Parser fixes for allowing more newlines in given instances

Author: odersky

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

@@ -918,8 +918,14 @@ object Parsers {
       val lookahead = in.LookaheadScanner()
       if lookahead.isIdent then
         lookahead.nextToken()
-      while lookahead.token == LPAREN || lookahead.token == LBRACKET do
-        lookahead.skipParens()
+      def skipParams(): Unit =
+        if lookahead.token == LPAREN || lookahead.token == LBRACKET then
+          lookahead.skipParens()
+          skipParams()
+        else if lookahead.isNewLine then
+          lookahead.nextToken()
+          skipParams()
+      skipParams()
       lookahead.isIdent(nme.as)
 
     def followingIsExtension() =
@@ -3483,14 +3489,21 @@ object Parsers {
 
       val gdef = in.endMarkerScope(if name.isEmpty then GIVEN else name) {
         val tparams = typeParamClauseOpt(ParamOwner.Def)
-        val vparamss = paramClauses(givenOnly = true)
+        newLineOpt()
+        val vparamss =
+          if in.token == LPAREN && in.lookaheadIn(nme.using)
+          then paramClauses(givenOnly = true)
+          else Nil
+        newLinesOpt()
         if !name.isEmpty || !tparams.isEmpty || !vparamss.isEmpty then
           accept(nme.as)
         def givenAlias(tpt: Tree) =
           accept(EQUALS)
           mods1 |= Final
           DefDef(name, tparams, vparamss, tpt, subExpr())
         if in.token == USCORE then
+          if !mods.is(Inline) then
+            syntaxError("`_ <:` is only allowed for given with `inline` modifier")
           in.nextToken()
           accept(SUBTYPE)
           givenAlias(TypeBoundsTree(EmptyTree, toplevelTyp()))

tests/pos/i5978.scala

@@ -13,7 +13,10 @@ package p1 {
       (using TokenParser[Char, Position[CharSequence]]) = ???
 
     given FromCharToken(using T: TokenParser[Char, Position[CharSequence]])
-      : Conversion[Char, Position[CharSequence]] = ???
+
+      // skipping newlines is OK here
+
+      as Conversion[Char, Position[CharSequence]] = ???
   }
 
   object Testcase {