My new Git utility `what-changed-twice` needs a new name(blog.plover.com)
blog.plover.com
My new Git utility `what-changed-twice` needs a new name
https://blog.plover.com/2025/09/21/#what-changed-twice
64 comments
At the time I started writing the article, the utility was called `analyze-commits`. Hard to think of a worse name than that!
By the time I finished writing it I had come up with a less crappy name, but I thought I'd leave the question in the post anyway.
By the time I finished writing it I had come up with a less crappy name, but I thought I'd leave the question in the post anyway.
If you’re looking for something descriptive and not clever/catchy, I propose ‘find-repeat-changes’.
Just gonna +1 this. It's still fairly short, descriptive and to the point, which I generally prefer to something more "trendy" or "clever". I like it.
What about git n-changed or even git nchanged. I feel like these commands need to be short and not consist of >3 words.
[deleted]
Or indeed "Find Repeat EDits" or fred for short.
Jujutsu has a command which is helpful for this sort of workflow called absorb which pushes all changes from the current commit into the most recent commit which modified that file. (Each file may be merged into a different commit).
This seems very similar to how I work by default. I sort of think in terms of "keyframes" and "frames", or "commits" and "fixes to commits."
Whenever I sit down to code with a purpose, I'll make a branch for that purpose: git checkout -b wip/[desc]
When I make changes that I think will be a "keyframe" commit, I use: git add . git commit -m "wip: desc of chunk" (like maybe "wip: readme")
if I make refinements, I'll do: git add . git commit --amend
and when I make a nee "keyframe commit": git commit -m "wip: [desc 2]"
and still amend fixes.
Occasionally I'll make a change that I know fixes something earlier (i.e. an earlier "keyframe" commit) but I won't remember it. I'll commit and then do: git add . git commit -m "fixup: wip desc, enough to describe which keyframe commit should be amended"
at the end I'll do a git rebase -i main and see something like:
123 wip: add readme (it's already had a number of amends made to it) 456 wip: add Makefile (also has had amendments) 789 wip: add server (ditto) 876 fixup: readme stuff 098 fixup: more readme 543 fixup: makefile
and I'll use git rebase -i to change it to reword for the good commits, and put the fixups right under the ones they edit. then i'll have a nice history to fast forward into main.
Whenever I sit down to code with a purpose, I'll make a branch for that purpose: git checkout -b wip/[desc]
When I make changes that I think will be a "keyframe" commit, I use: git add . git commit -m "wip: desc of chunk" (like maybe "wip: readme")
if I make refinements, I'll do: git add . git commit --amend
and when I make a nee "keyframe commit": git commit -m "wip: [desc 2]"
and still amend fixes.
Occasionally I'll make a change that I know fixes something earlier (i.e. an earlier "keyframe" commit) but I won't remember it. I'll commit and then do: git add . git commit -m "fixup: wip desc, enough to describe which keyframe commit should be amended"
at the end I'll do a git rebase -i main and see something like:
123 wip: add readme (it's already had a number of amends made to it) 456 wip: add Makefile (also has had amendments) 789 wip: add server (ditto) 876 fixup: readme stuff 098 fixup: more readme 543 fixup: makefile
and I'll use git rebase -i to change it to reword for the good commits, and put the fixups right under the ones they edit. then i'll have a nice history to fast forward into main.
I think you might be aware given the specific words you use but for the benefit of others:
Git commit --fixup lets you attach new commits to previous hashes you specify and then can automatically (or semi-manually depending on settings) squash them in rebases.
Git commit --fixup lets you attach new commits to previous hashes you specify and then can automatically (or semi-manually depending on settings) squash them in rebases.
You can combine this with the `:/<text>` syntax [0] for matching the most recent commit with a given text in the commit message, e.g.
$ commit frobinator/ -m "refactor the frobnicator"
[ more work ]
$ commit echaton/ -m "immanentize the eschaton"
[ oops, missed a typo ]
$ commit frobinator/ --fixup :/frobic
Thanks, I am —- but I always found it easier to just give the new commit a name I know how to squash rather than type in a SHA.
The other post about being able to do it on a substring match sounds way more ergonomic though, I’ll have to try that!
The other post about being able to do it on a substring match sounds way more ergonomic though, I’ll have to try that!
git-absorb (https://github.com/tummychow/git-absorb) does a bit more, figuring out the exact changes that should be fixed up.
git-autofixup is better and easier to install: https://github.com/torbiak/git-autofixup
Could you elaborate how it is better?
They are quite different methods, explained by the respective implementations. IME autofixup finds the relevant commit successfully more often. There's no reason you can't use both, of course. I would always check the results of either before actually doing the rebase.
JJ absorb does the same as far as I understand
[deleted]
Yes, totally useful compared to default git base commands.
And also - melding the "changed twice" (or thrice...) mutations into a single commit is a brilliant isolation of a subtle common pattern.
And also - melding the "changed twice" (or thrice...) mutations into a single commit is a brilliant isolation of a subtle common pattern.
git-absorb does exist [1]. It seems to be inspired by a mercurial subcommand of the same name. It's also available in most distro repos.
[1] https://github.com/tummychow/git-absorb
[1] https://github.com/tummychow/git-absorb
"what-changed-twice" tells me exactly what the command does. "squash-what" tells me nothing, why is the program name asking me what to squash, and then why does it not squash? The only inaccuracy I can think of in the name is that it's technically "what-changed-more-than-once." But if something has changed thrice, by definition it's also been changed twice.
> There's bonus information too. If a commit is not mentioned in the report, then it only changed files that didn't change in any other commit. That means that in a rebase, I can move that commit literally anywhere else in the sequence without creating a conflict. Only the commits in the report can cause conflicts if they are reordered.
This is only true in the textual level.
Semantically, re-shuffling commits like this can still cause conflicts. Ie it can break your tests. Not at the end, but for the intermediate commits.
This is only true in the textual level.
Semantically, re-shuffling commits like this can still cause conflicts. Ie it can break your tests. Not at the end, but for the intermediate commits.
This is why I no longer do atomic commits. I've just never had it be a benefit to walk through and guarantee that each commits tests and builds successfully. I so rarely back out changes that when I do, I test then that everything is working (and let's be honest, I back out usually at the PR level, not the commit).
The other benefit of this is the git bisect workflow. If you can’t build your intermediate commits then you likely can’t easily identify whether a bug was present on that commit (for many types of bug), and you therefore can’t identify the commit that introduced the bug.
Yes, but at least git bisect lets you mark a commit as 'skip' in these cases.
I often wonder what the point of using git at all is at this point. I suppose it's just your interface to the source repo, but a massively overly capable one. If you don't care about atomic commits then you might as well just do `git commit -a --amend --no-edit` periodically (you could even do it on every save). Then the reflog is your "undo" but you don't pollute the shared repo with shit commits.
If you want atomic commits, you need to set up your CI/CD to ensure that each intermediate commit builds and passes tests.
Most pull requests should probably be squashed to appear as a single commit in the final history. But you should have the option of leaving history intact, when you want that, and then your CI/CD should run the checks as above.
Most pull requests should probably be squashed to appear as a single commit in the final history. But you should have the option of leaving history intact, when you want that, and then your CI/CD should run the checks as above.
You don't need squash here, though. If your CI/CD ensures that merge commits (PRs) are atomic/build and pass tests, you can `git bisect --first-parent` to just bisect your merge commits/integration points/pull requests, without tossing the other history from the git DAG.
> I've just never had it be a benefit to walk through and guarantee that each commits tests and builds successfully.
If you never look at individual commits in your history, you might as well squash them.
If you never look at individual commits in your history, you might as well squash them.
I agree. I decided years ago that that was a lot of work for little or no benefit.
It's enough for the tests to pass at each merge point.
It's enough for the tests to pass at each merge point.
I would say most workplaces have settled similarly.
Sit in draft until you're ready to use the CI - which you verified locally or run manually in draft, before convert to reviewable - then review, maybe tweak, merge.
Atomic commits would endanger me losing unfinished work or eventual dead-ends with no record. This seems inefficient.
Sit in draft until you're ready to use the CI - which you verified locally or run manually in draft, before convert to reviewable - then review, maybe tweak, merge.
Atomic commits would endanger me losing unfinished work or eventual dead-ends with no record. This seems inefficient.
…and that’s why squash merge should be the default setting in PRs.
Yes, it should be the default, but ideally you have the option of preserving history (for PRs where that makes sense) and then your CI/CD should also check that the individual commits build and pass tests.
In general, your CI/CD should make sure that each commit that appears in the 'public' history of main builds and passes tests.
In general, your CI/CD should make sure that each commit that appears in the 'public' history of main builds and passes tests.
You can `git bisect --first-parent` just fine without needing to squash.
Tools like this are also useful if you need to cherry pick a patch onto a release branch and want to know potential dependencies:
You get false positives and false negatives: if B fixed a comment typo for example it’s not really a dependency, and if C updated a module imported in the new code in D you’d miss it. (For the latter, in Python at least, you can build an import DAG with ast. It’s a really useful module and is incredibly fast!)
So I would say the author’s tool is really multiple tools:
1/ build a dependency graph between commits based on file changes in a range of commits;
2/ automate the reordering and squashing of dependent commits on a private dev branch;
3/ automate cherry-picking commits onto a proposed release branch (which is basically the same as git-rebase -i); and
4/ build a dependency graph based on external analysis (in my example, Python module imports) rather than / as well as file changes.
Their use case is (1) and (2), (3) is a similar but slightly different tool to (2), and (4) is a language specific nicety that goes beyond the scope of simple git changes for, arguably, diminished returns.
↑ newer
D* fixes bug in crypto.py
C
B* rewrites crypto.sh in Python
A
0 last month’s release
↓ older
You get false positives and false negatives: if B fixed a comment typo for example it’s not really a dependency, and if C updated a module imported in the new code in D you’d miss it. (For the latter, in Python at least, you can build an import DAG with ast. It’s a really useful module and is incredibly fast!)
So I would say the author’s tool is really multiple tools:
1/ build a dependency graph between commits based on file changes in a range of commits;
2/ automate the reordering and squashing of dependent commits on a private dev branch;
3/ automate cherry-picking commits onto a proposed release branch (which is basically the same as git-rebase -i); and
4/ build a dependency graph based on external analysis (in my example, Python module imports) rather than / as well as file changes.
Their use case is (1) and (2), (3) is a similar but slightly different tool to (2), and (4) is a language specific nicety that goes beyond the scope of simple git changes for, arguably, diminished returns.
I am familiar with an algorithm that stably brings a disjoint selection of items together around a specified point. Sounds similar to this case, where the disjoint selection are changes that happened to a given file.
The name of the algorithm is “gather”, by Sean Parent and Marshall Clow.
The name of the algorithm is “gather”, by Sean Parent and Marshall Clow.
https://github.com/stlab/adobe_source_libraries/blob/7659244...
https://listarchives.boost.org/Archives/boost/2013/01/200366...
I gotta say, I don't see the greatness any more than most of the repliers in that Boost thread — it's just two stable_partitions in a row.
"[...] Or is there some optimization that gather provides over (stable_)partition? —— Nope. [...]"
https://listarchives.boost.org/Archives/boost/2013/01/200366...
I gotta say, I don't see the greatness any more than most of the repliers in that Boost thread — it's just two stable_partitions in a row.
"[...] Or is there some optimization that gather provides over (stable_)partition? —— Nope. [...]"
The Boost thread starts with an example of how Bjarne replaced a bunch of complicated code with it.
It may be just two stable partitions, but “just” is doing a lot of work there. The algorithm becomes obvious once someone has identified it.
It may be just two stable partitions, but “just” is doing a lot of work there. The algorithm becomes obvious once someone has identified it.
The talk: https://www.youtube.com/watch?v=OB-bdWKwXsU&t=52m49s
Sadly the 25-line original code isn't presented; the code that is presented is the 5-line replacement using the STL's `find_if` and `rotate`. Bjarne sketches the idea that those five lines can be further condensed into two lines with the non-STL `gather` algorithm:
Now, I think part of his point is that `stable_partition` is "simpler" than `gather` only because it's in the STL. If we add `gather` to the STL too and everyone learns what it means, then there's no objection to using `gather` for "simplification" like this: it would be a straightforward simplification in almost the same way that `std::equal_range(first, last, x)` is a straightforward simplification of `std::make_pair(std::lower_bound(first, last, x), std::upper_bound(first, last, x))`.
The "almost" is that actually there is an algorithmic advantage to `std::equal_range`: when you're looking for the upper bound, you don't have to consider any of the elements to the left of the lower bound you already found. You get a (very slight) performance boost by using the combined `equal_range` algorithm. `gather`, on the other hand, has no such advantage; and (as we've seen) has a (very slight) performance disadvantage when compared to the `rotate` that Bjarne's correspondent's code actually required.
We're not talking about replacing 25 lines of bespoke code with 1 line of Boost `gather`; we're talking about replacing 2 lines of STL `stable_partition` with 1 line of Boost `gather`. The former is probably worth it. The latter is not.
Sadly the 25-line original code isn't presented; the code that is presented is the 5-line replacement using the STL's `find_if` and `rotate`. Bjarne sketches the idea that those five lines can be further condensed into two lines with the non-STL `gather` algorithm:
auto dest = std::find_if(v.begin(), v.end(), contains(p));
stdx::gather(v.begin(), dest, v.end(), [](const auto& elt) { return &elt == &*source; });
Now, I think part of his point is that `stable_partition` is "simpler" than `gather` only because it's in the STL. If we add `gather` to the STL too and everyone learns what it means, then there's no objection to using `gather` for "simplification" like this: it would be a straightforward simplification in almost the same way that `std::equal_range(first, last, x)` is a straightforward simplification of `std::make_pair(std::lower_bound(first, last, x), std::upper_bound(first, last, x))`.
The "almost" is that actually there is an algorithmic advantage to `std::equal_range`: when you're looking for the upper bound, you don't have to consider any of the elements to the left of the lower bound you already found. You get a (very slight) performance boost by using the combined `equal_range` algorithm. `gather`, on the other hand, has no such advantage; and (as we've seen) has a (very slight) performance disadvantage when compared to the `rotate` that Bjarne's correspondent's code actually required.
We're not talking about replacing 25 lines of bespoke code with 1 line of Boost `gather`; we're talking about replacing 2 lines of STL `stable_partition` with 1 line of Boost `gather`. The former is probably worth it. The latter is not.
"muster" comes to mind and is different than "gather".
When I make Bash aliases or functions for Git functionality, I always name them as `git-something-or-other`. That way they're namespaced in a way that I find pleasant both for tab completion and for easy of memory. I think that should apply to more complex utilities, too.
By my usual naming conventions, this one would be `git-repeatedly-changed`.
By my usual naming conventions, this one would be `git-repeatedly-changed`.
Last but decidedly not least: if you have `git-foo` on the PATH, you can do `git foo` and it will automatically pick up your program.
If I remember early git days correctly, that's how git was implemented: a bunch of separate utilities working together on the database which is the .git folder.
If I remember early git days correctly, that's how git was implemented: a bunch of separate utilities working together on the database which is the .git folder.
These are called alternative "porcelains:"[0] third-party, user-friendly interfaces built on top of Git's stable, low-level plumbing commands.
0. https://git-scm.com/docs/git.html#_low_level_commands_plumbi...
0. https://git-scm.com/docs/git.html#_low_level_commands_plumbi...
I usually do that too, but this seemed to me like it's not really a git utility. It's just a filter.
I can see the argument in favor of `git-` also.
But I think I'd prefer `git-changed-twice` to be a wrapper that takes a reflist argument, and runs `git-log --stat reflist | what-changed-twice`.
I can see the argument in favor of `git-` also.
But I think I'd prefer `git-changed-twice` to be a wrapper that takes a reflist argument, and runs `git-log --stat reflist | what-changed-twice`.
I suggest group-commits-by-file , group-commits , or group-by-file, depending on whether you want it to make sense out of context and whether you ever group commits differently. You might then feel compelled to add a final line like “… and 12 files with 1 commit each”, or even to enumerate them, which sounds like it’d be useful anyway. “what” isn’t doing any work, there’s already an implicit “what” in the call-response paradigm. “Changed” implies you’re detecting changes, but you’re not, you’re operating on a data structure that happens to represent changes.
Suggestion: `git squash-report`. (Or `git rebase-report`, except I wouldn't call it that because it would interfere with my tab-completion of, and/or muscle memory of, `git rebase -i`.)
You know, I find myself partially agreeing that a number of utilities for git could be done quite nicely in perl.
Git's repository includes quite a bit of Perl, but they want to get rid of it.
Is there any reason for doing so?
It's a pain in the backside to run on Windows, for two reasons. Firstly, Windows doesn't have (by default) a lot of the tools that are preinstalled in most nix environments. Git for Windows ships half a Cygwin distribution (MSYS2) including Bash, Perl, and Tcl.
Second, Windows doesn't really have a 'fork' API. Creating a new process on Windows is a heavyweight operation compared to nix. As such, scripts that repeatedly invoke other commands are sluggish. Converting them to C and calling plumbing commands in-process has a radical effect on performance.
Git for Windows is more of a maintained fork than a real first-class platform.
Also, I believe it's a goal to make it possible to use Git as a library rather than as an executable. That's hard to do if half the logic is in a random scripting language. Library implementations exist - notably libgit2 - but it can never be fully up to date with the original. Search for 'git libification'.
Many IDEs started their Git integration with libgit2, but subsequently fell foul of things that libgit2 can't do or does inconsistently. Therefore they fall back on executing `git` with some fixed-format output.
Second, Windows doesn't really have a 'fork' API. Creating a new process on Windows is a heavyweight operation compared to nix. As such, scripts that repeatedly invoke other commands are sluggish. Converting them to C and calling plumbing commands in-process has a radical effect on performance.
Git for Windows is more of a maintained fork than a real first-class platform.
Also, I believe it's a goal to make it possible to use Git as a library rather than as an executable. That's hard to do if half the logic is in a random scripting language. Library implementations exist - notably libgit2 - but it can never be fully up to date with the original. Search for 'git libification'.
Many IDEs started their Git integration with libgit2, but subsequently fell foul of things that libgit2 can't do or does inconsistently. Therefore they fall back on executing `git` with some fixed-format output.
I don't get why everything needs to be a library? Using the OS to invoke things gets you parallelism and isolation for free. When you need to deal with complicated combination of parameters to an API, it doesn't become too different from argument parsing, so you might as well do that instead.
You can still wrap the interface to the executable in a library.
You can still wrap the interface to the executable in a library.
Why did you opt for "highly-abbreviated commit IDs"?
Instead of:
``` calendar/seasons.blog 196 40 d1
The tool should simply display:
``` calendar/seasons.blog 196e749 40c52f4 d142598 ```
That's it!
The second table only complicates the output.
PS:
`what-changed-twice` is a good name.
Instead of:
``` calendar/seasons.blog 196 40 d1
196 196e749
40 40c52f4
d1 d142598The tool should simply display:
``` calendar/seasons.blog 196e749 40c52f4 d142598 ```
That's it!
The second table only complicates the output.
PS:
`what-changed-twice` is a good name.
git-delta -n <times>
i.e. git-delta -n 2 = 'what changed twice'
or if its just what changed twice in every case then just 'git-delta-delta'
i.e. git-delta -n 2 = 'what changed twice'
or if its just what changed twice in every case then just 'git-delta-delta'
Website is down.
https://archive.ph/52C1y
https://archive.ph/52C1y
Double Jeopardy?
Oidia- Oops I did it again
No it does not.
FlipFlopStop?
FFS for short, which has suitably disgruntled other exclamatory meanings.
FFS for short, which has suitably disgruntled other exclamatory meanings.
oops-i-did-it-again
change-cluster?
I had a good idea of what it did before reading the article, it is a long name but not Java-long, and none of the suggestions so far are clear to me, even after reading the article.
The only somewhat confusing part is the "twice", because it can be more than twice. But if you think about it, if it has been changed more than twice, it had to be changed twice at some point, so it is not totally wrong.