fast-import: do not truncate exported marks file

Certain lines of the marks file might be corrupted (or the objects
missing due to a garbage collection), but that's no reason to truncate
the file and essentially destroy the rest of it.

Ideally missing objects should not cause a crash, we could just skip
them, but that's another patch.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

fast-import.c

@@ -329,6 +329,7 @@ static const char *export_marks_file;
 static const char *import_marks_file;
 static int import_marks_file_from_stream;
 static int import_marks_file_ignore_missing;
+static int import_marks_file_done;
 static int relative_marks_paths;
 
 /* Our last blob */
@@ -1802,7 +1803,7 @@ static void dump_marks(void)
 	static struct lock_file mark_lock;
 	FILE *f;
 
-	if (!export_marks_file)
+	if (!export_marks_file || (import_marks_file && !import_marks_file_done))
 		return;
 
 	if (hold_lock_file_for_update(&mark_lock, export_marks_file, 0) < 0) {
@@ -1835,7 +1836,7 @@ static void read_marks(void)
 	if (f)
 		;
 	else if (import_marks_file_ignore_missing && errno == ENOENT)
-		return; /* Marks file does not exist */
+		goto done; /* Marks file does not exist */
 	else
 		die_errno("cannot read '%s'", import_marks_file);
 	while (fgets(line, sizeof(line), f)) {
@@ -1865,6 +1866,8 @@ static void read_marks(void)
 		insert_mark(mark, e);
 	}
 	fclose(f);
+done:
+	import_marks_file_done = 1;
 }
 
 

t/t9300-fast-import.sh

@@ -2650,6 +2650,21 @@ test_expect_success 'R: ignore non-git options' '
 	git fast-import <input
 '
 
+test_expect_success 'R: corrupt lines do not mess marks file' '
+	rm -f io.marks &&
+	blob=$(echo hi | git hash-object --stdin) &&
+	cat >expect <<-EOF &&
+	:3 0000000000000000000000000000000000000000
+	:1 $blob
+	:2 $blob
+	EOF
+	cp expect io.marks &&
+	test_must_fail git fast-import --import-marks=io.marks --export-marks=io.marks <<-\EOF &&
+
+	EOF
+	test_cmp expect io.marks
+'
+
 ##
 ## R: very large blobs
 ##