inspect, asyncio: Use more TypeGuards

[AlexWaygood]

Fixes #8009.

[AlexWaygood]

Interesting. @erictraut, any idea why the test cases I've added in this PR are failing pyright? Mypy seems to have no trouble with them.

[AlexWaygood]

Mypy primer analysis

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Most of these are just noise: mypy is just emitting slightly different error messages for things that already failed to type check.

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+ discord/ext/tasks/__init__.py:622: error: Incompatible return value type (got "Callable[..., CoroutineType[Any, Any, Any]]", expected "ET")

This one looks like a true positive to me. Source code here: https://github.com/Rapptz/discord.py/blob/334ef1d7facce9dbfba2a6924bf57fc59bc827b5/discord/ext/tasks/__init__.py#L598-L622

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aiohttp (https://github.com/aio-libs/aiohttp)
+ aiohttp/helpers.py:126: error: Incompatible redefinition (redefinition with type "Callable[[Any], bool]", original type overloaded function)  [misc]

pyinstrument (https://github.com/joerick/pyinstrument)
+ pyinstrument/vendor/decorator.py:66: error: Incompatible redefinition (redefinition with type "Callable[[Any], Any]", original type overloaded function)

These are both a little unfortunate, but can't really be helped. I think they will simply have to add type: ignores to their code if this PR is merged.

• aiohttp source code: https://github.com/aio-libs/aiohttp/blob/3a41da05bcb1edde9f6f878d9092e108e70dff2a/aiohttp/helpers.py#L122-L129
• https://github.com/joerick/pyinstrument/blob/b833b3f4a6b039354ed8bb747371d5f0d539010c/pyinstrument/vendor/decorator.py#L62-L67

[erictraut]

@AlexWaygood, pyright doesn't currently support TypeGuard on overloaded functions. Evaluating overloads is very expensive in the type narrowing code path because all argument types need to be evaluated first, so it creates a bunch of dependencies between expressions. For that reason, I didn't initially add support for this case. I can think of ways to limit the performance impact, but it will take some work. I've filed this feature enhancement request to track this.

[AlexWaygood]

I've filed this feature enhancement request to track this.

Thanks @erictraut!

I can think of ways to limit the performance impact, but it will take some work.

I'm in no particular rush with this PR :)

Evaluating overloads is very expensive in the type narrowing code path

If the performance impact is too large for pyright to tolerate, I suppose I could simply exclude the test cases from this PR -- these are the only bits that fail pyright. It seems that since pyright doesn't yet support combining overloads with TypeGuards, it just infers the return type of these overloaded functions as bool -- and that's what they are at the moment, anyway, so there wouldn't be a regression in pyright's understanding of these functions.

I think it would be unfeasible to consider a version of this PR without the overloads, however: the results from mypy-primer indicate to me that merging a version of this PR without the overloads would lead to an unacceptable number of false-positive errors when type-checking.

(Yet another option is obviously to close this PR and not bother too much about it.)

[erictraut]

This is included in pyright 1.1.255, which I just published.

[AlexWaygood]

This is included in pyright 1.1.255, which I just published.

Thank you very much! Everything looks to be working well now; the tests I've added are passing CI nicely.

For reviewers: mypy-primer analysis is in this comment here: #8057 (comment)

[github-actions]

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

discord.py (https://github.com/Rapptz/discord.py)
- discord/ext/tasks/__init__.py:564: error: Incompatible types in assignment (expression has type "FT", variable has type "None")
+ discord/ext/tasks/__init__.py:564: error: Incompatible types in assignment (expression has type "Callable[[VarArg(<nothing>), KwArg(<nothing>)], CoroutineType[Any, Any, <nothing>]]", variable has type "None")
+ discord/ext/tasks/__init__.py:565: error: Incompatible return value type (got "Callable[[VarArg(<nothing>), KwArg(<nothing>)], CoroutineType[Any, Any, <nothing>]]", expected "FT")
- discord/ext/tasks/__init__.py:592: error: Incompatible types in assignment (expression has type "FT", variable has type "None")
+ discord/ext/tasks/__init__.py:592: error: Incompatible types in assignment (expression has type "Callable[[VarArg(<nothing>), KwArg(<nothing>)], CoroutineType[Any, Any, <nothing>]]", variable has type "None")
+ discord/ext/tasks/__init__.py:593: error: Incompatible return value type (got "Callable[[VarArg(<nothing>), KwArg(<nothing>)], CoroutineType[Any, Any, <nothing>]]", expected "FT")
+ discord/ext/tasks/__init__.py:623: error: Incompatible return value type (got "Callable[..., CoroutineType[Any, Any, Any]]", expected "ET")
- discord/ext/commands/cog.py:215: error: Item "Group" of "Union[Any, Group, Command[Any, Any, Any]]" has no attribute "__cog_listener_names__"
+ discord/ext/commands/cog.py:215: error: "Callable[..., CoroutineType[Any, Any, Any]]" has no attribute "__cog_listener_names__"
- discord/ext/commands/cog.py:215: error: Item "Command[Any, Any, Any]" of "Union[Any, Group, Command[Any, Any, Any]]" has no attribute "__cog_listener_names__"
- discord/ext/commands/cog.py:218: error: Item "Group" of "Union[Any, Group, Command[Any, Any, Any]]" has no attribute "__name__"
- discord/ext/commands/cog.py:218: error: Item "Command[Any, Any, Any]" of "Union[Any, Group, Command[Any, Any, Any]]" has no attribute "__name__"

aiohttp (https://github.com/aio-libs/aiohttp)
+ aiohttp/helpers.py:126: error: Incompatible redefinition (redefinition with type "Callable[[Any], bool]", original type overloaded function)  [misc]

pyinstrument (https://github.com/joerick/pyinstrument)
+ pyinstrument/vendor/decorator.py:66: error: Incompatible redefinition (redefinition with type "Callable[[Any], Any]", original type overloaded function)