dotty.tools.dotc.transform.ResolveSuper.scala Maven / Gradle / Ivy

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package dotty.tools.dotc
package transform

import core._
import MegaPhase._
import Contexts.Context
import Flags._
import SymUtils._
import Symbols._
import Decorators._
import DenotTransformers._
import NameOps._
import NameKinds._
import ResolveSuper._
import reporting.diagnostic.messages.IllegalSuperAccessor

/** This phase implements super accessors in classes that need them.
 *
 *  For every trait M directly implemented by the class (see SymUtils.mixin), in
 *  reverse linearization order, add the following definitions to C:
 *
 *  For every superAccessor ` def super$f[Ts](ps1)...(psN): U` in M:
 *
 *        def super$f[Ts](ps1)...(psN): U = super[S].f[Ts](ps1)...(psN)
 *
 *  where `S` is the superclass of `M` in the linearization of `C`.
 *
 *  This is the first part of what was the mixin phase. It is complemented by
 *  Mixin, which runs after erasure.
 */
class ResolveSuper extends MiniPhase with IdentityDenotTransformer { thisPhase =>
  import ast.tpd._

  override def phaseName: String = ResolveSuper.name

  override def runsAfter: Set[String] = Set(ElimByName.name, // verified empirically, need to figure out what the reason is.
                               AugmentScala2Traits.name,
                               PruneErasedDefs.name) // Erased decls make `isCurrent` work incorrectly

  override def changesMembers: Boolean = true // the phase adds super accessors

  override def transformTemplate(impl: Template)(implicit ctx: Context): Template = {
    val cls = impl.symbol.owner.asClass
    val ops = new MixinOps(cls, thisPhase)
    import ops._

    def superAccessors(mixin: ClassSymbol): List[Tree] =
      for (superAcc <- mixin.info.decls.filter(_.isSuperAccessor))
        yield {
          util.Stats.record("super accessors")
          polyDefDef(mkForwarderSym(superAcc.asTerm), forwarderRhsFn(rebindSuper(cls, superAcc)))
        }

    val overrides = mixins.flatMap(superAccessors)

    cpy.Template(impl)(body = overrides ::: impl.body)
  }

  override def transformDefDef(ddef: DefDef)(implicit ctx: Context): Tree = {
    val meth = ddef.symbol.asTerm
    if (meth.isSuperAccessor && !meth.is(Deferred)) {
      assert(ddef.rhs.isEmpty)
      val cls = meth.owner.asClass
      val ops = new MixinOps(cls, thisPhase)
      import ops._
      polyDefDef(meth, forwarderRhsFn(rebindSuper(cls, meth)))
    }
    else ddef
  }
}

object ResolveSuper {
  val name: String = "resolveSuper"

  /** Returns the symbol that is accessed by a super-accessor in a mixin composition.
   *
   *  @param base       The class in which everything is mixed together
   *  @param acc        The symbol statically referred to by the superaccessor in the trait
   */
  def rebindSuper(base: Symbol, acc: Symbol)(implicit ctx: Context): Symbol = {
    var bcs = base.info.baseClasses.dropWhile(acc.owner != _).tail
    var sym: Symbol = NoSymbol
    val SuperAccessorName(memberName) = acc.name.unexpandedName
    ctx.debuglog(i"starting rebindsuper from $base of ${acc.showLocated}: ${acc.info} in $bcs, name = $memberName")
    while (bcs.nonEmpty && sym == NoSymbol) {
      val other = bcs.head.info.nonPrivateDecl(memberName)
        .matchingDenotation(base.thisType, base.thisType.memberInfo(acc))
      ctx.debuglog(i"rebindsuper ${bcs.head} $other deferred = ${other.symbol.is(Deferred)}")
      if (other.exists) {
        sym = other.symbol
        // Having a matching denotation is not enough: it should also be a subtype
        // of the superaccessor's type, see i5433.scala for an example where this matters
        val otherTp = other.asSeenFrom(base.typeRef).info
        val accTp = acc.asSeenFrom(base.typeRef).info
        if (!(otherTp.overrides(accTp, matchLoosely = true)))
          ctx.error(IllegalSuperAccessor(base, memberName, acc, accTp, other.symbol, otherTp), base.sourcePos)
      }

      bcs = bcs.tail
    }
    assert(sym.exists)
    sym
  }
}