format-patch: make output filename configurable

For the past 15 years, we've used the hardcoded 64 as the length
limit of the filename of the output from the "git format-patch"
command.  Since the value is shorter than the 80-column terminal, it
could grow without line wrapping a bit.  At the same time, since the
value is longer than half of the 80-column terminal, we could fit
two or more of them in "ls" output on such a terminal if we allowed
to lower it.

Introduce a new command line option --filename-max-length=<n> and a
new configuration variable format.filenameMaxLength to override the
hardcoded default.

While we are at it, remove a check that the name of output directory
does not exceed PATH_MAX---this check is pointless in that by the
time control reaches the function, the caller would already have
done an equivalent of "mkdir -p", so if the system does not like an
overly long directory name, the control wouldn't have reached here,
and otherwise, we know that the system allowed the output directory
to exist.  In the worst case, we will get an error when we try to
open the output file and handle the error correctly anyway.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/format.txt

@@ -94,6 +94,11 @@ format.outputDirectory::
 	Set a custom directory to store the resulting files instead of the
 	current working directory. All directory components will be created.
 
+format.filenameMaxLength::
+	The maximum length of the output filenames generated by the
+	`format-patch` command; defaults to 64.  Can be overridden
+	by the `--filename-max-length=<n>` command line option.
+
 format.useAutoBase::
 	A boolean value which lets you enable the `--base=auto` option of
 	format-patch by default. Can also be set to "whenAble" to allow

Documentation/git-format-patch.txt

@@ -28,6 +28,7 @@ SYNOPSIS
 		   [--no-notes | --notes[=<ref>]]
 		   [--interdiff=<previous>]
 		   [--range-diff=<previous> [--creation-factor=<percent>]]
+		   [--filename-max-length=<n>]
 		   [--progress]
 		   [<common diff options>]
 		   [ <since> | <revision range> ]
@@ -200,6 +201,13 @@ populated with placeholder text.
 	allows for useful naming of a patch series, and can be
 	combined with the `--numbered` option.
 
+--filename-max-length=<n>::
+	Instead of the standard 64 bytes, chomp the generated output
+	filenames at around '<n>' bytes (too short a value will be
+	silently raised to a reasonable length).  Defaults to the
+	value of the `format.filenameMaxLength` configuration
+	variable, or 64 if unconfigured.
+
 --rfc::
 	Alias for `--subject-prefix="RFC PATCH"`. RFC means "Request For
 	Comments"; use this when sending an experimental patch for

builtin/log.c

@@ -37,6 +37,7 @@
 
 #define MAIL_DEFAULT_WRAP 72
 #define COVER_FROM_AUTO_MAX_SUBJECT_LEN 100
+#define FORMAT_PATCH_NAME_MAX_DEFAULT 64
 
 /* Set a default date-time format for git log ("log.date" config variable) */
 static const char *default_date_mode = NULL;
@@ -50,6 +51,7 @@ static int decoration_style;
 static int decoration_given;
 static int use_mailmap_config = 1;
 static const char *fmt_patch_subject_prefix = "PATCH";
+static int fmt_patch_name_max = FORMAT_PATCH_NAME_MAX_DEFAULT;
 static const char *fmt_pretty;
 
 static const char * const builtin_log_usage[] = {
@@ -150,6 +152,7 @@ static void cmd_log_init_defaults(struct rev_info *rev)
 	rev->abbrev_commit = default_abbrev_commit;
 	rev->show_root_diff = default_show_root;
 	rev->subject_prefix = fmt_patch_subject_prefix;
+	rev->patch_name_max = fmt_patch_name_max;
 	rev->show_signature = default_show_signature;
 	rev->encode_email_headers = default_encode_email_headers;
 	rev->diffopt.flags.allow_textconv = 1;
@@ -454,6 +457,10 @@ static int git_log_config(const char *var, const char *value, void *cb)
 		return git_config_string(&fmt_pretty, var, value);
 	if (!strcmp(var, "format.subjectprefix"))
 		return git_config_string(&fmt_patch_subject_prefix, var, value);
+	if (!strcmp(var, "format.filenamemaxlength")) {
+		fmt_patch_name_max = git_config_int(var, value);
+		return 0;
+	}
 	if (!strcmp(var, "format.encodeemailheaders")) {
 		default_encode_email_headers = git_config_bool(var, value);
 		return 0;
@@ -955,15 +962,9 @@ static int open_next_file(struct commit *commit, const char *subject,
 			 struct rev_info *rev, int quiet)
 {
 	struct strbuf filename = STRBUF_INIT;
-	int suffix_len = strlen(rev->patch_suffix) + 1;
 
 	if (output_directory) {
 		strbuf_addstr(&filename, output_directory);
-		if (filename.len >=
-		    PATH_MAX - FORMAT_PATCH_NAME_MAX - suffix_len) {
-			strbuf_release(&filename);
-			return error(_("name of output directory is too long"));
-		}
 		strbuf_complete(&filename, '/');
 	}
 
@@ -1751,6 +1752,8 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 			    N_("start numbering patches at <n> instead of 1")),
 		OPT_INTEGER('v', "reroll-count", &reroll_count,
 			    N_("mark the series as Nth re-roll")),
+		OPT_INTEGER(0, "filename-max-length", &fmt_patch_name_max,
+			    N_("max length of output filename")),
 		OPT_CALLBACK_F(0, "rfc", &rev, NULL,
 			    N_("Use [RFC PATCH] instead of [PATCH]"),
 			    PARSE_OPT_NOARG | PARSE_OPT_NONEG, rfc_callback),
@@ -1851,6 +1854,10 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 			     PARSE_OPT_KEEP_ARGV0 | PARSE_OPT_KEEP_UNKNOWN |
 			     PARSE_OPT_KEEP_DASHDASH);
 
+	/* Make sure "0000-$sub.patch" gives non-negative length for $sub */
+	if (fmt_patch_name_max <= strlen("0000-") + strlen(fmt_patch_suffix))
+		fmt_patch_name_max = strlen("0000-") + strlen(fmt_patch_suffix);
+
 	if (cover_from_description_arg)
 		cover_from_description_mode = parse_cover_from_description(cover_from_description_arg);
 
@@ -1935,6 +1942,7 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	rev.diffopt.output_format |= DIFF_FORMAT_PATCH;
 
 	rev.zero_commit = zero_commit;
+	rev.patch_name_max = fmt_patch_name_max;
 
 	if (!rev.diffopt.flags.text && !no_binary_diff)
 		rev.diffopt.flags.binary = 1;

log-tree.c

@@ -367,7 +367,7 @@ void fmt_output_subject(struct strbuf *filename,
 	const char *suffix = info->patch_suffix;
 	int nr = info->nr;
 	int start_len = filename->len;
-	int max_len = start_len + FORMAT_PATCH_NAME_MAX - (strlen(suffix) + 1);
+	int max_len = start_len + info->patch_name_max - (strlen(suffix) + 1);
 
 	if (0 < info->reroll_count)
 		strbuf_addf(filename, "v%d-", info->reroll_count);

log-tree.h

@@ -33,7 +33,6 @@ void log_write_email_headers(struct rev_info *opt, struct commit *commit,
 			     int maybe_multipart);
 void load_ref_decorations(struct decoration_filter *filter, int flags);
 
-#define FORMAT_PATCH_NAME_MAX 64
 void fmt_output_commit(struct strbuf *, struct commit *, struct rev_info *);
 void fmt_output_subject(struct strbuf *, const char *subject, struct rev_info *);
 void fmt_output_email_subject(struct strbuf *, struct rev_info *);

revision.h

@@ -238,6 +238,7 @@ struct rev_info {
 	const char	*extra_headers;
 	const char	*log_reencode;
 	const char	*subject_prefix;
+	int		patch_name_max;
 	int		no_inline;
 	int		show_log_size;
 	struct string_list *mailmap;

t/t4014-format-patch.sh

@@ -313,6 +313,60 @@ test_expect_success 'multiple files' '
 	ls patches/0001-Side-changes-1.patch patches/0002-Side-changes-2.patch patches/0003-Side-changes-3-with-n-backslash-n-in-it.patch
 '
 
+test_expect_success 'filename length limit' '
+	test_when_finished "rm -f 000*" &&
+	rm -rf 000[1-9]-*.patch &&
+	for len in 15 25 35
+	do
+		git format-patch --filename-max-length=$len -3 side &&
+		max=$(
+			for patch in 000[1-9]-*.patch
+			do
+				echo "$patch" | wc -c
+			done |
+			sort -nr |
+			head -n 1
+		) &&
+		test $max -le $len || return 1
+	done
+'
+
+test_expect_success 'filename length limit from config' '
+	test_when_finished "rm -f 000*" &&
+	rm -rf 000[1-9]-*.patch &&
+	for len in 15 25 35
+	do
+		git -c format.filenameMaxLength=$len format-patch -3 side &&
+		max=$(
+			for patch in 000[1-9]-*.patch
+			do
+				echo "$patch" | wc -c
+			done |
+			sort -nr |
+			head -n 1
+		) &&
+		test $max -le $len || return 1
+	done
+'
+
+test_expect_success 'filename limit applies only to basename' '
+	test_when_finished "rm -rf patches/" &&
+	rm -rf patches/ &&
+	for len in 15 25 35
+	do
+		git format-patch -o patches --filename-max-length=$len -3 side &&
+		max=$(
+			for patch in patches/000[1-9]-*.patch
+			do
+				echo "${patch#patches/}" | wc -c
+			done |
+			sort -nr |
+			head -n 1
+		) &&
+		test $max -le $len || return 1
+	done
+'
+
 test_expect_success 'reroll count' '
 	rm -fr patches &&
 	git format-patch -o patches --cover-letter --reroll-count 4 master..side >list &&