Welcome to the 75th edition of Git Rev News, a digest of all things Git. For our goals, the archives, the way we work, and how to contribute or to subscribe, see the Git Rev News page on git.github.io.
This edition covers what happened during the month of April 2021.
Git participates in GSoC (Google Summer of Code) 2021
The following two students have been officially accepted to work on Git as part of the GSoC 2021:
ZheNing Hu will work on the
Use ref-filter formats in git cat-file
project. He will be co-mentored by Hariom Verma and Christian
Couder. His first blog post about it is up.
Atharva Raykar will work on the Finish converting submodule to builtin project. He will be co-mentored by Shourya Shukla and Christian Couder. His first blog posts about it are also up.
Thanks to the students who applied and worked on micro-projects, but couldn’t be selected! We hope to continue to see you in the community!
Felipe Contreras posted a fun analysis of how often various commit
trailers (reviewed-by, tested-by, etc) appear in the git.git project.
Setting aside signed-off-by (which all contributions must include),
the most common trailers are acked-by (1945 occurences) and
reviewed-by (1729 occurences), together accounting for almost half
of all trailers.
The next 4 most common trailers give a great insight into just how
much collaboration goes on in the git.git project: helped-by (1336),
reported-by (960), mentored-by (379), and suggested-by (281).
Perhaps most interesting is the long list of trailers that have only
been seen once, though now that this list is out there we may see more
of deemed-obviously-correct-by, worriedly-acked-by, and cheered-on-by
in the future.
One can also note that this distribution roughly follows Zip’s law; the 10th most popular line (“improved-by”) is about 1/10 as popular as the 1st.
This script can be used to replicate the analysis.
[PATCH] [GSOC] pretty: provide human date format
ZheNing Hu sent a patch to the mailing list to add the new %ah and
%ch formatting options to the “pretty formats”. The “pretty
formats” are the main way for users to customize the output of the
git log, git show, git rev-list, and git diff-tree commands.
These formats are specified by the
--pretty[=<format>] or --format=<format>
command line flags, where <format>is the actual
“pretty format”,
and can be either a “built-in format”, like oneline, raw,
short, medium, etc, or format:<string>, which is called a
“format string”.
These format strings work in a similar way to printf() formats, as
they can contain placeholders starting with a % character, that
will be expanded by the command. For example %H will be expanded
to print the commit hash, %an the author name, etc.
A lot of placeholders already exist. For the author date, there are:
%ad, %aD, %ar, %at, %ai, %aI and %as. For the
committer date, there are the corresponding %cd, %cD, %cr,
%ct, %ci, %cI and %cs ones. Each pair of these placeholders uses
a different date format. For example, %aI and %cI use the “strict
ISO 8601 format”.
Formats %ad and %cd, though, are special as they use the format specified
by the --date=<format> command line flag, so for example with
--date=iso-strict, %ad and %cd will behave in the same way as
%aI and %cI.
ZheNing’s patch added the new %ah and %ch placeholders that
would behave in the same way as %ad and %cd with
--date=human. The rationale for the patch being that there are
placeholders corresponding to most of the --date=<format> options
except --date=human.
Taylor Blau was the first to review ZheNing’s patch and found it
“pretty good”, as it was similar to a previous patch by René Scharfe
that added the %as and %cs placeholders for dates in the “short
date format”. ZheNing acknowledged that he indeed learned from
René’s patch.
Philip Oakley, though, commented on the documentation part of the
patch suggesting to add an example similar to YYYY-MM-DD for the
short format. ZheNing replied that in the “human format” a date
could take many forms, so he said he would rather add links to the
documentation of the “human format”.
ZheNing then sent a version 2 of his patch where he had added the links. Philip suggested further small superficial changes to the link and the related text added in this version though.
Meanwhile Ævar Arnfjörð Bjarmason sent
a small patch series
that made a “couple of trivial changes” to the tests related to
%aI and %cI, and at the same time suggested ZheNing to make
similar changes to the tests in his patch.
ZheNing then sent a version 3 of his patch, taking Philip’s and Ævar’s suggestions into account. This patch contained a typo, though, so ZheNing sent a version 4 of his patch.
As the version 3 of the patch had already been merged to the “next” branch before ZheNing sent the version 4, the typo got noticed by Martin Ågren who sent a small patch series fixing this typo as well as another unrelated one.
Eventually both ZheNing’s patch and Martin’s patches were merged into the “master” branch, so that their improvements will appear in the soon upcoming Git version v2.32.0.
Who are you and what do you do?
I’m a software developer working at GitLab, more specifically in the team working on Gitaly. Gitaly is our RPC interface to all Git repositories, so it is the backbone to all things Git at GitLab.
In my own free time, I love to tinker with my Gentoo-based systems and tailor them to my own needs, which results in occasional drive-by patches to all kinds of open source projects to scratch my own itches.
What would you name your most important contribution to Git?
To me, this is the introduction of the reference-transaction hook, which gets executed whenever a reference is about to be updated. This allows tight control over all reference updates happening in a given repository in a command-agnostic way. At GitLab, we use this hook to coordinate reference updates across multiple replicas of the same repository such that we can be sure that all nodes have the same state and move to the same state.
My most important contributions I’d not locate in the Git project itself though, but instead in libgit2. While I unfortunately haven’t found the time to contribute to it lately, I’ve done a lot more work on libgit2 than I did on Git. And there it’s probably the initial introduction of support for worktrees, maintenance of the CMake build system and work on the gitconfig subsystem.
What are you doing on the Git project these days, and why?
My current work is mostly focussed on tuning performance of some areas
we have found to be slow for gitlab.com. This has motivated the recent
introduction of a new git-rev-list(1) filter which allows to filter by
object type via --filter=object:type=<type>. This makes it easy to
find for example all blobs introduced between two revisions.
And right now I’m trying to devise a new implementation of the object
connectivity check performed by git-receive-pack(1) whenever a push gets
accepted on the server side. Depending on the repository’s shape, the
current implementation can be a major bottleneck and take dozens of
seconds to compute even for small pushes. You may have noticed this
check when it says “Checking connectivity” on a push.
If you could get a team of expert developers to work full time on something in Git for a full year, what would it be?
I’m obviously biased coming from the libgit2 project, but I’d really love to further push the libification of Git. There has been great progress on this front already to make internal C interfaces look more like the typical interfaces you’d see from a linkable library. But my dream would be to merge the efforts of Git and libgit2 such that Git also provides an official library which can be linked against in your own program.
If you could remove something from Git without worrying about backwards compatibility, what would it be?
Tough question. There’s many user-facing commands which could benefit from a more consistent design, but my take is that these probably could provide an improved user interface while still retaining backwards compatibility.
But what I’d really love to get rid of is the file-based reference backend. It works reasonably well to represent references as file paths in smallish repositories, but even there it imposes limitations which are only a result of its implementation. It’s also inefficient for bigger repositories and does not really allow for atomic modification of multiple references at once. There luckily is ongoing work on the reftable backend, which fixes many of the shortcomings, but it will likely still take some time to land.
What is your favorite Git-related tool/library, outside of Git itself?
I guess the answer to that question is going to be obvious by now: libgit2.
Various
ecdsa-sk and ed25519-sk key types.Light reading
post-receive hook) by Ricardo Ander-Egg Aguilar.Git tools and sites
core.pager or pager.diff.This edition of Git Rev News was curated by Christian Couder <christian.couder@gmail.com>, Jakub Narębski <jnareb@gmail.com>, Markus Jansen <mja@jansen-preisler.de> and Kaartic Sivaraam <kaartic.sivaraam@gmail.com> with help from Patrick Steinhardt, Andrew Ardill, Felipe Contreras and Jonas Bernoulli.