git-arc: Add list mode support for the update command

This can be particularly useful to do bulk-updates of multiple commits
using the same message, e.g.

git arc update -lm "Move function xyz to libfoo" main..myfeature

Similar to the list mode for the create command, git arc will list all
the candidate revisions with a single prompt. Once that is confirmed,
all the revisions are updated without showing the diffs or pausing
further prompts.

Reviewed by: markj
Differential Revision: https://reviews.freebsd.org/D45050

tools/git: ensure git-arc is more platform indepdendent

Summary:
Linux systems' tail doesn't have `-r`.
Instead, we can use git's own `--reverse` sorting for `rev-list`s.

Reviewed by: markj, imp, jhibbits
Differential Revision: https://reviews.freebsd.org/D39975

git-arc: Retain color status messages

Newer versions of archanist have an --ansi option to always include the
ansi colors when doing an arc list (or any command really). Add this to
the arc list that's relevant. Add filter to filter out the 'bolding'
though since that interferes with our parsing. This should restore the
color output after df834e06bbc7.

Fixes: df834e06bbc7
Sponsored by: Netflix
Reviewed by: markj, jhb
Differential Revision: https://reviews.freebsd.org/D43459

git-arc: Add -c flag to patch to commit the change

git arc patch -c D1234 will download differential D1234, try to apply it
to the tree, and if successful will ask phab for the title and
summary. It will construct a commit message with that, the reviewers,
and the differential revision. It also tries its best to deduce the
proper 'author' to use for the commit, and warn if it thinks it has made
a bad choice.

Sponsored by: Netflix
Reviewed by: markj
Differential Revision: https://reviews.freebsd.org/D39992

git-arc: Cope with extra output

On my machine, for reasons beyond my understanding, I get this warning
two times when running arc:

Warning: Module "openssl" is already loaded in Unknown on line 0

so grep -v ^Warning: on all the arc call-conduit calls to filter them
out so we can properly parse the JSON with jq.

Sponsored by: Netflix
Reviewed by: markj, jhb
Differential Revision: https://reviews.freebsd.org/D36583

git-arc: Just strip escape sequences form arc log

Just strip escape sequences and Warning: lines from 'arc list' output. I
upgraded and they changed and git arc list broke. This restores its
functionality.

Note: jhb didn't like this, so if others object, I'll fix...

Sponsored by: Netflix
Reviewed by: markj
Differential Revision: https://reviews.freebsd.org/D36553

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

git-arc: Accept message via -m when updating reviews.

If a -m argument is given to update, it is passed through to arc diff
when updating each review. Note that if an empty message is specified
via -m, arc diff will update the review without adding a note.

If an -m argument is not given, then the user's editor is invoked by
arc to supply a message for each review matching the previous
behavior.

This can be used to simplify the process for updating a set of
reviews, e.g.:

git checkout foo
git rebase main
git arc update -m "Rebase" main..

This will rebase the 'foo' branch and update the reviews for all
commits on the branch without invoking the user's editor separately
for each review.

Reviewed by: markj
Differential Revision: https://reviews.freebsd.org/D37260

git-arc: Fix handling of review title containing double quotes

git-arc: Respect GIT_EDITOR and GIT_PAGER

git-arc: Fix whitespace

git-arc: Use --head to avoid changing the checkout.

Rather than using 'git checkout' to move to the commit in question for
create and update, use the '--head' argument to 'arc diff'. This
avoids the need to alter the current checkout and the related bits to
save/restore HEAD in the current checkout.

Reviewed by: imp, markj
Differential Revision: https://reviews.freebsd.org/D36248

git-arc: Fix the -y option

git-arc: Fix review title matching

Properly handle the case where the title of one commit is a suffix or
prefix of the title of a second commit, and one wishes to create reviews
for both.

Reported by: chuck

git-arc: with "create" allow to specify parent of the first commit

Reviewed by: markj
Differential revision: https://reviews.freebsd.org/D33045

git-arc: allow word splitting in build_commit_list()

git-rev-list expects commits to be listed separately, allow word
splitting and disable shellcheck SC2086 when using git-rev-list
to build the commit list.

Fixes: 4fd0c6ab1a9e ("Fix most shellcheck warnings in git-arc.sh")
Reviewed by: markj
Differential Revision: https://reviews.freebsd.org/D31838

git-arc.sh: Make it compatible with Ubuntu 18.04

dash does not allow function names containing a ":", so replace it with
a '_'. Additionally, Ubunutu 18.04 ships git 2.17 which does not support
the `--default false` flag for git config.

Reviewed By: markj
Differential Revision: https://reviews.freebsd.org/D29374

Fix most shellcheck warnings in git-arc.sh

Mostly adding quotes and replacing egrep/fgrep with grep -E/grep -F

Reviewed By: markj
Differential Revision: https://reviews.freebsd.org/D29373

git-arc: Handle commit ranges in the "update" verb

Reported by: imp

git-arc: Preserve the commit author when staging commits

Reported by: jhb

git-arc: Globally save and restore the git checkout head

This script uses -e, so it's prone to exiting in awkward places. In
particular, if arc diff fails, the script just exits without restoring
the checkout.

Mitigate this for now by using a global variable to record the previous
checkout and use a trap handler to restore it in the face of errors. A
better solution might be to use arc diff's --head parameter but that
will require more testing.

Reported by: kevans
Reviewed by: jhb
Differential Revision: https://reviews.freebsd.org/D28631

git-arc: Use a separate message file

Rather than putting revision metadata in .git/arc/create-message, create
a tmpfile and use that. Otherwise arc diff always prompts about it and
in some cases complains because its standard input is piped.

Reported by: imp
Differential Revision: https://reviews.freebsd.org/D28614

tools/git: Add git-arc

This is a handy script for creating and updating Differential revisions
from git commits. It tries to avoid forcing the user to manage their
git tree in any particular way, but makes two major assumptions:
- there is a one-to-one mapping between git commits and Differential
revisions,
- the title of a Differential revision is the same as the summary line
of the corresponding commit.

A verbose description of the script's functionality is provided in its
usage message, which should probably be converted to a man page.

A description of workflows using git-arc is here:
https://lists.freebsd.org/pipermail/freebsd-hackers/2021-January/056979.html

There are some loose ends but this is functional enough to be useful.

Discussed with: jhb
Differential Revision: https://reviews.freebsd.org/D28334