From 1c4c08fd3f85360b8e98d3afe1af0ba6e234ea2d Mon Sep 17 00:00:00 2001
From: "Kyle J. McKay" <mackyle@gmail.com>
Date: Fri, 20 Jan 2017 14:28:14 -0800
Subject: [PATCH] tg-update.sh: reduce number of checkouts slightly

Avoid running checkout (or its equivalent switch_to_base)
unless absolutely necessary.

Add a final checkout to the single branch update mode to
make sure tg-update ends up on the expected branch in that
case.

Do some minor cleanup while in there to the way the
"msg"s are set and passed in to the merge command.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>
---
 tg-update.sh | 37 ++++++++++++++++++++++++++-----------
 1 file changed, 26 insertions(+), 11 deletions(-)

diff --git a/tg-update.sh b/tg-update.sh
index 8c3db9a..edfc778 100644
--- a/tg-update.sh
+++ b/tg-update.sh
@@ -50,7 +50,9 @@ current="$(strip_ref "$(git symbolic-ref -q HEAD)")" || :
 if [ -z "$all" ]; then
 	name="$(verify_topgit_branch "${name:-HEAD}")"
 else
-	[ -n "$current" ] || die "cannot return to detached tree; switch to another branch"
+	[ -n "$current" ] || die "cannot return to detached HEAD; switch to another branch"
+	[ -n "$(git rev-parse --verify --quiet HEAD --)" ] ||
+		die "cannot return to unborn branch; switch to another branch"
 fi
 
 ensure_clean_tree
@@ -73,6 +75,7 @@ stash_now_if_requested() {
 
 recursive_update() {
 	_ret=0
+	on_base=
 	(
 		TG_RECURSIVE="[$1] $TG_RECURSIVE"
 		PS1="[$1] $PS1"
@@ -95,6 +98,18 @@ git_merge() {
 	return $_ret
 }
 
+on_base=
+do_base_switch() {
+	[ -n "$1" ] || return 0
+	if
+		[ "$1" != "$on_base" ] ||
+		[ "$(git symbolic-ref -q HEAD)" != "refs/$topbases/$1" ]
+	then
+		switch_to_base "$1"
+		on_base="$1"
+	fi
+}
+
 update_branch() {
 	# We are cacheable until the first change
 	become_cacheable
@@ -182,8 +197,8 @@ update_branch() {
 			esac
 		done <"$_depcheck.ideps"
 
-		# Make sure we're on the base branch now
-		switch_to_base "$_update_name"
+		# Make sure we end up on the correct base branch
+		on_base=
 
 		for fulldep in "$@"; do
 			# This will be either a proper topic branch
@@ -204,12 +219,10 @@ update_branch() {
 
 			# We need to switch to the base branch
 			# ...but only if we aren't there yet (from failed previous merge)
-			_HEAD="$(git symbolic-ref -q HEAD)" || :
-			if [ "$_HEAD" != "refs/$topbases/$_update_name" ]; then
-				switch_to_base "$_update_name"
-			fi
+			do_base_switch "$_update_name"
 
-			if ! git_merge -m "tgupdate: merge $dep into $topbases/$_update_name" "$fulldep^0"; then
+			msg="tgupdate: merge $dep into $topbases/$_update_name"
+			if ! git_merge -m "$msg" "$fulldep^0"; then
 				if [ -z "$TG_RECURSIVE" ]; then
 					resume="\`$tgdisplay update${skip:+ --skip} $_update_name\` again"
 				else # subshell
@@ -248,7 +261,8 @@ update_branch() {
 			become_non_cacheable
 			# *DETACH* our HEAD now!
 			git checkout -q --detach "refs/$topbases/$_update_name"
-			if ! git_merge -m "tgupdate: merge ${_rname#refs/} onto $topbases/$_update_name" "$_rname^0"; then
+			msg="tgupdate: merge ${_rname#refs/} onto $topbases/$_update_name"
+			if ! git_merge -m "$msg" "$_rname^0"; then
 				info "Oops, you will need to help me out here a bit."
 				info "Please commit merge resolution and call:"
 				info "git$gitcdopt checkout $_update_name && git$gitcdopt merge <commitid>"
@@ -272,7 +286,8 @@ update_branch() {
 	stash_now_if_requested
 	info "Updating $_update_name against new base..."
 	become_non_cacheable
-	if ! git_merge -m "tgupdate: merge ${plusextra}$topbases/$_update_name into $_update_name" "$merge_with^0"; then
+	msg="tgupdate: merge ${plusextra}$topbases/$_update_name into $_update_name"
+	if ! git_merge -m "$msg" "$merge_with^0"; then
 		if [ -z "$TG_RECURSIVE" ]; then
 			info "Please commit merge resolution. No need to do anything else"
 			info "You can abort this operation using \`git$gitcdopt reset --hard\` now"
@@ -289,7 +304,7 @@ update_branch() {
 tg_read_only=1
 v_create_ref_cache
 
-[ -z "$all" ] && { update_branch $name; exit; }
+[ -z "$all" ] && { update_branch "$name" && git checkout -q "$name"; exit; }
 
 do_non_annihilated_branches_patterns() {
 	while read -r _pat && [ -n "$_pat" ]; do
-- 
2.11.4.GIT