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

[Yuki Kokubun <orga.chem.job@gmail.com>]

> Yuki Kokubun <orga.chem.job@gmail.com> 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...?

Sorry, this is my wrong.
I wrongly thought only refs/replace can point at a blob or tree object.

> 
> 	... 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.

OK, I'm gonna drop the incorrect comment.

> 
> > +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.

I feel using "git rev-parse --verify" is a good way as you said.
I'm gonna modify the patch to use it.

> 
> >  test -s "$tempdir"/heads ||
> > diff --git a/t/t7003-filter-branch.sh b/t/t7003-filter-branch.sh
> > index 7cb60799b..efeaf5887 100755
> > --- a/t/t7003-filter-branch.sh
> > +++ b/t/t7003-filter-branch.sh
> > @@ -470,4 +470,17 @@ test_expect_success 'tree-filter deals with object name vs pathname ambiguity' '
> >  	git show HEAD:$ambiguous
> >  '
> >  
> > +test_expect_success 'rewrite repository including refs/replace that point to non commit object' '
> > +	test_when_finished "git reset --hard original" &&
> > +	tree=$(git rev-parse HEAD^{tree}) &&
> > +	test_when_finished "git replace -d $tree" &&
> > +	echo A >new &&
> > +	git add new &&
> > +	new_tree=$(git write-tree) &&
> > +	git replace $tree $new_tree &&
> 
> 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?

Sounds good. I'm gonna add such tags to the test case.

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