builtin-am: support and auto-detect StGit series files

Since c574e68 (git-am foreign patch support: StGIT support, 2009-05-27),
git-am.sh is able to read a single StGit series file and, for each StGit
patch listed in the file, convert the StGit patch into a RFC2822 mail
patch suitable for parsing with git-mailinfo, and queue them in the
state directory for applying.

Since 15ced75 (git-am foreign patch support: autodetect some patch
formats, 2009-05-27), git-am.sh is able to auto-detect StGit series
files by checking to see if the file starts with the string:

	# This series applies on GIT commit

Re-implement the above in builtin/am.c.

Signed-off-by: Paul Tan <pyokagan@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/am.c

@@ -80,7 +80,8 @@ static int str_isspace(const char *str)
 enum patch_format {
 	PATCH_FORMAT_UNKNOWN = 0,
 	PATCH_FORMAT_MBOX,
-	PATCH_FORMAT_STGIT
+	PATCH_FORMAT_STGIT,
+	PATCH_FORMAT_STGIT_SERIES
 };
 
 enum keep_type {
@@ -650,6 +651,11 @@ static int detect_patch_format(const char **paths)
 		goto done;
 	}
 
+	if (starts_with(l1.buf, "# This series applies on GIT commit")) {
+		ret = PATCH_FORMAT_STGIT_SERIES;
+		goto done;
+	}
+
 	strbuf_reset(&l2);
 	strbuf_getline_crlf(&l2, fp);
 	strbuf_reset(&l3);
@@ -800,6 +806,53 @@ static int stgit_patch_to_mail(FILE *out, FILE *in, int keep_cr)
 	return 0;
 }
 
+/**
+ * This function only supports a single StGit series file in `paths`.
+ *
+ * Given an StGit series file, converts the StGit patches in the series into
+ * RFC2822 messages suitable for parsing with git-mailinfo, and queues them in
+ * the state directory.
+ *
+ * Returns 0 on success, -1 on failure.
+ */
+static int split_mail_stgit_series(struct am_state *state, const char **paths,
+					int keep_cr)
+{
+	const char *series_dir;
+	char *series_dir_buf;
+	FILE *fp;
+	struct argv_array patches = ARGV_ARRAY_INIT;
+	struct strbuf sb = STRBUF_INIT;
+	int ret;
+
+	if (!paths[0] || paths[1])
+		return error(_("Only one StGIT patch series can be applied at once"));
+
+	series_dir_buf = xstrdup(*paths);
+	series_dir = dirname(series_dir_buf);
+
+	fp = fopen(*paths, "r");
+	if (!fp)
+		return error(_("could not open '%s' for reading: %s"), *paths,
+				strerror(errno));
+
+	while (!strbuf_getline(&sb, fp, '\n')) {
+		if (*sb.buf == '#')
+			continue; /* skip comment lines */
+
+		argv_array_push(&patches, mkpath("%s/%s", series_dir, sb.buf));
+	}
+
+	fclose(fp);
+	strbuf_release(&sb);
+	free(series_dir_buf);
+
+	ret = split_mail_conv(stgit_patch_to_mail, state, patches.argv, keep_cr);
+
+	argv_array_clear(&patches);
+	return ret;
+}
+
 /**
  * Splits a list of files/directories into individual email patches. Each path
  * in `paths` must be a file/directory that is formatted according to
@@ -830,6 +883,8 @@ static int split_mail(struct am_state *state, enum patch_format patch_format,
 		return split_mail_mbox(state, paths, keep_cr);
 	case PATCH_FORMAT_STGIT:
 		return split_mail_conv(stgit_patch_to_mail, state, paths, keep_cr);
+	case PATCH_FORMAT_STGIT_SERIES:
+		return split_mail_stgit_series(state, paths, keep_cr);
 	default:
 		die("BUG: invalid patch_format");
 	}
@@ -1880,6 +1935,8 @@ static int parse_opt_patchformat(const struct option *opt, const char *arg, int
 		*opt_value = PATCH_FORMAT_MBOX;
 	else if (!strcmp(arg, "stgit"))
 		*opt_value = PATCH_FORMAT_STGIT;
+	else if (!strcmp(arg, "stgit-series"))
+		*opt_value = PATCH_FORMAT_STGIT_SERIES;
 	else
 		return error(_("Invalid value for --patch-format: %s"), arg);
 	return 0;