Support for named tuples with new representation

Author: odersky

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

@@ -9,10 +9,10 @@ import Decorators.*
 import Annotations.Annotation
 import NameKinds.{UniqueName, ContextBoundParamName, ContextFunctionParamName, DefaultGetterName, WildcardParamName}
 import typer.{Namer, Checking}
-import util.{Property, SourceFile, SourcePosition, Chars}
+import util.{Property, SourceFile, SourcePosition, SrcPos, Chars}
 import config.Feature.{sourceVersion, migrateTo3, enabled}
 import config.SourceVersion.*
-import collection.mutable.ListBuffer
+import collection.mutable
 import reporting.*
 import annotation.constructorOnly
 import printing.Formatting.hl
@@ -248,7 +248,7 @@ object desugar {
 
   private def elimContextBounds(meth: DefDef, isPrimaryConstructor: Boolean)(using Context): DefDef =
     val DefDef(_, paramss, tpt, rhs) = meth
-    val evidenceParamBuf = ListBuffer[ValDef]()
+    val evidenceParamBuf = mutable.ListBuffer[ValDef]()
 
     var seenContextBounds: Int = 0
     def desugarContextBounds(rhs: Tree): Tree = rhs match
@@ -1454,22 +1454,101 @@ object desugar {
       AppliedTypeTree(
         TypeTree(defn.throwsAlias.typeRef).withSpan(op.span), tpt :: excepts :: Nil)
 
+  private def checkWellFormedTupleElems(elems: List[Tree])(using Context): List[Tree] =
+    val seen = mutable.Set[Name]()
+    for case arg @ NamedArg(name, _) <- elems do
+      if seen.contains(name) then
+        report.error(em"Duplicate tuple element name", arg.srcPos)
+      seen += name
+      if name.startsWith("_") && name.toString.tail.toIntOption.isDefined then
+        report.error(
+            em"$name cannot be used as the name of a tuple element because it is a regular tuple selector",
+            arg.srcPos)
+
+    elems match
+    case elem :: elems1 =>
+      val mismatchOpt =
+        if elem.isInstanceOf[NamedArg]
+        then elems1.find(!_.isInstanceOf[NamedArg])
+        else elems1.find(_.isInstanceOf[NamedArg])
+      mismatchOpt match
+        case Some(misMatch) =>
+          report.error(em"Illegal combination of named and unnamed tuple elements", misMatch.srcPos)
+          elems.mapConserve(dropNamedArg)
+        case None => elems
+    case _ => elems
+  end checkWellFormedTupleElems
+
   /** Translate tuple expressions of arity <= 22
    *
    *     ()             ==>   ()
    *     (t)            ==>   t
    *     (t1, ..., tN)  ==>   TupleN(t1, ..., tN)
    */
-  def smallTuple(tree: Tuple)(using Context): Tree = {
-    val ts = tree.trees
-    val arity = ts.length
-    assert(arity <= Definitions.MaxTupleArity)
-    def tupleTypeRef = defn.TupleType(arity).nn
-    if (arity == 0)
-      if (ctx.mode is Mode.Type) TypeTree(defn.UnitType) else unitLiteral
-    else if (ctx.mode is Mode.Type) AppliedTypeTree(ref(tupleTypeRef), ts)
-    else Apply(ref(tupleTypeRef.classSymbol.companionModule.termRef), ts)
-  }
+  def tuple(tree: Tuple, pt: Type)(using Context): Tree =
+    var elems = checkWellFormedTupleElems(tree.trees)
+    if ctx.mode.is(Mode.Pattern) then elems = adaptPatternArgs(elems, pt)
+    val elemValues = elems.mapConserve(dropNamedArg)
+    val tup =
+      val arity = elems.length
+      if arity <= Definitions.MaxTupleArity then
+        def tupleTypeRef = defn.TupleType(arity).nn
+        val tree1 =
+          if arity == 0 then
+            if ctx.mode is Mode.Type then TypeTree(defn.UnitType) else unitLiteral
+          else if ctx.mode is Mode.Type then AppliedTypeTree(ref(tupleTypeRef), elemValues)
+          else Apply(ref(tupleTypeRef.classSymbol.companionModule.termRef), elemValues)
+        tree1.withSpan(tree.span)
+      else
+        cpy.Tuple(tree)(elemValues)
+    val names = elems.collect:
+      case NamedArg(name, arg) => name
+    if names.isEmpty || ctx.mode.is(Mode.Pattern) then
+      tup
+    else
+      def namesTuple = inMode(ctx.mode &~ Mode.Pattern | Mode.Type):
+        tuple(Tuple(
+          names.map: name =>
+            SingletonTypeTree(Literal(Constant(name.toString))).withSpan(tree.span)),
+          WildcardType)
+      if ctx.mode.is(Mode.Type) then
+        AppliedTypeTree(ref(defn.NamedTupleTypeRef), namesTuple :: tup :: Nil)
+      else
+        TypeApply(
+          Apply(Select(ref(defn.NamedTupleModule), nme.withNames), tup),
+          namesTuple :: Nil)
+
+  /** When desugaring a list pattern arguments `elems` adapt them and the
+   *  expected type `pt` to each other. This means:
+   *   - If `elems` are named pattern elements, rearrange them to match `pt`.
+   *     This requires all names in `elems` to be also present in `pt`.
+   *   - If `elems` are unnamed elements, and `pt` is a named tuple, drop all
+   *     tuple element names from `pt`.
+   */
+  def adaptPatternArgs(elems: List[Tree], pt: Type)(using Context): List[Tree] =
+
+    def reorderedNamedArgs(wildcardSpan: Span): List[untpd.Tree] =
+      var selNames = pt.namedTupleElementTypes.map(_(0))
+      if selNames.isEmpty && pt.classSymbol.is(CaseClass) then
+        selNames = pt.classSymbol.caseAccessors.map(_.name.asTermName)
+      val nameToIdx = selNames.zipWithIndex.toMap
+      val reordered = Array.fill[untpd.Tree](selNames.length):
+        untpd.Ident(nme.WILDCARD).withSpan(wildcardSpan)
+      for case arg @ NamedArg(name: TermName, _) <- elems do
+        nameToIdx.get(name) match
+          case Some(idx) =>
+            if reordered(idx).isInstanceOf[Ident] then
+              reordered(idx) = arg
+            else
+              report.error(em"Duplicate named pattern", arg.srcPos)
+          case _ =>
+            report.error(em"No element named `$name` is defined in selector type $pt", arg.srcPos)
+      reordered.toList
+
+    elems match
+      case (first @ NamedArg(_, _)) :: _ => reorderedNamedArgs(first.span.startPos)
+      case _ => elems
+  end adaptPatternArgs
 
   private def isTopLevelDef(stat: Tree)(using Context): Boolean = stat match
     case _: ValDef | _: PatDef | _: DefDef | _: Export | _: ExtMethods => true
@@ -1986,7 +2065,7 @@ object desugar {
    *  without duplicates
    */
   private def getVariables(tree: Tree, shouldAddGiven: Context ?=> Bind => Boolean)(using Context): List[VarInfo] = {
-    val buf = ListBuffer[VarInfo]()
+    val buf = mutable.ListBuffer[VarInfo]()
     def seenName(name: Name) = buf exists (_._1.name == name)
     def add(named: NameTree, t: Tree): Unit =
       if (!seenName(named.name) && named.name.isTermName) buf += ((named, t))

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

@@ -244,6 +244,10 @@ trait TreeInfo[T <: Untyped] { self: Trees.Instance[T] =>
   def hasNamedArg(args: List[Any]): Boolean = args exists isNamedArg
   val isNamedArg: Any => Boolean = (arg: Any) => arg.isInstanceOf[Trees.NamedArg[?]]
 
+  def dropNamedArg(arg: Tree) = arg match
+    case NamedArg(_, arg1) => arg1
+    case arg => arg
+
   /** Is this pattern node a catch-all (wildcard or variable) pattern? */
   def isDefaultCase(cdef: CaseDef): Boolean = cdef match {
     case CaseDef(pat, EmptyTree, _) => isWildcardArg(pat)

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

@@ -530,15 +530,15 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
   def makeSelfDef(name: TermName, tpt: Tree)(using Context): ValDef =
     ValDef(name, tpt, EmptyTree).withFlags(PrivateLocal)
 
-  def makeTupleOrParens(ts: List[Tree])(using Context): Tree = ts match {
+  def makeTupleOrParens(ts: List[Tree])(using Context): Tree = ts match
+    case (t: NamedArg) :: Nil => Tuple(t :: Nil)
     case t :: Nil => Parens(t)
     case _ => Tuple(ts)
-  }
 
-  def makeTuple(ts: List[Tree])(using Context): Tree = ts match {
+  def makeTuple(ts: List[Tree])(using Context): Tree = ts match
+    case (t: NamedArg) :: Nil => Tuple(t :: Nil)
     case t :: Nil => t
     case _ => Tuple(ts)
-  }
 
   def makeAndType(left: Tree, right: Tree)(using Context): AppliedTypeTree =
     AppliedTypeTree(ref(defn.andType.typeRef), left :: right :: Nil)

compiler/src/dotty/tools/dotc/config/Feature.scala

@@ -33,6 +33,7 @@ object Feature:
   val pureFunctions = experimental("pureFunctions")
   val captureChecking = experimental("captureChecking")
   val into = experimental("into")
+  val namedTuples = experimental("namedTuples")
 
   val globalOnlyImports: Set[TermName] = Set(pureFunctions, captureChecking)
 

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

@@ -954,6 +954,9 @@ class Definitions {
     def TupleXXL_fromIterator(using Context): Symbol = TupleXXLModule.requiredMethod("fromIterator")
     def TupleXXL_unapplySeq(using Context): Symbol = TupleXXLModule.requiredMethod(nme.unapplySeq)
 
+  @tu lazy val NamedTupleModule = requiredModule("scala.NamedTuple")
+  @tu lazy val NamedTupleTypeRef: TypeRef = NamedTupleModule.termRef.select(tpnme.NamedTuple).asInstanceOf
+
   @tu lazy val RuntimeTupleMirrorTypeRef: TypeRef = requiredClassRef("scala.runtime.TupleMirror")
 
   @tu lazy val RuntimeTuplesModule: Symbol = requiredModule("scala.runtime.Tuples")
@@ -1305,6 +1308,14 @@ class Definitions {
     case ByNameFunction(_) => true
     case _ => false
 
+  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
+
   final def isCompiletime_S(sym: Symbol)(using Context): Boolean =
     sym.name == tpnme.S && sym.owner == CompiletimeOpsIntModuleClass
 

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

@@ -374,6 +374,7 @@ object StdNames {
     val MirroredMonoType: N     = "MirroredMonoType"
     val MirroredType: N         = "MirroredType"
     val Modifiers: N            = "Modifiers"
+    val NamedTuple: N           = "NamedTuple"
     val NestedAnnotArg: N       = "NestedAnnotArg"
     val NoFlags: N              = "NoFlags"
     val NoPrefix: N             = "NoPrefix"
@@ -647,6 +648,7 @@ object StdNames {
     val wildcardType: N         = "wildcardType"
     val withFilter: N           = "withFilter"
     val withFilterIfRefutable: N = "withFilterIfRefutable$"
+    val withNames: N            = "withNames"
     val WorksheetWrapper: N     = "WorksheetWrapper"
     val wrap: N                 = "wrap"
     val writeReplace: N         = "writeReplace"

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

@@ -4,7 +4,8 @@ package core
 
 import TypeErasure.ErasedValueType
 import Types.*, Contexts.*, Symbols.*, Flags.*, Decorators.*
-import Names.Name
+import Names.{Name, TermName}
+import Constants.Constant
 
 class TypeUtils {
   /** A decorator that provides methods on types
@@ -65,8 +66,12 @@ class TypeUtils {
           case tp: AppliedType if defn.isTupleNType(tp) && normalize =>
             Some(tp.args)  // if normalize is set, use the dealiased tuple
                            // otherwise rely on the default case below to print unaliased tuples.
+          case tp: SkolemType =>
+            recur(tp.underlying, bound)
           case tp: SingletonType =>
-            if tp.termSymbol == defn.EmptyTupleModule then Some(Nil) else None
+            if tp.termSymbol == defn.EmptyTupleModule then Some(Nil)
+            else if normalize then recur(tp.widen, bound)
+            else None
           case _ =>
             if defn.isTupleClass(tp.typeSymbol) && !normalize then Some(tp.dealias.argInfos)
             else None
@@ -114,6 +119,33 @@ 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)] =
+      (if normalize then self.normalized else self).dealias match
+        case defn.NamedTuple(nmes, vals) =>
+          val names = nmes.tupleElementTypesUpTo(bound, normalize).getOrElse(Nil).map:
+            case ConstantType(Constant(str: String)) => str.toTermName
+          val values = vals.tupleElementTypesUpTo(bound, normalize).getOrElse(Nil)
+          names.zip(values)
+        case t =>
+          Nil
+
+    def namedTupleElementTypes(using Context): List[(TermName, Type)] =
+      namedTupleElementTypesUpTo(Int.MaxValue)
+
+    def isNamedTupleType(using Context): Boolean = self match
+      case defn.NamedTuple(_, _) => true
+      case _ => false
+
+    /** Drop all named elements in tuple type */
+    def stripNamedTuple(using Context): Type = self.normalized.dealias match
+      case defn.NamedTuple(_, vals) =>
+        vals
+      case self @ AnnotatedType(tp, annot) =>
+        val tp1 = tp.stripNamedTuple
+        if tp1 ne tp then AnnotatedType(tp1, annot) else self
+      case _ =>
+        self
+
     def refinedWith(name: Name, info: Type)(using Context) = RefinedType(self, name, info)
 
     /** The TermRef referring to the companion of the underlying class reference