Coverage status reported for "not TYPE_CHECKING" blocks

I'm not sure whether this qualifies as a bug, feature request or discussion.

I have a code base that I want to be able to run on Python 3.5 (the version in Debian stable at the moment), without introducing additional runtime dependencies (depending on typing_extensions while type checking is fine, but I don't want to force every end user to install it). Therefore, I made the following workaround for NoReturn:

# NoReturn was introduced in Python 3.6.5.
if TYPE_CHECKING:
	from typing_extensions import NoReturn
else:
	NoReturn = None

This works fine, both at runtime and when type checking. However, when I ask mypy to produce a coverage report, the NoReturn = None line shows up red.

Other code I put in the else body, for example a print statement, also shows up red. My guess is that mypy doesn't type check the else body because TYPE_CHECKING is True and then marks all code that it doesn't have information on as red.

I use the coverage report to see if there is anything regarding type hinting that can be improved in modules and these red lines from not TYPE_CHECKING blocks are noise that makes it harder to spot areas that could be improved. So for my use case, it would be better if blocks that are deliberately unchecked would be marked in either green or a new low-attention color like white or grey.

首先跟踪 mypy 对 TYPE_CHECKING 分支的 coverage 报告处理，并比较 else 代码体是如何分类的。当 not TYPE_CHECKING 块中有意不检查的代码不再显示为需要处理的红色 coverage，同时普通的未覆盖代码仍可区分时，这项工作就完成了。