fast-export: support done feature

If fast-export is being used to generate a fast-import stream that
will be used afterwards it is desirable to indicate the end of the
stream with the new 'done' command.

Add a flag that causes fast-export to end with 'done'.

Signed-off-by: Sverre Rabbelier <srabbelier@gmail.com>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-fast-export.txt

@@ -82,6 +82,10 @@ marks the same across runs.
 	allow that.  So fake a tagger to be able to fast-import the
 	output.
 
+--use-done-feature::
+	Start the stream with a 'feature done' stanza, and terminate
+	it with a 'done' command.
+
 --no-data::
 	Skip output of blob objects and instead refer to blobs via
 	their original SHA-1 hash.  This is useful when rewriting the

builtin/fast-export.c

@@ -26,6 +26,7 @@ static int progress;
 static enum { ABORT, VERBATIM, WARN, STRIP } signed_tag_mode = ABORT;
 static enum { ERROR, DROP, REWRITE } tag_of_filtered_mode = ABORT;
 static int fake_missing_tagger;
+static int use_done_feature;
 static int no_data;
 static int full_tree;
 
@@ -627,6 +628,8 @@ int cmd_fast_export(int argc, const char **argv, const char *prefix)
 			     "Fake a tagger when tags lack one"),
 		OPT_BOOLEAN(0, "full-tree", &full_tree,
 			     "Output full tree for each commit"),
+		OPT_BOOLEAN(0, "use-done-feature", &use_done_feature,
+			     "Use the done feature to terminate the stream"),
 		{ OPTION_NEGBIT, 0, "data", &no_data, NULL,
 			"Skip output of blob data",
 			PARSE_OPT_NOARG | PARSE_OPT_NEGHELP, NULL, 1 },
@@ -648,6 +651,9 @@ int cmd_fast_export(int argc, const char **argv, const char *prefix)
 	if (argc > 1)
 		usage_with_options (fast_export_usage, options);
 
+	if (use_done_feature)
+		printf("feature done\n");
+
 	if (import_filename)
 		import_marks(import_filename);
 
@@ -675,5 +681,8 @@ int cmd_fast_export(int argc, const char **argv, const char *prefix)
 	if (export_filename)
 		export_marks(export_filename);
 
+	if (use_done_feature)
+		printf("done\n");
+
 	return 0;
 }