Re: [PATCH] filter-branch: consider refs can refer to an object other than commit or tag

Yuki Kokubun [off-list ref] writes:

"git filter-branch -- --all" can be confused when refs that refer to objects
other than commits or tags exists.
Because "git rev-parse --all" that is internally used can return refs that
refer to an object other than commit or tag. But it is not considered in the
phase of updating refs.

Could you describe what the consequence of that is?  We have a ref
that points directly at a blob object, or a ref that points at a tag
object that points at a blob object.  The current code leaves both of
these refs in "$tempdir/heads".  Then...?

	... goes and looks ...

There is a loop that looks like this:

	while read ref
	do
		sha1=$(git rev-parse "$ref^0")
		...
	done <"$tempdir/heads"

which would break on anything but a commit-ish.

 # The refs should be updated if their heads were rewritten
 git rev-parse --no-flags --revs-only --symbolic-full-name \
-	--default HEAD "$@" > "$tempdir"/raw-heads || exit
+	--default HEAD "$@" > "$tempdir"/raw-objects || exit
+# refs/replace can refer to an object other than commit or tag

Mention of replace refs in the proposed log message gives an easy to
understand example and is a good idea, but this in code comment does
not have to single out the replace refs.  A tag can also point at an
object with any type, e.g. "git tag v2.6.11-tree v2.6.11^{tree}"
would make "refs/tags/v2.6.11-tree" point at the tree at the top
level of the tree-ish "v2.6.11".  It probably is OK to drop this
comment altogether.

+while read ref
+do
+	type=$(git cat-file -t "$ref")
+	if test $type = commit || test $type = tag
+	then
+		echo "$ref"
+	fi
+done >"$tempdir"/raw-heads <"$tempdir"/raw-objects
 sed -e '/^^/d' "$tempdir"/raw-heads >"$tempdir"/heads

So... is the idea to limit the set of refs to be rewritten to those
that point at commits and tags?  As I already alluded to, I do not
think you want to accept a ref that points at any tag object---only
the ones that point at a tag that points at a commit-ish, so that
the code will not barf when doing "$ref^0".

So perhaps

	git rev-parse --no-flags ... >"$tempdir/raw-heads" || exit

	while read ref
	do
		case "$ref" in ^?*) continue ;; esac
		if git rev-parse --verify "$ref^0" 2>/dev/null
                then
			echo "$ref"
		fi
	done >"$tempdir/heads" <"$tempdir/raw-heads"

or something?  Note that you do not need the "sed" as the loop
already excludes the negative revs.

Perhaps something like this here:

	git tag -a "tag to a tree" treetag $new_tree &&

can tell su how well it works with a tag that points at a tree?

+	git reset --hard HEAD &&
+	git filter-branch -f -- --all >filter-output 2>&1 &&
+	! fgrep fatal filter-output
+'
+
 test_done