[RFC PATCH 4/7] rebase -i: Commit only once when rewriting picks

[Fabian Ruch <bafain@gmail.com>]

The options passed to `do_pick` determine whether the picked commit will
be rewritten or not. If the commit gets rewritten, because the user
requested to edit the commit message for instance, let `pick_one` merely
apply the changes introduced by the commit and do not commit the
resulting tree yet. If the commit is replayed as is, leave it to
`pick_one` to recreate the commit (possibly by fast-forwarding the
head). This makes it easier to combine git-commit options like `--edit`
and `--amend` in `do_pick` because git-cherry-pick does not support
`--amend`.

In the case of `--edit`, do not `exit_with_patch` but assign `rewrite`
to pick the changes with `-n`. If the pick conflicts, no commit is
created which we would have to amend when continuing the rebase. To
complete the pick after the conflicts are resolved the user just resumes
with `git rebase --continue`.

If `rebase--interactive` is used to rebase a complete branch onto some
head, `rebase` creates a sentinel commit that requires special treatment
by `do_pick`. Do not finalize the pick here either because its commit
message can be altered as for any other pick. Since the orphaned root
commit gets a temporary parent, it is always rewritten. Safely use the
rewrite infrastructure of `do_pick` to create the final commit.

Signed-off-by: Fabian Ruch <bafain@gmail.com>
---
 git-rebase--interactive.sh | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index f09eeae..f903599 100644
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -63,7 +63,8 @@ msgnum="$state_dir"/msgnum
 author_script="$state_dir"/author-script
 
 # When an "edit" rebase command is being processed, the SHA1 of the
-# commit to be edited is recorded in this file.  When "git rebase
+# commit to be edited is recorded in this file.  The same happens when
+# rewriting a commit fails, for instance "reword".  When "git rebase
 # --continue" is executed, if there are any staged changes then they
 # will be amended to the HEAD commit, but only provided the HEAD
 # commit is still the commit to be edited.  When any other rebase
@@ -508,12 +509,15 @@ record_in_rewritten() {
 #     commit message. The editor contents becomes the commit message of
 #     the new head.
 do_pick () {
-	edit=
+	rewrite=
+	rewrite_amend=
+	rewrite_edit=
 	while test $# -gt 0
 	do
 		case "$1" in
 		-e|--edit)
-			edit=y
+			rewrite=y
+			rewrite_edit=y
 			;;
 		-*)
 			warn "do_pick: ignored option -- $1"
@@ -528,6 +532,9 @@ do_pick () {
 
 	if test "$(git rev-parse HEAD)" = "$squash_onto"
 	then
+		rewrite=y
+		rewrite_amend=y
+		git rev-parse --verify HEAD >"$amend"
 		# Set the correct commit message and author info on the
 		# sentinel root before cherry-picking the original changes
 		# without committing (-n).  Finally, update the sentinel again
@@ -538,22 +545,20 @@ do_pick () {
 		# rebase --continue.
 		git commit --allow-empty --allow-empty-message --amend \
 			   --no-post-rewrite -n -q -C $1 &&
-			pick_one -n $1 &&
-			git commit --allow-empty --amend \
-				   --no-post-rewrite -n -q \
-				   ${gpg_sign_opt:+"$gpg_sign_opt"} ||
+			pick_one -n $1 ||
 			die_with_patch $1 "Could not apply $1... $2"
 	else
-		pick_one $1 ||
+		pick_one ${rewrite:+-n} $1 ||
 			die_with_patch $1 "Could not apply $1... $2"
 	fi
 
-	if test -n "$edit"
+	if test -n "$rewrite"
 	then
-		git commit --allow-empty --amend --no-post-rewrite -n -q ${gpg_sign_opt:+"$gpg_sign_opt"} || {
-			warn "Could not amend commit after successfully picking $1... $2"
-			exit_with_patch $1 1
-		}
+		git commit --allow-empty --no-post-rewrite -n -q \
+			   ${rewrite_amend:+--amend} \
+			   ${rewrite_edit:+--edit} \
+			   ${gpg_sign_opt:+"$gpg_sign_opt"} ||
+			die_with_patch $1 "Could not rewrite commit after successfully picking $1... $2"
 	fi
 }
 
-- 
2.0.0