move NamedTuple methods to separate scope. re-export (#20504)

By moving the methods to NamedTupleDecomposition, there is no issue with
trying to reconcile types at inlining

fixes #20427

library/src/scala/NamedTuple.scala

@@ -28,100 +28,27 @@ object NamedTuple:
   extension [V <: Tuple](x: V)
     inline def withNames[N <: Tuple]: NamedTuple[N, V] = x
 
-  export NamedTupleDecomposition.{Names, DropNames}
+  export NamedTupleDecomposition.{
+    Names, DropNames,
+    apply, size, init, last, tail, take, drop, splitAt, ++, map, reverse, zip, toList, toArray, toIArray
+  }
 
   extension [N <: Tuple, V <: Tuple](x: NamedTuple[N, V])
 
+    // ALL METHODS DEPENDING ON `toTuple` MUST BE EXPORTED FROM `NamedTupleDecomposition`
     /** The underlying tuple without the names */
     inline def toTuple: V = x
 
-    /** The number of elements in this tuple */
-    inline def size: Tuple.Size[V] = toTuple.size
-
     // This intentionally works for empty named tuples as well. I think NonEmptyTuple is a dead end
     // and should be reverted, just like NonEmptyList is also appealing at first, but a bad idea
     // in the end.
 
-    /** The value (without the name) at index `n` of this tuple */
-    inline def apply(n: Int): Tuple.Elem[V, n.type] =
-      inline toTuple match
-        case tup: NonEmptyTuple => tup(n).asInstanceOf[Tuple.Elem[V, n.type]]
-        case tup => tup.productElement(n).asInstanceOf[Tuple.Elem[V, n.type]]
-
     /** The first element value of this tuple */
-    inline def head: Tuple.Elem[V, 0] = apply(0)
-
-    /** The tuple consisting of all elements of this tuple except the first one */
-    inline def tail: NamedTuple[Tuple.Tail[N], Tuple.Tail[V]] =
-      toTuple.drop(1).asInstanceOf[NamedTuple[Tuple.Tail[N], Tuple.Tail[V]]]
-
-    /** The last element value of this tuple */
-    inline def last: Tuple.Last[V] = apply(size - 1).asInstanceOf[Tuple.Last[V]]
-
-    /** The tuple consisting of all elements of this tuple except the last one */
-    inline def init: NamedTuple[Tuple.Init[N], Tuple.Init[V]] =
-      toTuple.take(size - 1).asInstanceOf[NamedTuple[Tuple.Init[N], Tuple.Init[V]]]
-
-    /** The tuple consisting of the first `n` elements of this tuple, or all
-     *  elements if `n` exceeds `size`.
-     */
-    inline def take(n: Int): NamedTuple[Tuple.Take[N, n.type], Tuple.Take[V, n.type]] =
-      toTuple.take(n)
-
-    /** The tuple consisting of all elements of this tuple except the first `n` ones,
-     *  or no elements if `n` exceeds `size`.
-     */
-    inline def drop(n: Int): NamedTuple[Tuple.Drop[N, n.type], Tuple.Drop[V, n.type]] =
-      toTuple.drop(n)
-
-    /** The tuple `(x.take(n), x.drop(n))` */
-    inline def splitAt(n: Int):
-      (NamedTuple[Tuple.Take[N, n.type], Tuple.Take[V, n.type]],
-       NamedTuple[Tuple.Drop[N, n.type], Tuple.Drop[V, n.type]]) =
-        // would be nice if this could have type `Split[NamedTuple[N, V]]` instead, but
-        // we get a type error then. Similar for other methods here.
-      toTuple.splitAt(n)
-
-    /** The tuple consisting of all elements of this tuple followed by all elements
-     *  of tuple `that`. The names of the two tuples must be disjoint.
-     */
-    inline def ++ [N2 <: Tuple, V2 <: Tuple](that: NamedTuple[N2, V2])(using Tuple.Disjoint[N, N2] =:= true)
-      : NamedTuple[Tuple.Concat[N, N2], Tuple.Concat[V, V2]]
-      = toTuple ++ that.toTuple
+    inline def head: Tuple.Elem[V, 0] = x.apply(0)
 
     // inline def :* [L] (x: L): NamedTuple[Append[N, ???], Append[V, L] = ???
     // inline def *: [H] (x: H): NamedTuple[??? *: N], H *: V] = ???
 
-    /** The named tuple consisting of all element values of this tuple mapped by
-     *  the polymorphic mapping function `f`. The names of elements are preserved.
-     *  If `x = (n1 = v1, ..., ni = vi)` then `x.map(f) = `(n1 = f(v1), ..., ni = f(vi))`.
-     */
-    inline def map[F[_]](f: [t] => t => F[t]): NamedTuple[N, Tuple.Map[V, F]] =
-      toTuple.map(f).asInstanceOf[NamedTuple[N, Tuple.Map[V, F]]]
-
-    /** The named tuple consisting of all elements of this tuple in reverse */
-    inline def reverse: NamedTuple[Tuple.Reverse[N], Tuple.Reverse[V]] =
-      toTuple.reverse
-
-    /** The named tuple consisting of all elements values of this tuple zipped
-     *  with corresponding element values in named tuple `that`.
-     *  If the two tuples have different sizes,
-     *  the extra elements of the larger tuple will be disregarded.
-     *  The names of `x` and `that` at the same index must be the same.
-     *  The result tuple keeps the same names as the operand tuples.
-     */
-    inline def zip[V2 <: Tuple](that: NamedTuple[N, V2]): NamedTuple[N, Tuple.Zip[V, V2]] =
-      toTuple.zip(that.toTuple)
-
-    /** A list consisting of all element values */
-    inline def toList: List[Tuple.Union[V]] = toTuple.toList.asInstanceOf[List[Tuple.Union[V]]]
-
-    /** An array consisting of all element values */
-    inline def toArray: Array[Object] = toTuple.toArray
-
-    /** An immutable array consisting of all element values */
-    inline def toIArray: IArray[Object] = toTuple.toIArray
-
   end extension
 
   /** The size of a named tuple, represented as a literal constant subtype of Int */
@@ -212,6 +139,85 @@ end NamedTuple
 @experimental
 object NamedTupleDecomposition:
   import NamedTuple.*
+  extension [N <: Tuple, V <: Tuple](x: NamedTuple[N, V])
+      /** The value (without the name) at index `n` of this tuple */
+    inline def apply(n: Int): Tuple.Elem[V, n.type] =
+      inline x.toTuple match
+        case tup: NonEmptyTuple => tup(n).asInstanceOf[Tuple.Elem[V, n.type]]
+        case tup => tup.productElement(n).asInstanceOf[Tuple.Elem[V, n.type]]
+
+    /** The number of elements in this tuple */
+    inline def size: Tuple.Size[V] = x.toTuple.size
+
+    /** The last element value of this tuple */
+    inline def last: Tuple.Last[V] = apply(size - 1).asInstanceOf[Tuple.Last[V]]
+
+    /** The tuple consisting of all elements of this tuple except the last one */
+    inline def init: NamedTuple[Tuple.Init[N], Tuple.Init[V]] =
+      x.toTuple.take(size - 1).asInstanceOf[NamedTuple[Tuple.Init[N], Tuple.Init[V]]]
+
+    /** The tuple consisting of all elements of this tuple except the first one */
+    inline def tail: NamedTuple[Tuple.Tail[N], Tuple.Tail[V]] =
+      x.toTuple.drop(1).asInstanceOf[NamedTuple[Tuple.Tail[N], Tuple.Tail[V]]]
+
+    /** The tuple consisting of the first `n` elements of this tuple, or all
+     *  elements if `n` exceeds `size`.
+     */
+    inline def take(n: Int): NamedTuple[Tuple.Take[N, n.type], Tuple.Take[V, n.type]] =
+      x.toTuple.take(n)
+
+    /** The tuple consisting of all elements of this tuple except the first `n` ones,
+     *  or no elements if `n` exceeds `size`.
+     */
+    inline def drop(n: Int): NamedTuple[Tuple.Drop[N, n.type], Tuple.Drop[V, n.type]] =
+      x.toTuple.drop(n)
+
+    /** The tuple `(x.take(n), x.drop(n))` */
+    inline def splitAt(n: Int):
+      (NamedTuple[Tuple.Take[N, n.type], Tuple.Take[V, n.type]],
+       NamedTuple[Tuple.Drop[N, n.type], Tuple.Drop[V, n.type]]) =
+        // would be nice if this could have type `Split[NamedTuple[N, V]]` instead, but
+        // we get a type error then. Similar for other methods here.
+      x.toTuple.splitAt(n)
+
+    /** The tuple consisting of all elements of this tuple followed by all elements
+     *  of tuple `that`. The names of the two tuples must be disjoint.
+     */
+    inline def ++ [N2 <: Tuple, V2 <: Tuple](that: NamedTuple[N2, V2])(using Tuple.Disjoint[N, N2] =:= true)
+      : NamedTuple[Tuple.Concat[N, N2], Tuple.Concat[V, V2]]
+      = x.toTuple ++ that.toTuple
+
+    /** The named tuple consisting of all element values of this tuple mapped by
+     *  the polymorphic mapping function `f`. The names of elements are preserved.
+     *  If `x = (n1 = v1, ..., ni = vi)` then `x.map(f) = `(n1 = f(v1), ..., ni = f(vi))`.
+     */
+    inline def map[F[_]](f: [t] => t => F[t]): NamedTuple[N, Tuple.Map[V, F]] =
+      x.toTuple.map(f).asInstanceOf[NamedTuple[N, Tuple.Map[V, F]]]
+
+    /** The named tuple consisting of all elements of this tuple in reverse */
+    inline def reverse: NamedTuple[Tuple.Reverse[N], Tuple.Reverse[V]] =
+      x.toTuple.reverse
+
+    /** The named tuple consisting of all elements values of this tuple zipped
+     *  with corresponding element values in named tuple `that`.
+     *  If the two tuples have different sizes,
+     *  the extra elements of the larger tuple will be disregarded.
+     *  The names of `x` and `that` at the same index must be the same.
+     *  The result tuple keeps the same names as the operand tuples.
+     */
+    inline def zip[V2 <: Tuple](that: NamedTuple[N, V2]): NamedTuple[N, Tuple.Zip[V, V2]] =
+      x.toTuple.zip(that.toTuple)
+
+    /** A list consisting of all element values */
+    inline def toList: List[Tuple.Union[V]] = x.toTuple.toList.asInstanceOf[List[Tuple.Union[V]]]
+
+    /** An array consisting of all element values */
+    inline def toArray: Array[Object] = x.toTuple.toArray
+
+    /** An immutable array consisting of all element values */
+    inline def toIArray: IArray[Object] = x.toTuple.toIArray
+
+  end extension
 
   /** The names of a named tuple, represented as a tuple of literal string values. */
   type Names[X <: AnyNamedTuple] <: Tuple = X match

tests/pos/named-tuple-combinators.scala

@@ -0,0 +1,154 @@
+import scala.language.experimental.namedTuples
+
+object Test:
+  // original code from issue https://github.com/scala/scala3/issues/20427
+  type NT = NamedTuple.Concat[(hi: Int), (bla: String)]
+  def foo(x: NT) =
+    x.hi // error
+    val y: (hi: Int, bla: String) = x
+    y.hi // ok
+
+  // SELECTOR (reduces to apply)
+  def foo1(x: NT) =
+    val res1 = x.hi // error
+    summon[res1.type <:< Int]
+    val y: (hi: Int, bla: String) = x
+    val res2 = y.hi // ok
+    summon[res2.type <:< Int]
+
+  // toTuple
+  def foo2(x: NT) =
+    val res1 = x.toTuple
+    summon[res1.type <:< (Int, String)]
+    val y: (hi: Int, bla: String) = x
+    val res2 = y.toTuple
+    summon[res2.type <:< (Int, String)]
+
+  // apply
+  def foo3(x: NT) =
+    val res1 = x.apply(1)
+    summon[res1.type <:< String]
+    val y: (hi: Int, bla: String) = x
+    val res2 = y.apply(1)
+    summon[res2.type <:< String]
+
+  // size
+  def foo4(x: NT) =
+    class Box:
+      final val res1 = x.size // final val constrains to a singleton type
+      summon[res1.type <:< 2]
+      val y: (hi: Int, bla: String) = x
+      final val res2 = y.size // final val constrains to a singleton type
+      summon[res2.type <:< 2]
+
+  // head
+  def foo5(x: NT) =
+    val res1 = x.head
+    summon[res1.type <:< Int]
+    val y: (hi: Int, bla: String) = x
+    val res2 = y.head
+    summon[res2.type <:< Int]
+
+  // last
+  def foo6(x: NT) =
+    val res1 = x.last
+    summon[res1.type <:< String]
+    val y: (hi: Int, bla: String) = x
+    val res2 = y.last
+    summon[res2.type <:< String]
+
+  // init
+  def foo7(x: NT) =
+    val res1 = x.init
+    summon[res1.type <:< (hi: Int)]
+    val y: (hi: Int, bla: String) = x
+    val res2 = y.init
+    summon[res2.type <:< (hi: Int)]
+
+  // tail
+  def foo8(x: NT) =
+    val res1 = x.tail
+    summon[res1.type <:< (bla: String)]
+    val y: (hi: Int, bla: String) = x
+    val res2 = y.tail
+    summon[res2.type <:< (bla: String)]
+
+  // take
+  def foo9(x: NT) =
+    val res1 = x.take(1)
+    summon[res1.type <:< (hi: Int)]
+    val y: (hi: Int, bla: String) = x
+    val res2 = y.take(1)
+    summon[res2.type <:< (hi: Int)]
+
+  // drop
+  def foo10(x: NT) =
+    val res1 = x.drop(1)
+    summon[res1.type <:< (bla: String)]
+    val y: (hi: Int, bla: String) = x
+    val res2 = y.drop(1)
+    summon[res2.type <:< (bla: String)]
+
+  // splitAt
+  def foo11(x: NT) =
+    val res1 = x.splitAt(1)
+    summon[res1.type <:< ((hi: Int), (bla: String))]
+    val y: (hi: Int, bla: String) = x
+    val res2 = y.splitAt(1)
+    summon[res2.type <:< ((hi: Int), (bla: String))]
+
+  // ++
+  def foo12(x: NT) =
+    val res1 = x ++ (baz = 23)
+    summon[res1.type <:< (hi: Int, bla: String, baz: Int)]
+    val y: (hi: Int, bla: String) = x
+    val res2 = y ++ (baz = 23)
+    summon[res2.type <:< (hi: Int, bla: String, baz: Int)]
+
+  // map
+  def foo13(x: NT) =
+    val res1 = x.map([T] => (t: T) => Option(t))
+    summon[res1.type <:< (hi: Option[Int], bla: Option[String])]
+    val y: (hi: Int, bla: String) = x
+    val res2 = y.map([T] => (t: T) => Option(t))
+    summon[res2.type <:< (hi: Option[Int], bla: Option[String])]
+
+  // reverse
+  def foo14(x: NT) =
+    val res1 = x.reverse
+    summon[res1.type <:< (bla: String, hi: Int)]
+    val y: (hi: Int, bla: String) = x
+    val res2 = y.reverse
+    summon[res2.type <:< (bla: String, hi: Int)]
+
+  // zip
+  def foo15(x: NT) =
+    val res1 = x.zip((hi = "xyz", bla = true))
+    summon[res1.type <:< (hi: (Int, String), bla: (String, Boolean))]
+    val y: (hi: Int, bla: String) = x
+    val res2 = y.zip((hi = "xyz", bla = true))
+    summon[res2.type <:< (hi: (Int, String), bla: (String, Boolean))]
+
+  // toList
+  def foo16(x: NT) =
+    val res1 = x.toList
+    summon[res1.type <:< List[Tuple.Union[(Int, String)]]]
+    val y: (hi: Int, bla: String) = x
+    val res2 = y.toList
+    summon[res2.type <:< List[Tuple.Union[(Int, String)]]]
+
+  // toArray
+  def foo17(x: NT) =
+    val res1 = x.toArray
+    summon[res1.type <:< Array[Object]]
+    val y: (hi: Int, bla: String) = x
+    val res2 = y.toArray
+    summon[res2.type <:< Array[Object]]
+
+  // toIArray
+  def foo18(x: NT) =
+    val res1 = x.toIArray
+    summon[res1.type <:< IArray[Object]]
+    val y: (hi: Int, bla: String) = x
+    val res2 = y.toIArray
+    summon[res2.type <:< IArray[Object]]