fast-export: allow user to request tags be marked with --mark-tags

Add a new option, --mark-tags, which will output mark identifiers with
each tag object.  This improves the incremental export story with
--export-marks since it will allow us to record that annotated tags have
been exported, and it is also needed as a step towards supporting nested
tags.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-fast-export.txt

@@ -75,11 +75,20 @@ produced incorrect results if you gave these options.
 	Before processing any input, load the marks specified in
 	<file>.  The input file must exist, must be readable, and
 	must use the same format as produced by --export-marks.
+
+--mark-tags::
+	In addition to labelling blobs and commits with mark ids, also
+	label tags.  This is useful in conjunction with
+	`--export-marks` and `--import-marks`, and is also useful (and
+	necessary) for exporting of nested tags.  It does not hurt
+	other cases and would be the default, but many fast-import
+	frontends are not prepared to accept tags with mark
+	identifiers.
 +
-Any commits that have already been marked will not be exported again.
+Any commits (or tags) that have already been marked will not be
-If the backend uses a similar --import-marks file, this allows for
+exported again.  If the backend uses a similar --import-marks file,
-incremental bidirectional exporting of the repository by keeping the
+this allows for incremental bidirectional exporting of the repository
-marks the same across runs.
+by keeping the marks the same across runs.
 
 --fake-missing-tagger::
 	Some old repositories have tags without a tagger.  The

builtin/fast-export.c

@@ -40,6 +40,7 @@ static int no_data;
 static int full_tree;
 static int reference_excluded_commits;
 static int show_original_ids;
+static int mark_tags;
 static struct string_list extra_refs = STRING_LIST_INIT_NODUP;
 static struct string_list tag_refs = STRING_LIST_INIT_NODUP;
 static struct refspec refspecs = REFSPEC_INIT_FETCH;
@@ -861,6 +862,10 @@ static void handle_tag(const char *name, struct tag *tag)
 	if (starts_with(name, "refs/tags/"))
 		name += 10;
 	printf("tag %s\n", name);
+	if (mark_tags) {
+		mark_next_object(&tag->object);
+		printf("mark :%"PRIu32"\n", last_idnum);
+	}
 	if (tagged_mark)
 		printf("from :%d\n", tagged_mark);
 	else
@@ -1165,6 +1170,8 @@ int cmd_fast_export(int argc, const char **argv, const char *prefix)
 			 &reference_excluded_commits, N_("Reference parents which are not in fast-export stream by object id")),
 		OPT_BOOL(0, "show-original-ids", &show_original_ids,
 			    N_("Show original object ids of blobs/commits")),
+		OPT_BOOL(0, "mark-tags", &mark_tags,
+			    N_("Label tags with mark ids")),
 
 		OPT_END()
 	};

t/t9350-fast-export.sh

@@ -66,6 +66,20 @@ test_expect_success 'fast-export ^muss^{commit} muss' '
 	test_cmp expected actual
 '
 
+test_expect_success 'fast-export --mark-tags ^muss^{commit} muss' '
+	git fast-export --mark-tags --tag-of-filtered-object=rewrite ^muss^{commit} muss >actual &&
+	cat >expected <<-EOF &&
+	tag muss
+	mark :1
+	from $(git rev-parse --verify muss^{commit})
+	$(git cat-file tag muss | grep tagger)
+	data 9
+	valentin
+
+	EOF
+	test_cmp expected actual
+'
+
 test_expect_success 'fast-export master~2..master' '
 
 	git fast-export master~2..master >actual &&