rebase: teach --autosquash to match on sha1 in addition to message

Support lines of the form "fixup! 7a235b" that specify an exact commit
in addition to the normal "squash! Old commit message" form.

Signed-off-by: Kevin Ballard <kevin@sb.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase--interactive.sh

@@ -675,9 +675,27 @@ get_saved_options () {
 # comes immediately after the former, and change "pick" to
 # "fixup"/"squash".
 rearrange_squash () {
-	sed -n -e 's/^pick \([0-9a-f]*\) \(squash\)! /\1 \2 /p' \
-		-e 's/^pick \([0-9a-f]*\) \(fixup\)! /\1 \2 /p' \
-		"$1" >"$1.sq"
+	# extract fixup!/squash! lines and resolve any referenced sha1's
+	while read -r pick sha1 message
+	do
+		case "$message" in
+		"squash! "*|"fixup! "*)
+			action="${message%%!*}"
+			rest="${message#*! }"
+			echo "$sha1 $action $rest"
+			# if it's a single word, try to resolve to a full sha1 and
+			# emit a second copy. This allows us to match on both message
+			# and on sha1 prefix
+			if test "${rest#* }" = "$rest"; then
+				fullsha="$(git rev-parse -q --verify "$rest" 2>/dev/null)"
+				if test -n "$fullsha"; then
+					# prefix the action to uniquely identify this line as
+					# intended for full sha1 match
+					echo "$sha1 +$action $fullsha"
+				fi
+			fi
+		esac
+	done >"$1.sq" <"$1"
 	test -s "$1.sq" || return
 
 	used=
@@ -693,12 +711,20 @@ rearrange_squash () {
 			case " $used" in
 			*" $squash "*) continue ;;
 			esac
-			case "$message" in
-			"$msg"*)
+			emit=0
+			case "$action" in
+			+*)
+				action="${action#+}"
+				# full sha1 prefix test
+				case "$msg" in "$sha1"*) emit=1;; esac ;;
+			*)
+				# message prefix test
+				case "$message" in "$msg"*) emit=1;; esac ;;
+			esac
+			if test $emit = 1; then
 				printf '%s\n' "$action $squash $action! $msg"
 				used="$used$squash "
-				;;
-			esac
+			fi
 		done <"$1.sq"
 	done >"$1.rearranged" <"$1"
 	cat "$1.rearranged" >"$1"