This is a limitation of the current architecture of json_map macro that pre-computes some information at compile-time - it should be possible to fix it.

In the meantime, you should be able to use the runtime variant of an ordered map - the Jason.OrderedObject, e.g.

Jason.OrderedObject.new("my/key": "test")

it also allows for using string keys:

Jason.OrderedObject.new([{"my/key", "test"}])

and the keys can be dynamic:

Jason.OrderedObject.new([{my_key, "test"}])

PS. the key order jumbling comes likely from upgrading to Erlang 26, rather than Elixir 1.14

Running into a similar issue where I have a mix task that generates some JSON data that I commit to the repository. My diffs are noisy due to key order changing. It would be nice to be able to provide an option to pretty_print like sort_keys: true or something.

In the meantime, I just shell out to jq to sort the JSON.

An option to sort the keys for pretty printing would definitely work, perhaps even one for the base encoding and using maps iterators. I would welcome a PR with such a change

Hi @michalmuskala what is involved in allowing a custom sort function for maps to be passed into the encode function?

We would be willing to sponsor someone to implement this :)