stubtest: check typevar and paramspec (#12851)

Came up in #12825

Author: hauntsaninja

mypy/stubtest.py

@@ -12,6 +12,8 @@
 import re
 import sys
 import types
+import typing
+import typing_extensions
 import warnings
 from functools import singledispatch
 from pathlib import Path
@@ -867,8 +869,32 @@ def verify_overloadedfuncdef(
 def verify_typevarexpr(
     stub: nodes.TypeVarExpr, runtime: MaybeMissing[Any], object_path: List[str]
 ) -> Iterator[Error]:
-    if False:
-        yield None
+    if isinstance(runtime, Missing):
+        # We seem to insert these typevars into NamedTuple stubs, but they
+        # don't exist at runtime. Just ignore!
+        if stub.name == "_NT":
+            return
+        yield Error(object_path, "is not present at runtime", stub, runtime)
+        return
+    if not isinstance(runtime, TypeVar):
+        yield Error(object_path, "is not a TypeVar", stub, runtime)
+        return
+
+
+@verify.register(nodes.ParamSpecExpr)
+def verify_paramspecexpr(
+    stub: nodes.ParamSpecExpr, runtime: MaybeMissing[Any], object_path: List[str]
+) -> Iterator[Error]:
+    if isinstance(runtime, Missing):
+        yield Error(object_path, "is not present at runtime", stub, runtime)
+        return
+    maybe_paramspec_types = (
+        getattr(typing, "ParamSpec", None), getattr(typing_extensions, "ParamSpec", None)
+    )
+    paramspec_types = tuple([t for t in maybe_paramspec_types if t is not None])
+    if not paramspec_types or not isinstance(runtime, paramspec_types):
+        yield Error(object_path, "is not a ParamSpec", stub, runtime)
+        return
 
 
 def _verify_readonly_property(stub: nodes.Decorator, runtime: Any) -> Iterator[str]:

mypy/test/teststubtest.py

@@ -48,6 +48,9 @@ def __getitem__(self, typeargs: Any) -> object: ...
 class TypeVar:
     def __init__(self, name, covariant: bool = ..., contravariant: bool = ...) -> None: ...
 
+class ParamSpec:
+    def __init__(self, name: str) -> None: ...
+
 _T = TypeVar("_T")
 _T_co = TypeVar("_T_co", covariant=True)
 _K = TypeVar("_K")
@@ -329,8 +332,8 @@ def test_default_value(self) -> Iterator[Case]:
         yield Case(
             stub="""
             from typing import TypeVar
-            T = TypeVar("T", bound=str)
-            def f6(text: T = ...) -> None: ...
+            _T = TypeVar("_T", bound=str)
+            def f6(text: _T = ...) -> None: ...
             """,
             runtime="def f6(text = None): pass",
             error="f6",
@@ -1042,6 +1045,33 @@ def foo(self, x: int, y: bytes = ...) -> str: ...
             error="X.__init__"
         )
 
+    @collect_cases
+    def test_type_var(self) -> Iterator[Case]:
+        yield Case(
+            stub="from typing import TypeVar", runtime="from typing import TypeVar", error=None
+        )
+        yield Case(
+            stub="A = TypeVar('A')",
+            runtime="A = TypeVar('A')",
+            error=None,
+        )
+        yield Case(
+            stub="B = TypeVar('B')",
+            runtime="B = 5",
+            error="B",
+        )
+        if sys.version_info >= (3, 10):
+            yield Case(
+                stub="from typing import ParamSpec",
+                runtime="from typing import ParamSpec",
+                error=None
+            )
+            yield Case(
+                stub="C = ParamSpec('C')",
+                runtime="C = ParamSpec('C')",
+                error=None,
+            )
+
 
 def remove_color_code(s: str) -> str:
     return re.sub("\\x1b.*?m", "", s)  # this works!