Patch applies fake diffs from commit messages

This has come up multiple times before [1], and more generally it's come up hundreds of times with Unix style tools in general. It's always been a stupid idea for every tool to have its own barely documented file format.

This wouldn't be an issue if patches were XML or JSON with a well defined schema, but everything must be a boutique undocumented format in the world of Unix tools.

Maybe the worst part about this is that it can entirely come from a patch being exported by git and then imported straight back in to git. If you can't even handle your own undocumented format then what hope do other tools have that want to work with it?

[1]: https://mas.to/@zekjur/116022397626943871

> It matters (to me) because `wget`/`curl` plus `patch` is not some exotic lab setup.

If the point is to be able to do `curl https://...deadbeef.patch | patch -p1`, you can just change the extension provided to Github from `.patch` to `.diff`. That way, it just includes the hunks. E.g.

https://github.com/torvalds/linux/commit/dca922e019dd758b4c1...

I don't see it as a problem with the email format, because I can't imagine someone just patching from an email without looking at the email first.

Seems like this would probably be solved if github returned a patch file formatted like `git show` provides, specifically with the commit message indented? I do see that `git format-patch` doesn't do this indentation though.

In any case, agreed that it's not a great "feature" to use in-band signaling of when patch data starts, with no escaping. Confusion and misbehavior is pretty much guaranteed.

git-am(1) (apply patches) delimits the commit message from the patch/diff by looking for (1) a line `---` or (2) a line that starts with `diff -` or (3) a line that starts with `Index:SP` (SP is space). Only the first rule is necessary for patches generated git-format-patch(1). But git-am(1) is for applying patches, and you are free to bring patches from some other system. That’s why, I suppose, there are multiple options.

This means that it will try to apply any unindented diffs in the commit message. But you’re fine if you indent the diff. (Newschool code fencers will have a worse time here.)

I imagine that this worked fine for changes that were authored by one person and submitted by another person via email, or by their friend, or by someone trying to resurrect a previous attempt at getting something upstreamed. Someone is likely to notice that examples diffs are getting applied. But it won’t work well at all if you are some software distributor who is using patch files to apply modifications to packages.

Recall that git-am(1) will not apply indented diffs. Well have a look at my GNU patch 2.7.6:

    If the entire diff is indented by a consistent amount, if lines end in
    CRLF, or if a diff is encapsulated one or more times by prepending "- "
    to lines starting with "-" as specified by Internet RFC 934, this is
    taken into account.

    Larry Wall wrote the original version of patch.

But what problem does this actually introduce? If you are applying a patch you must already trust the source anyways and this isn’t harder to spot than a rogue file anywhere else in the patch as it looks the same.

I like that the site offers your choice of two fonts, but they're both ugly and hard to read. Mono is too narrow, and OpenDyslexic is cartoonish and o v e r k e r n e d.

Diff format being too forgiving and commit messages being too permissive are each fine on their own. The bug is the composition.

This looks like a feature.

Not sure why somebody thought it was a good idea. There probably was a use case at some point where it seemed smart to allow for things like this. Maybe it’s for CI, but I really can’t think of why.

But I really doubt this could be a bug. I mean why would patch even need to read the commit message if it wasn’t to scan it for diff?

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