TypingError: type checker will emit error with a message specified in typing stubs

Some ways to call certain functions are just wrong, and are known to be a bug. For example, passing type=bool to argparse's add_argument method doesn't work. To make type checkers warn about this, typeshed can currently do something like this:

@overload
def add_argument(self, unrelated args, type: Type[bool], more unrelated args) -> NoReturn: ...
@overload
def add_argument(self, unrelated args) -> None: ...

When add_argument is used wrongly, you would then get errors:

import argparse
parser = argparse.ArgumentParser(description="My parser")
parser.add_argument("--my_bool", type=bool)
print(parser.parse_args())  # Error: statement is unreachable

This approach has a couple problems:

• The type checker's error message doesn't say "you passed in type=bool and it's wrong". It says "statement is unreachable".
• The type checker's error message appears on a different line than where the buggy code is.
• Unreachable code warnings are disabled by default in mypy, even with --strict.

The solution I would like: if you declare the return type as TypingError["foo bar"], the type checker will display an error message foo bar. This is similar to how #error works in the C preprocessor.

Stub:

@overload
def add_argument(
    self, unrelated args, type: Type[bool], more unrelated args
) -> TypingError["type=bool doesn't work, see https://stackoverflow.com/q/15008758"]: ...
@overload
def add_argument(self, unrelated args) -> None: ...

Python file:

import argparse
parser = argparse.ArgumentParser(description="My parser")
parser.add_argument("--my_bool", type=bool)  # Error: type=bool doesn't work, see https://stackoverflow.com/q/15008758
print(parser.parse_args())

先从本 issue 中 TypingError 的返回类型提案和 overload 示例开始，然后确定相关的 type-checker 或 typing-spec 入口点。完成的标准是：checker 在出错的调用位置报告所提供的消息，同时保留正常的 overload 行为。