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Thanks for the improvement! If the lock file doesn't exist (initial), why wouldn't the rule start from empty instead of still requiring user to create the initial empty file?

Maybe something like this?

--- apt/extensions.bzl.orig
+++ apt/extensions.bzl
@@ -26,7 +26,11 @@
                     # buildifier: disable=print
                     print("\nNo lockfile was given, please run `bazel run @%s//:lock` to create the lockfile." % install.name)
             else:
-                lockf = lockfile.from_json(module_ctx, module_ctx.read(install.lock))
+                if module_ctx.file(install.lock.package + "/" + install.lock.name):
+                    lock_content = module_ctx.read(install.lock)
+                else:
+                    lock_content = None
+                lockf = lockfile.from_json(module_ctx, lock_content)
                 reproducible = True
 
             for (package) in lockf.packages():

Thanks for the improvement! If the lock file doesn't exist (initial), why wouldn't the rule start from empty instead of still requiring user to create the initial empty file?

Submitted PR #169