From: Jeff King <peff@peff.net>
Date: Fri, 23 May 2014 19:51:53 GMT
Subject: Re: [PATCH v1 1/3] replace: add --graft option
Message-ID: <20140523195153.GB19088@sigill.intra.peff.net>
In-Reply-To: <20140522213307.27162.14455.chriscool@tuxfamily.org>

On Thu, May 22, 2014 at 11:33:04PM +0200, Christian Couder wrote:

> The usage string for this option is:
> 
> git replace [-f] --graft <commit> [<parent>...]
> 
> First we create a new commit that is the same as <commit>
> except that its parents are [<parents>...]
> 
> Then we create a replace ref that replace <commit> with
> the commit we just created.
> 
> With this new option, it should be straightforward to
> convert grafts to replace refs, with something like:
> 
> cat .git/info/grafts | while read line
> do git replace --graft $line; done

I think this script at the end should end up in the documentation or a
contrib script (probably the former, as it is short enough that somebody
might just cut-and-paste).

The graft file ignores comments and blank lines, so maybe "grep '^[^#]'"
would be in order.

And maybe it's just me, but I think spacing it like:

  grep '^[^#]' .git/info/grafts |
  while read line; do
	git replace --graft $line
  done

is more readable (I think some would even argue for putting the "do" on
a separate line).

> +	/* make sure the commit is not corrupt */
> +	if (parse_commit_buffer(commit, buf.buf, buf.len))
> +		die(_("Could not parse commit: '%s'"), old_ref);

I guess the checks here are sufficient to make...

> +	/* find existing parents */
> +	parent_start = buf.buf;
> +	parent_start += 46; /* "tree " + "hex sha1" + "\n" */
> +	parent_end = parent_start;
> +
> +	while (starts_with(parent_end, "parent "))
> +		parent_end += 48; /* "parent " + "hex sha1" + "\n" */

...this number-based parsing safe, though it would miss removing a stray
parent line elsewhere in the commit. It still feels rather magical to
me, as we are depending on unspoken format guarantees defined inside
parse_commit_buffer. I'd prefer something like the line-based parser I
showed in the other thread, but I suppose it may just be a matter of
preference.

-Peff