Create VolatileOnVal message class

Author: AnotherMedo

compiler/src/dotty/tools/dotc/reporting/ErrorMessageID.scala

@@ -206,6 +206,7 @@ enum ErrorMessageID(val isActive: Boolean = true) extends java.lang.Enum[ErrorMe
   case PureUnitExpressionID // errorNumber: 190
   case MatchTypeLegacyPatternID // errorNumber: 191
   case UnstableInlineAccessorID // errorNumber: 192
+  case VolatileOnValID // errorNumber: 193
 
   def errorNumber = ordinal - 1
 

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -3146,3 +3146,8 @@ class UnstableInlineAccessor(accessed: Symbol, accessorTree: tpd.Tree)(using Con
     if accessor.owner.name.isPackageObjectName then accessor.owner.owner.name.stripModuleClassSuffix
     else accessor.owner.name.stripModuleClassSuffix
 }
+
+class VolatileOnVal()(using Context)
+extends SyntaxMsg(VolatileOnValID):
+  protected def msg(using Context): String = "values cannot be volatile"
+  protected def explain(using Context): String = ""

compiler/src/dotty/tools/dotc/typer/RefChecks.scala

@@ -1003,7 +1003,8 @@ object RefChecks {
 
   def checkVolatile(sym: Symbol)(using Context): Unit =
     if sym.isVolatile && !sym.is(Mutable) then 
-      report.warning(em"values cannot be volatile", sym.srcPos)
+      report.warning(VolatileOnVal(), sym.srcPos)
+  
   /** Check that unary method definition do not receive parameters.
    *  They can only receive inferred parameters such as type parameters and implicit parameters.
    */