Merge pull request #10089 from dotty-staging/fix-#10074

Fix #10074: Disallow `given as` syntax

Author: odersky

community-build/community-projects/scodec

@@ -3543,7 +3543,7 @@ object Parsers {
           then paramClauses(givenOnly = true)
           else Nil
         newLinesOpt()
-        if isIdent(nme.as) || !name.isEmpty || !tparams.isEmpty || !vparamss.isEmpty then
+        if !name.isEmpty || !tparams.isEmpty || !vparamss.isEmpty then
           accept(nme.as)
         val parents = constrApps(commaOK = true, templateCanFollow = true)
         if in.token == EQUALS && parents.length == 1 && parents.head.isType then

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

@@ -401,7 +401,7 @@ ObjectDef         ::=  id [Template]
 EnumDef           ::=  id ClassConstr InheritClauses EnumBody                   EnumDef(mods, name, tparams, template)
 GivenDef          ::=  [GivenSig] Type ‘=’ Expr
                     |  [GivenSig] ConstrApps [TemplateBody]
-GivenSig          ::=  [id] [DefTypeParamClause] {UsingParamClause} ‘as’
+GivenSig          ::=  [id] [DefTypeParamClause] {UsingParamClause} ‘as’       -- one of `id`, `DefParamClause`, `UsingParamClause` must appear
 Extension         ::=  ‘extension’ [DefTypeParamClause] ‘(’ DefParam ‘)’
                        {UsingParamClause}] ExtMethods
 ExtMethods        ::=  ExtMethod | [nl] ‘{’ ExtMethod {semi ExtMethod ‘}’

docs/docs/internals/syntax.md

@@ -1,4 +1,4 @@
 import scala.quoted._
 trait Bar
-inline given as Bar = ${ impl }
+inline given Bar = ${ impl }
 def impl(using qctx: QuoteContext): Expr[Bar] = report.throwError("Failed to expand!")

tests/neg-macros/i9014/Macros_1.scala

@@ -63,7 +63,7 @@ object GivenConversion {
   class Pow(self: Int):
     def **(other: Int): Int = math.pow(self, other).toInt
 
-  given as Conversion[Int, Pow] = (i: Int) => Pow(i)
+  given Conversion[Int, Pow] = (i: Int) => Pow(i)
 
   def foo[T](t: T, ev: T SUB Int) =
     ev match { case SUB.Refl() =>

tests/neg/gadt-approximation-interaction.scala

@@ -0,0 +1,3 @@
+class Context
+given Context = ???  // ok
+given as Context = ???     // error // error // error

tests/neg/i10074.scala

@@ -4,7 +4,7 @@ trait Foo[A]
 
 object Example {
 
-  given as Foo[Int] {
+  given Foo[Int] {
   }
 
   def foo0[A: Foo]: A => A = identity

tests/neg/i8896-a.scala

@@ -4,7 +4,7 @@ trait Foo[A]
 
 object Example {
 
-  given as Foo[Int] {
+  given Foo[Int] {
   }
 
   def foo0[A: Foo]: A => A = identity

tests/neg/i8896-b.scala

@@ -1,4 +1,4 @@
 trait Bar
 object Bar:
-  inline given as Bar = compiletime.error("Failed to expand!")
+  inline given Bar = compiletime.error("Failed to expand!")
   val tests = summon[Bar] // error

tests/neg/i9014.scala

@@ -1,6 +1,6 @@
 object a:
   type Foo[T]
-  given as Foo[Unit] = ???
+  given Foo[Unit] = ???
 
 val b = a
 

tests/pos/i9103.scala

@@ -63,7 +63,7 @@ object Test extends App {
     val minimum: T
   }
 
-  given as Ord[Int] {
+  given Ord[Int] {
     extension (x: Int) def compareTo(y: Int) =
       if (x < y) -1 else if (x > y) +1 else 0
     val minimum = Int.MinValue

tests/run/instances-anonymous.scala

@@ -1,7 +1,7 @@
 import compiletime.summonAll
 
 @main def Test =
-  given as Int = 10
-  given as String = "foo"
-  given as Double = 1.2
+  given Int = 10
+  given String = "foo"
+  given Double = 1.2
   println(summonAll[Int *: String *: Double *: EmptyTuple])