refactor: use lambda to allow test to mock repository_ctx

.bazelversion

@@ -1,4 +1,4 @@
-4.2.0
+5.0.0-pre.20211011.2
 # The first line of this file is used by Bazelisk and Bazel to be sure
 # the right version of Bazel is used to build and test this repo.
 # This also defines which version is used on CI.

js/private/translate_package_lock.bzl

@@ -83,10 +83,7 @@ def npm_repositories():
         )])
     return bzl_out
 
-def _define_aliases(repository_ctx, lockfile, do_writes = True):
-    # Return value if do_writes = False
-    aliases = {}
-
+def _define_aliases(repository_ctx, lockfile):
     # The lockfile format refers to the context as the package with empty name.
     # This gives us a way to know which deps the user declared in their package.json
     # (the direct dependencies).
@@ -105,17 +102,7 @@ alias(name = "{package}", actual = "{actual}", visibility = ["//visibility:publi
             package = direct_name.split("/")[-1],
             actual = "@" + _repo_name(direct_name, direct_dep["version"]),
         )
-        if do_writes:
-            repository_ctx.file(direct_name + "/BUILD.bazel", dep_build_content)
-        else:
-            # In a starlark unit test, there is no global mutable data structure
-            # that allows us to capture the writes using a mock repository_ctx
-            # so we need a different return type that lets us assert on what's written.
-            # We could do this for production use as well, but then we'd waste memory
-            # in large package-lock.json files holding references to values
-            # we no longer need.
-            aliases[direct_name + "/BUILD.bazel"] = dep_build_content
-    return None if do_writes else aliases
+        repository_ctx.file(direct_name + "/BUILD.bazel", dep_build_content)
 
 def _translate_package_lock(repository_ctx):
     lock_content = json.decode(repository_ctx.read(repository_ctx.attr.package_lock))

js/test/translate_package_lock_tests.bzl

@@ -84,8 +84,11 @@ def npm_repositories():
 
 def _aliases_test_impl(ctx):
     env = unittest.begin(ctx)
-    mock_repository_ctx = struct()
-    actual = translate_package_lock.testonly_define_aliases(mock_repository_ctx, _lockfile, False)
+    actual = {}
+    mock_repository_ctx = struct(
+        file = lambda path, content: actual.update({path: content}),
+    )
+    translate_package_lock.testonly_define_aliases(mock_repository_ctx, _lockfile)
     asserts.equals(env, 1, len(actual.items()))
 
     # Note: @gregmagolan/test-a should not appear here since it's only a transitive dependency