Allow newlines before parameter lists

Allow newline characters before a `(` token
that starts a formal parameter list.

Author: odersky

compiler/src/dotty/tools/dotc/core/Flags.scala

@@ -1,8 +1,6 @@
 package dotty.tools.dotc
 package core
 
-import language.implicitConversions
-
 object Flags {
 
   object opaques {

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

@@ -2309,6 +2309,7 @@ object Parsers {
                      ofInstance: Boolean = false): List[List[ValDef]] = {
       def recur(firstClause: Boolean, nparams: Int, contextualOnly: Boolean): List[List[ValDef]] = {
         var initialMods = EmptyModifiers
+        newLineOptWhenFollowedBy(LPAREN)
         if (in.token == GIVEN) {
           in.nextToken()
           initialMods |= Given

docs/docs/internals/syntax.md

@@ -298,7 +298,7 @@ HkTypeParam       ::=  {Annotation} [‘+’ | ‘-’] (Id[HkTypeParamClause] |
 
 ClsParamClauses   ::=  {ClsParamClause} [[nl] ‘(’ [‘implicit’] ClsParams ‘)’]
                     |  {ClsParamClause} {GivenClsParamClause}
-ClsParamClause    ::=  ‘(’ ClsParams ‘)’
+ClsParamClause    ::=  [nl] ‘(’ ClsParams ‘)’
 GivenClsParamClause::= ‘given’ (‘(’ ClsParams ‘)’ | GivenTypes)
 ClsParams         ::=  ClsParam {‘,’ ClsParam}
 ClsParam          ::=  {Annotation}                                             ValDef(mods, id, tpe, expr) -- point of mods on val/var
@@ -308,7 +308,7 @@ Param             ::=  id ‘:’ ParamType [‘=’ Expr]
 
 DefParamClauses   ::=  {DefParamClause} [[nl] ‘(’ [‘implicit’] DefParams ‘)’]
                     |  {DefParamClause} {GivenParamClause}
-DefParamClause    ::=  ‘(’ DefParams ‘)’
+DefParamClause    ::=  [nl] ‘(’ DefParams ‘)’
 GivenParamClause  ::=  ‘given’ (‘(’ DefParams ‘)’ | GivenTypes)
 DefParams         ::=  DefParam {‘,’ DefParam}
 DefParam          ::=  {Annotation} [‘inline’] Param                            ValDef(mods, id, tpe, expr) -- point of mods at id.
@@ -356,7 +356,7 @@ Dcl               ::=  RefineDcl
                     |  ‘var’ VarDcl
 ValDcl            ::=  ids ‘:’ Type                                             PatDef(_, ids, tpe, EmptyTree)
 VarDcl            ::=  ids ‘:’ Type                                             PatDef(_, ids, tpe, EmptyTree)
-DefDcl            ::=  DefSig [‘:’ Type]                                        DefDef(_, name, tparams, vparamss, tpe, EmptyTree)
+DefDcl            ::=  DefSig ‘:’ Type                                          DefDef(_, name, tparams, vparamss, tpe, EmptyTree)
 DefSig            ::=  [‘(’ DefParam ‘)’ [nl]] id
                        [DefTypeParamClause] DefParamClauses
 TypeDcl           ::=  id [TypeParamClause] SubtypeBounds [‘=’ Type]           TypeDefTree(_, name, tparams, bound

tests/pos/i5978.scala

@@ -9,8 +9,11 @@ package p1 {
   object TextParser {
     given TP as TokenParser[Char, Position[CharSequence]] {}
 
-    given FromCharToken as Conversion[Char, Position[CharSequence]]
-      given (T: TokenParser[Char, Position[CharSequence]]) = ???
+    def f given
+      TokenParser[Char, Position[CharSequence]] = ???
+
+    given FromCharToken as Conversion[Char, Position[CharSequence]] given
+      (T: TokenParser[Char, Position[CharSequence]]) = ???
   }
 
   object Testcase {