filter-branch: Big syntax change; support rewriting multiple refs

We used to take the first non-option argument as the name for the new
branch.  This syntax is not extensible to support rewriting more than just
HEAD.

Instead, we now have the following syntax:

	git filter-branch [<filter options>...] [<rev-list options>]

All positive refs given in <rev-list options> are rewritten.  Yes,
in-place.  If a ref was changed, the original head is stored in
refs/original/$ref now, for your inspecting pleasure, in addition to the
reflogs (since it is easier to inspect "git show-ref | grep original" than
to inspect all the reflogs).

This commit also adds the --force option to remove .git-rewrite/ and all
refs from refs/original/ before filtering.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 128 insertions, 22 deletions

diff --git a/git-filter-branch.sh b/git-filter-branch.sh
index 0d000ed306..0ff3475525 100755
--- a/git-filter-branch.sh
+++ b/git-filter-branch.sh
@@ -78,6 +78,8 @@ filter_msg=cat
 filter_commit='git commit-tree "$@"'
 filter_tag_name=
 filter_subdir=
+orig_namespace=refs/original/
+force=
 while case "$#" in 0) usage;; esac
 do
 	case "$1" in
@@ -85,6 +87,11 @@ do
 		shift
 		break
 		;;
+	--force|-f)
+		shift
+		force=t
+		continue
+		;;
 	-*)
 		;;
 	*)
@@ -126,24 +133,43 @@ do
 	--subdirectory-filter)
 		filter_subdir="$OPTARG"
 		;;
+	--original)
+		orig_namespace="$OPTARG"
+		;;
 	*)
 		usage
 		;;
 	esac
 done
 
-dstbranch="$1"
-shift
-test -n "$dstbranch" || die "missing branch name"
-git show-ref "refs/heads/$dstbranch" 2> /dev/null &&
-	die "branch $dstbranch already exists"
-
-test ! -e "$tempdir" || die "$tempdir already exists, please remove it"
+case "$force" in
+t)
+	rm -rf "$tempdir"
+;;
+'')
+	test -d "$tempdir" &&
+		die "$tempdir already exists, please remove it"
+esac
 mkdir -p "$tempdir/t" &&
+tempdir="$(cd "$tempdir"; pwd)" &&
 cd "$tempdir/t" &&
 workdir="$(pwd)" ||
 die ""
 
+# Make sure refs/original is empty
+git for-each-ref > "$tempdir"/backup-refs
+while read sha1 type name
+do
+	case "$force,$name" in
+	,$orig_namespace*)
+		die "Namespace $orig_namespace not empty"
+	;;
+	t,$orig_namespace*)
+		git update-ref -d "$name" $sha1
+	;;
+	esac
+done < "$tempdir"/backup-refs
+
 case "$GIT_DIR" in
 /*)
 	;;
@@ -153,6 +179,29 @@ case "$GIT_DIR" in
 esac
 export GIT_DIR GIT_WORK_TREE=.
 
+# These refs should be updated if their heads were rewritten
+
+git rev-parse --revs-only --symbolic "$@" |
+while read ref
+do
+	# normalize ref
+	case "$ref" in
+	HEAD)
+		ref="$(git symbolic-ref "$ref")"
+	;;
+	refs/*)
+	;;
+	*)
+		ref="$(git for-each-ref --format='%(refname)' |
+			grep /"$ref")"
+	esac
+
+	git check-ref-format "$ref" && echo "$ref"
+done > "$tempdir"/heads
+
+test -s "$tempdir"/heads ||
+	die "Which ref do you want to rewrite?"
+
 export GIT_INDEX_FILE="$(pwd)/../index"
 git read-tree || die "Could not seed the index"
 
@@ -174,6 +223,8 @@ commits=$(wc -l <../revs | tr -d " ")
 
 test $commits -eq 0 && die "Found nothing to rewrite"
 
+# Rewrite the commits
+
 i=0
 while read commit parents; do
 	i=$(($i+1))
@@ -234,22 +285,75 @@ while read commit parents; do
 		$(git write-tree) $parentstr < ../message > ../map/$commit
 done <../revs
 
-src_head=$(tail -n 1 ../revs | sed -e 's/ .*//')
-target_head=$(head -n 1 ../map/$src_head)
-case "$target_head" in
-'')
-	echo Nothing rewritten
+# In case of a subdirectory filter, it is possible that a specified head
+# is not in the set of rewritten commits, because it was pruned by the
+# revision walker.  Fix it by mapping these heads to the next rewritten
+# ancestor(s), i.e. the boundaries in the set of rewritten commits.
+
+# NEEDSWORK: we should sort the unmapped refs topologically first
+while read ref
+do
+	sha1=$(git rev-parse "$ref"^0)
+	test -f "$workdir"/../map/$sha1 && continue
+	# Assign the boundarie(s) in the set of rewritten commits
+	# as the replacement commit(s).
+	# (This would look a bit nicer if --not --stdin worked.)
+	for p in $((cd "$workdir"/../map; ls | sed "s/^/^/") |
+		git rev-list $ref --boundary --stdin |
+		sed -n "s/^-//p")
+	do
+		map $p >> "$workdir"/../map/$sha1
+	done
+done < "$tempdir"/heads
+
+# Finally update the refs
+
+_x40='[0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f]'
+_x40="$_x40$_x40$_x40$_x40$_x40$_x40$_x40$_x40"
+count=0
+echo
+while read ref
+do
+	# avoid rewriting a ref twice
+	test -f "$orig_namespace$ref" && continue
+
+	sha1=$(git rev-parse "$ref"^0)
+	rewritten=$(map $sha1)
+
+	test $sha1 = "$rewritten" &&
+		warn "WARNING: Ref '$ref' is unchanged" &&
+		continue
+
+	case "$rewritten" in
+	'')
+		echo "Ref '$ref' was deleted"
+		git update-ref -m "filter-branch: delete" -d "$ref" $sha1 ||
+			die "Could not delete $ref"
 	;;
-*)
-	git update-ref refs/heads/"$dstbranch" $target_head ||
-		die "Could not update $dstbranch with $target_head"
-	if [ $(wc -l <../map/$src_head) -gt 1 ]; then
-		echo "WARNING: Your commit filter caused the head commit to expand to several rewritten commits. Only the first such commit was recorded as the current $dstbranch head but you will need to resolve the situation now (probably by manually merging the other commits). These are all the commits:" >&2
-		sed 's/^/	/' ../map/$src_head >&2
-		ret=1
-	fi
+	$_x40)
+		echo "Ref '$ref' was rewritten"
+		git update-ref -m "filter-branch: rewrite" \
+				"$ref" $rewritten $sha1 ||
+			die "Could not rewrite $ref"
 	;;
-esac
+	*)
+		# NEEDSWORK: possibly add -Werror, making this an error
+		warn "WARNING: '$ref' was rewritten into multiple commits:"
+		warn "$rewritten"
+		warn "WARNING: Ref '$ref' points to the first one now."
+		rewritten=$(echo "$rewritten" | head -n 1)
+		git update-ref -m "filter-branch: rewrite to first" \
+				"$ref" $rewritten $sha1 ||
+			die "Could not rewrite $ref"
+	;;
+	esac
+	git update-ref -m "filter-branch: backup" "$orig_namespace$ref" $sha1
+	count=$(($count+1))
+done < "$tempdir"/heads
+
+# TODO: This should possibly go, with the semantics that all positive given
+#       refs are updated, and their original heads stored in refs/original/
+# Filter tags
 
 if [ "$filter_tag_name" ]; then
 	git for-each-ref --format='%(objectname) %(objecttype) %(refname)' refs/tags |
@@ -286,6 +390,8 @@ fi
 
 cd ../..
 rm -rf "$tempdir"
-printf "\nRewritten history saved to the $dstbranch branch\n"
+echo
+test $count -gt 0 && echo "These refs were rewritten:"
+git show-ref | grep ^"$orig_namespace"
 
 exit $ret