Merge pull request #10538 from dotty-staging/change-given-syntax-3

Givens without `as`

Author: odersky

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

@@ -800,10 +800,12 @@ object desugar {
             Nil
         }
       }
+      val classMods = if mods.is(Given) then mods &~ Given | Synthetic else mods
       cpy.TypeDef(cdef: TypeDef)(
         name = className,
         rhs = cpy.Template(impl)(constr, parents1, clsDerived, self1,
-          tparamAccessors ::: vparamAccessors ::: normalizedBody ::: caseClassMeths)): TypeDef
+          tparamAccessors ::: vparamAccessors ::: normalizedBody ::: caseClassMeths)
+      ).withMods(classMods)
     }
 
     // install the watch on classTycon

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

@@ -913,7 +913,7 @@ object Parsers {
           lookahead.nextToken()
           skipParams()
       skipParams()
-      lookahead.isIdent(nme.as)
+      lookahead.token == COLON || lookahead.isIdent(nme.as)
 
     def followingIsExtension() =
       val next = in.lookahead.token
@@ -1281,11 +1281,11 @@ object Parsers {
 
     def possibleTemplateStart(isNew: Boolean = false): Unit =
       in.observeColonEOL()
-      if in.token == COLONEOL then
+      if in.token == COLONEOL || in.token == WITHEOL then
         if in.lookahead.isIdent(nme.end) then in.token = NEWLINE
         else
           in.nextToken()
-          if in.token != INDENT then
+          if in.token != INDENT && in.token != LBRACE then
             syntaxErrorOrIncomplete(i"indented definitions expected, ${in}")
       else
         newLineOptWhenFollowedBy(LBRACE)
@@ -3512,9 +3512,8 @@ object Parsers {
         syntaxError(i"extension clause can only define methods", stat.span)
     }
 
-    /** GivenDef          ::=  [GivenSig] Type ‘=’ Expr
-     *                      |  [GivenSig] ConstrApps [TemplateBody]
-     *  GivenSig          ::=  [id] [DefTypeParamClause] {UsingParamClauses} ‘as’
+    /** GivenDef          ::=  [GivenSig] (Type [‘=’ Expr] | StructuralInstance)
+     *  GivenSig          ::=  [id] [DefTypeParamClause] {UsingParamClauses} ‘:’
      */
     def givenDef(start: Offset, mods: Modifiers, givenMod: Mod) = atSpan(start, nameStart) {
       var mods1 = addMod(mods, givenMod)
@@ -3531,23 +3530,35 @@ object Parsers {
           else Nil
         newLinesOpt()
         val noParams = tparams.isEmpty && vparamss.isEmpty
+        val newSyntax = in.token == COLON
         if !(name.isEmpty && noParams) then
-          accept(nme.as)
-        val parents = constrApps(commaOK = true)
-        if in.token == EQUALS && parents.length == 1 && parents.head.isType then
+          if isIdent(nme.as) then in.nextToken()
+          else accept(COLON)
+        val parents = constrApp() :: withConstrApps()
+        val parentsIsType = parents.length == 1 && parents.head.isType
+        if in.token == EQUALS && parentsIsType then
           accept(EQUALS)
           mods1 |= Final
           if noParams && !mods.is(Inline) then
             mods1 |= Lazy
             ValDef(name, parents.head, subExpr())
           else
             DefDef(name, tparams, vparamss, parents.head, subExpr())
+        else if newSyntax && in.token != WITH && in.token != WITHEOL && parentsIsType then
+          if name.isEmpty then
+            syntaxError(em"anonymous given cannot be abstract")
+          DefDef(name, tparams, vparamss, parents.head, EmptyTree)
         else
-          possibleTemplateStart()
           val tparams1 = tparams.map(tparam => tparam.withMods(tparam.mods | PrivateLocal))
           val vparamss1 = vparamss.map(_.map(vparam =>
             vparam.withMods(vparam.mods &~ Param | ParamAccessor | Protected)))
-          val templ = templateBodyOpt(makeConstructor(tparams1, vparamss1), parents, Nil)
+          val constr = makeConstructor(tparams1, vparamss1)
+          val templ =
+            if newSyntax || in.token == WITHEOL || in.token == WITH then
+              withTemplate(constr, parents)
+            else
+              possibleTemplateStart()
+              templateBodyOpt(makeConstructor(tparams1, vparamss1), parents, Nil)
           if tparams.isEmpty && vparamss.isEmpty then ModuleDef(name, templ)
           else TypeDef(name.toTypeName, templ)
       end gdef
@@ -3622,6 +3633,18 @@ object Parsers {
         else Nil
       t :: ts
 
+
+    /** `{`with` ConstrApp} but no EOL allowed after `with`.
+     */
+    def withConstrApps(): List[Tree] =
+      if in.token == WITH then
+        in.observeWithEOL() // converts token to WITHEOL if at end of line
+        if in.token == WITH && in.lookahead.token != LBRACE then
+          in.nextToken()
+          constrApp() :: withConstrApps()
+        else Nil
+      else Nil
+
     /** Template          ::=  InheritClauses [TemplateBody]
      *  InheritClauses    ::=  [‘extends’ ConstrApps] [‘derives’ QualId {‘,’ QualId}]
      */
@@ -3687,6 +3710,14 @@ object Parsers {
         template(emptyConstructor)
       r
 
+    /** with Template, with EOL <indent> interpreted */
+    def withTemplate(constr: DefDef, parents: List[Tree]): Template =
+      if in.token != WITHEOL then accept(WITH)
+      possibleTemplateStart() // consumes a WITHEOL token
+      val (self, stats) = templateBody()
+      Template(constr, parents, Nil, self, stats)
+        .withSpan(Span(constr.span.orElse(parents.head.span).start, in.lastOffset))
+
 /* -------- STATSEQS ------------------------------------------- */
 
     /** Create a tree representing a packaging */

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

@@ -150,6 +150,7 @@ object Scanners {
     private[Scanners] var allowLeadingInfixOperators = true
 
     var debugTokenStream = false
+    val showLookAheadOnDebug = false
 
     val rewrite = ctx.settings.rewrite.value.isDefined
     val oldSyntax = ctx.settings.oldSyntax.value
@@ -320,7 +321,8 @@ object Scanners {
     }
 
     final def printState() =
-      if debugTokenStream then print("[" + show + "]")
+      if debugTokenStream && (showLookAheadOnDebug || !isInstanceOf[LookaheadScanner]) then
+        print(s"[$show${if isInstanceOf[LookaheadScanner] then "(LA)" else ""}]")
 
     /** Insert `token` at assumed `offset` in front of current one. */
     def insert(token: Token, offset: Int) = {
@@ -510,12 +512,15 @@ object Scanners {
          |Previous indent : $lastWidth
          |Latest indent   : $nextWidth"""
 
-    def observeColonEOL(): Unit =
-      if token == COLON then
+    private def switchAtEOL(testToken: Token, eolToken: Token): Unit =
+      if token == testToken then
         lookAhead()
         val atEOL = isAfterLineEnd || token == EOF
         reset()
-        if atEOL then token = COLONEOL
+        if atEOL then token = eolToken
+
+    def observeColonEOL(): Unit = switchAtEOL(COLON, COLONEOL)
+    def observeWithEOL(): Unit = switchAtEOL(WITH, WITHEOL)
 
     def observeIndented(): Unit =
       if indentSyntax && isNewLine then

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

@@ -121,14 +121,14 @@ abstract class TokensCommon {
   def isKeyword(token: Token): Boolean = keywords contains token
 
   /** parentheses */
-  final val LPAREN = 90;           enter(LPAREN, "'('")
-  final val RPAREN = 91;           enter(RPAREN, "')'")
-  final val LBRACKET = 92;         enter(LBRACKET, "'['")
-  final val RBRACKET = 93;         enter(RBRACKET, "']'")
-  final val LBRACE = 94;           enter(LBRACE, "'{'")
-  final val RBRACE = 95;           enter(RBRACE, "'}'")
-  final val INDENT = 96;           enter(INDENT, "indent")
-  final val OUTDENT = 97;          enter(OUTDENT, "unindent")
+  final val LPAREN = 91;           enter(LPAREN, "'('")
+  final val RPAREN = 92;           enter(RPAREN, "')'")
+  final val LBRACKET = 93;         enter(LBRACKET, "'['")
+  final val RBRACKET = 94;         enter(RBRACKET, "']'")
+  final val LBRACE = 95;           enter(LBRACE, "'{'")
+  final val RBRACE = 96;           enter(RBRACE, "'}'")
+  final val INDENT = 97;           enter(INDENT, "indent")
+  final val OUTDENT = 98;          enter(OUTDENT, "unindent")
 
   final val firstParen = LPAREN
   final val lastParen = OUTDENT
@@ -204,10 +204,11 @@ object Tokens extends TokensCommon {
   final val QUOTE = 87;            enter(QUOTE, "'")
 
   final val COLONEOL = 88;         enter(COLONEOL, ":", ": at eol")
-  final val SELFARROW = 89;        enter(SELFARROW, "=>") // reclassified ARROW following self-type
+  final val WITHEOL = 89;          enter(WITHEOL, "with", "with at eol")
+  final val SELFARROW = 90;        enter(SELFARROW, "=>") // reclassified ARROW following self-type
 
   /** XML mode */
-  final val XMLSTART = 98;         enter(XMLSTART, "$XMLSTART$<") // TODO: deprecate
+  final val XMLSTART = 99;         enter(XMLSTART, "$XMLSTART$<") // TODO: deprecate
 
   final val alphaKeywords: TokenSet = tokenRange(IF, MACRO)
   final val symbolicKeywords: TokenSet = tokenRange(USCORE, CTXARROW)
@@ -276,7 +277,7 @@ object Tokens extends TokensCommon {
   final val closingRegionTokens = BitSet(RBRACE, RPAREN, RBRACKET, CASE) | statCtdTokens
 
   final val canStartIndentTokens: BitSet =
-    statCtdTokens | BitSet(COLONEOL, EQUALS, ARROW, LARROW, WHILE, TRY, FOR, IF)
+    statCtdTokens | BitSet(COLONEOL, WITHEOL, EQUALS, ARROW, LARROW, WHILE, TRY, FOR, IF)
       // `if` is excluded because it often comes after `else` which makes for awkward indentation rules  TODO: try to do without the exception
 
   /** Faced with the choice between a type and a formal parameter, the following

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

@@ -443,7 +443,7 @@ object Checking {
       fail(ParamsNoInline(sym.owner))
     if sym.isInlineMethod && !sym.is(Deferred) && sym.allOverriddenSymbols.nonEmpty then
       checkInlineOverrideParameters(sym)
-    if (sym.isOneOf(GivenOrImplicit)) {
+    if (sym.is(Implicit)) {
       if (sym.owner.is(Package))
         fail(TopLevelCantBeImplicit(sym))
       if (sym.isType)

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

@@ -241,7 +241,7 @@ class Namer { typer: Typer =>
 
     tree match {
       case tree: TypeDef if tree.isClassDef =>
-        val flags = checkFlags(tree.mods.flags &~ GivenOrImplicit)
+        val flags = checkFlags(tree.mods.flags &~ Implicit)
         val name = checkNoConflict(tree.name, flags.is(Private), tree.span).asTypeName
         val cls =
           createOrRefine[ClassSymbol](tree, name, flags, ctx.owner,

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

@@ -503,7 +503,9 @@ object RefChecks {
         def prelude = (
           if (clazz.isAnonymousClass || clazz.is(Module)) "object creation impossible"
           else if (mustBeMixin) s"$clazz needs to be a mixin"
-          else s"$clazz needs to be abstract") + ", since"
+          else if clazz.is(Synthetic) then "instance cannot be created"
+          else s"$clazz needs to be abstract"
+          ) + ", since"
 
         if (abstractErrors.isEmpty) abstractErrors ++= List(prelude, msg)
         else abstractErrors += msg

docs/docs/internals/syntax.md

@@ -205,9 +205,11 @@ Expr1             ::=  [‘inline’] ‘if’ ‘(’ Expr ‘)’ {nl} Expr [[
                     |  [SimpleExpr ‘.’] id ‘=’ Expr                             Assign(expr, expr)
                     |  SimpleExpr1 ArgumentExprs ‘=’ Expr                       Assign(expr, expr)
                     |  PostfixExpr [Ascription]
+                    |  StructuralInstance
                     |  ‘inline’ InfixExpr MatchClause
 Ascription        ::=  ‘:’ InfixType                                            Typed(expr, tp)
                     |  ‘:’ Annotation {Annotation}                              Typed(expr, Annotated(EmptyTree, annot)*)
+StructuralInstance ::=  ConstrApp {‘with’ ConstrApp} ‘with’ TemplateBody        New templ
 Catches           ::=  ‘catch’ (Expr | ExprCaseClause)
 PostfixExpr       ::=  InfixExpr [id]                                           PostfixOp(expr, op)
 InfixExpr         ::=  PrefixExpr
@@ -396,9 +398,8 @@ ClassConstr       ::=  [ClsTypeParamClause] [ConstrMods] ClsParamClauses
 ConstrMods        ::=  {Annotation} [AccessModifier]
 ObjectDef         ::=  id [Template]                                            ModuleDef(mods, name, template)  // no constructor
 EnumDef           ::=  id ClassConstr InheritClauses EnumBody                   EnumDef(mods, name, tparams, template)
-GivenDef          ::=  [GivenSig] Type ‘=’ Expr
-                    |  [GivenSig] ConstrApps [TemplateBody]
-GivenSig          ::=  [id] [DefTypeParamClause] {UsingParamClause} ‘as’       -- one of `id`, `DefParamClause`, `UsingParamClause` must appear
+GivenDef          ::=  [GivenSig] (Type [‘=’ Expr] | StructuralInstance)
+GivenSig          ::=  [id] [DefTypeParamClause] {UsingParamClause} ‘:’       -- one of `id`, `DefParamClause`, `UsingParamClause` must be present
 Extension         ::=  ‘extension’ [DefTypeParamClause] ‘(’ DefParam ‘)’
                        {UsingParamClause}] ExtMethods
 ExtMethods        ::=  ExtMethod | [nl] ‘{’ ExtMethod {semi ExtMethod ‘}’

docs/docs/reference/changed-features/implicit-resolution.md

@@ -41,10 +41,10 @@ no longer applies.
 **3.** Package prefixes no longer contribute to the implicit search scope of a type. Example:
 ```scala
   package p
-  given a as A
+  given a: A = A()
 
   object o {
-    given b as B
+    given b: B = B()
     type C
   }
 ```

docs/docs/reference/changed-features/numeric-literals.md

@@ -133,38 +133,32 @@ should produce the `BigFloat` number `BigFloat(-123, 997)`:
 The companion object of `BigFloat` defines an `apply` constructor method to construct a `BigFloat`
 from a `digits` string. Here is a possible implementation:
 ```scala
-object BigFloat {
+object BigFloat:
   import scala.util.FromDigits
 
-  def apply(digits: String): BigFloat = {
-    val (mantissaDigits, givenExponent) = digits.toUpperCase.split('E') match {
+  def apply(digits: String): BigFloat =
+    val (mantissaDigits, givenExponent) = digits.toUpperCase.split('E') match
       case Array(mantissaDigits, edigits) =>
         val expo =
           try FromDigits.intFromDigits(edigits)
-          catch {
-            case ex: FromDigits.NumberTooLarge =>
-              throw FromDigits.NumberTooLarge(s"exponent too large: $edigits")
-          }
+          catch case ex: FromDigits.NumberTooLarge =>
+            throw FromDigits.NumberTooLarge(s"exponent too large: $edigits")
         (mantissaDigits, expo)
       case Array(mantissaDigits) =>
         (mantissaDigits, 0)
-    }
-    val (intPart, exponent) = mantissaDigits.split('.') match {
+    val (intPart, exponent) = mantissaDigits.split('.') match
       case Array(intPart, decimalPart) =>
         (intPart ++ decimalPart, givenExponent - decimalPart.length)
       case Array(intPart) =>
         (intPart, givenExponent)
-    }
     BigFloat(BigInt(intPart), exponent)
-  }
 ```
 To accept `BigFloat` literals, all that's needed in addition is a `given` instance of type
 `FromDigits.Floating[BigFloat]`:
 ```scala
-  given FromDigits as FromDigits.Floating[BigFloat] {
+  given FromDigits: FromDigits.Floating[BigFloat] with
     def fromDigits(digits: String) = apply(digits)
-  }
-} // end BigFloat
+end BigFloat
 ```
 Note that the `apply` method does not check the format of the `digits` argument. It is
 assumed that only valid arguments are passed. For calls coming from the compiler

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

@@ -10,14 +10,12 @@ trait Codec[T] {
   def write(x: T): Unit
 }
 
-given intCodec as Codec[Int] = ???
+given intCodec: Codec[Int] = ???
 
-given optionCodec[T](using ev: => Codec[T]) as Codec[Option[T]] {
-  def write(xo: Option[T]) = xo match {
+given optionCodec[T](using ev: => Codec[T]): Codec[Option[T]] with
+  def write(xo: Option[T]) = xo match
     case Some(x) => ev.write(x)
     case None =>
-  }
-}
 
 val s = summon[Codec[Option[Int]]]
 
@@ -36,7 +34,7 @@ The precise steps for synthesizing an argument for a by-name context parameter o
  1. Create a new given of type `T`:
 
     ```scala
-    given lv as T = ???
+    given lv: T = ???
     ```
     where `lv` is an arbitrary fresh name.
 
@@ -46,7 +44,7 @@ The precise steps for synthesizing an argument for a by-name context parameter o
 
 
     ```scala
-    { given lv as T = E; lv }
+    { given lv: T = E; lv }
     ```
 
     Otherwise, return `E` unchanged.

docs/docs/reference/contextual/context-functions.md

@@ -13,7 +13,7 @@ Context functions are written using `?=>` as the "arrow" sign.
 They are applied to synthesized arguments, in
 the same way methods with context parameters are applied. For instance:
 ```scala
-  given ec as ExecutionContext = ...
+  given ec: ExecutionContext = ...
 
   def f(x: Int): ExecutionContext ?=> Int = ...
 
@@ -86,13 +86,13 @@ with context function types as parameters to avoid the plumbing boilerplate
 that would otherwise be necessary.
 ```scala
   def table(init: Table ?=> Unit) = {
-    given t as Table // note the use of a creator application; same as: given t as Table = new Table
+    given t: Table = Table()
     init
     t
   }
 
   def row(init: Row ?=> Unit)(using t: Table) = {
-    given r as Row
+    given r: Row = Row()
     init
     t.add(r)
   }