[PATCH] contrib git-resurrect: find traces of a branch name and resurrect it

[Thomas Rast <trast@student.ethz.ch>]

Add a tool 'git-resurrect.sh <branch>' that tries to find traces of
the <branch> in the HEAD reflog and, optionally, all merge commits in
the repository.  It can then resurrect the branch, pointing it at the
most recent of all candidate commits found.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
---

Boyd Stephen Smith Jr. wrote:
> I think it could be quite nice; "undelete"-type commands are generally 
> well-received by users and when run against reflogs alone, that's what the 
> command is.
> 
> It's useful enough to me that I'd love to see it mainlined.

So here's a version for contrib with more options and some other
tweaks.

I removed the ability to "batch resurrect" with several <name>
arguments since that would have conflicted with -b <newname>, but
otherwise the features are the same.

> In my particular case, it wasn't useful without the -m option, but I 
> understand why it is not the default.

Aside from the obvious speed reasons, I don't really want to teach
people that commits "know" the branch they were on.  It is a pure
coincidence if you can resurrect a topic branch from merge messages;
an equivalent merge could have gone through as a fast-forward, and
you'd never know.



 contrib/git-resurrect.sh |  140 ++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 140 insertions(+), 0 deletions(-)
 create mode 100755 contrib/git-resurrect.sh

diff --git a/contrib/git-resurrect.sh b/contrib/git-resurrect.sh
new file mode 100755
index 0000000..29bf723
--- /dev/null
+++ b/contrib/git-resurrect.sh
@@ -0,0 +1,140 @@
+#!/bin/sh
+
+USAGE="[-h] [-r] [-m] [-t] [-n] [-b <newname>] <name>"
+LONG_USAGE="git-resurrect attempts to find traces of a branch tip
+called <name>, and tries to resurrect it.  Currently, the reflog is
+searched for checkout messages, and with -r also merge messages.  With
+-m and -t, the history of all refs is scanned for Merge <name> into
+other/Merge <other> into <name> (respectively) commit subjects, which
+is rather slow but allows you to resurrect other people's topic
+branches."
+
+OPTIONS_SPEC="\
+git resurrect [-h] [-r] [-m] [-t] [-n] [-b <newname>] <name>
+--
+b,branch=            save branch as <newname> instead of <name>
+H,try-hard           same as -r -m -t
+r,reflog-merges      scan for merges recorded in reflog
+m,merges             scan for merges into other branches (slow)
+t,merge-targets      scan for merges of other branches into <name>
+n,dry-run            don't recreate the branch"
+
+. git-sh-setup
+cd_to_toplevel
+
+search_reflog () {
+        sed -n 's~^\([^ ]*\) .*\tcheckout: moving from '"$1"' .*~\1~p' \
+                < .git/logs/HEAD
+}
+
+search_reflog_merges () {
+        sed -n 's~^[^ ]* \([^ ]*\) .*\tmerge '"$1"':~\1~p' \
+                < .git/logs/HEAD
+}
+
+search_merges () {
+	git rev-list --pretty=tformat:"%h %p:%s" --all |
+	grep "Merge branch.*'$branch'.*into" |
+	while read sha rest; do
+		parents="$(echo "$rest" | cut -d: -f1)"
+		case "$parents" in
+		    *' '*' '*)
+			warn "$branch took part in octopus merge $sha"
+			warn "check manually!"
+			;;
+		    *' '*)
+			echo "$parents" | cut -d' ' -f2
+			;;
+		esac
+	done
+}
+
+search_merge_targets () {
+	git rev-list --pretty=tformat:"%h %s" --all |
+	grep "Merge branch '[^']*' into $branch$" |
+	cut -d' ' -f1
+}
+
+dry_run=
+scan_reflog_merges=
+scan_merges=
+scan_merge_targets=
+new_name=
+
+while test "$#" != 0; do
+	case "$1" in
+	    -b|--branch)
+		shift
+		new_name="$1"
+		;;
+	    -n|--dry-run)
+		dry_run=t
+		;;
+	    -m|--merges)
+		scan_merges=t
+		;;
+	    -r|--reflog_merges)
+		scan_reflog_merges=t
+		;;
+	    -t|--merge-targets)
+		scan_merge_targets=t
+		;;
+	    -H|--try-hard)
+		scan_reflog_merges=t
+		scan_merges=t
+		scan_merge_targets=t
+		;;
+	    --)
+		shift
+		break
+		;;
+	    *)
+		usage
+		;;
+	esac
+	shift
+done
+
+test "$#" = 1 || usage
+
+branch="$1"
+test -z "$new_name" && new_name="$branch"q
+
+candidates="$(search_reflog $1)"
+if test ! -z "$scan_reflog_merges"; then
+	candidates="$candidates $(search_reflog_merges $1)"
+fi
+if test ! -z "$scan_merges"; then
+	candidates="$candidates $(search_merges $1)"
+fi
+if test ! -z "$scan_merge_targets"; then
+	candidates="$candidates $(search_merge_targets $1)"
+fi
+
+candidates="$(git rev-parse $candidates | sort -u)"
+
+if test -z "$candidates"; then
+	hint=
+	test "z$scan_merges$scan_reflog_merges$scan_merge_targets" != "zttt" \
+		&& hint="(maybe try again with -H)"
+	die "no candidates for $branch found" $hint
+fi
+
+echo "** Candidates for $branch **"
+for cmt in $candidates; do
+	git --no-pager log --pretty=oneline --abbrev-commit -1 $cmt
+done
+
+newest="$(git rev-list -1 $candidates)"
+if test ! -z "$dry_run"; then
+	printf "Most recent: "
+	git --no-pager log -1 --pretty=tformat:"%h %s" $newest
+elif ! git rev-parse --verify --quiet $new_name >/dev/null; then
+	printf "** Restoring $new_name to "
+	git --no-pager log -1 --pretty=tformat:"%h %s" $newest
+	git branch $new_name $newest
+else
+	printf "Most recent: "
+	git --no-pager log -1 --pretty=tformat:"%h %s" $newest
+	echo "** $new_name already exists, doing nothing"
+fi
-- 
1.6.1.447.gbdf1d