Migrate the dollar check

Author: som-snytt

compiler/src/dotty/tools/dotc/config/MigrationVersion.scala

@@ -34,6 +34,7 @@ enum MigrationVersion(val warnFrom: SourceVersion, val errorFrom: SourceVersion)
   case GivenSyntax extends MigrationVersion(future, future)
   case ImplicitParamsWithoutUsing extends MigrationVersion(`3.7`, future)
   case Scala2Implicits extends MigrationVersion(future, future)
+  case IdentifierDollars extends MigrationVersion(`3.8`, `3.9`)
 
   require(warnFrom.ordinal <= errorFrom.ordinal)
 

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

@@ -1301,11 +1301,11 @@ object Parsers {
       val start = in.sourcePos()
       ident().tap: name =>
         if checkable && name.toSimpleName.contains('$') then
-          report.error(IllegalIdentifier(name), start)
+          report.errorOrMigrationWarning(IllegalIdentifier(name), start, MigrationVersion.IdentifierDollars)
 
     extension (nameTree: NameTree) def checkName: nameTree.type =
       if !isBackquoted(nameTree) && nameTree.name.toSimpleName.contains('$') then
-        report.error(IllegalIdentifier(nameTree.name), nameTree.srcPos)
+        report.errorOrMigrationWarning(IllegalIdentifier(nameTree.name), nameTree.srcPos, MigrationVersion.IdentifierDollars)
       nameTree
 
     /** Accept identifier and return Ident with its name as a term name. */

tests/neg/i18234.scala

@@ -1,3 +1,4 @@
+//> using options -source:3.9
 /* vals */
 val goodVal = 1
 val $startVal = 1 // error