JSON generation fails with json 3.0.0 due to Oj-specific options

[willnet]

Gon's JSON generation fails when multi_json uses the json gem as its backend with json 3.0.0.

The failure was observed in the test-multi-json-compatibility (1.20.1) CI job:

ArgumentError:
  unknown keywords: mode, escape_mode, time_format

# ./lib/gon/json_dumper.rb:20:in `dump'
# ./spec/gon/json_dumper_spec.rb:14

Cause

Gon::JsonDumper.dump passes these Oj-specific options to multi_json regardless of the selected backend:

{ mode: :compat, escape_mode: :xss_safe, time_format: :ruby }

When the json backend is selected, multi_json forwards them to JSON.generate. json 2.x ignored unknown options, but json 3.0.0 raises ArgumentError.

Running the existing json_dumper_spec.rb locally on Ruby 4.0.6 reproduced the failure:

multi_json	json 2.21.2	json 3.0.0
1.20.1	Pass	Fail
1.21.1	Pass	Fail

Upstream status

multi_json PR #67, released in v1.21.2, adds json 3.x compatibility. However, it primarily addresses parsing options and does not filter the Oj-specific generation options passed by gon.

Possible fix

Remove the explicit options from Gon::JsonDumper.dump, while preserving its final escape call:

• mode: :compat and time_format: :ruby are already defaults in multi_json's Oj adapter in modern versions.
• Gon's own escape method escapes <, >, &, U+2028, and U+2029 after JSON generation, providing the escaping needed for embedding JSON in a script tag.

Removing the options experimentally made the existing spec pass with json 3.0.0 for both tested multi_json versions.