[PATCH v6 3/6] fast-import: add feature command

@@ -303,6 +303,10 @@ and control the current import process.  More detailed discussion
 	standard output.  This command is optional and is not needed
 	to perform an import.
 
+`feature`::
+	Require that fast-import supports the specified feature, or
+	abort if it does not.
+
 `commit`
 ~~~~~~~~
 Create or update a branch with a new commit, recording one logical

@@ -813,6 +817,18 @@ Placing a `progress` command immediately after a `checkpoint` will
 inform the reader when the `checkpoint` has been completed and it
 can safely access the refs that fast-import updated.
 
+`feature`
+~~~~~~~~~
+Require that fast-import supports the specified feature, or abort if
+it does not.
+
+....
+	'feature' SP <feature> LF
+....
+
+The <feature> part of the command may be any string matching
+[a-zA-Z-] and should be understood by a version of fast-import.
+
 Crash Reports
 -------------
 If fast-import is supplied invalid input it will terminate with a

@@ -2450,6 +2450,17 @@ static void parse_one_option(const char *option)
 	}
 }
 
+static void parse_feature(void)
+{
+	char *feature = command_buf.buf + 8;
+
+	if (!prefixcmp(feature, "date-format=")) {
+		option_date_format(feature + 12);
+	} else {
+		die("This version of fast-import does not support feature %s.", feature);
+	}
+}
+
 static int git_pack_config(const char *k, const char *v, void *cb)
 {
 	if (!strcmp(k, "pack.depth")) {

@@ -2526,6 +2537,8 @@ int main(int argc, const char **argv)
 			parse_checkpoint();
 		else if (!prefixcmp(command_buf.buf, "progress "))
 			parse_progress();
+		else if (!prefixcmp(command_buf.buf, "feature "))
+			parse_feature();
 		else
 			die("Unsupported command: %s", command_buf.buf);
 	}