In the general case, the problem is that some invocations of arc, including arc land --pick A, may select an arbitrary range of commits to land which have some ancestors that we do NOT want to land.

git diff ...

Couple minor inlines, but looks good to me. I added you to Blessed Committers so you should be able to land this yourself -- see the description of that project for guidance, or let me know if you run into issues.

Broadly, I believe these "certain changes" are approximately changes which include a merge commit.

• Text tidying.

This is actually very subtle.

In general, Phacility production hosts may interact with logs as several different users:

This ran into some filesystem permissions issues and needs followup.

When we are importing a commit, we often don't have any legitimate user to act as: the commit may come from an observed repository (so we never authenticated a pusher), and the "Author" and "Committer" strings are arbitrary and untrusted in Git and Mercurial.

All three of these are almost certainly diffusion.rawdiffquery, I think the first one just predated D21463 reaching production so it didn't show the method.

This deployed, and appears resolved.

I deployed this and nothing blew up, presuming this is resolved.

Presuming this is resolved until evidence to the contrary arises.

Calls to preg_* can still be swapped to phutil_preg_* to improve behavior, but this seems basically resolved.

Enable the SSH and HTTP application logs on the web, repo and admin tiers.

• This was originally implemented in D19357.
• This was broken by a refactoring change in D20775.
• I made problem observable in D21575 fixed it in D21576.

See T13611. This was broken by D20775 (September 2019) until D21576 (February 2021).

This is a brute force approach to support "context blocks" without taking any steps backwards (i.e., it supports older transactions and newer, modular transactions), but it feels like this is a lot of steps sideways and this change would be far better if it took a nuanced approach through T12921.

When users are @mentioned on an object, render their name in a disabled style if they've been muted.

See also T13068, which suggests rendering mentions in a special style when the user has muted the object.

This presumably worked. T12404 survives it, but that task captures everything remaining here.

• T12921 is adjacent to mail rendering.
• T13439 mentioned the hovercard summary text.

D21574 implements the hovercard and summary length changes.