trait with named parameters would lead to compiler error in specific cases

[bohonghuang]

Minimized code

  trait A(a: Any, b: Int) {

  }                                             
//  class A(a: String, b: Int) {
//
//  }                                           //OK!
  object B extends A(b = 0, a = String(""))     
//  object B extends A(a = String(""), b = 0)   //OK!

Output

Error:dotc: Error: val a$1
java.util.NoSuchElementException: val a$1
at scala.collection.mutable.AnyRefMap$ExceptionDefault.apply(AnyRefMap.scala:504)
at scala.collection.mutable.AnyRefMap$ExceptionDefault.apply(AnyRefMap.scala:503)
at scala.collection.mutable.AnyRefMap.apply(AnyRefMap.scala:205)
at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder$locals$.load(BCodeSkelBuilder.scala:396)
at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:378)
at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genStat(BCodeBodyBuilder.scala:63)
at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genBlock$$anonfun$1(BCodeBodyBuilder.scala:912)
at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:15)
at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:10)
at scala.collection.immutable.List.foreach(List.scala:333)
at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genBlock(BCodeBodyBuilder.scala:912)
at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:395)
at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.emitNormalMethodBody$1(BCodeSkelBuilder.scala:597)
at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.genDefDef(BCodeSkelBuilder.scala:630)
at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.gen(BCodeSkelBuilder.scala:501)
at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.gen$$anonfun$1(BCodeSkelBuilder.scala:503)
at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:15)
at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:10)
at scala.collection.immutable.List.foreach(List.scala:333)
at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.gen(BCodeSkelBuilder.scala:503)
at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.genPlainClass(BCodeSkelBuilder.scala:109)
at dotty.tools.backend.jvm.GenBCodePipeline$Worker1.visit(GenBCode.scala:217)
at dotty.tools.backend.jvm.GenBCodePipeline$Worker1.run(GenBCode.scala:184)
at dotty.tools.backend.jvm.GenBCodePipeline.buildAndSendToDisk(GenBCode.scala:514)
at dotty.tools.backend.jvm.GenBCodePipeline.run(GenBCode.scala:480)
...

[nicolasstucki]

The definition of a$1 seems to not be properly transformed in mixin

result of Foo.scala after erasure:
package foo {
  @scala.annotation.internal.SourceFile("Foo.scala") trait A(a: Object, b: Int)
     extends
   Object {
    private def a(): Object
    private def b(): Int
  }
  final lazy module val B: foo.B$ = new foo.B$()
  @scala.annotation.internal.SourceFile("Foo.scala") final module class B$()
     extends
   Object(), {
    val a$1: String = new String("")
    new foo.A(a$1, 0)
  }, java.io.Serializable {
    private def writeReplace(): Object = 
      new scala.runtime.ModuleSerializationProxy(classOf[foo.B$])
  }
}
result of Foo.scala after MegaPhase{elimErasedValueType, vcElideAllocations, arrayApply, elimPolyFunction, tailrec, completeJavaEnums, mixin, lazyVals, memoize, nonLocalReturns, capturedVars}:
package foo {
  @scala.annotation.internal.SourceFile("Foo.scala") trait A() extends Object {
    def foo$A$$a(): Object
    def foo$A$$b(): Int
  }
  final lazy module val B: foo.B$ = new foo.B$()
  @scala.annotation.internal.SourceFile("Foo.scala") final module class B$()
     extends
   Object, foo.A, java.io.Serializable {
    super()
    private val foo$A$$a: Object = a$1
    def foo$A$$a(): Object = foo.B.foo$A$$a
    private val foo$A$$b: Int = 0
    def foo$A$$b(): Int = foo.B.foo$A$$b
    private def writeReplace(): Object = 
      new scala.runtime.ModuleSerializationProxy(classOf[foo.B$])
  }
}