fast-import: add feature command

This allows the fronted to require a specific feature to be supported
by the backend, or abort.

Also add support for four initial feature, date-format=, force=,
import-marks=, export-marks=.

Signed-off-by: Sverre Rabbelier <srabbelier@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-fast-import.txt

@@ -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
@@ -846,6 +850,27 @@ 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][a-zA-Z-]*$ and should be understood by fast-import.
+
+Feature work identical as their option counterparts.
+
+The following features are currently supported:
+
+* date-format
+* import-marks
+* export-marks
+* force
+
 Crash Reports
 -------------
 If fast-import is supplied invalid input it will terminate with a

fast-import.c

@@ -353,6 +353,7 @@ static struct recent_command *rc_free;
 static unsigned int cmd_save = 100;
 static uintmax_t next_mark;
 static struct strbuf new_data = STRBUF_INIT;
+static int seen_data_command;
 
 static void write_branch_report(FILE *rpt, struct branch *b)
 {
@@ -1704,6 +1705,11 @@ static int read_next_command(void)
 			if (stdin_eof)
 				return EOF;
 
+			if (!seen_data_command
+				&& prefixcmp(command_buf.buf, "feature ")) {
+				seen_data_command = 1;
+			}
+
 			rc = rc_free;
 			if (rc)
 				rc_free = rc->next;
@@ -2533,6 +2539,36 @@ static void parse_one_option(const char *option)
 	}
 }
 
+static int parse_one_feature(const char *feature)
+{
+	if (!prefixcmp(feature, "date-format=")) {
+		option_date_format(feature + 12);
+	} else if (!prefixcmp(feature, "import-marks=")) {
+		option_import_marks(feature + 13);
+	} else if (!prefixcmp(feature, "export-marks=")) {
+		option_export_marks(feature + 13);
+	} else if (!prefixcmp(feature, "force")) {
+		force_update = 1;
+	} else {
+		return 0;
+	}
+
+	return 1;
+}
+
+static void parse_feature(void)
+{
+	char *feature = command_buf.buf + 8;
+
+	if (seen_data_command)
+		die("Got feature command '%s' after data command", feature);
+
+	if (parse_one_feature(feature))
+		return;
+
+	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")) {
@@ -2612,6 +2648,8 @@ 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);
 	}

t/t9300-fast-import.sh

@@ -1254,4 +1254,74 @@ test_expect_success \
 	'Q: verify note for third commit' \
 	'git cat-file blob refs/notes/foobar:$commit3 >actual && test_cmp expect actual'
 
+###
+### series R (feature)
+###
+
+cat >input <<EOF
+feature no-such-feature-exists
+EOF
+
+test_expect_success 'R: abort on unsupported feature' '
+	test_must_fail git fast-import <input
+'
+
+cat >input <<EOF
+feature date-format=now
+EOF
+
+test_expect_success 'R: supported feature is accepted' '
+	git fast-import <input
+'
+
+cat >input << EOF
+blob
+data 3
+hi
+feature date-format=now
+EOF
+
+test_expect_success 'R: abort on receiving feature after data command' '
+	test_must_fail git fast-import <input
+'
+
+cat >input << EOF
+feature export-marks=git.marks
+blob
+mark :1
+data 3
+hi
+
+EOF
+
+test_expect_success \
+    'R: export-marks feature results in a marks file being created' \
+    'cat input | git fast-import &&
+    grep :1 git.marks'
+
+test_expect_success \
+    'R: export-marks options can be overriden by commandline options' \
+    'cat input | git fast-import --export-marks=other.marks &&
+    grep :1 other.marks'
+
+cat >input << EOF
+feature import-marks=marks.out
+feature export-marks=marks.new
+EOF
+
+test_expect_success \
+    'R: import to output marks works without any content' \
+    'cat input | git fast-import &&
+    test_cmp marks.out marks.new'
+
+cat >input <<EOF
+feature import-marks=nonexistant.marks
+feature export-marks=marks.new
+EOF
+
+test_expect_success \
+    'R: import marks prefers commandline marks file over the stream' \
+    'cat input | git fast-import --import-marks=marks.out &&
+    test_cmp marks.out marks.new'
+
 test_done