archive: add --mtime

Allow users to specify the modification time of archive entries.  The
new option --mtime uses approxidate() to parse a time specification and
overrides the default of using the current time for trees and the commit
time for tags and commits.  It can be used to create a reproducible
archive for a tree, or to use a specific mtime without creating a commit
with GIT_COMMITTER_DATE set.

This implementation doesn't support the negated form of the new option,
i.e. --no-mtime is not accepted.  It is not possible to have no mtime at
all.  We could use the Unix epoch or revert to the default behavior, but
since negation is not necessary for the intended use it's left undecided
for now.

Requested-by: Raul E Rangel <rrangel@chromium.org>
Suggested-by: demerphq <demerphq@gmail.com>
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-archive.txt

@@ -86,6 +86,11 @@ cases, write an untracked file and use `--add-file` instead.
 	Look for attributes in .gitattributes files in the working tree
 	as well (see <<ATTRIBUTES>>).
 
+--mtime=<time>::
+	Set modification time of archive entries.  Without this option
+	the committer time is used if `<tree-ish>` is a commit or tag,
+	and the current time if it is a tree.
+
 <extra>::
 	This can be any options that the archiver backend understands.
 	See next section.

archive.c

@@ -472,6 +472,8 @@ static void parse_treeish_arg(const char **argv,
 		commit_oid = NULL;
 		archive_time = time(NULL);
 	}
+	if (ar_args->mtime_option)
+		archive_time = approxidate(ar_args->mtime_option);
 
 	tree = parse_tree_indirect(&oid);
 	if (!tree)
@@ -586,6 +588,7 @@ static int parse_archive_args(int argc, const char **argv,
 	const char *remote = NULL;
 	const char *exec = NULL;
 	const char *output = NULL;
+	const char *mtime_option = NULL;
 	int compression_level = -1;
 	int verbose = 0;
 	int i;
@@ -607,6 +610,9 @@ static int parse_archive_args(int argc, const char **argv,
 		OPT_BOOL(0, "worktree-attributes", &worktree_attributes,
 			N_("read .gitattributes in working directory")),
 		OPT__VERBOSE(&verbose, N_("report archived files on stderr")),
+		{ OPTION_STRING, 0, "mtime", &mtime_option, N_("time"),
+		  N_("set modification time of archive entries"),
+		  PARSE_OPT_NONEG },
 		OPT_NUMBER_CALLBACK(&compression_level,
 			N_("set compression level"), number_callback),
 		OPT_GROUP(""),
@@ -668,6 +674,7 @@ static int parse_archive_args(int argc, const char **argv,
 	args->base = base;
 	args->baselen = strlen(base);
 	args->worktree_attributes = worktree_attributes;
+	args->mtime_option = mtime_option;
 
 	return argc;
 }

archive.h

@@ -16,6 +16,7 @@ struct archiver_args {
 	struct tree *tree;
 	const struct object_id *commit_oid;
 	const struct commit *commit;
+	const char *mtime_option;
 	timestamp_t time;
 	struct pathspec pathspec;
 	unsigned int verbose : 1;

t/t5000-tar-tree.sh

@@ -105,6 +105,18 @@ check_added() {
 	'
 }
 
+check_mtime() {
+	dir=$1
+	path_in_archive=$2
+	mtime=$3
+
+	test_expect_success " validate mtime of $path_in_archive" '
+		test-tool chmtime --get $dir/$path_in_archive >actual.mtime &&
+		echo $mtime >expect.mtime &&
+		test_cmp expect.mtime actual.mtime
+	'
+}
+
 test_expect_success 'setup' '
 	test_oid_cache <<-EOF
 	obj sha1:19f9c8273ec45a8938e6999cb59b3ff66739902a
@@ -174,6 +186,13 @@ test_expect_success 'git archive' '
 
 check_tar b
 
+test_expect_success 'git archive --mtime' '
+	git archive --mtime=2002-02-02T02:02:02-0200 HEAD >with_mtime.tar
+'
+
+check_tar with_mtime
+check_mtime with_mtime a/a 1012622522
+
 test_expect_success 'git archive --prefix=prefix/' '
 	git archive --prefix=prefix/ HEAD >with_prefix.tar
 '