rebase -i: add exec command to launch a shell command

The typical usage pattern would be to run a test (or simply a compilation
command) at given points in history.

The shell command is ran (from the worktree root), and the rebase is
stopped when the command fails, to give the user an opportunity to fix
the problem before continuing with "git rebase --continue".

This needs a little rework of skip_unnecessary_picks, which wasn't robust
enough to deal with lines like

  exec >"file    name with many spaces"

in the todolist. The new version extracts command, sha1 and rest from
each line, but outputs the line itself verbatim to avoid changing the
whitespace layout.
Signed-off-by: NMatthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-rebase.txt

@@ -459,6 +459,30 @@ sure that the current HEAD is "B", and call
 $ git rebase -i -p --onto Q O
 -----------------------------
 
+Reordering and editing commits usually creates untested intermediate
+steps.  You may want to check that your history editing did not break
+anything by running a test, or at least recompiling at intermediate
+points in history by using the "exec" command (shortcut "x").  You may
+do so by creating a todo list like this one:
+
+-------------------------------------------
+pick deadbee Implement feature XXX
+fixup f1a5c00 Fix to feature XXX
+exec make
+pick c0ffeee The oneline of the next commit
+edit deadbab The oneline of the commit after
+exec cd subdir; make test
+...
+-------------------------------------------
+
+The interactive rebase will stop when a command fails (i.e. exits with
+non-0 status) to give you an opportunity to fix the problem. You can
+continue with `git rebase --continue`.
+
+The "exec" command launches the command in a shell (the one specified
+in `$SHELL`, or the default shell if `$SHELL` is not set), so you can
+use shell features (like "cd", ">", ";" ...). The command is run from
+the root of the working tree.
 
 SPLITTING COMMITS
 -----------------

git-rebase--interactive.sh

@@ -537,6 +537,34 @@ do_next () {
 		esac
 		record_in_rewritten $sha1
 		;;
+	x|"exec")
+		read -r command rest < "$TODO"
+		mark_action_done
+		printf 'Executing: %s\n' "$rest"
+		# "exec" command doesn't take a sha1 in the todo-list.
+		# => can't just use $sha1 here.
+		git rev-parse --verify HEAD > "$DOTEST"/stopped-sha
+		${SHELL:-@SHELL_PATH@} -c "$rest" # Actual execution
+		status=$?
+		if test "$status" -ne 0
+		then
+			warn "Execution failed: $rest"
+			warn "You can fix the problem, and then run"
+			warn
+			warn "	git rebase --continue"
+			warn
+			exit "$status"
+		fi
+		# Run in subshell because require_clean_work_tree can die.
+		if ! (require_clean_work_tree)
+		then
+			warn "Commit or stash your changes, and then run"
+			warn
+			warn "	git rebase --continue"
+			warn
+			exit 1
+		fi
+		;;
 	*)
 		warn "Unknown command: $command $sha1 $rest"
 		if git rev-parse --verify -q "$sha1" >/dev/null
@@ -591,10 +619,13 @@ do_rest () {
 # skip picking commits whose parents are unchanged
 skip_unnecessary_picks () {
 	fd=3
-	while read -r command sha1 rest
+	while read -r line
 	do
+		command=$(echo "$line" | sed 's/  */ /' | cut -d ' ' -f 1)
+		sha1=$(echo "$line"    | sed 's/  */ /' | cut -d ' ' -f 2)
+		rest=$(echo "$line"    | sed 's/  */ /' | cut -d ' ' -f 3-)
 		# fd=3 means we skip the command
-		case "$fd,$command,$(git rev-parse --verify --quiet $sha1^)" in
+		case "$fd,$command,$(git rev-parse --verify --quiet "$sha1"^)" in
 		3,pick,"$ONTO"*|3,p,"$ONTO"*)
 			# pick a commit whose parent is current $ONTO -> skip
 			ONTO=$sha1
@@ -606,7 +637,7 @@ skip_unnecessary_picks () {
 			fd=1
 			;;
 		esac
-		echo "$command${sha1:+ }$sha1${rest:+ }$rest" >&$fd
+		echo "$line" >&$fd
 	done <"$TODO" >"$TODO.new" 3>>"$DONE" &&
 	mv -f "$TODO".new "$TODO" &&
 	case "$(peek_next_command)" in
@@ -957,6 +988,7 @@ first and then run 'git rebase --continue' again."
 #  e, edit = use commit, but stop for amending
 #  s, squash = use commit, but meld into previous commit
 #  f, fixup = like "squash", but discard this commit's log message
+#  x <cmd>, exec <cmd> = Run a shell command <cmd>, and stop if it fails
 #
 # If you remove a line here THAT COMMIT WILL BE LOST.
 # However, if you remove everything, the rebase will be aborted.

t/lib-rebase.sh

@@ -47,6 +47,8 @@ for line in $FAKE_LINES; do
 	case $line in
 	squash|fixup|edit|reword)
 		action="$line";;
+	exec*)
+		echo "$line" | sed 's/_/ /g' >> "$1";;
 	"#")
 		echo '# comment' >> "$1";;
 	">")

t/t3404-rebase-interactive.sh

@@ -64,6 +64,67 @@ test_expect_success 'setup' '
 	done
 '
 
+# "exec" commands are ran with the user shell by default, but this may
+# be non-POSIX. For example, if SHELL=zsh then ">file" doesn't work
+# to create a file. Unseting SHELL avoids such non-portable behavior
+# in tests.
+SHELL=
+
+test_expect_success 'rebase -i with the exec command' '
+	git checkout master &&
+	(
+	FAKE_LINES="1 exec_>touch-one
+		2 exec_>touch-two exec_false exec_>touch-three
+		3 4 exec_>\"touch-file__name_with_spaces\";_>touch-after-semicolon 5" &&
+	export FAKE_LINES &&
+	test_must_fail git rebase -i A
+	) &&
+	test -f touch-one &&
+	test -f touch-two &&
+	! test -f touch-three &&
+	test $(git rev-parse C) = $(git rev-parse HEAD) || {
+		echo "Stopped at wrong revision:"
+		echo "($(git describe --tags HEAD) instead of C)"
+		false
+	} &&
+	git rebase --continue &&
+	test -f touch-three &&
+	test -f "touch-file  name with spaces" &&
+	test -f touch-after-semicolon &&
+	test $(git rev-parse master) = $(git rev-parse HEAD) || {
+		echo "Stopped at wrong revision:"
+		echo "($(git describe --tags HEAD) instead of master)"
+		false
+	} &&
+	rm -f touch-*
+'
+
+test_expect_success 'rebase -i with the exec command runs from tree root' '
+	git checkout master &&
+	mkdir subdir && cd subdir &&
+	FAKE_LINES="1 exec_>touch-subdir" \
+		git rebase -i HEAD^ &&
+	cd .. &&
+	test -f touch-subdir &&
+	rm -fr subdir
+'
+
+test_expect_success 'rebase -i with the exec command checks tree cleanness' '
+	git checkout master &&
+	(
+	FAKE_LINES="exec_echo_foo_>file1 1" &&
+	export FAKE_LINES &&
+	test_must_fail git rebase -i HEAD^
+	) &&
+	test $(git rev-parse master^) = $(git rev-parse HEAD) || {
+		echo "Stopped at wrong revision:"
+		echo "($(git describe --tags HEAD) instead of master^)"
+		false
+	} &&
+	git reset --hard &&
+	git rebase --continue
+'
+
 test_expect_success 'no changes are a nop' '
 	git checkout branch2 &&
 	git rebase -i F &&