rebase -i: rearrange fixup/squash lines using the rebase--helper

This operation has quadratic complexity, which is especially painful
on Windows, where shell scripts are *already* slow (mainly due to the
overhead of the POSIX emulation layer).

Let's reimplement this with linear complexity (using a hash map to
match the commits' subject lines) for the common case; Sadly, the
fixup/squash feature's design neglected performance considerations,
allowing arbitrary prefixes (read: `fixup! hell` will match the
commit subject `hello world`), which means that we are stuck with
quadratic performance in the worst case.

The reimplemented logic also happens to fix a bug where commented-out
lines (representing empty patches) were dropped by the previous code.

While at it, clarify how the fixup/squash feature works in `git rebase
-i`'s man page.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 89 deletions

diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index af8d7bd77f..3b0340e7cc 100644
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -721,94 +721,6 @@ collapse_todo_ids() {
 	git rebase--helper --shorten-ids
 }
 
-# Rearrange the todo list that has both "pick sha1 msg" and
-# "pick sha1 fixup!/squash! msg" appears in it so that the latter
-# comes immediately after the former, and change "pick" to
-# "fixup"/"squash".
-#
-# Note that if the config has specified a custom instruction format
-# each log message will be re-retrieved in order to normalize the
-# autosquash arrangement
-rearrange_squash () {
-	format=$(git config --get rebase.instructionFormat)
-	# extract fixup!/squash! lines and resolve any referenced sha1's
-	while read -r pick sha1 message
-	do
-		test -z "${format}" || message=$(git log -n 1 --format="%s" ${sha1})
-		case "$message" in
-		"squash! "*|"fixup! "*)
-			action="${message%%!*}"
-			rest=$message
-			prefix=
-			# skip all squash! or fixup! (but save for later)
-			while :
-			do
-				case "$rest" in
-				"squash! "*|"fixup! "*)
-					prefix="$prefix${rest%%!*},"
-					rest="${rest#*! }"
-					;;
-				*)
-					break
-					;;
-				esac
-			done
-			printf '%s %s %s %s\n' "$sha1" "$action" "$prefix" "$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 $prefix $fullsha"
-				fi
-			fi
-		esac
-	done >"$1.sq" <"$1"
-	test -s "$1.sq" || return
-
-	used=
-	while read -r pick sha1 message
-	do
-		case " $used" in
-		*" $sha1 "*) continue ;;
-		esac
-		printf '%s\n' "$pick $sha1 $message"
-		test -z "${format}" || message=$(git log -n 1 --format="%s" ${sha1})
-		used="$used$sha1 "
-		while read -r squash action msg_prefix msg_content
-		do
-			case " $used" in
-			*" $squash "*) continue ;;
-			esac
-			emit=0
-			case "$action" in
-			+*)
-				action="${action#+}"
-				# full sha1 prefix test
-				case "$msg_content" in "$sha1"*) emit=1;; esac ;;
-			*)
-				# message prefix test
-				case "$message" in "$msg_content"*) emit=1;; esac ;;
-			esac
-			if test $emit = 1; then
-				if test -n "${format}"
-				then
-					msg_content=$(git log -n 1 --format="${format}" ${squash})
-				else
-					msg_content="$(echo "$msg_prefix" | sed "s/,/! /g")$msg_content"
-				fi
-				printf '%s\n' "$action $squash $msg_content"
-				used="$used$squash "
-			fi
-		done <"$1.sq"
-	done >"$1.rearranged" <"$1"
-	cat "$1.rearranged" >"$1"
-	rm -f "$1.sq" "$1.rearranged"
-}
-
 # Add commands after a pick or after a squash/fixup serie
 # in the todo list.
 add_exec_commands () {
@@ -1068,7 +980,7 @@ then
 fi
 
 test -s "$todo" || echo noop >> "$todo"
-test -n "$autosquash" && rearrange_squash "$todo"
+test -z "$autosquash" || git rebase--helper --rearrange-squash || exit
 test -n "$cmd" && add_exec_commands "$todo"
 
 todocount=$(git stripspace --strip-comments <"$todo" | wc -l)