Fix Missing error message on FailureToEliminateExistential

Author: CucumisSativus

compiler/src/dotty/tools/dotc/core/unpickleScala2/Scala2Unpickler.scala

@@ -28,6 +28,7 @@ import classfile.ClassfileParser
 import scala.collection.{ mutable, immutable }
 import scala.collection.mutable.ListBuffer
 import scala.annotation.switch
+import dotty.tools.dotc.reporting.diagnostic.messages.FailureToEliminateExistential
 
 object Scala2Unpickler {
 
@@ -676,11 +677,7 @@ class Scala2Unpickler(bytes: Array[Byte], classRoot: ClassDenotation, moduleClas
       val anyTypes = boundSyms map (_ => defn.AnyType)
       val boundBounds = boundSyms map (_.info.bounds.hi)
       val tp2 = tp1.subst(boundSyms, boundBounds).subst(boundSyms, anyTypes)
-      ctx.warning(s"""failure to eliminate existential
-                      |original type    : $tp forSome {${ctx.dclsText(boundSyms, "; ").show}
-                      |reduces to       : $tp1
-                      |type used instead: $tp2
-                      |proceed at own risk.""".stripMargin)
+      ctx.warning(FailureToEliminateExistential(tp, tp1, tp2, boundSyms))
       tp2
     } else tp1
   }

compiler/src/dotty/tools/dotc/reporting/diagnostic/ErrorMessageID.java

@@ -101,6 +101,7 @@ public enum ErrorMessageID {
     ReturnOutsideMethodDefinitionID,
     UncheckedTypePatternID,
     ExtendFinalClassID,
+    FailureToEliminateExistentialID
     ;
 
     public int errorNumber() {

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

@@ -1778,4 +1778,15 @@ object messages {
       hl"""A class marked with the ${"final"} keyword cannot be extended"""
   }
 
+  case class FailureToEliminateExistential(tp: Types.Type, tp1: Types.Type, tp2: Types.Type, boundSyms: List[Symbols.Symbol])(implicit ctx: Context)
+    extends Message(FailureToEliminateExistentialID) {
+    val kind = "Syntax"
+    val msg = hl"failure to eliminate existential"
+    val explanation =
+      hl"""original type    : $tp forSome {${ctx.dclsText(boundSyms, "; ").show}
+          |reduces to       : $tp1
+          |type used instead: $tp2
+          |proceed at own risk.
+          |"""
+  }
 }