sequencer (rebase -i): implement the 'exec' command

The 'exec' command is a little special among rebase -i's commands, as it
does *not* have a SHA-1 as first parameter. Instead, everything after the
`exec` command is treated as command-line to execute.

Let's reuse the arg/arg_len fields of the todo_item structure (which hold
the oneline for pick/edit commands) to point to the command-line.

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

sequencer.c

@@ -18,6 +18,7 @@
 #include "quote.h"
 #include "trailer.h"
 #include "log-tree.h"
+#include "wt-status.h"
 
 #define GIT_REFLOG_ACTION "GIT_REFLOG_ACTION"
 
@@ -632,6 +633,8 @@ enum todo_command {
 	TODO_PICK = 0,
 	TODO_REVERT,
 	TODO_EDIT,
+	/* commands that do something else than handling a single commit */
+	TODO_EXEC,
 	/* commands that do nothing but are counted for reporting progress */
 	TODO_NOOP
 };
@@ -640,6 +643,7 @@ static const char *todo_command_strings[] = {
 	"pick",
 	"revert",
 	"edit",
+	"exec",
 	"noop"
 };
 
@@ -938,6 +942,12 @@ static int parse_insn_line(struct todo_item *item, const char *bol, char *eol)
 		return -1;
 	bol += padding;
 
+	if (item->command == TODO_EXEC) {
+		item->arg = bol;
+		item->arg_len = (int)(eol - bol);
+		return 0;
+	}
+
 	end_of_object_name = (char *) bol + strcspn(bol, " \t\n");
 	saved = *end_of_object_name;
 	*end_of_object_name = '\0';
@@ -1397,6 +1407,46 @@ static int error_with_patch(struct commit *commit,
 	return exit_code;
 }
 
+static int do_exec(const char *command_line)
+{
+	const char *child_argv[] = { NULL, NULL };
+	int dirty, status;
+
+	fprintf(stderr, "Executing: %s\n", command_line);
+	child_argv[0] = command_line;
+	status = run_command_v_opt(child_argv, RUN_USING_SHELL);
+
+	/* force re-reading of the cache */
+	if (discard_cache() < 0 || read_cache() < 0)
+		return error(_("could not read index"));
+
+	dirty = require_clean_work_tree("rebase", NULL, 1, 1);
+
+	if (status) {
+		warning(_("execution failed: %s\n%s"
+			  "You can fix the problem, and then run\n"
+			  "\n"
+			  "  git rebase --continue\n"
+			  "\n"),
+			command_line,
+			dirty ? N_("and made changes to the index and/or the "
+				"working tree\n") : "");
+		if (status == 127)
+			/* command not found */
+			status = 1;
+	} else if (dirty) {
+		warning(_("execution succeeded: %s\nbut "
+			  "left changes to the index and/or the working tree\n"
+			  "Commit or stash your changes, and then run\n"
+			  "\n"
+			  "  git rebase --continue\n"
+			  "\n"), command_line);
+		status = 1;
+	}
+
+	return status;
+}
+
 static int pick_commits(struct todo_list *todo_list, struct replay_opts *opts)
 {
 	int res = 0;
@@ -1425,6 +1475,13 @@ static int pick_commits(struct todo_list *todo_list, struct replay_opts *opts)
 					item->arg, item->arg_len, opts, res,
 					!res);
 			}
+		} else if (item->command == TODO_EXEC) {
+			char *end_of_arg = (char *)(item->arg + item->arg_len);
+			int saved = *end_of_arg;
+
+			*end_of_arg = '\0';
+			res = do_exec(item->arg);
+			*end_of_arg = saved;
 		} else if (!is_noop(item->command))
 			return error(_("unknown command %d"), item->command);