[PATCH v2 17/23] rebase -i: prepare for squash in terms of do_pick --amend

[Fabian Ruch <bafain@gmail.com>]

Rewrite `squash` and `fixup` handling in `do_next` using the sequence

    pick_one
    commit

in order to test the correctness of a single `do_squash` or
parameterised `do_pick` and make the subsequent patch reimplementing
`squash` in terms of such a single function more readable.

Do not call `rm -f "$GIT_DIR"/MERGE_MSG` since it has no effect on
the state after git-rebase--interactive terminates. The option `-F`
makes git-commit ignore `MERGE_MSG` for the log message. If
git-commit succeeds, `MERGE_MSG` is removed, and if it fails,
`MERGE_MSG` is overwritten by the error sequence `die_failed_squash`.
In summary, removing `MERGE_MSG` neither influences the squash commit
message nor the file state after git-commit returns.

Moreover, `pick_one` ignores `$GIT_DIR/SQUASH_MSG` and does not touch
`$squash_msg` so that it is correct to execute `pick_one` immediately
before git-commit.

Might be squashed into the subsequent commit.

Signed-off-by: Fabian Ruch <bafain@gmail.com>
---
 git-rebase--interactive.sh | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index 0fbf773..601a2ff 100644
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -623,15 +623,15 @@ do_next () {
 		author_script_content=$(get_author_ident_from_commit HEAD)
 		echo "$author_script_content" > "$author_script"
 		eval "$author_script_content"
-		if ! pick_one -n $sha1
-		then
-			git rev-parse --verify HEAD >"$amend"
-			die_failed_squash $sha1 "$rest"
-		fi
 		case "$(peek_next_command)" in
 		squash|s|fixup|f)
 			# This is an intermediate commit; its message will only be
 			# used in case of trouble.  So use the long version:
+			if ! pick_one -n $sha1
+			then
+				git rev-parse --verify HEAD >"$amend"
+				die_failed_squash $sha1 "Could not apply $sha1... $rest"
+			fi
 			do_with_author output git commit --allow-empty-message --allow-empty \
 				--amend --no-verify -F "$squash_msg" \
 				${gpg_sign_opt:+"$gpg_sign_opt"} ||
@@ -641,13 +641,22 @@ do_next () {
 			# This is the final command of this squash/fixup group
 			if test -f "$fixup_msg"
 			then
+				if ! pick_one -n $sha1
+				then
+					git rev-parse --verify HEAD >"$amend"
+					die_failed_squash $sha1 "Could not apply $sha1... $rest"
+				fi
 				do_with_author output git commit --allow-empty-message --allow-empty \
 					--amend --no-verify -F "$fixup_msg" \
 					${gpg_sign_opt:+"$gpg_sign_opt"} ||
 					die_failed_squash $sha1 "$rest"
 			else
 				cp "$squash_msg" "$GIT_DIR"/SQUASH_MSG || exit
-				rm -f "$GIT_DIR"/MERGE_MSG
+				if ! pick_one -n $sha1
+				then
+					git rev-parse --verify HEAD >"$amend"
+					die_failed_squash $sha1 "Could not apply $sha1... $rest"
+				fi
 				do_with_author output git commit --allow-empty --amend --no-pre-commit -F "$GIT_DIR"/SQUASH_MSG -e \
 					${gpg_sign_opt:+"$gpg_sign_opt"} ||
 					die_failed_squash $sha1 "$rest"
-- 
2.0.1