Fix @reify type hints

[atugushev]

What do these changes do?

Fixes an issue where mypy would incorrectly infer types from wrapped methods by @reify decorator (e.g., web.Request.match_info).

The solution inspired by @cached_property type hints from typeshed repository. Thanks to @asottile for the assistance!

Before

# t.py
from typing import Callable
from typing import Any


class reify:
    def __init__(self, wrapped: Callable[..., Any]) -> None:
        ...

    def __get__(self, inst: Any, owner: Any) -> Any:
        ...

    def __set__(self, inst: Any, value: Any) -> None:
        ...


class Foo:
    @reify
    def bar(self) -> str:
        return "I'm Bar!"


foo = Foo()
print(foo.bar + 42)  # Note str + int 

$ mypy t.py
Success: no issues found in 1 source file

After

# t.py
from typing import Callable
from typing import Generic
from typing import Optional
from typing import Type
from typing import TypeVar
from typing import Any

_T = TypeVar("_T")
_S = TypeVar("_S")


class reify(Generic[_T]):
    def __init__(self, wrapped: Callable[..., _T]) -> None:
        ...

    def __get__(self, inst: _S, owner: Type[Any] = None) -> _T:
        ...

    def __set__(self, inst: _S, value: _T) -> None:
        raise AttributeError("read-only")


class Foo:
    @reify
    def bar(self) -> str:
        return "I'm Bar!"


foo = Foo()
print(foo.bar + 42)  # Note str + int 

$ mypy t.py
t.py:30: error: Unsupported operand types for + ("str" and "int")
Found 1 error in 1 file (checked 1 source file)

Are there changes in behavior for the user?

The mypy users would probably notice this change since mypy now can infer types from various aiohttp objects. For example,request.match_info["foo"] now infers to str (previously Any).

Related issue number

None.

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> for example (588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the pr
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: "Fix issue with non-ascii contents in doctest text files."

[atugushev]

Ouch, this is much more complicated than I would expect. Sorry for the ping! I'll fix up later.

[codecov-io]

Codecov Report

Merging #4736 into master will decrease coverage by 0.01%.
The diff coverage is 90.00%.

@@            Coverage Diff             @@
##           master    #4736      +/-   ##
==========================================
- Coverage   97.62%   97.60%   -0.02%     
==========================================
  Files          43       43              
  Lines        8936     8946      +10     
  Branches     1407     1409       +2     
==========================================
+ Hits         8724     8732       +8     
- Misses         95       96       +1     
- Partials      117      118       +1     

Flag	Coverage Δ
#unit	97.60% <90.00%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
aiohttp/web_urldispatcher.py	98.79% <50.00%> (-0.30%)	⬇️
aiohttp/client_exceptions.py	100.00% <100.00%> (ø)
aiohttp/helpers.py	96.65% <100.00%> (+0.04%)	⬆️
aiohttp/http_websocket.py	98.64% <100.00%> (ø)
aiohttp/web_request.py	97.59% <100.00%> (+0.01%)	⬆️

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[atugushev]

It's ready for the review. I've fixed typing issues wich required by mypy due to changes to @reify. Feel free to bikeshed variable names I've picked. I'm not good at naming. :D

Also, it seems I've touched uncovered lines, so I presume we could ignore failed codecov checks.

[atugushev]

@webknjaz gentle ping

[asvetlov]

Great!
Thanks!

[github-actions]

💔 Backport was not successful

The PR was attempted backported to the following branches:

• ❌ 3.7: Commit could not be cherrypicked due to conflicts