typing: add `from __future__ import annotations` to most files Now that py36 is no longer supported, we can postpone annotation evaluation. This means that the quoting is usually optional (for things imported under the guard of `if typing.TYPE_CHECKING:` to avoid circular imports), and there's less overhead on startup[1]. There may be some missing here. I backed out 6000f5b25c9b (which removed the `from __future__ import ...` that was supporting py2), reverted the changes in `contrib/`, `doc/`, and `tests/`, and then ran: $ hg status -n --change . | \ xargs sed -i -e 's/from __future__ import .*$/from __future__ import annotations/' There were some minor tweaks needed when reviewing (mostly making the spacing around the import consistent, and `mercurial/testing/__init__.py` had a multiline import that wasn't fully rewritten. [1] https://docs.python.org/3/whatsnew/3.7.html#pep-563-postponed-evaluation-of-annotations

format: add many "missing" comma Black was not adding them until the next changeset introduced a bunch of `from __future__ import annotations` to most file. Since it make the next changeset hard to read we introduce them in advance.

typing: simplify archive.gz writing and drop a few pytype suppressions I was waiting until 3.8 to use `Literal` to fix this, but there's also the ":" and "|" characters that are passed along here, meant only for the non-gz archive types. But manipulating what the local caller passes is silly- we know we're writing, so just open it for writing. As an added bonus, PyCharm stops flagging the call too (since it doesn't know about pytype suppression comments).