Compiler crash with SuspendException happening during PostTyper

[smarter]

Compiler version

3.4.0-RC1-bin-20230901-89e8dba-NIGHTLY

Minimized code

Caller.scala:

package dummy

trait BG {
	val   description: { type Structure }
	type  Structure =  description.Structure
}

abstract class Caller extends BG {
	type Foo >: this.type <: this.type

	transparent inline def generate2() =
		${Macro.impl() }

	final val description = {
		generate2()
	}
}

Macro.scala:

package dummy

import scala.quoted.*

object Macro:
	def impl()(using quotes:Quotes) : Expr[Any] =
	  '{ null }

User.scala:

package dummy

trait User:
        final def bar(cell:Any) : Unit =
                (cell : cell.type) match
                        case c: (Caller & cell.type) => ()

Output (click arrow to expand)

Exception in thread "main" dotty.tools.dotc.CompilationUnit$SuspendException

No stack trace is shown since SuspendException extends NoStackTrace, if we remove that parent then we get:

        at dotty.tools.dotc.CompilationUnit.suspend(CompilationUnit.scala:97)
        at dotty.tools.dotc.typer.Namer$SuspendCompleter.complete(Namer.scala:1639)
        at dotty.tools.dotc.core.SymDenotations$SymDenotation.completeFrom(SymDenotations.scala:174)
        at dotty.tools.dotc.core.Denotations$Denotation.completeInfo$1(Denotations.scala:187)
        at dotty.tools.dotc.core.Denotations$Denotation.info(Denotations.scala:189)
        at dotty.tools.dotc.core.Denotations$SingleDenotation.signature(Denotations.scala:619)
        at dotty.tools.dotc.core.Denotations$SingleDenotation.matchesLoosely(Denotations.scala:1027)
        at dotty.tools.dotc.core.Denotations$SingleDenotation.matches(Denotations.scala:1011)
        at dotty.tools.dotc.core.Denotations$SingleDenotation.filterDisjoint(Denotations.scala:1061)
        at dotty.tools.dotc.core.Denotations$SingleDenotation.mapInherited(Denotations.scala:1056)
        at dotty.tools.dotc.core.Denotations$SingleDenotation.mapInherited(Denotations.scala:1053)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.collect$1(SymDenotations.scala:2160)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.collect$1(SymDenotations.scala:2156)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.addInherited(SymDenotations.scala:2165)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.computeMembersNamed(SymDenotations.scala:2150)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.membersNamed(SymDenotations.scala:2117)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.membersNamedNoShadowingBasedOnFlags(SymDenotations.scala:2140)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.nonPrivateMembersNamed(SymDenotations.scala:2130)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.findMember(SymDenotations.scala:2168)
        at dotty.tools.dotc.core.Types$Type.go$1(Types.scala:741)
        at dotty.tools.dotc.core.Types$Type.goThis$1(Types.scala:847)
        at dotty.tools.dotc.core.Types$Type.go$1(Types.scala:758)
        at dotty.tools.dotc.core.Types$Type.findMember(Types.scala:920)
        at dotty.tools.dotc.core.Types$Type.memberBasedOnFlags(Types.scala:714)
        at dotty.tools.dotc.core.Types$Type.nonPrivateMember(Types.scala:704)
        at dotty.tools.dotc.core.Types$NamedType.memberDenot(Types.scala:2474)
        at dotty.tools.dotc.core.Types$NamedType.reload$1(Types.scala:2807)
        at dotty.tools.dotc.core.Types$NamedType.withPrefix(Types.scala:2822)
        at dotty.tools.dotc.core.Types$NamedType.derivedSelect(Types.scala:2755)
        at dotty.tools.dotc.core.Types$TypeMap.derivedSelect(Types.scala:5755)
        at dotty.tools.dotc.core.Types$ApproximatingTypeMap.derivedSelect(Types.scala:6075)
        at dotty.tools.dotc.core.TypeOps$AsSeenFromMap.apply(TypeOps.scala:103)
        at dotty.tools.dotc.core.TypeOps$AsSeenFromMap.op$proxy2$1(TypeOps.scala:103)
        at dotty.tools.dotc.core.TypeOps$AsSeenFromMap.apply(TypeOps.scala:103)
        at dotty.tools.dotc.core.Types$TypeMap.op$proxy19$1(Types.scala:5839)
        at dotty.tools.dotc.core.Types$TypeMap.mapOver(Types.scala:5839)
        at dotty.tools.dotc.core.TypeOps$AsSeenFromMap.apply(TypeOps.scala:111)
        at dotty.tools.dotc.core.TypeOps$.asSeenFrom(TypeOps.scala:56)
        at dotty.tools.dotc.core.Types$Type.asSeenFrom(Types.scala:1074)
        at dotty.tools.dotc.core.Denotations$SingleDenotation.derived$1(Denotations.scala:1094)
        at dotty.tools.dotc.core.Denotations$SingleDenotation.computeAsSeenFrom(Denotations.scala:1121)
        at dotty.tools.dotc.core.Denotations$SingleDenotation.computeAsSeenFrom(Denotations.scala:1074)
        at dotty.tools.dotc.core.Denotations$PreDenotation.asSeenFrom(Denotations.scala:134)
        at dotty.tools.dotc.core.Denotations$SingleDenotation.mapInherited(Denotations.scala:1055)
        at dotty.tools.dotc.core.Denotations$SingleDenotation.mapInherited(Denotations.scala:1053)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.collect$1(SymDenotations.scala:2160)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.collect$1(SymDenotations.scala:2156)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.addInherited(SymDenotations.scala:2165)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.computeMembersNamed(SymDenotations.scala:2150)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.membersNamed(SymDenotations.scala:2117)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.findMember(SymDenotations.scala:2168)
        at dotty.tools.dotc.core.Types$Type.go$1(Types.scala:741)
        at dotty.tools.dotc.core.Types$Type.goThis$1(Types.scala:847)
        at dotty.tools.dotc.core.Types$Type.go$1(Types.scala:758)
        at dotty.tools.dotc.core.Types$Type.findMember(Types.scala:920)
        at dotty.tools.dotc.core.Types$Type.memberBasedOnFlags(Types.scala:714)
        at dotty.tools.dotc.core.Types$Type.member(Types.scala:698)
        at dotty.tools.dotc.core.Types$nonClassTypeNameFilter$.apply(Types.scala:6574)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.maybeAdd$1(SymDenotations.scala:2346)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.computeMemberNames$$anonfun$1$$anonfun$1(SymDenotations.scala:2352)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.Set$Set1.foreach(Set.scala:168)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.computeMemberNames$$anonfun$1(SymDenotations.scala:2352)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.computeMemberNames(SymDenotations.scala:2352)
        at dotty.tools.dotc.core.SymDenotations$MemberNamesImpl.apply(SymDenotations.scala:2944)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.memberNames(SymDenotations.scala:2341)
        at dotty.tools.dotc.core.Types$Type.memberNames(Types.scala:949)
        at dotty.tools.dotc.core.Types$Type.memberDenots(Types.scala:966)
        at dotty.tools.dotc.core.Types$Type.nonClassTypeMembers(Types.scala:1013)
        at dotty.tools.dotc.core.CheckRealizable.dotty$tools$dotc$core$CheckRealizable$$boundsRealizability(CheckRealizable.scala:154)
        at dotty.tools.dotc.core.CheckRealizable.realizability(CheckRealizable.scala:128)
        at dotty.tools.dotc.core.CheckRealizable$.realizability(CheckRealizable.scala:47)
        at dotty.tools.dotc.core.Types$Type.isStable(Types.scala:186)
        at dotty.tools.dotc.core.TypeOps$.isLegalPrefix(TypeOps.scala:127)
        at dotty.tools.dotc.core.TypeOps$AsSeenFromMap.toPrefix$1(TypeOps.scala:85)
        at dotty.tools.dotc.core.TypeOps$AsSeenFromMap.apply(TypeOps.scala:107)
        at dotty.tools.dotc.core.Types$TypeMap.mapOver(Types.scala:5843)
        at dotty.tools.dotc.core.TypeOps$AsSeenFromMap.apply(TypeOps.scala:111)
        at dotty.tools.dotc.core.TypeOps$.asSeenFrom(TypeOps.scala:56)
        at dotty.tools.dotc.core.Types$Type.asSeenFrom(Types.scala:1074)
        at dotty.tools.dotc.core.Denotations$SingleDenotation.derived$1(Denotations.scala:1094)
        at dotty.tools.dotc.core.Denotations$SingleDenotation.computeAsSeenFrom(Denotations.scala:1121)
        at dotty.tools.dotc.core.Denotations$SingleDenotation.computeAsSeenFrom(Denotations.scala:1074)
        at dotty.tools.dotc.core.Denotations$PreDenotation.asSeenFrom(Denotations.scala:134)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.findMember(SymDenotations.scala:2172)
        at dotty.tools.dotc.core.Types$Type.go$1(Types.scala:741)
        at dotty.tools.dotc.core.Types$Type.goAnd$1(Types.scala:896)
        at dotty.tools.dotc.core.Types$Type.go$1(Types.scala:775)
        at dotty.tools.dotc.core.Types$Type.findMember(Types.scala:920)
        at dotty.tools.dotc.core.Types$Type.memberBasedOnFlags(Types.scala:714)
        at dotty.tools.dotc.core.Types$Type.member(Types.scala:698)
        at dotty.tools.dotc.typer.Checking$.checkNonCyclicInherited$$anonfun$1(Checking.scala:468)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.dotc.typer.Checking$.checkNonCyclicInherited(Checking.scala:476)
        at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform(PostTyper.scala:450)
        at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1537)
        at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:49)
        at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform(PostTyper.scala:476)
        at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1583)
        at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:49)
        at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform(PostTyper.scala:439)
        at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1551)
        at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:49)
        at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform(PostTyper.scala:287)
        at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform$$anonfun$1(Trees.scala:1635)
        at scala.collection.immutable.List.mapConserve(List.scala:472)
        at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1635)
        at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transformSub(Trees.scala:1639)
        at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1549)
        at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:49)
        at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform(PostTyper.scala:499)
        at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1595)
        at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:40)
        at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform$$anonfun$5(PostTyper.scala:393)
        at dotty.tools.dotc.transform.SuperAccessors.wrapDefDef(SuperAccessors.scala:229)
        at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform(PostTyper.scala:393)
        at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.loop$2(tpd.scala:1250)
        at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1250)
        at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transformStats(PostTyper.scala:508)
        at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1252)
        at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:47)
        at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform$$anonfun$4$$anonfun$1(PostTyper.scala:378)
        at dotty.tools.dotc.transform.SuperAccessors.wrapTemplate(SuperAccessors.scala:214)
        at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform$$anonfun$4(PostTyper.scala:378)
        at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.withNoCheckNews(PostTyper.scala:109)
        at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform(PostTyper.scala:380)
        at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1597)
        at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:40)
        at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform(PostTyper.scala:435)
        at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.loop$2(tpd.scala:1250)
        at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1250)
        at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transformStats(PostTyper.scala:508)
        at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1252)
        at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1608)
        at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:40)
        at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform(PostTyper.scala:499)
        at dotty.tools.dotc.transform.MacroTransform.run(MacroTransform.scala:18)
        at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:327)
        at scala.collection.immutable.List.map(List.scala:250)
        at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:331)
        at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:246)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1321)
        at dotty.tools.dotc.Run.runPhases$1(Run.scala:262)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:270)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:279)
        at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:71)
        at dotty.tools.dotc.Run.compileUnits(Run.scala:279)
        at dotty.tools.dotc.Run.compileSources(Run.scala:194)
        at dotty.tools.dotc.Run.compile(Run.scala:179)
        at dotty.tools.dotc.Driver.doCompile(Driver.scala:37)
        at dotty.tools.dotc.Driver.process(Driver.scala:197)
        at dotty.tools.dotc.Driver.process(Driver.scala:165)
        at dotty.tools.dotc.Driver.process(Driver.scala:177)
        at dotty.tools.dotc.Driver.main(Driver.scala:207)

So a symbol is completed during PostTyper by calling SuspendCompleter#complete which throws SuspendException, but we only catch SuspendException in Typer and Inliner. Explicitly catching the exception in MacroTransform.scala fixes the error:

diff --git compiler/src/dotty/tools/dotc/transform/MacroTransform.scala compiler/src/dotty/tools/dotc/transform/MacroTransform.scala
index 7bb7ed365eb..325e32d0de6 100644
--- compiler/src/dotty/tools/dotc/transform/MacroTransform.scala
+++ compiler/src/dotty/tools/dotc/transform/MacroTransform.scala
@@ -15,7 +15,8 @@ abstract class MacroTransform extends Phase {

   override def run(using Context): Unit = {
     val unit = ctx.compilationUnit
-    unit.tpdTree = atPhase(transformPhase)(newTransformer.transform(unit.tpdTree))
+    try unit.tpdTree = atPhase(transformPhase)(newTransformer.transform(unit.tpdTree))
+    catch case _: CompilationUnit.SuspendException => ()
   }

   protected def newTransformer(using Context): Transformer

But it's not clear to me if this is a valid way to use SuspendException, wdyt @odersky ?

[odersky]

I think it's probably OK. Maybe only do it for PostTyper, and leave generral macro transforms alone?

[smarter]

I would prefer to do it for all phases unless we can guarantee that SuspendCompleter will always be completed at a specific phase?

[odersky]

It should be completed after inlining, I think.

[smarter]

It should be completed after inlining, I think.

In fact it can happen later than inlining, here's a crash I just got in PruneErasedDefs#transformSym indirectly called from Mixin#tranformSym:

[error] ## Exception when compiling 17 sources to /home/smarter/forj/sw/forj_core/target/scala-3.6.0-RC1-bin-SNAPSHOT/classes
[error] dotty.tools.dotc.CompilationUnit$SuspendException
[error] dotty.tools.dotc.CompilationUnit.suspend(CompilationUnit.scala:110)
[error] dotty.tools.dotc.typer.Namer$SuspendCompleter.complete(Namer.scala:1746)
[error] dotty.tools.dotc.core.SymDenotations$SymDenotation.completeFrom(SymDenotations.scala:175)
[error] dotty.tools.dotc.core.Denotations$Denotation.completeInfo$1(Denotations.scala:190)
[error] dotty.tools.dotc.core.Denotations$Denotation.info(Denotations.scala:192)
[error] dotty.tools.dotc.core.SymDenotations$SymDenotation.ensureCompleted(SymDenotations.scala:393)
[error] dotty.tools.dotc.core.SymDenotations$SymDenotation.flags(SymDenotations.scala:66)
[error] dotty.tools.dotc.core.SymDenotations$SymDenotation.isOneOf(SymDenotations.scala:116)
[error] dotty.tools.dotc.core.SymDenotations$SymDenotation.isEffectivelyErased(SymDenotations.scala:1033)
[error] dotty.tools.dotc.transform.PruneErasedDefs.transformSym(PruneErasedDefs.scala:39)
[error] dotty.tools.dotc.core.DenotTransformers$SymTransformer.transform(DenotTransformers.scala:72)
[error] dotty.tools.dotc.core.DenotTransformers$SymTransformer.transform$(DenotTransformers.scala:67)
[error] dotty.tools.dotc.transform.PruneErasedDefs.transform(PruneErasedDefs.scala:26)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:838)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:855)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:855)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:855)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:855)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:855)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:855)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:855)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:855)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:855)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:855)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:855)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:855)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:855)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Symbols$Symbol.recomputeDenot(Symbols.scala:124)
[error] dotty.tools.dotc.core.Symbols$Symbol.computeDenot(Symbols.scala:118)
[error] dotty.tools.dotc.core.Symbols$Symbol.denot(Symbols.scala:109)
[error] dotty.tools.dotc.core.Symbols$.toDenot(Symbols.scala:544)
[error] dotty.tools.dotc.transform.Mixin.needsTraitSetter(Mixin.scala:176)
[error] dotty.tools.dotc.transform.Mixin.transformSym$$anonfun$1(Mixin.scala:155)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.immutable.List.foreach(List.scala:334)
[error] dotty.tools.dotc.core.Scopes$Scope.foreach(Scopes.scala:94)
[error] dotty.tools.dotc.transform.Mixin.transformSym(Mixin.scala:159)
[error] dotty.tools.dotc.core.DenotTransformers$SymTransformer.transform(DenotTransformers.scala:72)
[error] dotty.tools.dotc.core.DenotTransformers$SymTransformer.transform$(DenotTransformers.scala:67)
[error] dotty.tools.dotc.transform.Mixin.transform(Mixin.scala:115)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:838)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:855)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:855)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:855)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.goForward$1(Denotations.scala:855)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:884)
[error] dotty.tools.dotc.core.Types$NamedType.computeDenot(Types.scala:2481)
[error] dotty.tools.dotc.core.Types$NamedType.denot(Types.scala:2444)
[error] dotty.tools.dotc.core.Types$NamedType.info(Types.scala:2433)
[error] dotty.tools.dotc.core.TypeComparer.compareNamed$1(TypeComparer.scala:306)
[error] dotty.tools.dotc.core.TypeComparer.firstTry$1(TypeComparer.scala:357)
[error] dotty.tools.dotc.core.TypeComparer.recur(TypeComparer.scala:1594)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:229)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:239)
[error] dotty.tools.dotc.core.TypeComparer.topLevelSubType(TypeComparer.scala:147)
[error] dotty.tools.dotc.core.TypeComparer$.topLevelSubType(TypeComparer.scala:3342)
[error] dotty.tools.dotc.core.Types$Type.$less$colon$less(Types.scala:1127)
[error] dotty.tools.dotc.ast.tpd$TreeOps$.ensureConforms$extension(tpd.scala:1047)
[error] dotty.tools.dotc.transform.Memoize.adaptToField$1(Memoize.scala:133)
[error] dotty.tools.dotc.transform.Memoize.transformDefDef(Memoize.scala:148)
[error] dotty.tools.dotc.transform.MegaPhase.goDefDef(MegaPhase.scala:1041)
[error] dotty.tools.dotc.transform.MegaPhase.goDefDef(MegaPhase.scala:1042)
[error] dotty.tools.dotc.transform.MegaPhase.goDefDef(MegaPhase.scala:1042)
[error] dotty.tools.dotc.transform.MegaPhase.goDefDef(MegaPhase.scala:1042)
[error] dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:268)
[error] dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:452)
[error] dotty.tools.dotc.transform.MegaPhase.loop$1(MegaPhase.scala:465)
[error] dotty.tools.dotc.transform.MegaPhase.transformStats(MegaPhase.scala:465)
[error] dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:376)
[error] dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
[error] dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:272)
[error] dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:452)
[error] dotty.tools.dotc.transform.MegaPhase.loop$1(MegaPhase.scala:465)
[error] dotty.tools.dotc.transform.MegaPhase.transformStats(MegaPhase.scala:465)
[error] dotty.tools.dotc.transform.MegaPhase.mapPackage$1(MegaPhase.scala:396)
[error] dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:399)
[error] dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
[error] dotty.tools.dotc.transform.MegaPhase.loop$1(MegaPhase.scala:465)
[error] dotty.tools.dotc.transform.MegaPhase.transformStats(MegaPhase.scala:465)
[error] dotty.tools.dotc.transform.MegaPhase.mapPackage$1(MegaPhase.scala:396)
[error] dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:399)
[error] dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
[error] dotty.tools.dotc.transform.MegaPhase.transformUnit(MegaPhase.scala:481)
[error] dotty.tools.dotc.transform.MegaPhase.run(MegaPhase.scala:493)
[error] dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:380)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.immutable.List.foreach(List.scala:334)
[error] dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:373)
[error] dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:343)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
[error] dotty.tools.dotc.Run.runPhases$1(Run.scala:336)
[error] dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:384)
[error] dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:396)
[error] dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:69)
[error] dotty.tools.dotc.Run.compileUnits(Run.scala:396)
[error] dotty.tools.dotc.Run.compileSources(Run.scala:282)
[error] dotty.tools.dotc.Run.compile(Run.scala:267)
[error] dotty.tools.dotc.Driver.doCompile(Driver.scala:37)
[error] dotty.tools.xsbt.CompilerBridgeDriver.run(CompilerBridgeDriver.java:141)
[error] dotty.tools.xsbt.CompilerBridge.run(CompilerBridge.java:22)
[error] sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:91)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$7(MixedAnalyzingCompiler.scala:194)
[error] scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
[error] sbt.internal.inc.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:249)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4(MixedAnalyzingCompiler.scala:184)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4$adapted(MixedAnalyzingCompiler.scala:164)
[error] sbt.internal.inc.JarUtils$.withPreviousJar(JarUtils.scala:239)
[error] sbt.internal.inc.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:164)
[error] sbt.internal.inc.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:212)
[error] sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1(IncrementalCompilerImpl.scala:534)
[error] sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1$adapted(IncrementalCompilerImpl.scala:534)
[error] sbt.internal.inc.Incremental$.$anonfun$apply$3(Incremental.scala:178)
[error] sbt.internal.inc.Incremental$.$anonfun$apply$3$adapted(Incremental.scala:176)
[error] sbt.internal.inc.Incremental$$anon$2.run(Incremental.scala:454)
[error] sbt.internal.inc.IncrementalCommon$CycleState.next(IncrementalCommon.scala:117)
[error] sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:56)
[error] sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:52)
[error] sbt.internal.inc.IncrementalCommon.cycle(IncrementalCommon.scala:265)
[error] sbt.internal.inc.Incremental$.$anonfun$incrementalCompile$8(Incremental.scala:409)
[error] sbt.internal.inc.Incremental$.withClassfileManager(Incremental.scala:496)
[error] sbt.internal.inc.Incremental$.incrementalCompile(Incremental.scala:396)
[error] sbt.internal.inc.Incremental$.apply(Incremental.scala:170)
[error] sbt.internal.inc.IncrementalCompilerImpl.compileInternal(IncrementalCompilerImpl.scala:534)
[error] sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileIncrementally$1(IncrementalCompilerImpl.scala:488)
[error] sbt.internal.inc.IncrementalCompilerImpl.handleCompilationError(IncrementalCompilerImpl.scala:332)
[error] sbt.internal.inc.IncrementalCompilerImpl.compileIncrementally(IncrementalCompilerImpl.scala:425)
[error] sbt.internal.inc.IncrementalCompilerImpl.compile(IncrementalCompilerImpl.scala:137)
[error] sbt.Defaults$.compileIncrementalTaskImpl(Defaults.scala:2427)
[error] sbt.Defaults$.$anonfun$compileIncrementalTask$2(Defaults.scala:2377)
[error] sbt.internal.server.BspCompileTask$.$anonfun$compute$1(BspCompileTask.scala:41)
[error] sbt.internal.io.Retry$.apply(Retry.scala:47)
[error] sbt.internal.io.Retry$.apply(Retry.scala:29)
[error] sbt.internal.io.Retry$.apply(Retry.scala:24)
[error] sbt.internal.server.BspCompileTask$.compute(BspCompileTask.scala:41)
[error] sbt.Defaults$.$anonfun$compileIncrementalTask$1(Defaults.scala:2375)
[error] scala.Function1.$anonfun$compose$1(Function1.scala:49)
[error] sbt.internal.util.$tilde$greater.$anonfun$$u2219$1(TypeFunctions.scala:63)
[error] sbt.std.Transform$$anon$4.work(Transform.scala:69)
[error] sbt.Execute.$anonfun$submit$2(Execute.scala:283)
[error] sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:24)
[error] sbt.Execute.work(Execute.scala:292)
[error] sbt.Execute.$anonfun$submit$1(Execute.scala:283)
[error] sbt.ConcurrentRestrictions$$anon$4.$anonfun$submitValid$1(ConcurrentRestrictions.scala:265)
[error] sbt.CompletionService$$anon$2.call(CompletionService.scala:65)
[error] java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317)
[error] java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:572)
[error] java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317)
[error] java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
[error] java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
[error] java.base/java.lang.Thread.run(Thread.java:1583)

The change I originally proposed in MacroTransform is not enough to handle this since PruneErasedDefs is a MiniPhase, I tried catching it in Phase:

diff --git compiler/src/dotty/tools/dotc/core/Phases.scala compiler/src/dotty/tools/dotc/core/Phases.scala
index 7f925b0fc3..73fd170959 100644
--- compiler/src/dotty/tools/dotc/core/Phases.scala
+++ compiler/src/dotty/tools/dotc/core/Phases.scala
@@ -378,9 +378,11 @@ object Phases {
               ()
             else
               run
-          catch case ex: Throwable if !ctx.run.enrichedErrorMessage =>
-            println(ctx.run.enrichErrorMessage(s"unhandled exception while running $phaseName on $unit"))
-            throw ex
+          catch
+            case _: CompilationUnit.SuspendException => // this unit will be run again in `Run#compileSuspendedUnits`
+            case ex: Throwable if !ctx.run.enrichedErrorMessage =>
+              println(ctx.run.enrichErrorMessage(s"unhandled exception while running $phaseName on $unit"))
+              throw ex
           finally ctx.run.advanceUnit()
           buf += unitCtx.compilationUnit
         end if

But that seems to lead to an infinite loop in my case.

[smarter]

Ok, here's a patch that seems to do the correct thing, I'll submit a PR:

diff --git compiler/src/dotty/tools/dotc/core/Phases.scala compiler/src/dotty/tools/dotc/core/Phases.scala
index 7f925b0fc3..a438c9fcf5 100644
--- compiler/src/dotty/tools/dotc/core/Phases.scala
+++ compiler/src/dotty/tools/dotc/core/Phases.scala
@@ -378,14 +378,18 @@ object Phases {
               ()
             else
               run
-          catch case ex: Throwable if !ctx.run.enrichedErrorMessage =>
-            println(ctx.run.enrichErrorMessage(s"unhandled exception while running $phaseName on $unit"))
-            throw ex
+            buf += unitCtx.compilationUnit
+          catch
+            case _: CompilationUnit.SuspendException => // this unit will be run again in `Run#compileSuspendedUnits`
+            case ex: Throwable if !ctx.run.enrichedErrorMessage =>
+              println(ctx.run.enrichErrorMessage(s"unhandled exception while running $phaseName on $unit"))
+              throw ex
           finally ctx.run.advanceUnit()
-          buf += unitCtx.compilationUnit
         end if
       end for
-      buf.result()
+      val res = buf.result()
+      ctx.run.nn.checkSuspendedUnits(res)
+      res
     end runOn

     /** Convert a compilation unit's tree to a string; can be overridden */