[3.6] bpo-30266: support "= None" pattern in AbstractContextManager (…

[Mariatta]

…GH-1448)

contextlib.AbstractContextManager now supports anti-registration
by setting enter = None or exit = None, following the pattern
introduced in bpo-25958..
(cherry picked from commit 57161aa)

[gvanrossum]

Note the subject of the commit message got truncated and the overflow went into the body.

Also I wonder if it's useful for bpo to send out email when a closed issue is mentioned by a PR. I got pinged on this issue even though it was closed for nearly a year and mentioned, because it was mentioned in the commit message here.

[Mariatta]

Thanks @gvanrossum :)

Seems like this PR was incorrectly linked to an old issue (bpo-25958), it should only be linked to bpo-30266, which is referenced in the title.

I have just opened in up a bug for it here and unlinked this PR from bpo-25958.

Also I wonder if it's useful for bpo to send out email when a closed issue is mentioned by a PR.

Maybe this can be asked to a broader audience, e.g. at core-workflow :)

The text overflow is just in the PR title and description. The actual commit message will not be broken up, and we do get the opportunity to clean up the commit message:

[Mariatta]

Hmm unlinking it didn't work...