Implement SIP 64 as non-experimental (scala#21668)

For the new syntax of givens and context bounds, see the diffs in
reference/syntax.md.

Author: odersky

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

@@ -1261,7 +1261,7 @@ object desugar {
     str.toTermName.asSimpleName
 
   /** Extract a synthesized given name from a type tree. This is used for
-   *  both anonymous givens and (under x.modularity) deferred givens.
+   *  both anonymous givens and deferred givens.
    *  @param followArgs   if true include argument types in the name
    */
   private class NameExtractor(followArgs: Boolean) extends UntypedTreeAccumulator[String] {

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

@@ -119,7 +119,6 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
   case class PatDef(mods: Modifiers, pats: List[Tree], tpt: Tree, rhs: Tree)(implicit @constructorOnly src: SourceFile) extends DefTree
   case class ExtMethods(paramss: List[ParamClause], methods: List[Tree])(implicit @constructorOnly src: SourceFile) extends Tree
   case class ContextBoundTypeTree(tycon: Tree, paramName: TypeName, ownName: TermName)(implicit @constructorOnly src: SourceFile) extends Tree
-    // `paramName: tycon as ownName`, ownName != EmptyTermName only under x.modularity
   case class MacroTree(expr: Tree)(implicit @constructorOnly src: SourceFile) extends Tree
 
   case class ImportSelector(imported: Ident, renamed: Tree = EmptyTree, bound: Tree = EmptyTree)(implicit @constructorOnly src: SourceFile) extends Tree {

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

@@ -30,6 +30,7 @@ enum MigrationVersion(val warnFrom: SourceVersion, val errorFrom: SourceVersion)
   case ImportRename extends MigrationVersion(future, future)
   case ParameterEnclosedByParenthesis extends MigrationVersion(future, future)
   case XmlLiteral extends MigrationVersion(future, future)
+  case GivenSyntax extends MigrationVersion(future, never)
 
   require(warnFrom.ordinal <= errorFrom.ordinal)
 

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

@@ -16,6 +16,8 @@ enum SourceVersion:
   // !!! Keep in sync with scala.runtime.stdlibPatches.language !!!
   case `future-migration`, `future`
 
+  case `never`    // needed for MigrationVersion.errorFrom if we never want to issue an error
+
   val isMigrating: Boolean = toString.endsWith("-migration")
 
   def stable: SourceVersion =
@@ -32,7 +34,7 @@ object SourceVersion extends Property.Key[SourceVersion]:
   def defaultSourceVersion = `3.6`
 
   /** language versions that may appear in a language import, are deprecated, but not removed from the standard library. */
-  val illegalSourceVersionNames = List("3.1-migration").map(_.toTermName)
+  val illegalSourceVersionNames = List("3.1-migration", "never").map(_.toTermName)
 
   /** language versions that the compiler recognises. */
   val validSourceVersionNames = values.toList.map(_.toString.toTermName)

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

@@ -994,8 +994,8 @@ object Parsers {
       skipParams()
       lookahead.isColon
       && {
-        !in.featureEnabled(Feature.modularity)
-        || { // with modularity language import, a `:` at EOL after an identifier represents a single identifier given
+        !sourceVersion.isAtLeast(`3.6`)
+        || { // in the new given syntax, a `:` at EOL after an identifier represents a single identifier given
              // Example:
              //    given C:
              //      def f = ...
@@ -1833,7 +1833,7 @@ object Parsers {
       infixOps(t, canStartInfixTypeTokens, operand, Location.ElseWhere, ParseKind.Type,
         isOperator = !followingIsVararg()
                      && !isPureArrow
-                     && !(isIdent(nme.as) && in.featureEnabled(Feature.modularity))
+                     && !(isIdent(nme.as) && sourceVersion.isAtLeast(`3.6`))
                      && nextCanFollowOperator(canStartInfixTypeTokens))
 
     /** RefinedType   ::=  WithType {[nl] Refinement} [`^` CaptureSet]
@@ -2226,20 +2226,30 @@ object Parsers {
     def contextBound(pname: TypeName): Tree =
       val t = toplevelTyp()
       val ownName =
-        if isIdent(nme.as) && in.featureEnabled(Feature.modularity) then
+        if isIdent(nme.as) && sourceVersion.isAtLeast(`3.6`) then
           in.nextToken()
           ident()
         else EmptyTermName
       ContextBoundTypeTree(t, pname, ownName)
 
-    /** ContextBounds     ::= ContextBound | `{` ContextBound {`,` ContextBound} `}`
+    /** ContextBounds     ::= ContextBound [`:` ContextBounds]
+     *                      | `{` ContextBound {`,` ContextBound} `}`
      */
     def contextBounds(pname: TypeName): List[Tree] =
       if in.isColon then
         in.nextToken()
-        if in.token == LBRACE && in.featureEnabled(Feature.modularity)
+        if in.token == LBRACE && sourceVersion.isAtLeast(`3.6`)
         then inBraces(commaSeparated(() => contextBound(pname)))
-        else contextBound(pname) :: contextBounds(pname)
+        else
+          val bound = contextBound(pname)
+          val rest =
+            if in.isColon then
+              report.errorOrMigrationWarning(
+                em"Multiple context bounds should be enclosed in `{ ... }`",
+                in.sourcePos(), MigrationVersion.GivenSyntax)
+              contextBounds(pname)
+            else Nil
+          bound :: rest
       else if in.token == VIEWBOUND then
         report.errorOrMigrationWarning(
           em"view bounds `<%' are no longer supported, use a context bound `:' instead",
@@ -4014,7 +4024,7 @@ object Parsers {
           case SEMI | NEWLINE | NEWLINES | COMMA | RBRACE | OUTDENT | EOF =>
             makeTypeDef(typeAndCtxBounds(tname))
           case _ if (staged & StageKind.QuotedPattern) != 0
-              || in.featureEnabled(Feature.modularity) && in.isColon =>
+              || sourceVersion.isAtLeast(`3.6`) && in.isColon =>
             makeTypeDef(typeAndCtxBounds(tname))
           case _ =>
             syntaxErrorOrIncomplete(ExpectedTypeBoundOrEquals(in.token))
@@ -4189,7 +4199,7 @@ object Parsers {
     def givenDef(start: Offset, mods: Modifiers, givenMod: Mod) = atSpan(start, nameStart) {
       var mods1 = addMod(mods, givenMod)
       val nameStart = in.offset
-      var newSyntaxAllowed = in.featureEnabled(Feature.modularity)
+      var newSyntaxAllowed = sourceVersion.isAtLeast(`3.6`)
       val hasEmbeddedColon = !in.isColon && followingIsGivenDefWithColon()
       val name = if isIdent && hasEmbeddedColon then ident() else EmptyTermName
 
@@ -4260,6 +4270,9 @@ object Parsers {
             in.nextToken()
             newSignature()
           else if hasEmbeddedColon then
+            report.errorOrMigrationWarning(
+              em"This old given syntax is no longer supported; use `=>` instead of `:`",
+              in.sourcePos(), MigrationVersion.GivenSyntax)
             newSyntaxAllowed = false
             val tparamsOld = typeParamClauseOpt(ParamOwner.Given)
             newLineOpt()
@@ -4294,10 +4307,10 @@ object Parsers {
           if name.isEmpty then
             syntaxError(em"Anonymous given cannot be abstract, or maybe you want to define a concrete given and are missing a `()` argument?", in.lastOffset)
           if newSyntaxAllowed then
-            warning(
-              em"""This defines an abstract given, which is deprecated. Use a `deferred` given instead.
+            report.errorOrMigrationWarning(
+              em"""This defines an abstract given, which is no longer supported. Use a `deferred` given instead.
                   |Or, if you intend to define a concrete given, follow the type with `()` arguments.""",
-              in.lastOffset)
+              in.sourcePos(in.lastOffset), MigrationVersion.GivenSyntax)
           DefDef(name, adjustDefParams(joinParams(tparams, vparamss)), parents.head, EmptyTree)
         else
           // structural instance
@@ -4487,6 +4500,9 @@ object Parsers {
 
     /** with Template, with EOL <indent> interpreted */
     def withTemplate(constr: DefDef, parents: List[Tree]): Template =
+      report.errorOrMigrationWarning(
+          em"Given member definitions starting with `with` are no longer supported; use `{...}` or `:` followed by newline instead",
+          in.sourcePos(), MigrationVersion.GivenSyntax)
       accept(WITH)
       val (self, stats) = templateBody(parents, rewriteWithColon = false)
       Template(constr, parents, Nil, self, stats)

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

@@ -24,6 +24,8 @@ import TypeApplications.*
 import NameKinds.{WildcardParamName, DefaultGetterName}
 import util.Chars.isOperatorPart
 import config.{Config, Feature}
+import config.Feature.sourceVersion
+import config.SourceVersion.*
 
 import dotty.tools.dotc.util.SourcePosition
 import dotty.tools.dotc.ast.untpd.{MemberDef, Modifiers, PackageDef, RefTree, Template, TypeDef, ValOrDefDef}
@@ -751,7 +753,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
       case GenAlias(pat, expr) =>
         toText(pat) ~ " = " ~ toText(expr)
       case ContextBounds(bounds, cxBounds) =>
-        if Feature.enabled(Feature.modularity) then
+        if sourceVersion.isAtLeast(`3.6`) then
           def boundsText(bounds: Tree) = bounds match
             case ContextBoundTypeTree(tpt, _, ownName) =>
               toText(tpt) ~ (" as " ~ toText(ownName) `provided` !ownName.isEmpty)

docs/_docs/internals/syntax.md

@@ -223,7 +223,9 @@ TypeArgs          ::=  ‘[’ Types ‘]’
 Refinement        ::=  :<<< [RefineDcl] {semi [RefineDcl]} >>>                  ds
 TypeBounds        ::=  [‘>:’ Type] [‘<:’ Type]                                  TypeBoundsTree(lo, hi)
 TypeAndCtxBounds  ::=  TypeBounds [‘:’ ContextBounds]                           ContextBounds(typeBounds, tps)
-ContextBounds     ::=  ContextBound | '{' ContextBound {',' ContextBound} '}'
+ContextBounds     ::=  ContextBound
+                    |  ContextBound `:` ContextBounds                           -- to be deprecated
+                    |  '{' ContextBound {',' ContextBound} '}'
 ContextBound      ::=  Type ['as' id]
 Types             ::=  Type {‘,’ Type}
 NamesAndTypes     ::=  NameAndType {‘,’ NameAndType}
@@ -464,7 +466,7 @@ TypeDef           ::=  id [HkTypeParamClause] {FunParamClause} TypeAndCtxBounds
 TmplDef           ::=  ([‘case’] ‘class’ | ‘trait’) ClassDef
                     |  [‘case’] ‘object’ ObjectDef
                     |  ‘enum’ EnumDef
-                    |  ‘given’ GivenDef
+                    |  ‘given’ (GivenDef | OldGivenDef)
 ClassDef          ::=  id ClassConstr [Template]                                ClassDef(mods, name, tparams, templ)
 ClassConstr       ::=  [ClsTypeParamClause] [ConstrMods] ClsParamClauses        with DefDef(_, <init>, Nil, vparamss, EmptyTree, EmptyTree) as first stat
 ConstrMods        ::=  {Annotation} [AccessModifier]
@@ -483,6 +485,10 @@ GivenConditional  ::=  DefTypeParamClause
                     |  GivenType
 GivenType         ::=  AnnotType1 {id [nl] AnnotType1}
 
+OldGivenDef       ::=  [OldGivenSig] (AnnotType [‘=’ Expr] | StructuralInstance) -- syntax up to Scala 3.5, to be deprecated in the future
+OldGivenSig       ::=  [id] [DefTypeParamClause] {UsingParamClause} ‘:’          -- one of `id`, `DefTypeParamClause`, `UsingParamClause` must be present
+StructuralInstance ::=  ConstrApp {‘with’ ConstrApp} [‘with’ WithTemplateBody]
+
 Extension         ::=  ‘extension’ [DefTypeParamClause] {UsingParamClause}
                        ‘(’ DefTermParam ‘)’ {UsingParamClause} ExtMethods
 ExtMethods        ::=  ExtMethod | [nl] <<< ExtMethod {semi ExtMethod} >>>

docs/_docs/reference/contextual/by-name-context-parameters.md

@@ -12,7 +12,7 @@ trait Codec[T]:
 
 given intCodec: Codec[Int] = ???
 
-given optionCodec[T](using ev: => Codec[T]): Codec[Option[T]] with
+given optionCodec: [T] => (ev: => Codec[T]) => Codec[Option[T]]:
   def write(xo: Option[T]) = xo match
     case Some(x) => ev.write(x)
     case None =>