Handle cases with only data dependencies in pkg_tar

pkg/private/pkg_files.bzl

@@ -437,8 +437,13 @@ def add_from_default_info(
             # Computing the runfiles root is subtle. It should be based off of
             # the executable, but that is not always obvious. When in doubt,
             # the first file of DefaultInfo.files should be the right target.
-            base_file = the_executable or all_files[0]
-            base_file_path = dest_path(base_file, data_path, data_path_without_prefix)
+            # If there are no files, these are just runfiles / data dependencies,
+            # just package them in ".runfiles".
+            base_file_path = ""
+            if the_executable != None:
+                base_file_path = dest_path(the_executable, data_path, data_path_without_prefix)
+            elif len(all_files) > 0:
+                base_file_path = dest_path(all_files[0], data_path, data_path_without_prefix)
             base_root_path = base_file_path + ".runfiles"
             base_path = base_root_path + "/" + workspace_name
 

tests/BUILD

@@ -52,6 +52,15 @@ filegroup(
     srcs = glob(["**/*.txt"]),
 )
 
+filegroup(
+    name = "data_filegroup",
+    data = [
+        "testdata/hello.txt",
+        "testdata/loremipsum.txt",
+    ],
+    visibility = ["//visibility:public"],
+)
+
 #
 # Data source for Unicode handling tests
 #

tests/tar/BUILD

@@ -369,6 +369,23 @@ verify_archive_test(
     target = ":test-tar-with-runfiles",
 )
 
+pkg_tar(
+    name = "test-tar-with-only-runfiles",
+    srcs = [
+        "//tests:data_filegroup",
+    ],
+    include_runfiles = True,
+)
+
+verify_archive_test(
+    name = "runfiles_only_test",
+    must_contain = [
+        ".runfiles/_main/tests/testdata/loremipsum.txt",
+        ".runfiles/_main/tests/testdata/hello.txt",
+    ],
+    target = ":test-tar-with-only-runfiles",
+)
+
 pkg_tar(
     name = "test-tar-remap-runfiles-base-path",
     srcs = [