Fix various crahses on recursive type variable defaults by ilevkivskyi · Pull Request #21491 · python/mypy

ilevkivskyi · 2026-05-15T15:12:28Z

Fixes #17716
Fixes #20698
Fixes #21128
Fixes #21269

Although the main idea is relatively simple (replace explicit type variable defaults with Any in cases where they would cause infinite recursion), this required a lot of "plumbing", because:

We always call fix_instance() eagerly and early.
There are four different cases to handle (classes vs aliases, and old style vs new style).
Relevant pieces of information are available in "distant" places (and I don't want to add any global state).

Some additional notes:

I clean-up some weirdness with deferral on type variable defaults with placeholders (especially in type aliases).
I remove an unwarranted get_proper_type() call during semantic analysis.
Now we handle rare edge case of unused alias type variables in BoolTypeQuery (possible with new style aliases).
Type variable defaults should be considered in __eq__() to correctly detect progress.

…ashes

ilevkivskyi · 2026-05-15T16:10:19Z

Hm, it looks like something went wrong. I will take a look later today or tomorrow.

ilevkivskyi · 2026-05-16T00:28:22Z

OK, this is ready for review now.

Btw the mypy_primer changes in steam.py are good illustration of why I took this (more complex) approach rather than trying to tune mark_incomplete() usage.

ilevkivskyi · 2026-05-16T21:27:57Z

Oh, it looks like this fixes #20698 as well.

…ashes

ilevkivskyi · 2026-05-20T09:58:19Z

@JukkaL @hauntsaninja @cdce8p Ping here.

…ashes

github-actions · 2026-05-21T17:18:25Z

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

steam.py (https://github.com/Gobot1234/steam.py)
- steam/_const.py:29: error: Module "steam.clan" has no attribute "Clan"  [attr-defined]
- steam/_const.py:30: error: Module "steam.group" has no attribute "Group"  [attr-defined]
- steam/types/user.py:16: error: Module "steam.user" has no attribute "User"  [attr-defined]
- steam/types/user.py:139: error: Cannot resolve name "Author" (possible cyclic definition)  [misc]
- steam/invite.py:16: error: Module "steam.clan" has no attribute "Clan"  [attr-defined]
- steam/invite.py:19: error: Module "steam.group" has no attribute "Group"  [attr-defined]
- steam/invite.py:21: error: Module "steam.user" has no attribute "User"  [attr-defined]
- steam/invite.py:118: error: Cannot resolve name "ChatGroupInvite" (possible cyclic definition)  [misc]
- steam/ext/commands/errors.py:12: error: Module "steam.ext.commands.commands" has no attribute "Command"; maybe "command"?  [attr-defined]
- steam/role.py:15: error: Module "steam.chat" has no attribute "ChatGroup"  [attr-defined]
- steam/role.py:15: error: Module "steam.chat" has no attribute "Member"; maybe "MemberT"?  [attr-defined]
- steam/role.py:16: error: Module "steam.clan" has no attribute "Clan"  [attr-defined]
- steam/role.py:17: error: Module "steam.group" has no attribute "Group"  [attr-defined]
- steam/app.py:41: error: Module "steam.clan" has no attribute "Clan"  [attr-defined]
- steam/app.py:42: error: Module "steam.friend" has no attribute "Friend"  [attr-defined]
- steam/app.py:396: error: Cannot resolve Self upper bound (possible cyclic definition)  [misc]
- steam/trade.py:27: error: Module "steam.friend" has no attribute "Friend"  [attr-defined]
- steam/trade.py:30: error: Module "steam.user" has no attribute "User"  [attr-defined]
- steam/reaction.py:22: error: Module "steam.message" does not explicitly export attribute "Message"  [attr-defined]
- steam/package.py:29: error: Module "steam.user" has no attribute "User"  [attr-defined]
- steam/profile.py:26: error: Module "steam.clan" has no attribute "Clan"  [attr-defined]
- steam/profile.py:27: error: Module "steam.friend" has no attribute "Friend"  [attr-defined]
- steam/profile.py:32: error: Module "steam.user" has no attribute "User"  [attr-defined]
- steam/abc.py:37: error: Module "steam.clan" has no attribute "Clan"  [attr-defined]
- steam/abc.py:38: error: Module "steam.comment" has no attribute "Comment"; maybe "CommentID" or "Commentable"?  [attr-defined]
- steam/abc.py:40: error: Module "steam.group" has no attribute "Group"  [attr-defined]
- steam/abc.py:43: error: Module "steam.message" has no attribute "UserMessage"; maybe "Message" or "UserMessageAuthorT"?  [attr-defined]
- steam/abc.py:49: error: Module "steam.user" has no attribute "User"  [attr-defined]
- steam/abc.py:58: error: Cannot resolve name "Message" (possible cyclic definition)  [misc]
- steam/abc.py:58: error: TypeVar "bound" must be a type  [misc]
- steam/abc.py:58: error: TypeVar "default" must be a type  [misc]
- steam/user.py:33: error: Module "steam.channel" has no attribute "UserChannel"; maybe "Channel"?  [attr-defined]
- steam/user.py:34: error: Module "steam.friend" has no attribute "Friend"  [attr-defined]
- steam/user.py:36: error: Module "steam.message" has no attribute "UserMessage"; maybe "Message" or "UserMessageAuthorT"?  [attr-defined]
- steam/published_file.py:28: error: Module "steam.friend" has no attribute "Friend"  [attr-defined]
+ steam/published_file.py:509: error: List comprehension has incompatible type List[Friend | None]; expected List[Friend]  [misc]
- steam/event.py:22: error: Module "steam.clan" has no attribute "Clan"  [attr-defined]
- steam/chat.py:37: error: Module "steam.clan" has no attribute "Clan"  [attr-defined]
- steam/chat.py:38: error: Module "steam.group" has no attribute "Group"  [attr-defined]
- steam/chat.py:41: error: Module "steam.message" has no attribute "ClanMessage"; maybe "ChatMessage", "Message", or "ClanMessageAuthorT"?  [attr-defined]
- steam/chat.py:41: error: Module "steam.message" has no attribute "GroupMessage"; maybe "GroupMessageAuthorT"?  [attr-defined]
- steam/chat.py:45: error: Cannot resolve name "Chat" (possible cyclic definition)  [misc]
- steam/chat.py:45: error: TypeVar "bound" must be a type  [misc]
- steam/chat.py:45: error: TypeVar "default" must be a type  [misc]
- steam/chat.py:46: error: Cannot resolve name "Member" (possible cyclic definition)  [misc]
- steam/chat.py:46: error: TypeVar "bound" must be a type  [misc]
- steam/chat.py:46: error: TypeVar "default" must be a type  [misc]
- steam/chat.py:412: error: Unused "type: ignore" comment  [unused-ignore]
+ steam/chat.py:402: error: List item 0 has incompatible type "type[ClanT]"; expected "type[Group] | type[None] | type[Clan]"  [list-item]
+ steam/chat.py:402: error: List item 1 has incompatible type "type[GroupT]"; expected "type[Group] | type[None] | type[Clan]"  [list-item]
+ steam/chat.py:428: error: Argument 1 to "append" of "list" has incompatible type "GroupMessage[PartialMember | GroupMember] | ClanMessage[PartialMember | ClanMember]"; expected "ChatMessageT"  [arg-type]
- steam/message.py:15: error: Module "steam.channel" has no attribute "ClanChannel"; maybe "Channel"?  [attr-defined]
- steam/message.py:15: error: Module "steam.channel" has no attribute "GroupChannel"; maybe "GroupChannelProtos"?  [attr-defined]
- steam/message.py:15: error: Module "steam.channel" has no attribute "UserChannel"; maybe "Channel"?  [attr-defined]
- steam/message.py:16: error: Module "steam.clan" has no attribute "Clan"  [attr-defined]
- steam/message.py:16: error: Module "steam.clan" has no attribute "ClanMember"  [attr-defined]
- steam/message.py:18: error: Module "steam.group" has no attribute "Group"  [attr-defined]
- steam/message.py:18: error: Module "steam.group" has no attribute "GroupMember"  [attr-defined]
- steam/channel.py:16: error: Module "steam.clan" has no attribute "Clan"  [attr-defined]
- steam/channel.py:18: error: Module "steam.group" has no attribute "Group"  [attr-defined]
- steam/group.py:24: error: Cannot resolve name "Group" (possible cyclic definition)  [misc]
- steam/clan.py:55: error: TypeVar "bound" must be a type  [misc]
- steam/clan.py:58: error: Cannot resolve name "Clan" (possible cyclic definition)  [misc]
- steam/state.py:1476: error: Unused "type: ignore" comment  [unused-ignore]
- steam/state.py:1515: error: Unused "type: ignore" comment  [unused-ignore]
+ steam/state.py:2400: error: Argument 1 to "add" of "set" has incompatible type "CommentID | _ReadOnlyProto[CommentID]"; expected "int"  [arg-type]
- steam/client.py:74: error: Module "steam.ext.commands.bot" has no attribute "Bot"  [attr-defined]
+ steam/client.py:1290: error: Redundant cast to "list[TradeOffer[MovedItem[User], MovedItem[ClientUser], User]]"  [redundant-cast]
+ steam/client.py:1906: error: The erased type of self "steam.ext.commands.bot.Bot" is not a supertype of its class "steam.client.Client"  [misc]
+ steam/client.py:1915: error: The erased type of self "steam.ext.commands.bot.Bot" is not a supertype of its class "steam.client.Client"  [misc]
- steam/ext/commands/cooldown.py:16: error: Module "steam.ext.commands.context" has no attribute "Context"  [attr-defined]
- steam/ext/commands/cooldown.py:71: error: Argument 1 to "BucketTypeType" has incompatible type "Any | Role | RoleID | None"; expected "int | None"  [arg-type]
+ steam/ext/commands/cooldown.py:71: error: Argument 1 to "BucketTypeType" has incompatible type "Clan | Role | RoleID | None"; expected "int | None"  [arg-type]
+ steam/ext/commands/cooldown.py:77: error: Argument 1 to "BucketTypeType" has incompatible type "Clan | bool | None"; expected "int | None"  [arg-type]
- steam/ext/commands/context.py:21: error: Module "steam.ext.commands.bot" has no attribute "Bot"  [attr-defined]
- steam/ext/commands/context.py:22: error: Module "steam.ext.commands.commands" has no attribute "Command"; maybe "command"?  [attr-defined]
- steam/ext/commands/converters.py:44: error: Module "steam.ext.commands.bot" has no attribute "Bot"  [attr-defined]
- steam/ext/commands/commands.py:47: error: Module "steam.ext.commands.bot" has no attribute "Bot"  [attr-defined]
- steam/ext/commands/commands.py:48: error: Module "steam.ext.commands.cog" has no attribute "Cog"; maybe "CogT"?  [attr-defined]
- steam/ext/commands/commands.py:66: error: Cannot resolve name "CheckType" (possible cyclic definition)  [misc]
- steam/ext/commands/commands.py:69: error: Cannot resolve name "Command" (possible cyclic definition)  [misc]
- steam/ext/commands/commands.py:111: error: Cannot resolve name "GroupMixin" (possible cyclic definition)  [misc]
- steam/ext/commands/commands.py:111: error: Cannot resolve name "Group" (possible cyclic definition)  [misc]
- steam/ext/commands/commands.py:117: error: Cannot resolve name "Command" (possible cyclic definition)  [misc]
- steam/ext/commands/commands.py:117: error: TypeVar "bound" must be a type  [misc]
- steam/ext/commands/commands.py:117: error: TypeVar "default" must be a type  [misc]
- steam/ext/commands/commands.py:575: error: Cannot resolve name "CallbackT" (possible cyclic definition)  [misc]
- steam/ext/commands/commands.py:732: error: Unused "type: ignore" comment  [unused-ignore]
- steam/ext/commands/commands.py:831: error: Incompatible return value type (got "Any | Command[Any, Any, Any]", expected "C")  [return-value]
+ steam/ext/commands/commands.py:831: error: Incompatible return value type (got "C | Command[Any, Any, Any]", expected "C")  [return-value]
- steam/ext/commands/help.py:35: error: Redundant cast to "CommandKwargs[Any]"  [redundant-cast]
+ steam/ext/commands/help.py:35: error: Redundant cast to "CommandKwargs[Command[Cog[Bot] | Bot | None, [VarArg(Any), KwArg(Any)], Any]]"  [redundant-cast]
- steam/ext/commands/help.py:138: note:          def on_error(self, ctx: Context[Any], error: Exception) -> Coroutine[Any, Any, None]
+ steam/ext/commands/help.py:138: note:          def on_error(self, ctx: Context[Bot], error: Exception) -> Coroutine[Any, Any, None]
- steam/ext/commands/cog.py:20: error: Module "steam.ext.commands.bot" has no attribute "Bot"  [attr-defined]
- steam/ext/commands/cog.py:25: error: Cannot resolve name "UnboundListenerType" (possible cyclic definition)  [misc]
- steam/ext/commands/bot.py:49: error: Cannot resolve name "CommandPrefixType" (possible cyclic definition)  [misc]
- steam/ext/commands/bot.py:49: error: Cannot resolve name "Bot" (possible cyclic definition)  [misc]
- steam/ext/commands/bot.py:597: error: Unused "type: ignore" comment  [unused-ignore]
- steam/ext/commands/bot.py:599: error: Unused "type: ignore" comment  [unused-ignore]

Tanjun (https://github.com/FasterSpeeding/Tanjun)
- tanjun/hooks.py:191: error: Name "_MaybeAwaitable" is not defined  [name-defined]
- tanjun/hooks.py:207: error: Name "_MaybeAwaitable" is not defined  [name-defined]
- tanjun/hooks.py:221: error: Name "_MaybeAwaitable" is not defined  [name-defined]
- tanjun/components.py:147: error: Name "_MaybeAwaitable" is not defined  [name-defined]
- tanjun/commands/base.py:147: error: Name "_MaybeAwaitable" is not defined  [name-defined]
- tanjun/clients.py:147: error: Name "_MaybeAwaitable" is not defined  [name-defined]

ilevkivskyi · 2026-05-22T15:15:59Z

@JukkaL this is another PR in case you missed it.

ilevkivskyi added 5 commits May 10, 2026 23:08

Add limited implementation

7a07960

Merge remote-tracking branch 'upstream/master' into fix-tv-default-cr…

8efda98

…ashes

Support non-recursive incomplete defaults

cddf39f

Add more tests, fix new style classes

dbe1c63

Some cleanup

8597fc7

ilevkivskyi requested review from JukkaL, cdce8p and hauntsaninja May 15, 2026 15:12

ilevkivskyi added 2 commits May 15, 2026 16:27

Fix self-compilation

43586b6

Try better self-compilation fix

e456cbe

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ilevkivskyi added 2 commits May 15, 2026 19:15

Fix base classes

0f47216

Add custom note in case Any was forced

c0e7eda

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Merge remote-tracking branch 'upstream/master' into fix-tv-default-cr…

3d3a217

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Merge remote-tracking branch 'upstream/master' into fix-tv-default-cr…

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Fix various crahses on recursive type variable defaults#21491

Fix various crahses on recursive type variable defaults#21491
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