Re: Programmatic patches (transform commits)

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Aug 19, 2022, 10:15 UTC
Message-ID: <n7prrp62-41o1-r280-qo55-9q7rnqs723p1@tzk.qr>
In-Reply-To: <CAED_RJPh28o8bFsBEEzAYvp1DXhff2JWiTk3zHh3VbaHZephgg@mail.gmail.com>

Hi Mark,

On Thu, 18 Aug 2022, Mark Fulton wrote:

Show 12 quoted lines

> Is there a way to commit a transform script that programmatically
> applies file changes rather than committing the file changes directly?
>
> e.g. Imagine in a large repository that a contributor wants to replace
> certain instances of "abc" with "xyz". A transform script might be
> like the following:
>
> ```sh
> #!/bin/sh
>
> sed -i 's/abc/xyz/g' $(find .)
> ```

I do have a script to do such a thing, and I am sure other users do, too. It would be a simpler script if it did not have to accommodate for `sed`'s `-i` option behaving differently between GNU and BSD variants. For the GNU variant, I use

	git grep -zl "$regex" | xargs -0r sed -i "s/$regex/$replacement/g"

and for the BSD variant I use `sed -i ''` (i.e. an extra, empty argument) and skip the `-r` option because BSD `xargs` does not understand it.

Show 6 quoted lines

> Applying such a "programmatic patch" will potentially edit many files.
> Doing a code review on such a change is error prone due to authors
> resolving merge conflicts manually, etc. while reviewing the patch in
> some circumstances is much easier (especially tools for specifically
> this type of file transformations are used to make it easy to parse
> code, traverse abstract syntax trees, make edits, etc.).

In the Git project, we do have a track record of mentioning the exact commands for automated transformation in the commit message, see e.g. https://github.com/git/git/commit/8dcf73c5c940.

The idea is that any reviewer could run the same command, verify that the outcome is the same, and give their ACK. Or, in case of merge conflicts, they would re-run the command and commit the result using the original commit message.

Ciao, Dscho