diff --git a/tools/build_defs/repo/BUILD b/tools/build_defs/repo/BUILD
index 5106cd4aa4a06e..7f4421ec4a22bf 100644
--- a/tools/build_defs/repo/BUILD
+++ b/tools/build_defs/repo/BUILD
@@ -40,6 +40,7 @@ genrule(
 )
 
 REPO_BZL_FILES = [
+    "cache",
     "git",
     "http",
     "local",
diff --git a/tools/build_defs/repo/cache.bzl b/tools/build_defs/repo/cache.bzl
index c4b13695c6ec3a..c25f03a0a3d51c 100644
--- a/tools/build_defs/repo/cache.bzl
+++ b/tools/build_defs/repo/cache.bzl
@@ -37,7 +37,14 @@ machines without the file in the cache. This behavior can be disabled with
 """.format(env = DEFAULT_CANONICAL_ID_ENV)
 
 def get_default_canonical_id(repository_ctx, urls):
-    """Returns the default canonical id to use for downloads."""
+    """Returns the default canonical id to use for downloads.
+    
+    Args:
+      repository_ctx: The repository context of the repository rule calling this utility
+        function.
+      urls: A list of URLs matching what is passed to `repository_ctx.download` and
+        `repository_ctx.download_and_extract`.
+    """
     if repository_ctx.os.environ.get(DEFAULT_CANONICAL_ID_ENV) == "0":
         return ""