missing method to_json on struct type

[dududko]

Description of the problem / feature request:

Missing method to_json on struct type. This is a breaking change which is not documented, and it results in build failure of many bazel extensions including rules_docker

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

rule.bzl

def  my_rule_impl(ctx):
    s = struct()
    print(s.to_json())

my_rule = rule(
    implementation = my_rule_impl,
)

BUILD.bazel

load("//:rule.bzl", "my_rule")

my_rule(
    name = "my_target"
)

bazel build //:my_target

What operating system are you running Bazel on?

macOS Catalina 10.15.7

What's the output of bazel info release?

release 4.0.0

Have you found anything relevant by searching the web?

No

Any other information, logs, or outputs that you want to share?

bazel build //...
(19:10:58) INFO: Invocation ID: 724bb149-9541-4e98-b610-e620c46a1572
(19:10:59) INFO: Current date is 2021-02-09
(19:11:39) INFO: SHA256 (https://golang.org/dl/?mode=json&include=all) = 7008033e0ab99ec03d6eb9593445b9a94bec029ac91450ffb4318c059ca427dc
(19:12:15) ERROR: /Users/dududko/myproject/chart/frontend/test/test-frontend/BUILD.bazel:14:16: in container_layer_ rule //chart/frontend/test/test-frontend:layer:
Traceback (most recent call last):
	File "/private/var/tmp/_bazel_dududko/14485085ed56a1ffbc0109316724dc49/external/io_bazel_rules_docker/container/layer.bzl", line 232, column 42, in _impl
		unzipped_layer, diff_id = build_layer(
	File "/private/var/tmp/_bazel_dududko/14485085ed56a1ffbc0109316724dc49/external/io_bazel_rules_docker/container/layer.bzl", line 146, column 46, in build_layer
		ctx.actions.write(manifest_file, manifest.to_json())
Error: 'struct' value has no field or method 'to_json'
Available attributes: debs, empty_dirs, empty_files, empty_root_dirs, files, symlinks, tars
(19:12:15) ERROR: Analysis of target '//chart/frontend/test/test-frontend:layer' failed; build aborted: Analysis of target '//chart/frontend/test/test-frontend:layer' failed
(19:12:15) INFO: Elapsed time: 76.346s
(19:12:15) INFO: 0 processes.
(19:12:15) FAILED: Build did NOT complete successfully (259 packages loaded, 8837 targets configured)
    Fetching @com_github_aws_aws_sdk_go; fetching 25s
    Fetching @io_cirello_dynamolock; fetching 25s
    Fetching @com_github_stretchr_testify; fetching 25s
    Fetching @com_github_pelletier_go_toml; fetching 24s

[dmivankov]

258dfe9

• The Starlark json module is now available.
  Use json.encode(x) to encode a Starlark value as JSON.
  struct.to_json(x) is deprecated and will be disabled by
  the --incompatible_struct_has_no_methods flag.

is --incompatible_struct_has_no_methods on?

[dmivankov]

Shouldn't be on by default I think, looking at 4.0.0 release info https://blog.bazel.build/2021/01/19/bazel-4-0.html#starlark

[dududko]

I did not enable this option. I can confirm that build is successful if this option is explicitly disabled --incompatible_struct_has_no_methods=false.

[brandjon]

Are you using --all_incompatible_changes? That would turn it on. Also check your bazelrc file.

[dududko]

@brandjon yes I do
I totally forgot about this option.
Sorry for you time, you can close this ticket.