ParsePatchHeader: Copy functionality of git mailinfo's cleanup_subject

[gwd]

Primarily to get rid of [PATCH] at the front, but while we're here
just be generally compatible with git am:

• Remove re and variations
• Remove whitespace
• Remove anything in brackets

But only at the very beginning of the subject.

Inspired by
https://github.com/git/git/blob/master/mailinfo.c:cleanup_subject()

Signed-off-by: George Dunlap [email protected]

This fixes issue #16

[bluekeyes]

Thanks for implementing this and including tests! I had a few style comments and a thought about the API:

One of the goals of this library is to be relatively un-opinionated about how parsed information is presented to clients. To that end, I'd prefer if this cleaning wasn't mandatory (and in fact git am offers flags to disable it.) My first thought is to define a standalone CleanPatchTitle function that cleans the title string. Clients could assign the result to the Title field if they want to persist it.

Another option might be add a RawTitle field in addition to the Title field, which now contains the cleaned version. But I think I like the function better: parsed dates used to have a "raw" field and I removed it because it was confusing to use.

I'm also open to other suggestions if you have ideas.

[gwd]

Re the API: I was originally thinking, nobody would ever want to make a commit with [PATCH] or Re: in the title. But at very least, someone might want to be able to parse version / series information out of something like [PATCH v3 5/17].

Probably the most useful thing to do for the latter case would be to keep whatever we end up deleting from the beginning of the subject line and putting it in another field inside PatchHeader. Maybe "SubjectPrefix"? I think the most common case would be for people to parse out the version / series information, and then possibly apply the patch to a tree. If people really want to apply the prefixes, they can just always apply SubjectPrefix + Title + \n + Body.

[bluekeyes]

After thinking about this a bit more, SubjectPrefix feels like a reasonable approach to solve this. It matches the default behavior of both format-patch and am, replicating the function of the -k flag is easy for clients who want that, and it fits with the contract of PatchHeader that some fields may be empty after parsing. Thanks again for submitting and updating this.

[gwd]

No prob, thanks for writing the package! Saved me a lot of work. :-)

Re API -- I was thinking, since you already have Title and Body broken down, and you have the Message "convenience method", to put them together, what you might do is add options to Message to emulate the -k flag. I've been playing around with https://dave.cheney.net/2014/10/17/functional-options-for-friendly-apis and found it pretty convenient. So then if you wanted to duplicate git am behavior, you'd just call ph.Message(); but if you wanted git am -k, you'd call ph.Message(gitdiff.OptKeepPrefix()) or something like that.

That's not something I have time to do at the moment, but it's worth thinking about.