Handle TypeProxy of Named Tuples in unapply (#22325)

Fixes #22150.
Previously, there were several ways to check if something was a Named
Tuple (`derivesFromNamedTuple`, `isNamedTupleType` and
`NamedTuple.unapply`), this PR moves everything into
`NamedTuple.unapply`. `namedTupleElementTypes` now takes an argument
`derived` that when false will skip `unapply` (to avoid infinite
recursion, used in desugaring and RefinedPrinter where trees can have
invalid cycles).

Author: odersky

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -1744,7 +1744,7 @@ object desugar {
   def adaptPatternArgs(elems: List[Tree], pt: Type)(using Context): List[Tree] =
 
     def reorderedNamedArgs(wildcardSpan: Span): List[untpd.Tree] =
-      var selNames = pt.namedTupleElementTypes.map(_(0))
+      var selNames = pt.namedTupleElementTypes(false).map(_(0))
       if selNames.isEmpty && pt.classSymbol.is(CaseClass) then
         selNames = pt.classSymbol.caseAccessors.map(_.name.asTermName)
       val nameToIdx = selNames.zipWithIndex.toMap

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

@@ -1337,10 +1337,25 @@ class Definitions {
   object NamedTuple:
     def apply(nmes: Type, vals: Type)(using Context): Type =
       AppliedType(NamedTupleTypeRef, nmes :: vals :: Nil)
-    def unapply(t: Type)(using Context): Option[(Type, Type)] = t match
-      case AppliedType(tycon, nmes :: vals :: Nil) if tycon.typeSymbol == NamedTupleTypeRef.symbol =>
-        Some((nmes, vals))
-      case _ => None
+    def unapply(t: Type)(using Context): Option[(Type, Type)] =
+      t match
+        case AppliedType(tycon, nmes :: vals :: Nil) if tycon.typeSymbol == NamedTupleTypeRef.symbol =>
+          Some((nmes, vals))
+        case tp: TypeProxy =>
+          val t = unapply(tp.superType); t
+        case tp: OrType =>
+          (unapply(tp.tp1), unapply(tp.tp2)) match
+            case (Some(lhsName, lhsVal), Some(rhsName, rhsVal)) if lhsName == rhsName =>
+              Some(lhsName, lhsVal | rhsVal)
+            case _ => None
+        case tp: AndType =>
+          (unapply(tp.tp1), unapply(tp.tp2)) match
+            case (Some(lhsName, lhsVal), Some(rhsName, rhsVal)) if lhsName == rhsName =>
+              Some(lhsName, lhsVal & rhsVal)
+            case (lhs, None) => lhs
+            case (None, rhs) => rhs
+            case _ => None
+        case _ => None
 
   final def isCompiletime_S(sym: Symbol)(using Context): Boolean =
     sym.name == tpnme.S && sym.owner == CompiletimeOpsIntModuleClass

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

@@ -127,8 +127,17 @@ class TypeUtils:
         case Some(types) => TypeOps.nestedPairs(types)
         case None => throw new AssertionError("not a tuple")
 
-    def namedTupleElementTypesUpTo(bound: Int, normalize: Boolean = true)(using Context): List[(TermName, Type)] =
+    def namedTupleElementTypesUpTo(bound: Int, derived: Boolean, normalize: Boolean = true)(using Context): List[(TermName, Type)] =
       (if normalize then self.normalized else self).dealias match
+        // for desugaring and printer, ignore derived types to avoid infinite recursion in NamedTuple.unapply
+        case AppliedType(tycon, nmes :: vals :: Nil) if !derived && tycon.typeSymbol == defn.NamedTupleTypeRef.symbol =>
+          val names = nmes.tupleElementTypesUpTo(bound, normalize).getOrElse(Nil).map(_.dealias).map:
+            case ConstantType(Constant(str: String)) => str.toTermName
+            case t => throw TypeError(em"Malformed NamedTuple: names must be string types, but $t was found.")
+          val values = vals.tupleElementTypesUpTo(bound, normalize).getOrElse(Nil)
+          names.zip(values)
+        case t if !derived => Nil
+        // default cause, used for post-typing
         case defn.NamedTuple(nmes, vals) =>
           val names = nmes.tupleElementTypesUpTo(bound, normalize).getOrElse(Nil).map(_.dealias).map:
             case ConstantType(Constant(str: String)) => str.toTermName
@@ -138,22 +147,13 @@ class TypeUtils:
         case t =>
           Nil
 
-    def namedTupleElementTypes(using Context): List[(TermName, Type)] =
-      namedTupleElementTypesUpTo(Int.MaxValue)
+    def namedTupleElementTypes(derived: Boolean)(using Context): List[(TermName, Type)] =
+      namedTupleElementTypesUpTo(Int.MaxValue, derived)
 
     def isNamedTupleType(using Context): Boolean = self match
       case defn.NamedTuple(_, _) => true
       case _ => false
 
-    def derivesFromNamedTuple(using Context): Boolean = self match
-      case defn.NamedTuple(_, _) => true
-      case tp: MatchType =>
-        tp.bound.derivesFromNamedTuple || tp.reduced.derivesFromNamedTuple
-      case tp: TypeProxy => tp.superType.derivesFromNamedTuple
-      case tp: AndType => tp.tp1.derivesFromNamedTuple || tp.tp2.derivesFromNamedTuple
-      case tp: OrType => tp.tp1.derivesFromNamedTuple && tp.tp2.derivesFromNamedTuple
-      case _ => false
-
     /** Drop all named elements in tuple type */
     def stripNamedTuple(using Context): Type = self.normalized.dealias match
       case defn.NamedTuple(_, vals) =>

compiler/src/dotty/tools/dotc/interactive/Completion.scala

@@ -532,7 +532,7 @@ object Completion:
       def namedTupleCompletionsFromType(tpe: Type): CompletionMap =
         val freshCtx = ctx.fresh.setExploreTyperState()
         inContext(freshCtx):
-          tpe.namedTupleElementTypes
+          tpe.namedTupleElementTypes(true)
             .map { (name, tpe) =>
               val symbol = newSymbol(owner = NoSymbol, name, EmptyFlags, tpe)
               val denot = SymDenotation(symbol, NoSymbol, name, EmptyFlags, tpe)
@@ -543,7 +543,7 @@ object Completion:
             .groupByName
 
       val qualTpe = qual.typeOpt
-      if qualTpe.derivesFromNamedTuple then
+      if qualTpe.isNamedTupleType then
         namedTupleCompletionsFromType(qualTpe)
       else if qualTpe.derivesFrom(defn.SelectableClass) then
         val pre = if !TypeOps.isLegalPrefix(qualTpe) then Types.SkolemType(qualTpe) else qualTpe

compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -248,8 +248,9 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
     def appliedText(tp: Type): Text = tp match
       case tp @ AppliedType(tycon, args) =>
         val namedElems =
-          try tp.namedTupleElementTypesUpTo(200, normalize = false)
-          catch case ex: TypeError => Nil
+          try tp.namedTupleElementTypesUpTo(200, false, normalize = false)
+          catch
+            case ex: TypeError => Nil
         if namedElems.nonEmpty then
           toTextNamedTuple(namedElems)
         else tp.tupleElementTypesUpTo(200, normalize = false) match

compiler/src/dotty/tools/dotc/typer/Applications.scala

@@ -110,7 +110,7 @@ object Applications {
   }
 
   def namedTupleOrProductTypes(tp: Type)(using Context): List[Type] =
-    if tp.isNamedTupleType then tp.namedTupleElementTypes.map(_(1))
+    if tp.isNamedTupleType then tp.namedTupleElementTypes(true).map(_(1))
     else productSelectorTypes(tp, NoSourcePosition)
 
   def productSelectorTypes(tp: Type, errorPos: SrcPos)(using Context): List[Type] = {

compiler/src/dotty/tools/dotc/typer/Implicits.scala

@@ -876,7 +876,7 @@ trait Implicits:
        || inferView(dummyTreeOfType(from), to)
             (using ctx.fresh.addMode(Mode.ImplicitExploration).setExploreTyperState()).isSuccess
           // TODO: investigate why we can't TyperState#test here
-       || from.widen.derivesFromNamedTuple && to.derivesFrom(defn.TupleClass)
+       || from.widen.isNamedTupleType && to.derivesFrom(defn.TupleClass)
            && from.widen.stripNamedTuple <:< to
        )
 

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -799,7 +799,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
 
     // Otherwise, try to expand a named tuple selection
     def tryNamedTupleSelection() =
-      val namedTupleElems = qual.tpe.widenDealias.namedTupleElementTypes
+      val namedTupleElems = qual.tpe.widenDealias.namedTupleElementTypes(true)
       val nameIdx = namedTupleElems.indexWhere(_._1 == selName)
       if nameIdx >= 0 && Feature.enabled(Feature.namedTuples) then
         typed(
@@ -875,7 +875,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
       then
         val pre = if !TypeOps.isLegalPrefix(qual.tpe) then SkolemType(qual.tpe) else qual.tpe
         val fieldsType = pre.select(tpnme.Fields).widenDealias.simplified
-        val fields = fieldsType.namedTupleElementTypes
+        val fields = fieldsType.namedTupleElementTypes(true)
         typr.println(i"try dyn select $qual, $selName, $fields")
         fields.find(_._1 == selName) match
           case Some((_, fieldType)) =>
@@ -4663,7 +4663,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
         case _: SelectionProto =>
           tree // adaptations for selections are handled in typedSelect
         case _ if ctx.mode.is(Mode.ImplicitsEnabled) && tree.tpe.isValueType =>
-          if tree.tpe.derivesFromNamedTuple && pt.derivesFrom(defn.TupleClass) then
+          if tree.tpe.isNamedTupleType && pt.derivesFrom(defn.TupleClass) then
             readapt(typed(untpd.Select(untpd.TypedSplice(tree), nme.toTuple)))
           else if pt.isRef(defn.AnyValClass, skipRefined = false)
               || pt.isRef(defn.ObjectClass, skipRefined = false)

tests/run/i22150.check

@@ -0,0 +1,3 @@
+0
+1
+2

tests/run/i22150.scala

@@ -0,0 +1,26 @@
+//> using options -experimental -language:experimental.namedTuples
+import language.experimental.namedTuples
+
+val directionsNT = IArray(
+  (dx = 0, dy = 1), // up
+  (dx = 1, dy = 0), // right
+  (dx = 0, dy = -1), // down
+  (dx = -1, dy = 0), // left
+)
+val IArray(UpNT @ _, _, _, _) = directionsNT
+
+object NT:
+  def foo[T <: (x: Int, y: String)](tup: T): Int =
+    tup.x
+
+  def union[T](tup: (x: Int, y: String) | (x: Int, y: String)): Int =
+    tup.x
+
+  def intersect[T](tup: (x: Int, y: String) & T): Int =
+    tup.x
+
+
+@main def Test =
+  println(UpNT.dx)
+  println(NT.union((1, "a")))
+  println(NT.intersect((2, "b")))