fix(write_source_files): fix writing to workspace root

.gitignore

@@ -1 +1,2 @@
 bazel-*
+test-out/

BUILD.bazel

@@ -20,3 +20,16 @@ bzl_library(
         "@bazel_tools//tools/build_defs/repo:utils.bzl",
     ],
 )
+
+# write_source_files() to a git ignored subdirectory of the root
+load("//lib:write_source_files.bzl", "write_source_files")
+genrule(
+    name = "write_source_file_root",
+    outs = ["write_source_file-root_directory"],
+    cmd = "mkdir -p $@ && echo 'test' > $@/test.txt",
+    visibility = ["//visibility:private"],
+)
+write_source_files(
+    name = "write_source_file_root-test",
+    files = {"test-out/dist/write_source_file_root-test": ":write_source_file_root"},
+)

lib/private/write_source_file.bzl

@@ -266,7 +266,7 @@ def _write_source_file_impl(ctx):
         else:
             fail("in file %s must be a single file or a target that provides DefaultOutputPathInfo or DirectoryPathInfo" % ctx.attr.in_file.label)
 
-        out_path = "/".join([ctx.label.package, ctx.attr.out_file])
+        out_path = "/".join([ctx.label.package, ctx.attr.out_file]) if len(ctx.label.package) > 0 else ctx.attr.out_file
         paths.append((in_path, out_path))
 
     if ctx.attr.is_windows: