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

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 [off-list ref] 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>

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