Default values of var-based properties are not documented properly

[Simon3]

Generating configuration metadata from @ConfigurationProperties items written in Kotlin doesn't work for defaultValue fields. It works fine for all the other fields. In java, it works fine for everything. Here is an example. Note that I'm using Spring Boot 2.0 and Gradle.

kapt 'org.springframework.boot:spring-boot-configuration-processor'
kapt {
  arguments {
    arg("org.springframework.boot.configurationprocessor.additionalMetadataLocations", "$projectDir/src/main/resources")
   }
}
compileJava.dependsOn(processResources)

My @ConfigurationProperties file looks like this:

@Component
@ConfigurationProperties("flowr.epg")
class EpgProperties {
    /** Whether or not schedules should be computed/refreshed on (re)start */
    var refreshOnRestart = true
    /** Number of threads used to store new images */
    var nImagesUploadThreads = 10
}

The result looks like this:

{
  "hints": [],
  "groups": [
    {
      "sourceType": "com.taktik.flowr.epg.properties.EpgProperties",
      "name": "flowr.epg",
      "type": "com.taktik.flowr.epg.properties.EpgProperties"
    }
  ],
  "properties": [
{
  "sourceType": "com.taktik.flowr.epg.properties.EpgProperties",
  "defaultValue": false,
  "name": "flowr.epg.refresh-on-restart",
  "description": "Whether or not schedules should be computed\/refreshed on (re)start",
  "type": "java.lang.Boolean"
},
{
  "sourceType": "com.taktik.flowr.epg.properties.EpgProperties",
  "defaultValue": 0,
  "name": "flowr.epg.n-images-upload-threads",
  "description": "Number of threads used to store new images",
  "type": "java.lang.Integer"
}
}

Support for default values in Kotlin would be a really nice feature to have for my company.

Note: replicated from https://stackoverflow.com/questions/53636533/spring-boot-configurationproperties-metadata-generation-wrong-default-values

[snicoll]

It's actually worse. It doesn't detect the default value and use default value for the underlying type. I guess we will need to see if we can't hook into some low-level APIs as we've done for the Java compiler.

[darioseidl]

I'm seeing the same problem. Just to be clear: the problem is only with the generated metadata, the default values specified in Kotlin @ConfigurationProperties do get picked up, they are just not documented in the metadata, right?

[Simon3]

Correct.

[snicoll]

Unfortunately there's not much we can do at the moment, please vote for KT-30164. In the meantime, we could attempt to detect that the source model is a Kotlin class and then deactivate default handling to avoid writing wrong value in the metadata.

[Simon3]

Ok, yes I guess it would be a good idea to do that in the meantime.
Thanks for everything!