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Support Mirror for generic tuples arity > 22 #23363

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Support Mirror for generic tuples arity > 22 #23363

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22 changes: 13 additions & 9 deletions compiler/src/dotty/tools/dotc/typer/Synthesizer.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -432,13 +432,24 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
makeProductMirror(typeElems, elemLabels, tpnme.NamedTuple, mirrorRef)
end makeNamedTupleProductMirror

def makeTupleProductMirror(tps: List[Type]): TreeWithErrors =
val arity = tps.size
if arity < Definitions.MaxTupleArity then
val tupleCls = defn.TupleType(arity).nn.classSymbol
makeClassProductMirror(tupleCls.owner.reachableThisType, tupleCls, Some(tps))
else
val elemLabels = (for i <- 1 to arity yield ConstantType(Constant(s"_$i"))).toList
val mirrorRef: Type => Tree = _ => newTupleMirror(arity)
makeProductMirror(tps, elemLabels, s"Tuple$arity".toTermName, mirrorRef)
end makeTupleProductMirror

def makeClassProductMirror(pre: Type, cls: Symbol, tps: Option[List[Type]]) =
val accessors = cls.caseAccessors
val elemLabels = accessors.map(acc => ConstantType(Constant(acc.name.toString)))
val typeElems = tps.getOrElse(accessors.map(mirroredType.resultType.memberInfo(_).widenExpr))
val mirrorRef = (monoType: Type) =>
if cls.useCompanionAsProductMirror then companionPath(pre, cls, span)
else if defn.isTupleClass(cls) then newTupleMirror(typeElems.size) // TODO: cls == defn.PairClass when > 22
else if defn.isTupleClass(cls) then newTupleMirror(typeElems.size)
else anonymousMirror(monoType, MirrorImpl.OfProduct(pre), span)
makeProductMirror(typeElems, elemLabels, cls.name, mirrorRef)
end makeClassProductMirror
Expand Down Expand Up @@ -478,14 +489,7 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
}
withNoErrors(singletonPath.cast(mirrorType).withSpan(span))
case MirrorSource.GenericTuple(tps) =>
val maxArity = Definitions.MaxTupleArity
val arity = tps.size
if tps.size <= maxArity then
val tupleCls = defn.TupleType(arity).nn.classSymbol
makeClassProductMirror(tupleCls.owner.reachableThisType, tupleCls, Some(tps))
else
val reason = s"it reduces to a tuple with arity $arity, expected arity <= $maxArity"
withErrors(i"${defn.PairClass} is not a generic product because $reason")
makeTupleProductMirror(tps)
case MirrorSource.NamedTuple(nameTypePairs) =>
makeNamedTupleProductMirror(nameTypePairs)
case MirrorSource.ClassSymbol(pre, cls) =>
Expand Down
0 tests/neg/i14127.scala → tests/pos/i14127.scala
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9 changes: 9 additions & 0 deletions tests/pos/i15398.scala
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Original file line number Diff line number Diff line change
@@ -0,0 +1,9 @@
object i15398 {
type Tuple23 = (Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int)

summon[Tuple.Size[Tuple23] =:= 23]
val m = summon[scala.deriving.Mirror.Of[Tuple23]]
summon[m.MirroredLabel =:= "Tuple23"]
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@bishabosha bishabosha Jun 14, 2025 •
edited
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I guess this is the main bike-shedding moment - i.e. should it include arity, or just Tuple (or another variant) - i.e. case class can evolve over time to add new fields but its MirroredLabel doesn't change - so I dont think unique label is necessary.

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should also update the docs (or create an issue to) for Mirror generation here https://www.scala-lang.org/api/3.7.1/docs/docs/reference/contextual/derivation.html

summon[m.MirroredElemTypes =:= Tuple23]
summon[m.MirroredElemLabels =:= ("_1", "_2", "_3", "_4", "_5", "_6", "_7", "_8", "_9", "_10", "_11", "_12", "_13", "_14", "_15", "_16", "_17", "_18", "_19", "_20", "_21", "_22", "_23")]
}
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