Fix #9839: Drop old extension method syntax

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

@@ -3286,40 +3286,11 @@ object Parsers {
         makeConstructor(Nil, vparamss, rhs).withMods(mods).setComment(in.getDocComment(start))
       }
       else {
-        var mods1 = addFlag(mods, Method)
-        var isInfix = false
-        def extParamss() =
-          try paramClause(0, prefix = true) :: Nil
-          finally
-            mods1 = addFlag(mods, ExtensionMethod)
-            if in.token == DOT then in.nextToken()
-            else
-              isInfix = true
-              newLineOpt()
-        val (leadingTparams, leadingVparamss) =
-          if in.token == LBRACKET then
-            (typeParamClause(ParamOwner.Def), extParamss())
-          else if in.token == LPAREN then
-            (Nil, extParamss())
-          else
-            (Nil, Nil)
+        val mods1 = addFlag(mods, Method)
         val ident = termIdent()
         var name = ident.name.asTermName
-        if mods1.is(ExtensionMethod) then name = name.toExtensionName
-        if isInfix && !name.isOperatorName then
-          val infixAnnot = Apply(wrapNew(scalaAnnotationDot(tpnme.infix)), Nil)
-              .withSpan(Span(start, start))
-          mods1 = mods1.withAddedAnnotation(infixAnnot)
-        val tparams =
-          if in.token == LBRACKET then
-            if mods1.is(ExtensionMethod) then syntaxError("no type parameters allowed here")
-            typeParamClause(ParamOwner.Def)
-          else leadingTparams
-        val vparamss = paramClauses() match
-          case rparams :: rparamss if leadingVparamss.nonEmpty && ident.name.isRightAssocOperatorName =>
-            rparams :: leadingVparamss ::: rparamss
-          case rparamss =>
-            leadingVparamss ::: rparamss
+        val tparams = typeParamClauseOpt(ParamOwner.Def)
+        val vparamss = paramClauses()
         var tpt = fromWithinReturnType {
           if in.token == COLONEOL then in.token = COLON
      	      // a hack to allow

compiler/test/dotty/tools/repl/ReplCompilerTests.scala

@@ -170,8 +170,8 @@ class ReplCompilerTests extends ReplTest {
       run("""
         |trait Ord[T] {
         |  def compare(x: T, y: T): Int
-        |  def (x: T) < (y: T) = compare(x, y) < 0
-        |  def (x: T) > (y: T) = compare(x, y) > 0
+        |  extension (x: T) def < (y: T) = compare(x, y) < 0
+        |  extension (x: T) def > (y: T) = compare(x, y) > 0
         |}
         |
         |given IntOrd as Ord[Int] {

tests/pos/i7700.scala

@@ -7,6 +7,6 @@ object Macros:
   extension (sc: StringContext) inline def show(args: =>Any*): String = ???
 
 object Show:
-  def[A] (a: A) show(using S: Show[A]): String = S.show(a)
+  extension [A] (a: A) def show(using S: Show[A]): String = S.show(a)
 
   export Macros.show

tests/pos/i8198.scala

@@ -1,10 +1,11 @@
 trait Eq[A] {
-  def (x: A) === (y: A): Boolean
-  def (x: A) /== (y: A): Boolean = !(x === y)
+  extension (x: A)
+    def === (y: A): Boolean
+    def /== (y: A): Boolean = !(x === y)
 }
 
 case class Id[T](id: T)
 
 given idEq[A](using eqA: Eq[A]) as Eq[Id[A]] = new {
-  def (i1: Id[A]) === (i2: Id[A]) = !(i1.id /== i2.id)
+  extension (i1: Id[A]) def === (i2: Id[A]) = !(i1.id /== i2.id)
 }

tests/run/extension-methods.scala

@@ -62,8 +62,8 @@ object Test extends App {
   }
 
   class ListOrd[T: Ord] extends Ord[List[T]] {
-    def (xs: List[T])
-        compareTo (ys: List[T]): Int = (xs, ys) match {
+    extension (xs: List[T])
+      def compareTo (ys: List[T]): Int = (xs, ys) match {
       case (Nil, Nil) => 0
       case (Nil, _) => -1
       case (_, Nil) => +1
@@ -89,11 +89,9 @@ object Test extends App {
   }
 
   trait Monad[F[_]] extends Functor[F] {
-    def [A, B](x: F[A])
-        flatMap (f: A => F[B]): F[B]
-
-    def [A, B](x: F[A])
-        map (f: A => B) = x.flatMap(f `andThen` pure)
+    extension [A, B](x: F[A])
+      def flatMap (f: A => F[B]): F[B]
+      def map (f: A => B) = x.flatMap(f `andThen` pure)
 
     def pure[A](x: A): F[A]
   }