Slightly better error messages from plugin

plugin/src/main/scala-2.10/coursier/ResolutionError.scala

@@ -1,5 +1,7 @@
 package coursier
 
+import scala.collection.mutable.ArrayBuffer
+
 sealed abstract class ResolutionError extends Product with Serializable {
   def cause: Option[Throwable] = this match {
     case ResolutionError.MaximumIterationsReached => None
@@ -20,15 +22,8 @@ sealed abstract class ResolutionError extends Product with Serializable {
     case ResolutionError.Conflicts(description) =>
       description
 
-    case ResolutionError.MetadataDownloadErrors(errors) =>
-      s"Encountered ${errors.length} error(s) in dependency resolution:\n" +
-        errors.map {
-          case (dep, errs) =>
-            s"  ${dep.module}:${dep.version}:\n" +
-              errs
-                .map("    " + _.replace("\n", "    \n"))
-                .mkString("\n")
-        }.mkString("\n")
+    case err: ResolutionError.MetadataDownloadErrors =>
+      err.description()
 
     case err: ResolutionError.DownloadErrors =>
       err.description(verbose = true)
@@ -47,7 +42,49 @@ object ResolutionError {
   case class UnknownException(ex: Throwable) extends ResolutionError
   case class UnknownDownloadException(ex: Throwable) extends ResolutionError
   case class Conflicts(description: String) extends ResolutionError
-  case class MetadataDownloadErrors(errors: Seq[(Dependency, Seq[String])]) extends ResolutionError
+
+  case class MetadataDownloadErrors(errors: Seq[(Dependency, Seq[String])]) extends ResolutionError {
+    def description(): String = {
+
+      def grouped(errs: Seq[String]) =
+        errs
+          .map { s =>
+            val idx = s.indexOf(": ")
+            if (idx >= 0)
+              (s.take(idx), s.drop(idx + ": ".length))
+            else
+              ("", s)
+          }
+          .groupBy(_._1)
+          .mapValues(_.map(_._2))
+          .toVector
+          .sortBy(_._1)
+
+      val lines = new ArrayBuffer[String]
+
+      lines += s"Encountered ${errors.length} error(s) in dependency resolution:"
+
+      for ((dep, errs) <- errors) {
+        lines += s"  ${dep.module}:${dep.version}:"
+
+        for ((type0, errs0) <- grouped(errs))
+          if (type0.isEmpty)
+            for (err <- errs0)
+              lines += s"    $err"
+          else
+            errs0 match {
+              case Seq(err) =>
+                lines += s"    $type0: $err"
+              case _ =>
+                lines += s"    $type0:"
+                for (err <- errs0)
+                  lines += s"      $err"
+            }
+      }
+
+      lines.mkString("\n")
+    }
+  }
 
   case class DownloadErrors(errors: Seq[FileError]) extends ResolutionError {
 

plugin/src/main/scala-2.10/coursier/Tasks.scala

@@ -439,8 +439,10 @@ object Tasks {
         }
       }
 
+      val internalRepositories = Seq(globalPluginsRepo, interProjectRepo)
+
       val repositories =
-        Seq(globalPluginsRepo, interProjectRepo) ++
+        internalRepositories ++
         sourceRepositories0 ++
         resolvers.flatMap { resolver =>
           FromSbt.repository(
@@ -528,9 +530,21 @@ object Tasks {
           ).throwException()
         }
 
-        if (res.errors.nonEmpty)
-          ResolutionError.MetadataDownloadErrors(res.errors)
+        if (res.errors.nonEmpty) {
+          val internalRepositoriesLen = internalRepositories.length
+          val errors =
+            if (repositories.length > internalRepositoriesLen)
+              // drop internal repository errors
+              res.errors.map {
+                case (dep, errs) =>
+                  dep -> errs.drop(internalRepositoriesLen)
+              }
+            else
+              res.errors
+
+          ResolutionError.MetadataDownloadErrors(errors)
             .throwException()
+        }
 
         if (verbosityLevel >= 0)
           log.info(s"Resolved ${projectDescription(currentProject)} dependencies")