with a generic return value
+        if isinstance(type_context, mypy.types.CallableType):
+            if isinstance(type_context.ret_type, mypy.types.TypeVarType):
+                skip_type_object_type = True
+        # Type[x] where x is generic
+        if isinstance(type_context, mypy.types.TypeType):
+            if isinstance(type_context.item, mypy.types.TypeVarType):
+                skip_type_object_type = True
+
+    if isinstance(runtime, type) and not skip_type_object_type:
+
+        def _named_type(name: str) -> mypy.types.Instance:
+            parts = name.rsplit(".", maxsplit=1)
+            node = get_mypy_node_for_name(parts[0], parts[1])
+            assert isinstance(node, nodes.TypeInfo)
+            any_type = mypy.types.AnyType(mypy.types.TypeOfAny.special_form)
+            return mypy.types.Instance(node, [any_type] * len(node.defn.type_vars))
+
+        # Try and look up a stub for the runtime object itself
+        # The logic here is similar to ExpressionChecker.analyze_ref_expr
+        type_info = get_mypy_node_for_name(runtime.__module__, runtime.__name__)
+        if isinstance(type_info, nodes.TypeInfo):
+            result: mypy.types.Type | None = None
+            result = mypy.typeops.type_object_type(type_info, _named_type)
+            if mypy.checkexpr.is_type_type_context(type_context):
+                # This is the type in a type[] expression, so substitute type
+                # variables with Any.
+                result = mypy.erasetype.erase_typevars(result)
+            return result
+
+    # Try and look up a stub for the runtime object's type
+    type_info = get_mypy_node_for_name(type(runtime).__module__, type(runtime).__name__)
+    if type_info is None:
         return None
-    type_info = stub.names[type_name].node
     if isinstance(type_info, nodes.Var):
         return type_info.type
     if not isinstance(type_info, nodes.TypeInfo):

mypy/test/teststubtest.py

@@ -2636,6 +2636,31 @@ class _X1: ...
             error=None,
         )
 
+    @collect_cases
+    def test_type_default_protocol(self) -> Iterator[Case]:
+        yield Case(
+            stub="""
+            from typing import Protocol
+
+            class _FormatterClass(Protocol):
+                def __call__(self, *, prog: str) -> HelpFormatter: ...
+
+            class ArgumentParser:
+                def __init__(self, formatter_class: _FormatterClass = ...) -> None: ...
+
+            class HelpFormatter:
+                def __init__(self, prog: str, indent_increment: int = 2) -> None: ...
+            """,
+            runtime="""
+            class HelpFormatter:
+                def __init__(self, prog, indent_increment=2) -> None: ...
+
+            class ArgumentParser:
+                def __init__(self, formatter_class=HelpFormatter): ...
+            """,
+            error=None,
+        )
+
 
 def remove_color_code(s: str) -> str:
     return re.sub("\\x1b.*?m", "", s)  # this works!