2 files changed, 153 insertions, 0 deletions
diff --git a/git-rewrite-branch b/git-rewrite-branch
new file mode 100755
index 0000000..a2b3c81
--- /dev/null
+++ b/git-rewrite-branch
@@ -0,0 +1,149 @@
+#!/bin/bash -euE
+
+# when $gitmode is true, $ibranch's commits are used as IDs
+gitmode=true
+tag='git-rewrite-id'
+
+ibranch=''
+obranch=''
+wbranch=''
+
+usage() {
+	echo 'malformed call to internal function'
+}
+
+verbose() {
+	: "$*"
+	#echo "$*"
+}
+
+################################################################################
+
+id2commit() {
+	[[ $# = 2 ]] || { usage; return 1; }
+	local branch=$1
+	local id=$2
+	if [[ $branch == $ibranch ]] && $gitmode; then
+		printf '%s\n' "$id"
+	else
+		git log "$branch" --pretty=format:'%H' --grep "${tag}: ${id}"
+	fi
+}
+
+commit2id() {
+	[[ $# = 2 ]] || { usage; return 1; }
+	local branch=$1
+	local commit=$2
+	if [[ $branch == $ibranch ]] && $gitmode; then
+		printf '%s\n' "$commit"
+	else
+		git log "$branch" -n1 --pretty=formtat:'%B' "$commit" | sed -n "s|^\s*${tag}: ||p"
+	fi
+}
+
+# commit2commit
+c2c() {
+	[[ $# = 3 ]] || { usage; return 1; }
+	local from=$1
+	local to=$2
+	local commit=$3
+	if [[ "$from" == "$to" ]]; then
+		# optimization
+		# also, properly normalizes $ibranch when $gitmode=true
+		git log "$commit" -n1 --pretty=format:'%H'
+	else
+		id2commit "$to" "$(commit2id "$from" "$commit")"
+	fi
+}
+
+################################################################################
+
+main() {
+	# Parse command line arguments #########################################
+	if [[ $1 = '--svn' ]]; then
+		gitmode=false
+		tag='git-svn-id'
+		shift
+	fi
+
+	if [[ $# < 3 ]]; then
+		usage
+		exit 1
+	fi
+
+	ibranch=$1
+	obranch=$2
+	shift 2
+
+	local filters=();
+	if $gitmode; then
+		filters=(--msg-filter "git-rewrite-branch--appendid '${tag}'")
+	fi
+	filters+=("$@")
+
+	# Main #################################################################
+
+	if git checkout "$obranch" -- 2>/dev/null; then
+		# obranch exists, update it
+		echo 'Updating existing rewritten branch...'
+
+		local icommit="$(c2c "$ibranch" "$ibranch" "$ibranch")"
+		local ocommit="$(c2c "$obranch" "$ibranch" "$obranch")"
+		if [[ "$icommit" == "$ocommit" ]]; then
+			echo "Nothing to do"
+			return 0
+		fi
+
+		# Just to be safe
+		git branch -D "$obranch.tmp" 2>/dev/null || true
+
+		wbranch="$obranch.tmp"
+		local common="$(c2c "$obranch" "$ibranch" "$obranch")"
+		if c2c "$ibranch" "$ibranch" "${common}^" &>/dev/null; then
+			revlist="$(c2c "$obranch" "$ibranch" "$obranch")^..${wbranch}"
+		else
+			# There is only one commit from $ibranch in $obranch
+			revlist="$wbranch"
+		fi
+	else
+		# obranch does not exist, create it
+		echo 'Creating new rewritten branch...'
+		wbranch=$obranch
+		revlist=$wbranch
+	fi
+
+	git checkout "$ibranch"
+	git checkout -b "$wbranch"
+	git filter-branch -f "${filters[@]}" "$revlist"
+
+	if [[ "$obranch" != "$wbranch" ]]; then
+		# rebase the changes in wbranch onto obranch
+		echo 'Rebasing rewrites onto existing branch...'
+		local wcommit="$(c2c "$wbranch" "$ibranch" "$wbranch")"
+		if [[ "$wcommit" == "$ocommit" ]]; then
+			echo "Nothing to do"
+			return 0
+		fi
+
+		local commonish="$(c2c "$obranch" "$wbranch" "$obranch")"
+		cmd=(git rebase --onto "$obranch" "$commonish" "$wbranch")
+
+		verbose
+		verbose "  o---o---o $obranch"
+		verbose '          :'
+		verbose "  o---o---o---o---o $ibranch"
+		verbose '       \  :'
+		verbose '        `-C---o---o '"$wbranch"
+		verbose
+		verbose "  C = $commonish"
+		verbose
+		verbose "  ${cmd[*]}"
+		verbose
+
+		"${cmd[@]}"
+		git checkout "$obranch"
+		git branch -d "$wbranch"
+	fi
+}
+
+main "$@"
diff --git a/git-rewrite-branch--appendid b/git-rewrite-branch--appendid
new file mode 100755
index 0000000..e44180a
--- /dev/null
+++ b/git-rewrite-branch--appendid
@@ -0,0 +1,4 @@
+#!/bin/bash
+
+tag=$1
+sed '$a'"${tag}: ${GIT_COMMIT}"