pkl-config-java: Migrate nullness to jSpecify

[odenix]

Questions that came up while working on this PR:

1. Should Config be thread-safe? Currently, it isn't, as some Converter implementations aren't.
2. Should Config.makeConfig() be part of the public API? Currently, it is.

[HT154]

Looks like changes are needed in pkl-config-kotlin for this to compile. Is this expected?

diff --git a/pkl-config-kotlin/src/main/kotlin/org/pkl/config/kotlin/ConfigExtensions.kt b/pkl-config-kotlin/src/main/kotlin/org/pkl/config/kotlin/ConfigExtensions.kt
index 6bf47437..16513274 100644
--- a/pkl-config-kotlin/src/main/kotlin/org/pkl/config/kotlin/ConfigExtensions.kt
+++ b/pkl-config-kotlin/src/main/kotlin/org/pkl/config/kotlin/ConfigExtensions.kt
@@ -36,10 +36,10 @@ import org.pkl.config.kotlin.mapper.KotlinConverterFactories
  * * easier to use with parameterized types: `to<List<String>>()` vs.
  *   `as(JavaType.listOf(String::class.java))`
  */
-inline fun <reified T> Config.to(): T {
+inline fun <reified T : Any> Config.to(): T {
   val javaType = object : JavaType<T>() {}
   // `as T?` may no longer be required after switching to JSpecify
-  val result = `as`<T>(javaType.type) as T?
+  val result = `as`(javaType.type) as T?
   if (result == null && null !is T) {
     throw ConversionException(
       "Expected a non-null value but got `null`. " +
diff --git a/pkl-config-kotlin/src/main/kotlin/org/pkl/config/kotlin/mapper/PPairToKotlinPair.kt b/pkl-config-kotlin/src/main/kotlin/org/pkl/config/kotlin/mapper/PPairToKotlinPair.kt
index cf93536a..7e38a8e0 100644
--- a/pkl-config-kotlin/src/main/kotlin/org/pkl/config/kotlin/mapper/PPairToKotlinPair.kt
+++ b/pkl-config-kotlin/src/main/kotlin/org/pkl/config/kotlin/mapper/PPairToKotlinPair.kt
@@ -42,7 +42,7 @@ internal class PPairToKotlinPair : ConverterFactory {
     )
   }
 
-  private class ConverterImpl<F, S>(
+  private class ConverterImpl<F : Any, S : Any>(
     private val firstTargetType: Type,
     private val secondTargetType: Type,
   ) : Converter<PPair<Any, Any>, Pair<F, S>> {

[odenix]

Yes, I'm on it. kotlinc has direct support for jSpecify and is very strict about nullness. Unfortunately, a local gradlew clean build didn't catch this (didn't rerun the failing compileKotlin task). Only --rerun-tasks did the job.

[odenix]

@HT154 force-pushed because I had missed some org.pkl.core.utils.Nullable imports

[bioball]

1. Should Config be thread-safe? Currently, it isn't, as some Converter implementations aren't.

Yeah, I'd consider it a bug if it isn't.

2. Should Config.makeConfig() be part of the public API? Currently, it is.

I don't think so. Happy to accept a PR to move this out.

[bioball]

Nice, thanks!

[bioball]

Nice!