Fix decorator typing issue.

[rodrigogiraoserrao]

@willmcgugan like I mentioned previously, this seems to be the issue and Pylance is happy about it but mypy complains in other places about the changes I made.

In particular, running mypy (both 1.7.1 and 1.9.0+dev.0567da99784c376e723907daf4f16df2f03368c1 0567da9) in our codebase introduces these type errors:

new mypy errors

src/textual/widgets/_log.py:120: error: Argument 1 has incompatible type "Callable[[Log, int, List[str]], None]"; expected "Union[Callable[[VarArg(Never), KwArg(Never)], Never], Callable[[VarArg(Never), KwArg(Never)], Coroutine[Any, Any, Never]]]"  [arg-type]
src/textual/widgets/_log.py:223: error: Invalid self argument "Self" to attribute function "_update_size" with type "Callable[[VarArg(Never), KwArg(Never)], Worker[Never]]"  [misc]
src/textual/widgets/_log.py:223: error: Argument 1 to "_update_size" of "Log" has incompatible type "int"; expected Never  [arg-type]
src/textual/widgets/_log.py:223: error: Argument 2 to "_update_size" of "Log" has incompatible type "List[str]"; expected Never  [arg-type]
src/textual/widgets/_directory_tree.py:182: error: Invalid self argument "DirectoryTree" to attribute function "_loader" with type "Callable[[VarArg(Never), KwArg(Never)], Worker[Never]]"  [misc]
src/textual/widgets/_directory_tree.py:396: error: Argument 1 has incompatible type "Callable[[DirectoryTree, TreeNode[DirEntry]], List[Path]]"; expected "Union[Callable[[VarArg(Never), KwArg(Never)], Never], Callable[[VarArg(Never), KwArg(Never)], Coroutine[Any, Any, Never]]]"  [arg-type]
src/textual/widgets/_directory_tree.py:414: error: Argument 1 has incompatible type "Callable[[DirectoryTree], Coroutine[Any, Any, None]]"; expected "Union[Callable[[VarArg(Never), KwArg(Never)], Never], Callable[[VarArg(Never), KwArg(Never)], Coroutine[Any, Any, Never]]]"  [arg-type]
src/textual/widgets/_directory_tree.py:426: error: Invalid self argument "DirectoryTree" to attribute function "_load_directory" with type "Callable[[VarArg(Never), KwArg(Never)], Worker[Never]]"  [misc]
src/textual/widgets/_directory_tree.py:426: error: Argument 1 to "_load_directory" of "DirectoryTree" has incompatible type "TreeNode[DirEntry]"; expected Never  [arg-type]
src/textual/command.py:810: error: Argument 1 has incompatible type "Callable[[CommandPalette, str], Coroutine[Any, Any, None]]"; expected "Union[Callable[[VarArg(Never), KwArg(Never)], Never], Callable[[VarArg(Never), KwArg(Never)], Coroutine[Any, Any, Never]]]"  [arg-type]
src/textual/command.py:948: error: Invalid self argument "CommandPalette" to attribute function "_gather_commands" with type "Callable[[VarArg(Never), KwArg(Never)], Worker[Never]]"  [misc]
src/textual/command.py:948: error: Argument 1 to "_gather_commands" of "CommandPalette" has incompatible type "str"; expected Never  [arg-type]

It does get rid of the errors in _work_decorator.py, both for mypy and pylance.

I'll leave it up to you if we want to roll with these changes, mark this as draft, or just reject the PR.

Extra context:

• See [typing] Inconsistent typing in the work decorator #3510 (comment)

Fixes #3510 .

[rodrigogiraoserrao]

Coroutines like async def foo() -> T: ... have their type inferred as Coroutine[Any, Any, T], so I swapped all of the Coroutine[None, None, T] for Coroutine[Any, Any, T] under the assumption that the usage of None was a mistake.

[davep]

Is it possible to get a concise explanation/example of what this addresses? I've followed the reference chain here but there's a lot of discussion and it's not clear to me what this finally changes and why. For example:

It does get rid of the errors in _work_decorator.py, both for mypy and pylance.

As I look at _work_decorator.py using pyright, I don't see any errors. What should I be looking for?

[rodrigogiraoserrao]

What should I be looking for?

Running make typecheck (at the tip of main, 03fb1b1 at the time of writing) will surface one error here:

textual/src/textual/_work_decorator.py

Line 74 in 03fb1b1

) -> Decorator[..., ReturnType]:

src/textual/_work_decorator.py:74: error: Type variable "textual._work_decorator.ReturnType" is unbound  [valid-type]
src/textual/_work_decorator.py:74: note: (Hint: Use "Generic[ReturnType]" or "Protocol[ReturnType]" base class to bind "ReturnType" inside a class)
src/textual/_work_decorator.py:74: note: (Hint: Use "ReturnType" in function signature to bind "ReturnType" inside a function)

Additionally, in the signature of the concrete definition of work,

textual/src/textual/_work_decorator.py

Lines 78 to 89 in 03fb1b1

	def work(
	method: Callable[FactoryParamSpec, ReturnType]
	| Callable[FactoryParamSpec, Coroutine[None, None, ReturnType]]
	| None = None,
	*,
	name: str = "",
	group: str = "default",
	exit_on_error: bool = True,
	exclusive: bool = False,
	description: str | None = None,
	thread: bool = False,
	) -> Callable[FactoryParamSpec, Worker[ReturnType]] | Decorator:

Pylance complains that

1. the return type of work is partially unknown; and
2. it expected type arguments for the generic type alias Decorator in the return type.

On top of this, typing in places where this decorator is used gets screwed up because inference breaks.

[rodrigogiraoserrao]

@willmcgugan Feel free to take a look when you're ready. Might be worth considering #3937 as well.

[willmcgugan]

@rodrigogiraoserrao I don't think we can accept this if it causes other others. Are the other errors a direct consequence of this change, and could they be fixes relatively easily?

[rodrigogiraoserrao]

They are direct consequences.
In principle they cannot be fixed easily because it looks like it surfaced a mypy bug.
At this point, the external PR #3937 supersedes this one.
I'm keen on closing this so as to not waste any more time on this specific PR.