sequencer: prepare for rebase -i's commit functionality

In interactive rebases, we commit a little bit differently than the
sequencer did so far: we heed the "author-script", the "message" and the
"amend" files in the .git/rebase-merge/ subdirectory.

Likewise, we may want to edit the commit message *even* when providing a
file containing the suggested commit message. Therefore we change the
code to not even provide a default message when we do not want any, and
to call the editor explicitly.

Also, in "interactive rebase" mode we want to skip reading the options
in the state directory of the cherry-pick/revert commands.

Finally, as interactive rebase's GPG settings are configured differently
from how cherry-pick (and therefore sequencer) handles them, we will
leave support for that to the next commit.

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

Author: dscho

sequencer.c

@@ -27,6 +27,19 @@ static GIT_PATH_FUNC(git_path_todo_file, "sequencer/todo")
 static GIT_PATH_FUNC(git_path_opts_file, "sequencer/opts")
 static GIT_PATH_FUNC(git_path_head_file, "sequencer/head")
 
+/*
+ * A script to set the GIT_AUTHOR_NAME, GIT_AUTHOR_EMAIL, and
+ * GIT_AUTHOR_DATE that will be used for the commit that is currently
+ * being rebased.
+ */
+static GIT_PATH_FUNC(rebase_path_author_script, "rebase-merge/author-script")
+
+/* We will introduce the 'interactive rebase' mode later */
+static inline int is_rebase_i(const struct replay_opts *opts)
+{
+	return 0;
+}
+
 static const char *get_dir(const struct replay_opts *opts)
 {
 	return git_path_seq_dir();
@@ -369,20 +382,80 @@ static int is_index_unchanged(void)
 	return !hashcmp(active_cache_tree->sha1, head_commit->tree->object.oid.hash);
 }
 
+/*
+ * Read the author-script file into an environment block, ready for use in
+ * run_command(), that can be free()d afterwards.
+ */
+static char **read_author_script(void)
+{
+	struct strbuf script = STRBUF_INIT;
+	int i, count = 0;
+	char *p, *p2, **env;
+	size_t env_size;
+
+	if (strbuf_read_file(&script, rebase_path_author_script(), 256) <= 0)
+		return NULL;
+
+	for (p = script.buf; *p; p++)
+		if (skip_prefix(p, "'\\\\''", (const char **)&p2))
+			strbuf_splice(&script, p - script.buf, p2 - p, "'", 1);
+		else if (*p == '\'')
+			strbuf_splice(&script, p-- - script.buf, 1, "", 0);
+		else if (*p == '\n') {
+			*p = '\0';
+			count++;
+		}
+
+	env_size = (count + 1) * sizeof(*env);
+	strbuf_grow(&script, env_size);
+	memmove(script.buf + env_size, script.buf, script.len);
+	p = script.buf + env_size;
+	env = (char **)strbuf_detach(&script, NULL);
+
+	for (i = 0; i < count; i++) {
+		env[i] = p;
+		p += strlen(p) + 1;
+	}
+	env[count] = NULL;
+
+	return env;
+}
+
 /*
  * If we are cherry-pick, and if the merge did not result in
  * hand-editing, we will hit this commit and inherit the original
  * author date and name.
+ *
  * If we are revert, or if our cherry-pick results in a hand merge,
  * we had better say that the current user is responsible for that.
+ *
+ * An exception is when run_git_commit() is called during an
+ * interactive rebase: in that case, we will want to retain the
+ * author metadata.
  */
 static int run_git_commit(const char *defmsg, struct replay_opts *opts,
 			  int allow_empty)
 {
+	char **env = NULL;
 	struct argv_array array;
 	int rc;
 	const char *value;
 
+	if (is_rebase_i(opts)) {
+		env = read_author_script();
+		if (!env)
+			return error("You have staged changes in your working "
+				"tree. If these changes are meant to be\n"
+				"squashed into the previous commit, run:\n\n"
+				"  git commit --amend $gpg_sign_opt_quoted\n\n"
+				"If they are meant to go into a new commit, "
+				"run:\n\n"
+				"  git commit $gpg_sign_opt_quoted\n\n"
+				"In both cases, once you're done, continue "
+				"with:\n\n"
+				"  git rebase --continue\n");
+	}
+
 	argv_array_init(&array);
 	argv_array_push(&array, "commit");
 	argv_array_push(&array, "-n");
@@ -391,23 +464,25 @@ static int run_git_commit(const char *defmsg, struct replay_opts *opts,
 		argv_array_pushf(&array, "-S%s", opts->gpg_sign);
 	if (opts->signoff)
 		argv_array_push(&array, "-s");
-	if (!opts->edit) {
-		argv_array_push(&array, "-F");
-		argv_array_push(&array, defmsg);
-		if (!opts->signoff &&
-		    !opts->record_origin &&
-		    git_config_get_value("commit.cleanup", &value))
-			argv_array_push(&array, "--cleanup=verbatim");
-	}
+	if (defmsg)
+		argv_array_pushl(&array, "-F", defmsg, NULL);
+	if (opts->edit)
+		argv_array_push(&array, "-e");
+	else if (!opts->signoff && !opts->record_origin &&
+		 git_config_get_value("commit.cleanup", &value))
+		argv_array_push(&array, "--cleanup=verbatim");
 
 	if (allow_empty)
 		argv_array_push(&array, "--allow-empty");
 
 	if (opts->allow_empty_message)
 		argv_array_push(&array, "--allow-empty-message");
 
-	rc = run_command_v_opt(array.argv, RUN_GIT_CMD);
+	rc = run_command_v_opt_cd_env(array.argv, RUN_GIT_CMD, NULL,
+			(const char *const *)env);
 	argv_array_clear(&array);
+	free(env);
+
 	return rc;
 }
 
@@ -657,7 +732,8 @@ static int do_pick_commit(enum todo_command command, struct commit *commit,
 		goto leave;
 	}
 	if (!opts->no_commit)
-		res = run_git_commit(git_path_merge_msg(), opts, allow);
+		res = run_git_commit(opts->edit ? NULL : git_path_merge_msg(),
+				     opts, allow);
 
 leave:
 	free_message(commit, &msg);
@@ -879,6 +955,9 @@ static int populate_opts_cb(const char *key, const char *value, void *data)
 
 static int read_populate_opts(struct replay_opts *opts)
 {
+	if (is_rebase_i(opts))
+		return 0;
+
 	if (!file_exists(git_path_opts_file()))
 		return 0;
 	/*