Re: fast-import, merges, and file changes -- lack of clarity in docs, possible minor bug, or PEBKAC?

From: Elijah Newren <newren@gmail.com>
Date: Feb 17, 2009, 05:47 UTC
Message-ID: <51419b2c0902162147y588ad4dfk58271f3434dea66c@mail.gmail.com>
In-Reply-To: <51419b2c0902161628x7a3475e6p2a70310e5b294444@mail.gmail.com>

I think I've at least partially discovered the answer my own question(s), so I figured I'd document them in case anyone else was wondering...

On Mon, Feb 16, 2009 at 5:28 PM, Elijah Newren <newren@gmail.com> wrote:

> It appears the documentation for fast-import does not specify the
> basis on which a commit command's file changes (filemodify,
> filedelete, filecopy, or filerename) are relative to.

<snip>

Show 5 quoted lines

> Is this intentional?  I believe we could change this behavior without
> breaking backward compatibility with older fast-export output streams,
> since such older streams would simply be providing redundant
> information.  But is there a reason for this behavior that I'm
> missing?

It is documented...though implicitly in discussion of other commands. In particular, "...a `merge` command may be used instead of `from` to start the commit with an empty tree" and later "If the `from` command is omitted when creating a new branch, the first `merge` commit will be the first ancestor of the current commit, and the branch will start out with no files." This implies that the files of a `merge` parent are ignored and any content must from that parent that is contained in the commit must be explicitly spelled out to be included.

Also, as far as backward compatibility, my suggestion would not be compatible; deletions involved in such merges would be handled by current fast-export streams by simply omitting the file in the list of file changes in the merge commit. My suggestion would require explicitly specified file deletion to ensure its removal.

So, it appears this is intentional, any behavior change such as I suggested would require different/new syntax, and would require support in fast-export too for my purposes. That certainly makes my git-fast-filter script (a script in a pipeline between fast-export and fast-import designed to act somewhat like filter-branch but with better performance on my large repositories) much harder. Oh, well.

Elijah