Print pretty error message when Result.Failure is thrown (Backport #3391

) (#3393)

The new `.getOrThrow` API allows to short-circuit the result of a
`Result`. This prints a correct error message when `Result.Failure` is
thrown in a method returning `T`, instead of returned via a method
returning `Result[T]`.

Backport of pull request: #3391

Pull Request: #3393

main/eval/src/mill/eval/Evaluator.scala

@@ -79,8 +79,9 @@ object Evaluator {
     (for ((k, fs) <- evaluated.failing.items())
       yield {
         val fss = fs.map {
-          case ex: Result.Exception => ex.toString
           case Result.Failure(t, _) => t
+          case Result.Exception(Result.Failure(t, _), _) => t
+          case ex: Result.Exception => ex.toString
         }
         s"${k.render} ${fss.iterator.mkString(", ")}"
       }).mkString("\n")