Deserialiaze with null vs constructor with 0 parameter

[jmfayard]

Hello

I try to model Github Actions workflow like this

data class YamlWorkflow(
    val name: String,
    val on: YamlWorkflowTriggers,
)
data class YamlWorkflowTriggers(
    val push: Push? = null,
    val pull_request: PullRequest? = null,
)

Deserialization works if I pass parameters to push: and pull_request:

But GitHub Actions also allows to say:

name: all-triggers

on:
  push:
  pull_request:

Here I expect: YamlWorkflowTriggers(Push(), PullRequest())

But I get YamlWorkflowTriggers(null, null)

as if the YAML file was

name: all-triggers

on:

[charleskorn]

Thanks for the question @jmfayard. I'm guessing GitHub Actions is doing some magic under the hood there - in YAML, an empty value like that is considered a null value.

One solution might be to write a custom serializer for YamlWorkflowTriggers that translates a present-but-null value like that into an empty object.

[jmfayard]

They even accept this syntax :(

on: [ push, pull_request ]

[charleskorn]

That's not going to map nicely to that Kotlin model either - in order to support all of these different scenarios, you'll need to create a custom serializer unfortunately.

[jmfayard]

Instead of fighting the type system, I ended up writing an intermediate function fun String.normalizeYaml(): String
that normalize the input to

name: all-triggers

on:
  push: {}
  pull_request: {}