Add CyclicImplicitVal error to messages

Author: felixmulder

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

@@ -899,4 +899,15 @@ object messages {
     val msg = hl"trying to define package with same name as `$existing`"
     val explanation = ""
   }
+
+  case class CyclicImplicitVal(cycleSym: Symbol)(implicit ctx: Context)
+  extends Message(34) {
+    val kind = "Cyclic Reference"
+    val msg = em"cyclic reference involving $cycleSym"
+    val explanation =
+      hl"""|This happens when the right hand-side of $cycleSym's definition
+           |involves an implicit search.
+           |
+           |To avoid the error, give $cycleSym an explicit type."""
+  }
 }

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

@@ -28,7 +28,7 @@ object ErrorReporting {
 
   def cyclicErrorMsg(ex: CyclicReference)(implicit ctx: Context) = {
     val cycleSym = ex.denot.symbol
-    def errorMsg(msg: String, cx: Context): String =
+    def errorMsg(msg: String, cx: Context): Message =
       if (cx.mode is Mode.InferringReturnType) {
         cx.tree match {
           case tree: untpd.ValOrDefDef =>
@@ -48,9 +48,7 @@ object ErrorReporting {
       } else msg
 
       if (cycleSym.is(Implicit, butNot = Method) && cycleSym.owner.isTerm)
-        em"""cyclic reference involving implicit $cycleSym
-            |This happens when the right hand-side of $cycleSym's definition involves an implicit search.
-            |To avoid the error, give $cycleSym an explicit type."""
+        CyclicImplicitVal(cycleSym)
       else
         errorMsg(ex.show, ctx)
   }