fix: srcs is not mandatory (#786)

Author: thesayyn

docs/tar.md

@@ -50,7 +50,6 @@ _tar_attrs = {
 
         If any of the srcs are binaries with runfiles, those are copied into the resulting tar as well.
         """,
-        mandatory = True,
         allow_files = True,
     ),
     "mode": attr.string(
@@ -88,7 +87,7 @@ _tar_attrs = {
 }
 
 _mtree_attrs = {
-    "srcs": attr.label_list(doc = "Files that are placed into the tar", mandatory = True, allow_files = True),
+    "srcs": attr.label_list(doc = "Files that are placed into the tar", allow_files = True),
     "out": attr.output(doc = "Resulting specification file to write"),
 }
 

lib/private/tar.bzl

@@ -328,3 +328,17 @@ assert_tar_listing(
         "-rwxr-xr-x  0 0      0       11358 Jan  1  2023 a",
     ],
 )
+
+# Case 11: Can create tar without srcs
+tar(
+    name = "create_tmp",
+    mtree = ["./tmp time=1501783453.0 mode=1777 gid=0 uid=0 type=dir"],
+)
+
+assert_tar_listing(
+    name = "test_create_create_tmp",
+    actual = "create_tmp",
+    expected = [
+        "drwxrwxrwt  0 0      0           0 Aug  3  2017 ./tmp/",
+    ],
+)