Re: git-archive and tar options

[Jeff King <peff@peff.net>]

On Thu, Jul 14, 2011 at 07:45:07PM +0200, René Scharfe wrote:

> > We didn't when git-archive was written, but these days we have
> > get_sha1_with_context to remember incidental things about an object we
> > look up. It should perhaps remember the commit (if any) we used to reach
> > a treeish, and then the above command line could still insert the pax
> > header.
> 
> That's a good idea to increase consistency, as there shouldn't really be
> a difference in output between the two subdirectory syntaxes.

The patch to do this is pretty tiny. See below.

There are a few issues, though:

  1. I think this is probably the right thing to do, and most people
     will be happy about it. But I guess I can see an argument that the
     commit-id should not be there, as the subtree does not represent
     that commit.

     IOW, if you assume the commit-id in the output means
     "by the way, this came from commit X", this change is a good thing.
     If you assume it means "this is the tree from commit X", then it's
     not.  I have no idea how people use it. I never have, but I always
     assumed the use case was "I have this random tarball. Where did it
     come from?".

  2. The object_context already has the sha1 we want, but it is under
     the name "tree", which is not an accurate name. It's actually
     "whatever is on the left side of the :". Which should be a
     tree-ish, but could be a commit or a tree.

  3. It looks like we fill in object_context whenever we see something
     like "tree-ish:path". But we should perhaps also do so when peeling
     something like "tree-ish^{tree}".

> I always wondered, however, if the embedded commit ID has really been
> used to identify the corresponding version of an archive that somehow
> lost its filename (due to being piped?).

I dunno. I've never used it.

-- >8 --
Subject: [PATCH] archive: look harder for commit id

When "git archive" is given a commit, the output will
contain the commit sha1 (either as a pax header for tar
format, or in a file comment for zip).

When it's given a name that resolves to a tree, like:

  git archive git-1.7.0:Documentation

then the archive code never sees the commit, and no
commit-id is output. We can use get_sha1_with_context to
remember the commit that led us to that tree (if any).

Signed-off-by: Jeff King <peff@peff.net>
---
 archive.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/archive.c b/archive.c
index 42f2d2f..d0ba7fb 100644
--- a/archive.c
+++ b/archive.c
@@ -256,11 +256,14 @@ static void parse_treeish_arg(const char **argv,
 	struct tree *tree;
 	const struct commit *commit;
 	unsigned char sha1[20];
+	struct object_context oc;
 
-	if (get_sha1(name, sha1))
+	if (get_sha1_with_context(name, sha1, &oc))
 		die("Not a valid object name");
 
 	commit = lookup_commit_reference_gently(sha1, 1);
+	if (!commit)
+		commit = lookup_commit_reference_gently(oc.tree, 1);
 	if (commit) {
 		commit_sha1 = commit->object.sha1;
 		archive_time = commit->date;
-- 
1.7.6.38.ge5b33