Add basic support for typing_extensions.TypeVar

[cdce8p]

This PR only adds the existing TypeVar support for the typing_extensions variant.
I.e. it does not include support for default or infer_variance.

Fixes #14312

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

steam.py (https://github.com/Gobot1234/steam.py)
+ steam/types/user.py:45: error: Unexpected argument to "TypeVar()": "default"  [misc]
+ steam/types/user.py:47: error: Unexpected argument to "TypeVar()": "default"  [misc]
+ steam/id.py:222: error: Unexpected argument to "TypeVar()": "default"  [misc]
- steam/role.py:48: error: MemberT? has no attribute "roles"  [attr-defined]
+ steam/app.py:50: error: Unexpected argument to "TypeVar()": "default"  [misc]
+ steam/trade.py:39: error: Unexpected argument to "TypeVar()": "default"  [misc]
+ steam/trade.py:239: error: Unexpected argument to "TypeVar()": "default"  [misc]
+ steam/package.py:37: error: Unexpected argument to "TypeVar()": "default"  [misc]
+ steam/profile.py:77: error: Unexpected argument to "TypeVar()": "default"  [misc]
+ steam/abc.py:53: error: Unexpected argument to "TypeVar()": "default"  [misc]
+ steam/event.py:33: error: Unexpected argument to "TypeVar()": "default"  [misc]
+ steam/event.py:34: error: Unexpected argument to "TypeVar()": "default"  [misc]
+ steam/comment.py:23: error: Unexpected argument to "TypeVar()": "default"  [misc]
- steam/chat.py:130: error: "ChatGroup" expects no type arguments, but 2 given  [type-arg]
+ steam/chat.py:158: error: Unexpected argument to "TypeVar()": "default"  [misc]
- steam/chat.py:178: error: Variable "steam.chat.MemberT" is not valid as a type  [valid-type]
- steam/chat.py:178: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:292: error: Variable "steam.chat.ChatMessageT" is not valid as a type  [valid-type]
- steam/chat.py:292: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:296: error: "ChatGroup" expects no type arguments, but 2 given  [type-arg]
- steam/chat.py:303: error: Variable "steam.chat.ChatMessageT" is not valid as a type  [valid-type]
- steam/chat.py:303: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:340: error: Variable "steam.chat.ChatMessageT" is not valid as a type  [valid-type]
- steam/chat.py:340: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:352: error: Variable "steam.chat.ChatMessageT" is not valid as a type  [valid-type]
- steam/chat.py:352: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:369: error: Variable "steam.chat.ChatMessageT" is not valid as a type  [valid-type]
- steam/chat.py:369: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:372: error: No overload variant of "__new__" of "type" matches argument type "Type[ChatMessageT?]"  [call-overload]
+ steam/chat.py:372: error: No overload variant of "__new__" of "type" matches argument type "Type[ChatMessageT]"  [call-overload]
+ steam/chat.py:422: error: Unexpected argument to "TypeVar()": "default"  [misc]
- steam/chat.py:466: error: Variable "steam.chat.MemberT" is not valid as a type  [valid-type]
- steam/chat.py:466: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:468: error: Variable "steam.chat.ChatT" is not valid as a type  [valid-type]
- steam/chat.py:468: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:522: error: Variable "steam.chat.MemberT" is not valid as a type  [valid-type]
- steam/chat.py:522: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:523: error: Argument 2 to "__get__" of "classproperty" has incompatible type "Type[ChatGroup]"; expected "Type[Self]"  [arg-type]
+ steam/chat.py:523: error: Argument 2 to "__get__" of "classproperty" has incompatible type "Type[ChatGroup[MemberT, ChatT]]"; expected "Type[Self]"  [arg-type]
- steam/chat.py:527: error: Cannot instantiate type "Type[MemberT?]"  [misc]
- steam/chat.py:534: error: Variable "steam.chat.MemberT" is not valid as a type  [valid-type]
- steam/chat.py:534: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:544: error: Argument 2 to "__get__" of "classproperty" has incompatible type "Type[ChatGroup]"; expected "Type[Self]"  [arg-type]
+ steam/chat.py:544: error: Argument 2 to "__get__" of "classproperty" has incompatible type "Type[ChatGroup[MemberT, ChatT]]"; expected "Type[Self]"  [arg-type]
- steam/chat.py:549: error: Cannot instantiate type "Type[ChatT?]"  [misc]
- steam/chat.py:550: error: ChatT? has no attribute "id"  [attr-defined]
- steam/chat.py:552: error: ChatT? has no attribute "_update"  [attr-defined]
- steam/chat.py:578: error: Variable "steam.chat.MemberT" is not valid as a type  [valid-type]
- steam/chat.py:578: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:582: error: Variable "steam.chat.MemberT" is not valid as a type  [valid-type]
- steam/chat.py:582: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:590: note:     def get(self, ID32, /) -> Optional[MemberT?]
+ steam/chat.py:590: note:     def get(self, ID32, /) -> Optional[MemberT]
- steam/chat.py:590: note:     def [_T] get(self, ID32, Union[MemberT?, _T], /) -> Union[MemberT?, _T]
+ steam/chat.py:590: note:     def [_T] get(self, ID32, Union[MemberT, _T], /) -> Union[MemberT, _T]
- steam/chat.py:596: error: Variable "steam.chat.MemberT" is not valid as a type  [valid-type]
- steam/chat.py:596: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:601: error: Variable "steam.chat.MemberT" is not valid as a type  [valid-type]
- steam/chat.py:601: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:608: error: Variable "steam.chat.MemberT" is not valid as a type  [valid-type]
- steam/chat.py:608: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:612: error: Variable "steam.chat.MemberT" is not valid as a type  [valid-type]
- steam/chat.py:612: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:617: error: Variable "steam.chat.MemberT" is not valid as a type  [valid-type]
- steam/chat.py:617: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:622: error: Variable "steam.chat.ChatT" is not valid as a type  [valid-type]
- steam/chat.py:622: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:626: error: Variable "steam.chat.ChatT" is not valid as a type  [valid-type]
- steam/chat.py:626: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:637: error: Variable "steam.chat.ChatT" is not valid as a type  [valid-type]
- steam/chat.py:637: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:667: error: Variable "steam.chat.MemberT" is not valid as a type  [valid-type]
- steam/chat.py:667: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:673: error: Variable "steam.chat.MemberT" is not valid as a type  [valid-type]
- steam/chat.py:673: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
- steam/chat.py:691: error: Argument 2 to "__get__" of "classproperty" has incompatible type "Type[ChatGroup]"; expected "Type[Self]"  [arg-type]
+ steam/chat.py:691: error: Argument 2 to "__get__" of "classproperty" has incompatible type "Type[ChatGroup[MemberT, ChatT]]"; expected "Type[Self]"  [arg-type]
- steam/chat.py:693: error: Cannot instantiate type "Type[MemberT?]"  [misc]
+ steam/message.py:29: error: Unexpected argument to "TypeVar()": "default"  [misc]
+ steam/message.py:104: error: Unexpected argument to "TypeVar()": "default"  [misc]
- steam/message.py:109: error: "ChatMessage" expects no type arguments, but 2 given  [type-arg]
+ steam/message.py:109: error: "ChatMessage" expects 1 type argument, but 2 given  [type-arg]
+ steam/message.py:120: error: Unexpected argument to "TypeVar()": "default"  [misc]
- steam/message.py:125: error: "ChatMessage" expects no type arguments, but 2 given  [type-arg]
+ steam/message.py:125: error: "ChatMessage" expects 1 type argument, but 2 given  [type-arg]
- steam/channel.py:171: error: "Chat" expects no type arguments, but 1 given  [type-arg]
- steam/channel.py:197: error: "Chat" expects no type arguments, but 1 given  [type-arg]
- steam/group.py:32: error: "ChatGroup" expects no type arguments, but 3 given  [type-arg]
+ steam/group.py:32: error: "ChatGroup" expects 2 type arguments, but 3 given  [type-arg]
- steam/clan.py:281: error: "ChatGroup" expects no type arguments, but 3 given  [type-arg]
+ steam/clan.py:281: error: "ChatGroup" expects 2 type arguments, but 3 given  [type-arg]
- steam/clan.py:366: error: Incompatible types in assignment (expression has type "Dict[int, ClanChannel]", base class "ChatGroup" defined the type as "Dict[ChatID, ChatT?]")  [assignment]
+ steam/clan.py:366: error: Incompatible types in assignment (expression has type "Dict[int, ClanChannel]", base class "ChatGroup" defined the type as "Dict[ChatID, Any]")  [assignment]
+ steam/bundle.py:23: error: Unexpected argument to "TypeVar()": "default"  [misc]

[cdce8p]

The primer output looks as expected, since we don't support default just yet.

[JelleZijlstra]

Looks good, surprised only one place in the code needed to change. I verified with grep.