Meta-annotations written at use-site are ignored

[bchazalet]

Compiler version

3.0.0

Minimized code

This is an issue I've encountered while trying to port squeryl to scala 3.

In a MyColumnBase.java file:

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

@Retention(RetentionPolicy.RUNTIME)
public @interface MyColumnBase {

    String value() default "";
    
    String name() default "";

}

and in a scala file:

import annotation.meta.field

type MyColumn = MyColumnBase @field

class MyTable(
  @MyColumn(name="BRAND_NAME")
  val brandName: String
) {
    @MyColumn(name="WEIGHT")
    val weightInGrams: Option[String] = None
}

val clasz = classOf[MyTable]

for(m <- clasz.getDeclaredFields) {
  m.setAccessible(true)
  if(m.getName == "weightInGrams" || m.getName == "brandName"){
    println(s"inspecting field ${m.getName}")
    assert(m.getAnnotations().size == 1, s"no annotation found for ${m.getName}")
  }
}

Output

Array() had size 0 instead of expected size 1 no annotation found for brandName

Expectation

I would expect to see the annotation on the field brandName. In scala 2.13, I can at least.

[bchazalet]

can someone hint me as to where the parsing of the constructor params is done? I could perhaps try to understand where the problem lies in the code.

[OlivierBlanvillain]

@bchazalet I don't think this is a parsing issue, the annotation shows up with -Xprint:typer:

sbt:scala3> run -Xprint:typer /tmp/foo.java /tmp/bar.scala
[info] running (fork) dotty.tools.dotc.Main -classpath /home/olivier/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.5/scala-library-2.13.5.jar:/home/olivier/workspace/dotty/library/../out/bootstrap/scala3-library-bootstrapped/scala-3.0.1-RC1-bin-SNAPSHOT-nonbootstrapped/scala3-library_3-3.0.1-RC1-bin-SNAPSHOT.jar -Xprint:typer /tmp/foo.java /tmp/bar.scala
result of /tmp/bar.scala after typer:
package <empty> {
  import annotation.meta.field
  class MyTable(@MyColumn(_, name = "BRAND_NAME") brandName: String) extends
    Object
  () {
    @MyColumn(_, name = "BRAND_NAME") val brandName: String
    @MyColumn(_, name = "WEIGHT") val weightInGrams: Option[String] = None
  }
  final lazy module val bar$package: bar$package$ = new bar$package$()
  final module class bar$package$() extends Object() { this: bar$package.type =>
    type MyColumn = MyColumnBase @annotation.meta.field()
    @main() def test: Unit =
      {
        val clasz: Class[MyTable] = classOf[MyTable]
        refArrayOps[java.lang.reflect.Field](clasz.getDeclaredFields()).foreach[
          Unit
        ](
          {
            def $anonfun(m: java.lang.reflect.Field): Unit =
              {
                m.setAccessible(true)
                if
                  m.getName().==("weightInGrams").||(m.getName().==("brandName")
                    )
                 then
                  {
                    println(
                      _root_.scala.StringContext.apply(
                        ["inspecting field ","" : String]*
                      ).s([m.getName() : Any]*)
                    )
                    if
                      refArrayOps[java.lang.annotation.Annotation](
                        m.getAnnotations()
                      ).size.==(1).unary_!
                     then
                      scala.runtime.Scala3RunTime.assertFailed(
                        _root_.scala.StringContext.apply(
                          ["no annotation found for ","" : String]*
                        ).s([m.getName() : Any]*)
                      )
                     else ()
                  }
                 else ()
              }
            closure($anonfun)
          }
        )
      }
  }
  final class test() extends Object() {
    <static> def main(args: Array[String]): Unit =
      try test catch
        {
          case error @ _:scala.util.CommandLineParser.ParseError =>
            scala.util.CommandLineParser.showError(error)
        }
  }
}

[bchazalet]

thanks for the info @OlivierBlanvillain. Is there somewhere I can find the order of the different phases so that I can maybe try to identify in which one it gets 'lost'?

[bchazalet]

I found the useful -Xprint:all option. It looks like this is where it's happening:

result of /tmp/bar.scala after posttyper:
package <empty> {
  import annotation.meta.field
  @scala.annotation.internal.SourceFile("/tmp/bar.scala") class MyTable(
    @MyColumn(_, name = "BRAND_NAME") brandName: String
  ) extends Object() {
    val brandName: String
    @MyColumn(_, name = "WEIGHT") val weightInGrams: Option[String] = None
  }
  final lazy module val bar$package: bar$package$ = new bar$package$()
  @scala.annotation.internal.SourceFile("/tmp/bar.scala") final module class
    bar$package$
  () extends Object() { this: bar$package.type =>
    private def writeReplace(): AnyRef =
      new scala.runtime.ModuleSerializationProxy(classOf[bar$package.type])
    type MyColumn = MyColumnBase @annotation.meta.field()
    @main() def main(): Unit =
      {
        val clasz: Class[MyTable] = classOf[MyTable]
        refArrayOps[java.lang.reflect.Field](clasz.getDeclaredFields()).foreach[
          Unit
        ](
          {
            def $anonfun(m: java.lang.reflect.Field): Unit =
              {
                m.setAccessible(true)
                if
                  m.getName().==("weightInGrams").||(m.getName().==("brandName")
                    )
                 then
                  {
                    println(
                      _root_.scala.StringContext.apply(
                        ["inspecting field ","" : String]*
                      ).s([m.getName() : Any]*)
                    )
                    if
                      refArrayOps[java.lang.annotation.Annotation](
                        m.getAnnotations()
                      ).size.==(1).unary_!
                     then
                      scala.runtime.Scala3RunTime.assertFailed(
                        _root_.scala.StringContext.apply(
                          ["no annotation found for ","" : String]*
                        ).s([m.getName() : Any]*)
                      )
                     else ()
                  }
                 else ()
              }
            closure($anonfun)
          }
        )
      }
  }
  @scala.annotation.internal.SourceFile("/tmp/bar.scala") final class main()
     extends
   Object() {
    <static> def main(args: Array[String]): Unit =
      try main() catch
        {
          case error @ _:scala.util.CommandLineParser.ParseError =>
            scala.util.CommandLineParser.showError(error)
        }
  }
}

The annotation doesn't disappear, it's still there on the constructor param but it is not set on the val brandName: String unlike what happens for weightInGrams.

[smarter]

The issue is that we look for meta-annotations on the symbol definition (https://github.com/lampepfl/dotty/blob/a956774180d124adc98527863b919c35d5f9db92/compiler/src/dotty/tools/dotc/transform/PostTyper.scala#L158, https://github.com/lampepfl/dotty/blob/a956774180d124adc98527863b919c35d5f9db92/compiler/src/dotty/tools/dotc/transform/Memoize.scala#L112), whereas here the meta-annotation @field is part of the type (hidden behind an alias here, but it could just as well be written @(MyColumnBase @field) val brandName: String).

[bchazalet]

@smarter does that explain why it works for weightInGrams? The meta-annotation is part of the type in this case too, but the annotation is present on the private field anyway.

[smarter]

In that case the meta-annotation isn't needed since we're directly annotating a field (from https://www.scala-lang.org/api/current/scala/annotation/meta/index.html):

By default, annotations on (val-, var- or plain) constructor parameters end up on the parameter, not on any other entity. Annotations on fields by default only end up on the field.

[pjfanning]

I'm not sure if this test case is related but annotation in this example seems to be ignored by the Scala3 compiler (while it is handled by Scala2 compiler).

import com.fasterxml.jackson.annotation.JsonValue
import com.fasterxml.jackson.module.scala.DefaultScalaModule

import scala.annotation.meta.getter

object TestJsonValue {
  case class ValueClass(@(JsonValue @getter) value: String)
}

val clz = classOf[TestJsonValue.ValueClass]
val mtd = clz.getMethod("value")
println(mtd.toString + " " + mtd.getAnnotations.toSeq)

Scala 2.13.7: https://scastie.scala-lang.org/0JhMWXbvQPKbcNZjqALHAg (final println shows the 1 expected annotation)
Scala 3.1.0: https://scastie.scala-lang.org/IiOpcSSYSUSYDZh6csEb9w (final println shows 0 annotations)

[smarter]

Same thing yes.