GraalVM native-image with Scala 3 reflection hell

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  • sbt-native-image

    Plugin to generate native-image binaries with sbt

    The reason seems to be Scala 3's new encoding for lazy vals, where a reflective access to a variable called bitmap takes place. To demonstrate this, I took the http4s g8 template, set it up with Scala 3.1.0, added sbt native-image, started the nativeImageRunAgent and ran a single request against GET /joke. After stopping the server, the native-image run agent generated the reflective configs that are required for this path of execution. Comparing the generated Scala 2.13 with the Scala 3 configs, yields a bloated version for Scala 3 that contains these additional rules:

  • scala-3-lazy-reflective-access

    Showcase of GraalVM native-image's configuration bloating up with Scala 3

    Here is the sample code, based on the http4s g8 template:

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  • dotty

    The Scala 3 compiler, also known as Dotty.

    See, maybe the graalvm reflection config format could be enriched to support wildcards if it doesn't already?

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