Use the built-in JSON library

[elfenlaid]

Address #6461

The changes set the built-in JSON library as a default JSON library.

The idea is to check whether the built-in JSON library is present and use it if so:

  @default_json_library if Code.ensure_loaded?(JSON), do: JSON, else: Jason

  def json_library do
    Application.get_env(:phoenix, :json_library, @default_json_library)
  end

Correct me if I'm wrong, but I think a naive check of whether the library is present during compilation time should work, as it's a built-in library.

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What I'm not sure about is whether such a move results in a breaking change.

It could be a breaking change for projects that don't specify the json_library and use @derive Jason.Encoder on structures passed to Phoenix.Controller.json/2. That sounds pretty niche, especially given that the template project includes:

config :phoenix, :json_library, Jason

Also, I'm specifically leaving the jason dependency in place for pre-27 OTP versions.

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Please let me know what you think and whether the changes make sense. In other words, maybe it would be better to stick with Jason until Phoenix requires OTP 28.

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Similar discussions / changes:

Use Jason instead of Poison for json encoding by chrismccord #2734phoenixframework/phoenix
Investigate using Jason instead of Poison #2693phoenixframework/phoenix

Use JSON instead of Jason by kubosuke #234felt/geo

[elfenlaid]

Not the most elegant solution, but...

[SteffenDE]

Looks good to me! But if we actually change new projects to use JSON, we'll also need to bump the minimum version we set to Elixir 1.18, see

phoenix/installer/mix.exs

Lines 12 to 20 in 9fc21c6

	# If the elixir requirement is updated, we need to update:
	#
	# 1. all mix.exs generated by the installer
	# 2. guides/introduction/installation.md
	# 3. guides/deployment/releases.md
	# 4. test/test_helper.exs at the root
	# 5. installer/lib/mix/tasks/phx.new.ex
	#
	@elixir_requirement "~> 1.15"

I wonder if we should postpone this change to a future Phoenix 1.9? @josevalim

[josevalim]

Yes, v1.9 material for sure. But it looks good. We can probably assign a v1.9 milestone and merge it once we finally branch v1.8 out. I don’t think it is worth branching out though, as I dont think there is anything beyond this PR for now?

[elfenlaid]

Yes, v1.9 material for sure. But it looks good. We can probably assign a v1.9 milestone and merge it once we finally branch v1.8 out. I don’t think it is worth branching out though, as I dont think there is anything beyond this PR for now?

I don't think there's anything else I can add to this PR. Thank you everyone for looking into this! 🙇