New Proposal (simple) for Metadata in Git Commits: git-meta

Hi,

I had this idea a day or so again, and have written a simple implementation to storing some semi-structured data in a git commit message. This means that it's much easier for data to be found and scraped from a certain commit, for instance what issue numbers commits refer to or close.

The entirety of the idea is expressed here: http://lenary.github.com/hackery/2009/12/git-meta/

I have so far built an implementation of a way to get the data out of a commit. I am still investigating how to get this info into the commit message before the git-commit command so that it doesn't have to be entirely hand-written.

I was just looking for feedback and to see whether the mailing list thinks this is a good idea or not? Any help would also be greatly appreciated.

Thanks!

Sam -- Sam Elliott sam@lenary.co.uk --

Sam Elliott <sam@lenary.co.uk> wrote:

So from your web page, this is basically just YAML shoved into the footer of the message:

--8<--
	Written half of the functionality. Namely the querying half.

	---git-meta---
	awesome: true
	Github:
	  user: lenary
	---git-meta---
-->8--

Why do we need the --git-meta-- delimiter lines?

JGit and Gerrit Code Review have already been following Git tradition by using footer messages as metadata. E.g. we have lines like:

--8<--
    init: Don't abort on empty directory
    
    The following sequence should work:
    
      mkdir testgit
      java -jar gerrit.war init -d testgit
    
    Since testgit is empty, it should be acceptable for us to populate the
    directory with our files.
    
    Bug: issue 358
    Change-Id: Ia85f31802066f8d39b042d3d057d33950a5035fd
    Signed-off-by: Shawn O. Pearce <sop@google.com>
-->8--

The JGit commit message parser has special logic to handle lines that smell like one of these tag lines. So long as there is no blank line in the footer paragraph, each of these tags can be read and processed. Continuation lines should start with whitespace.

I don't remember my YAML well enough, but isn't this existing standard still parseable by a YAML processor?

If you dropped the --git-meta-- tags above, JGit would happily recognize the awesome: and Github: tags, but it might need a bit more work to recognize the nested user: tag. Also, you'd be able to use git-meta on the git and Linux kernel repositories to pull out and work with Signed-off-by, Acked-by, etc.

Sam Elliott <sam@lenary.co.uk> wrote:

Ah, good point. But as you point out, it should be simple enough to detect a PGP signature on the bottom and just clip that off the end, and then perform the YAML-like data parsing on the footer.

On Wednesday 16 December 2009, Shawn O. Pearce wrote:

I agree with Shawn's point that it should be possible to do this without embedding it in custom ---tags---.

I would even try to parse the _entire_ commit message, and then discard everything that didn't match the "<word>: <free-form value>" format (with possible continuation lines). Even though this will generate some false positives (probably non-sensical "key: value" pairs), I don't see this as a major problem , since most users of this functionality are looking for a small set of specific keywords (which are even more unlikely to turn up as false positives)

In future versions of Git, you might also want to check for YAML-like data in the notes object corresponding to the commit in question (see git-notes in v1.6.6 for more details on the new notes feature). This would allow users to add/edit such metadata after the commit was made, without having to rewrite the commit itself.

Have fun! :)

...Johan