contrib: add convert-grafts-to-replace-refs.sh

This patch adds into contrib/ an example script to convert
grafts from an existing grafts file into replace refs using
the new --graft option of "git replace".

While at it let's mention this new script in the
"git replace" documentation for the --graft option.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-replace.txt

@@ -79,7 +79,9 @@ OPTIONS
 	content as <commit> except that its parents will be
 	[<parent>...] instead of <commit>'s parents. A replacement ref
 	is then created to replace <commit> with the newly created
-	commit.
+	commit. See contrib/convert-grafts-to-replace-refs.sh for an
+	example script based on this option that can convert grafts to
+	replace refs.
 
 -l <pattern>::
 --list <pattern>::

contrib/convert-grafts-to-replace-refs.sh

@@ -0,0 +1,28 @@
+#!/bin/sh
+
+# You should execute this script in the repository where you
+# want to convert grafts to replace refs.
+
+GRAFTS_FILE="${GIT_DIR:-.git}/info/grafts"
+
+. $(git --exec-path)/git-sh-setup
+
+test -f "$GRAFTS_FILE" || die "Could not find graft file: '$GRAFTS_FILE'"
+
+grep '^[^# ]' "$GRAFTS_FILE" |
+while read definition
+do
+	if test -n "$definition"
+	then
+		echo "Converting: $definition"
+		git replace --graft $definition ||
+			die "Conversion failed for: $definition"
+	fi
+done
+
+mv "$GRAFTS_FILE" "$GRAFTS_FILE.bak" ||
+	die "Could not rename '$GRAFTS_FILE' to '$GRAFTS_FILE.bak'"
+
+echo "Success!"
+echo "All the grafts in '$GRAFTS_FILE' have been converted to replace refs!"
+echo "The grafts file '$GRAFTS_FILE' has been renamed: '$GRAFTS_FILE.bak'"