Bazel 4.0.0 --incompatible_struct_has_no_methods

[qzmfranklin]

Bazel 4.0.0
skylib 1.0.3

.bazelrc contains the following flag:

build --incompatible_struct_has_no_methods

Then

load('@bazel_skylib//lib:structs.bzl', 'structs')

structs.to_dict(struct(foo=1))

This yield the error messages resembling the following:

        File "/var/bazel/1000/output_user_root/4967436ade8e5feb89c2f0210af1073a/external/bazel_skylib/lib/structs.bzl", line 29, column 22, in _to_dict
                attributes.remove("to_json")
Error in remove: item "to_json" not found in list

Suggestion: Use hasattr to probe whether the struct has to_proto and to_json or not before removing these two methods.