Make Named Tuples a stable feature in 3.7 (#22753)

We make the Named Tuples again a standard feature, after they were
delayed before 3.6 release #22045

Includes fixes to make deprecated syntax warnings and its migration
still work - in many cases `untpd.Tuple` has become `untpd.Parens`

Author: odersky

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

@@ -33,7 +33,6 @@ object Feature:
   val pureFunctions = experimental("pureFunctions")
   val captureChecking = experimental("captureChecking")
   val into = experimental("into")
-  val namedTuples = experimental("namedTuples")
   val modularity = experimental("modularity")
   val quotedPatternsWithPolymorphicFunctions = experimental("quotedPatternsWithPolymorphicFunctions")
   val betterFors = experimental("betterFors")
@@ -63,7 +62,6 @@ object Feature:
     (pureFunctions, "Enable pure functions for capture checking"),
     (captureChecking, "Enable experimental capture checking"),
     (into, "Allow into modifier on parameter types"),
-    (namedTuples, "Allow named tuples"),
     (modularity, "Enable experimental modularity features"),
     (betterFors, "Enable improvements in `for` comprehensions")
   )

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -671,7 +671,7 @@ object Parsers {
       else leading :: Nil
 
     def maybeNamed(op: () => Tree): () => Tree = () =>
-      if isIdent && in.lookahead.token == EQUALS && in.featureEnabled(Feature.namedTuples) then
+      if isIdent && in.lookahead.token == EQUALS && sourceVersion.enablesNamedTuples then
         atSpan(in.offset):
           val name = ident()
           in.nextToken()
@@ -1160,6 +1160,13 @@ object Parsers {
             patch(source, infixOp.span, asApply.show(using ctx.withoutColors))
             asApply // allow to use pre-3.6 syntax in migration mode
           else infixOp
+        case Parens(assign @ Assign(ident, value)) if !isNamedTupleOperator =>
+          report.errorOrMigrationWarning(DeprecatedInfixNamedArgumentSyntax(), infixOp.right.srcPos, MigrationVersion.AmbiguousNamedTupleSyntax)
+          if MigrationVersion.AmbiguousNamedTupleSyntax.needsPatch then
+            val asApply = cpy.Apply(infixOp)(Select(opInfo.operand, opInfo.operator.name), assign :: Nil)
+            patch(source, infixOp.span, asApply.show(using ctx.withoutColors))
+            asApply // allow to use pre-3.6 syntax in migration mode
+          else infixOp
         case _ => infixOp
     }
 
@@ -2177,7 +2184,7 @@ object Parsers {
 
       if namedOK && isIdent && in.lookahead.token == EQUALS then
         commaSeparated(() => namedArgType())
-      else if tupleOK && isIdent && in.lookahead.isColon && in.featureEnabled(Feature.namedTuples) then
+      else if tupleOK && isIdent && in.lookahead.isColon && sourceVersion.enablesNamedTuples then
         commaSeparated(() => namedElem())
       else
         commaSeparated(() => argType())

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -3362,7 +3362,7 @@ end QuotedTypeMissing
 
 final class DeprecatedAssignmentSyntax(key: Name, value: untpd.Tree)(using Context) extends SyntaxMsg(DeprecatedAssignmentSyntaxID):
   override protected def msg(using Context): String =
-    i"""Deprecated syntax: in the future it would be interpreted as a named tuple with one element,
+    i"""Deprecated syntax: since 3.7 this is interpreted as a named tuple with one element,
       |not as an assignment.
       |
       |To assign a value, use curly braces: `{${key} = ${value}}`."""
@@ -3372,9 +3372,9 @@ final class DeprecatedAssignmentSyntax(key: Name, value: untpd.Tree)(using Conte
 
 class DeprecatedInfixNamedArgumentSyntax()(using Context) extends SyntaxMsg(DeprecatedInfixNamedArgumentSyntaxID):
   def msg(using Context) =
-    i"""Deprecated syntax: infix named arguments lists are deprecated; in the future it would be interpreted as a single name tuple argument.
+    i"""Deprecated syntax: infix named arguments lists are deprecated; since 3.7 it is interpreted as a single name tuple argument.
        |To avoid this warning, either remove the argument names or use dotted selection."""
-        + Message.rewriteNotice("This", version = SourceVersion.`3.6-migration`)
+        + Message.rewriteNotice("This", version = SourceVersion.`3.7-migration`)
 
   def explain(using Context) = ""
 

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

@@ -825,7 +825,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
     def tryNamedTupleSelection() =
       val namedTupleElems = qual.tpe.widenDealias.namedTupleElementTypes(true)
       val nameIdx = namedTupleElems.indexWhere(_._1 == selName)
-      if nameIdx >= 0 && Feature.enabled(Feature.namedTuples) then
+      if nameIdx >= 0 && sourceVersion.enablesNamedTuples then
         typed(
           untpd.Apply(
             untpd.Select(untpd.TypedSplice(qual), nme.apply),
@@ -3500,19 +3500,22 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
  /** Checks if `tree` is a named tuple with one element that could be
   *  interpreted as an assignment, such as `(x = 1)`. If so, issues a warning.
   */
-  def checkDeprecatedAssignmentSyntax(tree: untpd.Tuple)(using Context): Unit =
-    tree.trees match
-      case List(NamedArg(name, value)) =>
+  def checkDeprecatedAssignmentSyntax(tree: untpd.Tuple | untpd.Parens)(using Context): Unit =
+    val assignmentArgs = tree match {
+      case untpd.Tuple(List(NamedArg(name, value))) =>
         val tmpCtx = ctx.fresh.setNewTyperState()
         typedAssign(untpd.Assign(untpd.Ident(name), value), WildcardType)(using tmpCtx)
-        if !tmpCtx.reporter.hasErrors then
-          // If there are no errors typing the above, then the named tuple is
-          // ambiguous and we issue a warning.
-          report.migrationWarning(DeprecatedAssignmentSyntax(name, value), tree.srcPos)
-          if MigrationVersion.AmbiguousNamedTupleSyntax.needsPatch then
-            patch(tree.source, Span(tree.span.start, tree.span.start + 1), "{")
-            patch(tree.source, Span(tree.span.end - 1, tree.span.end), "}")
-      case _ => ()
+        Option.unless(tmpCtx.reporter.hasErrors)(name -> value)
+      case untpd.Parens(Assign(ident: untpd.Ident, value)) => Some(ident.name -> value)
+      case _ => None
+    }
+    assignmentArgs.foreach: (name, value) =>
+      // If there are no errors typing the above, then the named tuple is
+      // ambiguous and we issue a warning.
+      report.migrationWarning(DeprecatedAssignmentSyntax(name, value), tree.srcPos)
+      if MigrationVersion.AmbiguousNamedTupleSyntax.needsPatch then
+        patch(tree.source, Span(tree.span.start, tree.span.start + 1), "{")
+        patch(tree.source, Span(tree.span.end - 1, tree.span.end), "}")
 
   /** Retrieve symbol attached to given tree */
   protected def retrieveSym(tree: untpd.Tree)(using Context): Symbol = tree.removeAttachment(SymOfTree) match {
@@ -3621,6 +3624,9 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
           case tree: untpd.SplicePattern => typedSplicePattern(tree, pt)
           case tree: untpd.MacroTree => report.error("Unexpected macro", tree.srcPos); tpd.nullLiteral  // ill-formed code may reach here
           case tree: untpd.Hole => typedHole(tree, pt)
+          case tree: untpd.Parens =>
+            checkDeprecatedAssignmentSyntax(tree)
+            typedUnadapted(desugar(tree, pt), pt, locked)
           case _ => typedUnadapted(desugar(tree, pt), pt, locked)
         }
 

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -79,7 +79,7 @@ class CompilationTests {
       compileFile("tests/rewrites/i20002.scala", defaultOptions.and("-indent", "-rewrite")),
       compileDir("tests/rewrites/annotation-named-pararamters", defaultOptions.and("-rewrite", "-source:3.6-migration")),
       compileFile("tests/rewrites/i21418.scala", unindentOptions.and("-rewrite", "-source:3.5-migration")),
-      compileFile("tests/rewrites/infix-named-args.scala", defaultOptions.and("-rewrite", "-source:3.6-migration")),
+      compileFile("tests/rewrites/infix-named-args.scala", defaultOptions.and("-rewrite", "-source:3.7-migration")),
       compileFile("tests/rewrites/ambiguous-named-tuple-assignment.scala", defaultOptions.and("-rewrite", "-source:3.6-migration")),
       compileFile("tests/rewrites/i21382.scala", defaultOptions.and("-indent", "-rewrite")),
       compileFile("tests/rewrites/unused.scala", defaultOptions.and("-rewrite", "-Wunused:all")),

docs/_docs/reference/experimental/named-tuples.md renamed to docs/_docs/reference/other-new-features/named-tuples.md

@@ -1,10 +1,11 @@
 ---
 layout: doc-page
 title: "Named Tuples"
-nightlyOf: https://docs.scala-lang.org/scala3/reference/experimental/named-tuples.html
+nightlyOf: https://docs.scala-lang.org/scala3/reference/other-new-features/named-tuples.html
 ---
 
-The elements of a tuple can now be named. Example:
+Starting in Scala 3.7, the elements of a tuple can be named.
+Example:
 ```scala
 type Person = (name: String, age: Int)
 val Bob: Person = (name = "Bob", age = 33)

docs/sidebar.yml

@@ -72,6 +72,7 @@ subsection:
           - page: reference/other-new-features/export.md
           - page: reference/other-new-features/opaques.md
           - page: reference/other-new-features/opaques-details.md
+          - page: reference/other-new-features/named-tuples.md
           - page: reference/other-new-features/open-classes.md
           - page: reference/other-new-features/parameter-untupling.md
           - page: reference/other-new-features/parameter-untupling-spec.md
@@ -158,7 +159,6 @@ subsection:
           - page: reference/experimental/cc.md
           - page: reference/experimental/purefuns.md
           - page: reference/experimental/tupled-function.md
-          - page: reference/experimental/named-tuples.md
           - page: reference/experimental/modularity.md
           - page: reference/experimental/typeclasses.md
           - page: reference/experimental/runtimeChecked.md

language-server/test/dotty/tools/languageserver/CompletionTest.scala

@@ -1725,8 +1725,7 @@ class CompletionTest {
      .completion(m6, Set())
 
   @Test def namedTupleCompletion: Unit =
-    code"""|import scala.language.experimental.namedTuples
-           |
+    code"""|
            |val person: (name: String, city: String) =
            |  (name = "Jamie", city = "Lausanne")
            |

library/src/scala/NamedTuple.scala

@@ -1,8 +1,6 @@
 package scala
-import annotation.experimental
 import compiletime.ops.boolean.*
 
-@experimental
 object NamedTuple:
 
   /** The type to which named tuples get mapped to. For instance,
@@ -133,7 +131,6 @@ object NamedTuple:
 end NamedTuple
 
 /** Separate from NamedTuple object so that we can match on the opaque type NamedTuple. */
-@experimental
 object NamedTupleDecomposition:
   import NamedTuple.*
   extension [N <: Tuple, V <: Tuple](x: NamedTuple[N, V])

library/src/scala/runtime/stdLibPatches/language.scala

@@ -97,6 +97,7 @@ object language:
      *  @see [[https://dotty.epfl.ch/docs/reference/experimental/named-tuples]]
      */
     @compileTimeOnly("`namedTuples` can only be used at compile time in import statements")
+    @deprecated("The experimental.namedTuples language import is no longer needed since the feature is now standard", since = "3.7")
     object namedTuples
 
     /** Experimental support for new features for better modularity, including