Improve dict's constructor type

[sobolevn]

This is quite hard. So, let me explain.

Right now when doing something like this:

from typing import Iterable, Tuple
x1: Iterable[Tuple[str, bool]]
reveal_type(dict(x1, arg=True))  # N: Revealed type is "builtins.dict[builtins.str, builtins.bool]"

x2: Iterable[Tuple[int, bool]]
reveal_type(dict(x2, arg=True))  # E: Keyword argument only valid with "str" key type in call to "dict"

mypy has to special-case this check. Which is not good.

I think this can be easily expressed by the type-system itself.

[AlexWaygood]

Please note the comments on lines 1017-1018 :)

[AlexWaygood]

Can you add some test cases for the various exotic ways of constructing a dict that the stub is trying to account for? 6 overloads is frying my brain a little :(

[sobolevn]

Looks like pyright does a lot of quite different things to mypy in terms of dict analysis 🤔

[sobolevn]

What should we do in this case? All mypy tests pass, but pyright fails

[sobolevn]

  /home/runner/work/typeshed/typeshed/test_cases/stdlib/builtins/test_dict.py:39:13 - error: "assert_type" mismatch: expected "int" but received "Literal[1, 2]"
  /home/runner/work/typeshed/typeshed/test_cases/stdlib/builtins/test_dict.py:40:13 - error: "assert_type" mismatch: expected "str" but received "Literal['a', 'b']"

🤣

[sobolevn]

I think I finally solved it! 🎉
(by removing ones that were problematic, but anyways)

I think in the future we can end up doing something like the runtime does:

>>> i = [(1, True)]
>>> dict(i, arg=1.5)
{1: True, 'arg': 1.5}

Probably like:

class dict(MutableMapping[_KT, _VT], Generic[_KT, _VT]):
    def __init__(self: dict[_KT | str, _VT | _NVT], __iterable: Iterable[tuple[_KT, _VT]], **kwargs: _NVT) -> None: ...

But, this will be very major change! This 100% needs proper discussion.

For now, I consider this PR complete 🙂

[sobolevn]

Adding suggetions now work again, I think it is a proper time for an old meme!

[AlexWaygood]

Hooray!

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉