Fix #9091: Drop deprecated extension method syntax

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

@@ -3320,11 +3320,7 @@ object Parsers {
           mods1 = mods1.withAddedAnnotation(infixAnnot)
         val tparams =
           if in.token == LBRACKET then
-            if mods1.is(Extension) then
-              if leadingTparams.isEmpty then
-                deprecationWarning("type parameters in extension methods should be written after `def`")
-              else
-                syntaxError("no type parameters allowed here")
+            if mods1.is(Extension) then syntaxError("no type parameters allowed here")
             typeParamClause(ParamOwner.Def)
           else leadingTparams
         val vparamss = paramClauses() match

tests/init/crash/i5606.scala

@@ -1,6 +1,6 @@
 object Test extends App {
 
-  def (f: A => B) `$`[A, B](a: A): B = f(a)
+  def [A, B](f: A => B) `$` (a: A): B = f(a)
 
   assert((((a: Int) => a.toString()) `$` 10) == "10")
 

tests/neg/i6662.scala

@@ -1,9 +1,9 @@
 opaque type Opt[A >: Null] = A
 
-inline def (x: Opt[A]) nonEmpty[A >: Null]: Boolean = x.get != null // error: Implementation restriction
-inline def (x: Opt[A]) isEmpty[A >: Null]: Boolean = x.get == null // error: Implementation restriction
-inline def (x: Opt[A]) isDefined[A >: Null]: Boolean = x.nonEmpty // error: Implementation restriction
-inline def (x: Opt[A]) get[A >: Null]: A = Opt.unOpt(x) // error: Implementation restriction
+inline def [A >: Null](x: Opt[A]) nonEmpty: Boolean = x.get != null // error: Implementation restriction
+inline def [A >: Null](x: Opt[A]) isEmpty: Boolean = x.get == null // error: Implementation restriction
+inline def [A >: Null](x: Opt[A]) isDefined: Boolean = x.nonEmpty // error: Implementation restriction
+inline def [A >: Null](x: Opt[A]) get: A = Opt.unOpt(x) // error: Implementation restriction
 
 object Opt
 {

tests/neg/i6762b.scala

@@ -9,5 +9,5 @@ type Liftable
 given Liftable = ???
 
 implicit object ExprOps {
-  def (x: T).toExpr[T](using Liftable): Expr[T] = ???
+  def [T](x: T).toExpr(using Liftable): Expr[T] = ???
 }

tests/neg/i6779.scala

@@ -3,7 +3,7 @@ type G[T]
 type Stuff
 given Stuff = ???
 
-def (x: T).f[T](using Stuff): F[T] = ???
+def [T](x: T).f(using Stuff): F[T] = ???
 
 
 def g1[T](x: T): F[G[T]] = x.f(using summon[Stuff]) // error

tests/neg/i7438.scala

@@ -1,5 +1,5 @@
 type Tr[+A]
-inline def (tr: Tr[A]).map[A, B](f: A => B): Tr[B] = ???
+inline def [A, B](tr: Tr[A]).map(f: A => B): Tr[B] = ???
 
 def (d: Double).func: None.type => Some[Double] = ???
 

tests/pos/i6565.scala

@@ -3,8 +3,8 @@ class Err
 type Lifted[A] = Err | A
 
 def point[O](o: O): Lifted[O] = o
-def (o: Lifted[O]) map [O, U] (f: O => U): Lifted[U] = ???
-def (o: Lifted[O]) flatMap [O, U] (f: O => Lifted[U]): Lifted[U] = ???
+def [O, U](o: Lifted[O]).map(f: O => U): Lifted[U] = ???
+def [O, U](o: Lifted[O]).flatMap(f: O => Lifted[U]): Lifted[U] = ???
 
 val error: Err = Err()
 

tests/run-macros/i6772/Macro_1.scala

@@ -7,7 +7,7 @@ object Macros {
   def mImpl()(using QuoteContext): Expr[Any] =
     List(Expr(1), Expr(2), Expr(3)).toExprOfList
 
-  def (list: List[Expr[T]]).toExprOfList[T](using Type[T], QuoteContext): Expr[List[T]] = '{
+  def [T](list: List[Expr[T]]).toExprOfList(using Type[T], QuoteContext): Expr[List[T]] = '{
     val buff = List.newBuilder[T]
     ${ Expr.block(list.map(v => '{ buff +=  $v }), '{ buff.result() }) }
   }

tests/run-macros/reflect-sourceCode/Macro_1.scala

@@ -1,7 +1,7 @@
 import scala.quoted._
 
 object api {
-  inline def (x: => T) reflect[T] : String =
+  inline def [T](x: => T).reflect: String =
     ${ reflImpl('x) }
 
   private def reflImpl[T](x: Expr[T])(implicit qctx: QuoteContext): Expr[String] = {