Drop unnamed tuple <: named tuple, but allow literal tuple to conform

We can drop the unnamed tuple <: named tuple relationship, but still allow tuple syntax to conform to a named tuple prototype, with a small change in Desugar#tuple.
dwijnand · Jan 26, 2024 · c367a50 · c367a50
1 parent 800aa0e
commit c367a50
Show file tree

Hide file tree

Showing 4 changed files with 32 additions and 12 deletions.
diff --git a/compiler/src/dotty/tools/dotc/ast/Desugar.scala b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
@@ -1502,8 +1502,11 @@ object desugar {
         tree1.withSpan(tree.span)
       else
         cpy.Tuple(tree)(elemValues)
-    val names = elems.collect:
+    var names = elems.collect:
       case NamedArg(name, arg) => name
+    if names.isEmpty then
+      typer.Inferencing.isFullyDefined(pt, typer.ForceDegree.failBottom)
+      names = pt.namedTupleNames
     if names.isEmpty || ctx.mode.is(Mode.Pattern) then
       tup
     else

diff --git a/compiler/src/dotty/tools/dotc/core/TypeUtils.scala b/compiler/src/dotty/tools/dotc/core/TypeUtils.scala
@@ -134,6 +134,13 @@ class TypeUtils {
     def namedTupleElementTypes(using Context): List[(TermName, Type)] =
       namedTupleElementTypesUpTo(Int.MaxValue)
 
+    def namedTupleNames(using Context): List[Name] =
+      self.normalized.dealias match
+        case defn.NamedTuple(nmes, _) =>
+          nmes.tupleElementTypes.getOrElse(Nil).map:
+            case ConstantType(Constants.Constant(str: String)) => str.toTermName
+        case _ => Nil
+
     def isNamedTupleType(using Context): Boolean = self match
       case defn.NamedTuple(_, _) => true
       case _ => false

diff --git a/library/src/scala/NamedTuple.scala b/library/src/scala/NamedTuple.scala
@@ -6,7 +6,7 @@ import compiletime.ops.boolean.*
 object NamedTuple:
 
   opaque type AnyNamedTuple = Any
-  opaque type NamedTuple[N <: Tuple, +V <: Tuple] >: V <: AnyNamedTuple = V
+  opaque type NamedTuple[N <: Tuple, +V <: Tuple] <: AnyNamedTuple = V
 
   def apply[N <: Tuple, V <: Tuple](x: V): NamedTuple[N, V] = x
 

diff --git a/tests/neg/named-tuples.check b/tests/neg/named-tuples.check
@@ -61,14 +61,24 @@
 28 |    case (name = n, age = a) => () // error // error
    |                    ^^^^^^^
    |                    No element named `age` is defined in selector type (String, Int)
--- [E172] Type Error: tests/neg/named-tuples.scala:30:27 ---------------------------------------------------------------
+-- [E007] Type Mismatch Error: tests/neg/named-tuples.scala:30:21 ------------------------------------------------------
 30 |  val pp = person ++ (1, 2)  // error
-   |                           ^
-   |            Cannot prove that Tuple.Disjoint[(("name" : String), ("age" : String)), Tuple] =:= (true : Boolean).
--- [E172] Type Error: tests/neg/named-tuples.scala:33:18 ---------------------------------------------------------------
+   |                     ^^^^^^
+   |                     Found:    (Int, Int)
+   |                     Required: NamedTuple.NamedTuple[N2, Tuple]
+   |
+   |                     where:    N2 is a type variable with constraint <: Tuple
+   |
+   | longer explanation available when compiling with `-explain`
+-- [E007] Type Mismatch Error: tests/neg/named-tuples.scala:33:12 ------------------------------------------------------
 33 |  person ++ (1, 2) match // error
-   |                  ^
-   |            Cannot prove that Tuple.Disjoint[(("name" : String), ("age" : String)), Tuple] =:= (true : Boolean).
+   |            ^^^^^^
+   |            Found:    (Int, Int)
+   |            Required: NamedTuple.NamedTuple[N2, Tuple]
+   |
+   |            where:    N2 is a type variable with constraint <: Tuple
+   |
+   | longer explanation available when compiling with `-explain`
 -- Error: tests/neg/named-tuples.scala:36:17 ---------------------------------------------------------------------------
 36 |  val bad = ("", age = 10) // error
    |                 ^^^^^^^^
@@ -103,8 +113,8 @@
 -- Warning: tests/neg/named-tuples.scala:25:29 -------------------------------------------------------------------------
 25 |  val (name = x, agee = y) = person // error
    |                             ^^^^^^
-   |pattern's type (String, Int) is more specialized than the right hand side expression's type (name : String, age : Int)
+   |    pattern's type (String, Int) does not match the right hand side expression's type (name : String, age : Int)
    |
-   |If the narrowing is intentional, this can be communicated by adding `: @unchecked` after the expression,
-   |which may result in a MatchError at runtime.
-   |This patch can be rewritten automatically under -rewrite -source 3.2-migration.
+   |    If the narrowing is intentional, this can be communicated by adding `: @unchecked` after the expression,
+   |    which may result in a MatchError at runtime.
+   |    This patch can be rewritten automatically under -rewrite -source 3.2-migration.