Revert "Emit mixin forwarders as ordinary, non-bridge methods again" (#23613)

Reverts #21890

The new build catches an issue when building
`scala3-sbt-bridge-bootstrapped`.
At the moment, I don't have the resources to handle the failure.

Author: hamzaremmal

.gitmodules

@@ -100,7 +100,6 @@
 [submodule "community-build/community-projects/scala-parallel-collections"]
 	path = community-build/community-projects/scala-parallel-collections
 	url = https://github.com/dotty-staging/scala-parallel-collections.git
-	branch = serialisation-stability-fix
 [submodule "community-build/community-projects/scala-collection-compat"]
 	path = community-build/community-projects/scala-collection-compat
 	url = https://github.com/dotty-staging/scala-collection-compat.git

community-build/community-projects/scala-parallel-collections

@@ -31,7 +31,6 @@ import dotty.tools.dotc.core.Types.*
 import dotty.tools.dotc.core.TypeErasure
 import dotty.tools.dotc.transform.GenericSignatures
 import dotty.tools.dotc.transform.ElimErasedValueType
-import dotty.tools.dotc.transform.Mixin
 import dotty.tools.io.AbstractFile
 import dotty.tools.dotc.report
 
@@ -396,20 +395,12 @@ trait BCodeHelpers extends BCodeIdiomatic {
      */
     def getGenericSignature(sym: Symbol, owner: Symbol): String = {
       atPhase(erasurePhase) {
-        def computeMemberTpe(): Type =
+        val memberTpe =
           if (sym.is(Method)) sym.denot.info
           else if sym.denot.validFor.phaseId > erasurePhase.id && sym.isField && sym.getter.exists then
             // Memoization field of getter entered after erasure, see run/i17069 for an example
             sym.getter.denot.info.resultType
           else owner.denot.thisType.memberInfo(sym)
-
-        val memberTpe = if sym.is(MixedIn) then
-          mixinPhase.asInstanceOf[Mixin].mixinForwarderGenericInfos.get(sym) match
-            case Some(genericInfo) => genericInfo
-            case none              => computeMemberTpe()
-        else
-          computeMemberTpe()
-
         getGenericSignatureHelper(sym, owner, memberTpe).orNull
       }
     }
@@ -500,7 +491,7 @@ trait BCodeHelpers extends BCodeIdiomatic {
       report.debuglog(s"Potentially conflicting names for forwarders: $conflictingNames")
 
       for (m0 <- sortedMembersBasedOnFlags(moduleClass.info, required = Method, excluded = ExcludedForwarder)) {
-        val m = if (m0.isOneOf(Bridge | MixedIn)) m0.nextOverriddenSymbol else m0
+        val m = if (m0.is(Bridge)) m0.nextOverriddenSymbol else m0
         if (m == NoSymbol)
           report.log(s"$m0 is a bridge method that overrides nothing, something went wrong in a previous phase.")
         else if (m.isType || m.is(Deferred) || (m.owner eq defn.ObjectClass) || m.isConstructor || m.name.is(ExpandedName))
@@ -516,7 +507,10 @@ trait BCodeHelpers extends BCodeIdiomatic {
           // we generate ACC_SYNTHETIC forwarders so Java compilers ignore them.
           val isSynthetic =
             m0.name.is(NameKinds.SyntheticSetterName) ||
-            m0.is(Bridge)
+            // Only hide bridges generated at Erasure, mixin forwarders are also
+            // marked as bridge but shouldn't be hidden since they don't have a
+            // non-bridge overload.
+            m0.is(Bridge) && m0.initial.validFor.firstPhaseId == erasurePhase.next.id
           addForwarder(jclass, moduleClass, m, isSynthetic)
         }
       }

compiler/src/dotty/tools/backend/jvm/BCodeHelpers.scala

@@ -299,7 +299,7 @@ class BTypesFromSymbols[I <: DottyBackendInterface](val int: I, val frontendAcce
         // illegal combination of modifiers at the bytecode level so
         // suppress final if abstract if present.
         && !sym.isOneOf(AbstractOrTrait)
-        // Bridges can be final, but final bridges confuse some frameworks
+        //  Mixin forwarders are bridges and can be final, but final bridges confuse some frameworks
         && !sym.is(Bridge), ACC_FINAL)
       .addFlagIf(sym.isStaticMember, ACC_STATIC)
       .addFlagIf(sym.is(Bridge), ACC_BRIDGE | ACC_SYNTHETIC)

compiler/src/dotty/tools/backend/jvm/BTypesFromSymbols.scala

@@ -239,7 +239,6 @@ object Phases {
     private var myErasurePhase: Phase = uninitialized
     private var myElimErasedValueTypePhase: Phase = uninitialized
     private var myLambdaLiftPhase: Phase = uninitialized
-    private var myMixinPhase: Phase = uninitialized
     private var myCountOuterAccessesPhase: Phase = uninitialized
     private var myFlattenPhase: Phase = uninitialized
     private var myGenBCodePhase: Phase = uninitialized
@@ -267,7 +266,6 @@ object Phases {
     final def gettersPhase: Phase = myGettersPhase
     final def erasurePhase: Phase = myErasurePhase
     final def elimErasedValueTypePhase: Phase = myElimErasedValueTypePhase
-    final def mixinPhase: Phase = myMixinPhase
     final def lambdaLiftPhase: Phase = myLambdaLiftPhase
     final def countOuterAccessesPhase = myCountOuterAccessesPhase
     final def flattenPhase: Phase = myFlattenPhase
@@ -297,7 +295,6 @@ object Phases {
       myErasurePhase = phaseOfClass(classOf[Erasure])
       myElimErasedValueTypePhase = phaseOfClass(classOf[ElimErasedValueType])
       myPatmatPhase = phaseOfClass(classOf[PatternMatcher])
-      myMixinPhase = phaseOfClass(classOf[Mixin])
       myLambdaLiftPhase = phaseOfClass(classOf[LambdaLift])
       myCountOuterAccessesPhase = phaseOfClass(classOf[CountOuterAccesses])
       myFlattenPhase = phaseOfClass(classOf[Flatten])
@@ -553,7 +550,6 @@ object Phases {
   def gettersPhase(using Context): Phase                = ctx.base.gettersPhase
   def erasurePhase(using Context): Phase                = ctx.base.erasurePhase
   def elimErasedValueTypePhase(using Context): Phase    = ctx.base.elimErasedValueTypePhase
-  def mixinPhase(using Context): Phase                  = ctx.base.mixinPhase
   def lambdaLiftPhase(using Context): Phase             = ctx.base.lambdaLiftPhase
   def flattenPhase(using Context): Phase                = ctx.base.flattenPhase
   def genBCodePhase(using Context): Phase               = ctx.base.genBCodePhase

compiler/src/dotty/tools/dotc/core/Phases.scala

@@ -16,7 +16,6 @@ import StdNames.*
 import Names.*
 import NameKinds.*
 import NameOps.*
-import Phases.erasurePhase
 import ast.Trees.*
 
 import dotty.tools.dotc.transform.sjs.JSSymUtils.isJSType
@@ -116,15 +115,6 @@ object Mixin {
 class Mixin extends MiniPhase with SymTransformer { thisPhase =>
   import ast.tpd.*
 
-  /** Infos before erasure of the generated mixin forwarders.
-   *
-   *  These will be used to generate Java generic signatures of the mixin
-   *  forwarders. Normally we use the types before erasure; we cannot do that
-   *  for mixin forwarders since they are created after erasure, and therefore
-   *  their type history does not have anything recorded for before erasure.
-   */
-  val mixinForwarderGenericInfos = MutableSymbolMap[Type]()
-
   override def phaseName: String = Mixin.name
 
   override def description: String = Mixin.description
@@ -315,25 +305,8 @@ class Mixin extends MiniPhase with SymTransformer { thisPhase =>
       for (meth <- mixin.info.decls.toList if needsMixinForwarder(meth))
       yield {
         util.Stats.record("mixin forwarders")
-        transformFollowing(DefDef(mkMixinForwarderSym(meth.asTerm), forwarderRhsFn(meth)))
-      }
-
-    def mkMixinForwarderSym(target: TermSymbol): TermSymbol =
-      val sym = mkForwarderSym(target, extraFlags = MixedIn)
-      val (infoBeforeErasure, isDifferentThanInfoNow) = atPhase(erasurePhase) {
-        val beforeErasure = cls.thisType.memberInfo(target)
-        (beforeErasure, !(beforeErasure =:= sym.info))
+        transformFollowing(DefDef(mkForwarderSym(meth.asTerm, Bridge), forwarderRhsFn(meth)))
       }
-      if isDifferentThanInfoNow then
-        // The info before erasure would not have been the same as the info now.
-        // We want to store it for the backend to compute the generic Java signature.
-        // However, we must still avoid doing that if erasing that signature would
-        // not give the same erased type. If it doesn't, we'll just give a completely
-        // incorrect Java signature. (This could be improved by generating dedicated
-        // bridges, but we don't go that far; scalac doesn't either.)
-        if TypeErasure.transformInfo(target, infoBeforeErasure) =:= sym.info then
-          mixinForwarderGenericInfos(sym) = infoBeforeErasure
-      sym
 
     cpy.Template(impl)(
       constr =

compiler/src/dotty/tools/dotc/transform/Mixin.scala

@@ -12,11 +12,13 @@ i9473.scala
 i13433.scala
 i13433b.scala
 macros-in-same-project1
+mixin-forwarder-overload
 t10889
 t3452d
 t3452e
 t3452g
 t7374
+t8905
 tuple-drop.scala
 tuple-ops.scala
 tuple-ops.scala

compiler/test/dotc/run-test-pickling.excludelist

@@ -193,45 +193,7 @@ object Scala2LibraryBootstrappedMiMaFilters {
         "scala.util.matching.Regex.Groups", "scala.util.matching.Regex.Match",
         "scala.util.package.chaining",
         "scala.util.Using.Manager", "scala.util.Using.Releasable", "scala.util.Using#Releasable.AutoCloseableIsReleasable",
-      ).map(ProblemFilters.exclude[MissingFieldProblem]) ++ Seq(
-        // DirectMissingMethodProblem by flags being changed from ACC_PUBLIC, ACC_BRIDGE, ACC_SYNTHETIC to ACC_PUBLIC in mixin forwarders:
-        // * from java.util.Comparator:
-        Seq("reversed", "thenComparing", "thenComparingInt", "thenComparingLong", "thenComparingInt", "thenComparingDouble").flatMap { method =>
-          Seq(
-            ProblemFilters.exclude[DirectMissingMethodProblem](s"scala.Enumeration#ValueOrdering.$method"),
-            ProblemFilters.exclude[DirectMissingMethodProblem](s"scala.concurrent.duration.Deadline#DeadlineIsOrdered.$method"),
-            ProblemFilters.exclude[DirectMissingMethodProblem](s"scala.concurrent.duration.Duration#DurationIsOrdered.$method"),
-            ProblemFilters.exclude[DirectMissingMethodProblem](s"scala.concurrent.duration.FiniteDuration#FiniteDurationIsOrdered.$method"),
-            ProblemFilters.exclude[DirectMissingMethodProblem](s"scala.math.Numeric#*.$method"),
-            ProblemFilters.exclude[DirectMissingMethodProblem](s"scala.math.Ordering#*.$method"),
-          )
-        },
-        // * from java.util.Spliterator:
-        Seq("getExactSizeIfKnown", "hasCharacteristics", "getComparator").flatMap { method =>
-          Seq(
-            ProblemFilters.exclude[DirectMissingMethodProblem](s"scala.collection.DoubleStepper#DoubleStepperSpliterator.$method"),
-            ProblemFilters.exclude[DirectMissingMethodProblem](s"scala.collection.IntStepper#IntStepperSpliterator.$method"),
-            ProblemFilters.exclude[DirectMissingMethodProblem](s"scala.collection.LongStepper#LongStepperSpliterator.$method"),
-          )
-        },
-        // * from java.util.Enumeration:
-        Seq(
-          ProblemFilters.exclude[DirectMissingMethodProblem]("scala.collection.convert.JavaCollectionWrappers#IteratorWrapper.asIterator"),
-        ),
-        // * from java.lang.CharSequence:
-        Seq(
-          ProblemFilters.exclude[DirectMissingMethodProblem]("scala.Predef#ArrayCharSequence.isEmpty"),
-          ProblemFilters.exclude[DirectMissingMethodProblem]("scala.Predef#SeqCharSequence.isEmpty"),
-          ProblemFilters.exclude[DirectMissingMethodProblem]("scala.runtime.ArrayCharSequence.isEmpty")
-        ),
-        // FinalMethodProblem - seems to be a bug in MiMa, as neither new or old version do not have final modifier.
-        // What did change is that sizeHint, and requireBounds had `final` added, but that does not get reported.
-        Seq(
-          ProblemFilters.exclude[FinalMethodProblem]("scala.**.sizeHint$default$2"),
-          ProblemFilters.exclude[FinalMethodProblem]("scala.collection.mutable.ArrayDeque.requireBounds$default$2")
-        )
-      ).flatten
-
+      ).map(ProblemFilters.exclude[MissingFieldProblem])
     }
   )
 }