git-rewrite-branch: generalize to support arbitrary existing tags

1 files changed, 30 insertions, 24 deletions

diff --git a/git-rewrite-branch b/git-rewrite-branch
index b9c6ab3..390170b 100755
--- a/git-rewrite-branch
+++ b/git-rewrite-branch
@@ -1,22 +1,34 @@
-#!/bin/bash -eE
+#!/bin/bash
 #
 # Copyright (c) 2012-2013 Luke Shumaker <lukeshu@sbcglobal.net>
 #
 
-USAGE='[-h|-v|--svn] <in-branch> <out-branch> <filters>...'
+set -eE
+
+USAGE='[-h|-v|--no-tag|--tag=tag] <in-branch> <out-branch> <filters>...'
 LONG_USAGE='Like filter-branch, but can be used to update branches.
 
 This creates or updates <out-branch> from <in-branch>.  If <in-branch> already
 exists, it only runs new commits through the filter.  This way, this can be
-used to pull from a remote with a different layout than yours.
+used to pull from a remote repository with a different layout than yours.
 
-This will append "git-rewrite-id" to all commit messages, similar to
-"git-svn-id" with `git-svn`.
+New commits are detected by examining a "tag" in the commit messages of
+<out-branch> that can be used to tie those commits to corresponding commits in
+<in-branch>.  By default, the tag is "git-rewrite-id: " followed by the commit
+hash of the corresponding commit; similar to the "git-svn-id" appended by
+`git-svn`.  However, if <in-branch> already has suitable tags in the commit
+messages (such as "git-svn-id"), then that can be used, and the commit message
+does not need to be edited.
 
     -h               Show this text
     -v               Be more verbose
     --svn            Use an existing "git-svn-id" instead of "git-rewrite-id"
                      (in-branch was generated by git-svn)
+    --tag=<tag>      Use the exiting <tag> as found in <in-branch>, instead of
+                     the commit hash.
+    --no-tag         Disregard a previous "--tag="; set "git-rewrite-id" to
+                     the commit hash.
+    --svn            An alias for "--tag=git-svn-id"
 
 <filters> is passed directly to `git filter-branch`, and therefore has the same
 format.
@@ -27,8 +39,8 @@ OPTIONS_SPEC=
 . git-sh-i18n
 require_work_tree_exists
 
-# when $gitmode is true, $ibranch's commits are used as IDs
-gitmode=true
+# I $hastag is false, $ibranch's commit hashes are used as IDs
+hastag=false # whether ibranch already has tags
 tag='git-rewrite-id'
 
 ibranch=''
@@ -56,7 +68,7 @@ id2commit() {
 	[[ $# == 2 ]] || panic
 	local branch=$1
 	local id=$2
-	if [[ $branch == $ibranch ]] && $gitmode; then
+	if [[ $branch == $ibranch ]] && ! $hastag; then
 		printf '%s\n' "$id"
 	else
 		git log "$branch" --pretty=format:'%H' --grep "${tag}: ${id}"
@@ -69,7 +81,7 @@ commit2id() {
 	[[ $# == 2 ]] || panic
 	local branch=$1
 	local commit=$2
-	if [[ $branch == $ibranch ]] && $gitmode; then
+	if [[ $branch == $ibranch ]] && ! $hastag; then
 		printf '%s\n' "$commit"
 	else
 		git log "$branch" -n1 --pretty=formtat:'%B' "$commit" | sed -n "s|^\s*${tag}: ||p"
@@ -87,7 +99,7 @@ c2c() {
 	local commit=$3
 	if [[ "$from" == "$to" ]]; then
 		# optimization
-		# also, properly normalizes $ibranch when $gitmode=true
+		# also, properly normalizes $ibranch when $hastag=false
 		git log "$commit" -n1 --pretty=format:'%H'
 	else
 		id2commit "$to" "$(commit2id "$from" "$commit")"
@@ -100,22 +112,16 @@ main() {
 	# Parse command line arguments #########################################
 	while true; do
 		case "${1:-}" in
-			--svn)
-				gitmode=false
-				tag='git-svn-id'
-				shift
-				;;
-			-h)
-				usage
-				return 0
-				;;
+			--svn)    hastag=true;  tag='git-svn-id'    ; shift 1 ;;
+			--tag=*)  hastag=true;  tag="${1#*=}"       ; shift 1 ;;
+			--tag)    hastag=true;  tag=$2              ; shift 2 ;;
+			--no-tag) hastag=false; tag='git-rewrite-id'; shift 1 ;;
+			-h) usage; return 0;;
 			-v)
 				verbose() { echo "$*"; }
 				shift
 				;;
-			*)
-				break
-				;;
+			*) break;;
 		esac
 	done
 
@@ -129,12 +135,12 @@ main() {
 	shift 2
 
 	local filters=();
-	if $gitmode; then
+	if ! $hastag; then
 		# Add a filter to append the id to the commit message.
 		# This is a little confusing to read because of double quoting.
 		filters=(--msg-filter "sed '\$a'\"${tag}: \${GIT_COMMIT}\"")
 		# Here it is annotated; "@" indicates characters to be taken
-		# literally, and "^" indicates string expansion.
+		# literally, and "^" indicates string interpolation.
 		#
 		# Argument to git-filter-branch:
 		#    sed '$a'"${tag}: ${GIT_COMMIT}"