pack-objects: add --keep-pack-from-file

"--keep-pack" names one pack per occurrence, and there is only so much
room on the command line: ARG_MAX is shared with the environment, and
on Windows the whole line is capped at 32,767 characters, which a few
hundred pack names fill. Past that the spawn fails before pack-objects
has started. fetch-pack grew "--stdin" in 078b895fef (fetch-pack: new
--stdin option to read refs from stdin, 2012-04-02) for the same
reason.

stdin is taken here: every mode repack drives pack-objects in already
uses it, for the revision list under "-a", object names for the
promisor pack, and pack lists for "--stdin-packs" and "--cruft". So
read the names from a file instead, one per line, skipping empty
lines. They go into the same list as the "--keep-pack" names and are
treated exactly alike: matched against local packs, ignored when they
match nothing, and kept open under "--stdin-packs=follow". A relative
path is resolved against the directory the user ran from, as
"--refs-snapshot" of "git multi-pack-index write" is.

The list now holds strings from two sources, so let it own its copies.

repack is about to use this to hand pack-objects its own snapshot of
the packs that have a ".keep" file.

Signed-off-by: Qin ShiCheng <qeesung@live.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-pack-objects.adoc

@@ -13,6 +13,7 @@ SYNOPSIS
 		   [--no-reuse-delta] [--delta-base-offset] [--non-empty]
 		   [--local] [--incremental] [--window=<n>] [--depth=<n>]
 		   [--revs [--unpacked | --all]] [--keep-pack=<pack-name>]
+		   [--keep-pack-from-file=<file>]
 		   [--cruft] [--cruft-expiration=<time>]
 		   [--stdout [--filter=<filter-spec>] | <base-name>]
 		   [--shallow] [--keep-true-parents] [--[no-]sparse]
@@ -193,6 +194,13 @@ depth is 4095.
 	leading directory (e.g. `pack-123.pack`). The option could be
 	specified multiple times to keep multiple packs.
 
+--keep-pack-from-file=<file>::
+	Read names of packs to keep from `<file>`, one per line, and
+	treat each of them as if it had been given with `--keep-pack`.
+	Empty lines are ignored. This is meant for callers such as
+	linkgit:git-repack[1] that may have to name more packs than fit
+	on a command line.
+
 --incremental::
 	This flag causes an object already in a pack to be ignored
 	even if it would have otherwise been packed.

builtin/pack-objects.c

@@ -194,6 +194,7 @@ static const char *const pack_usage[] = {
 	   "                 [--no-reuse-delta] [--delta-base-offset] [--non-empty]\n"
 	   "                 [--local] [--incremental] [--window=<n>] [--depth=<n>]\n"
 	   "                 [--revs [--unpacked | --all]] [--keep-pack=<pack-name>]\n"
+	   "                 [--keep-pack-from-file=<file>]\n"
 	   "                 [--cruft] [--cruft-expiration=<time>]\n"
 	   "                 [--stdout [--filter=<filter-spec>] | <base-name>]\n"
 	   "                 [--shallow] [--keep-true-parents] [--[no-]sparse]\n"
@@ -5002,6 +5003,26 @@ static void get_object_list(struct rev_info *revs, struct strvec *argv)
 	oid_array_clear(&recent_objects);
 }
 
+/*
+ * Read pack names from the file, one per line, as if each of them had
+ * been given with "--keep-pack".
+ */
+static void read_keep_pack_list(struct string_list *names, const char *path)
+{
+	struct strbuf buf = STRBUF_INIT;
+	FILE *fp = xfopen(path, "r");
+
+	while (strbuf_getline(&buf, fp) != EOF) {
+		if (!buf.len)
+			continue;
+		string_list_append(names, buf.buf);
+	}
+	if (ferror(fp))
+		die_errno(_("could not read '%s'"), path);
+	fclose(fp);
+	strbuf_release(&buf);
+}
+
 static void add_extra_kept_packs(struct string_list *names,
 				 enum stdin_packs_mode stdin_packs)
 {
@@ -5142,8 +5163,10 @@ int cmd_pack_objects(int argc,
 	int rev_list_index = 0;
 	enum stdin_packs_mode stdin_packs = STDIN_PACKS_MODE_NONE;
 	struct string_list keep_pack_list = {
+		.strdup_strings = 1,
 		.cmp = fspathcmp,
 	};
+	char *keep_pack_from_file = NULL;
 	struct list_objects_filter_options filter_options =
 		LIST_OBJECTS_FILTER_INIT;
 	struct repo_config_values *cfg = repo_config_values(the_repository);
@@ -5228,6 +5251,8 @@ int cmd_pack_objects(int argc,
 			 N_("ignore packs that have companion .keep file")),
 		OPT_STRING_LIST(0, "keep-pack", &keep_pack_list, N_("name"),
 				N_("ignore this pack")),
+		OPT_FILENAME(0, "keep-pack-from-file", &keep_pack_from_file,
+			     N_("ignore the packs named in <file>")),
 		OPT_INTEGER(0, "compression", &cfg->pack_compression_level,
 			    N_("pack compression level")),
 		OPT_BOOL(0, "keep-true-parents", &grafts_keep_true_parents,
@@ -5455,6 +5480,8 @@ int cmd_pack_objects(int argc,
 	if (progress && all_progress_implied)
 		progress = 2;
 
+	if (keep_pack_from_file)
+		read_keep_pack_list(&keep_pack_list, keep_pack_from_file);
 	add_extra_kept_packs(&keep_pack_list, stdin_packs);
 	if (ignore_packed_keep_on_disk) {
 		struct packed_git *p;
@@ -5549,6 +5576,7 @@ cleanup:
 	clear_packing_data(&to_pack);
 	list_objects_filter_release(&filter_options);
 	string_list_clear(&keep_pack_list, 0);
+	free(keep_pack_from_file);
 	strvec_clear(&rp);
 
 	return 0;

t/t5331-pack-objects-stdin.sh

@@ -561,4 +561,50 @@ test_expect_success '--stdin-packs with !-delimited pack without follow' '
 	)
 '
 
+test_expect_success '--keep-pack-from-file names packs to keep' '
+	test_when_finished "rm -fr repo" &&
+
+	git init repo &&
+	(
+		cd repo &&
+		git config set maintenance.auto false &&
+
+		test_commit A &&
+		test_commit B &&
+		test_commit C &&
+
+		A="$(echo A | git pack-objects --revs $packdir/pack)" &&
+		B="$(echo A..B | git pack-objects --revs $packdir/pack)" &&
+		C="$(echo B..C | git pack-objects --revs $packdir/pack)" &&
+		git prune-packed &&
+
+		# Empty lines and names that match no pack are ignored,
+		# as they would be with --keep-pack.
+		cat >keep <<-EOF &&
+		pack-$A.pack
+
+		pack-$B.pack
+		pack-does-not-exist.pack
+		EOF
+
+		P=$(git pack-objects --all --keep-pack=pack-$A.pack \
+			--keep-pack=pack-$B.pack from-argv </dev/null) &&
+		packed_objects from-argv-$P.idx >expect &&
+
+		P=$(git pack-objects --all --keep-pack-from-file=keep \
+			from-file </dev/null) &&
+		packed_objects from-file-$P.idx >actual &&
+		test_cmp expect actual &&
+
+		objects_in_packs $C >expect &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success '--keep-pack-from-file with a missing file' '
+	test_must_fail git pack-objects --stdout \
+		--keep-pack-from-file=does-not-exist </dev/null 2>err &&
+	test_grep "could not open .does-not-exist. for reading" err
+'
+
 test_done