Fix Time serialization regression from dropping MultiJson

[numbata]

Summary

Version 1.0.3 introduced a silent breaking change for all API consumers: Time fields switched from ISO 8601 format ("2026-04-16T10:55:10.597Z") to Ruby's default Time#to_s format ("2026-04-16 10:55:10 UTC"). This breaks any client parsing timestamps from the API.

What happened

PR #385 replaced MultiJson.dump with JSON.dump in Entity#to_json to drop the multi_json dependency. While the intent was correct, JSON.dump and MultiJson.dump behave differently when ActiveSupport is present:

• MultiJson.dump(hash) internally calls Hash#to_json, which ActiveSupport overrides to run as_json recursively on all values — giving Time the ISO 8601 representation.
• JSON.dump(hash) goes directly to Ruby's C extension JSON generator, bypassing ActiveSupport's Hash#to_json override entirely — so Time falls back to Time#to_s.

Since ActiveSupport is a runtime dependency of grape-entity, every user is affected.

An additional problem noted by @stevenou: the intermediate Grape::Entity::Json constant used defined?(::MultiJson) at require time to decide which backend to use. For apps with gem "multi_json", require: false, MultiJson wasn't loaded yet at that point, so it always fell back to ::JSON regardless — making the MultiJson detection dead code in practice.

How this fix works

Replaces Grape::Entity::Json.dump(serializable_hash(options)) with serializable_hash(options).to_json.

Hash#to_json is the method ActiveSupport overrides. This single change resolves all reported problems:

1. Time serialization — Hash#to_json goes through ActiveSupport's as_json chain, restoring ISO 8601 output for Time and any other type with an as_json override.
2. Nested exposures — OutputBuilder (a SimpleDelegator wrapping a Hash) properly delegates .to_json to the underlying Hash.
3. MultiJson load-order race — eliminated entirely. We no longer check for or use MultiJson at all, so require: false scenarios are irrelevant.

The now-unused Grape::Entity::Json constant and grape_entity/json.rb are removed.

Fixes #403

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[Copilot]

Pull request overview

Fixes a regression introduced when switching from MultiJson.dump to JSON.dump by restoring ActiveSupport-aware JSON serialization for Time values in Grape::Entity#to_json.

Changes:

• Switch Entity#to_json to serialize via serializable_hash(...).to_json to re-enable ActiveSupport’s as_json chain (restoring ISO 8601 Time output).
• Remove the now-unused Grape::Entity::Json shim and its spec.
• Add specs asserting Time serialization uses as_json, including for nested exposures.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
spec/grape_entity/json_spec.rb	Removes spec for the deleted Grape::Entity::Json constant.
spec/grape_entity/entity_spec.rb	Adds regression coverage for Time serialization (top-level + nested exposures).
lib/grape_entity/json.rb	Removes the Grape::Entity::Json backend-selection shim.
lib/grape_entity/entity.rb	Updates #to_json implementation to call to_json on the serializable output (ActiveSupport-aware).

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[Copilot]

Pull request overview

This PR fixes a serialization regression introduced when switching JSON backends by ensuring Time (and other ActiveSupport-enhanced types) are serialized through ActiveSupport’s as_json chain again, restoring ISO 8601 timestamp output for API consumers.

Changes:

• Switch Grape::Entity#to_json to serialize via serializable_hash(...).to_json (ActiveSupport-aware) instead of MultiJson.dump.
• Remove the multi_json runtime dependency from the gemspec.
• Document the fix and dependency removal in the changelog.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
lib/grape_entity/entity.rb	Restores ActiveSupport-aware JSON serialization by using Hash#to_json on the computed serializable output.
grape-entity.gemspec	Drops the multi_json dependency now that it’s no longer used.
CHANGELOG.md	Notes the regression fix and dependency removal in the Unreleased fixes section.

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