Better error reporting

4 files changed, 20 insertions, 15 deletions

diff --git a/build.sbt b/build.sbt
index e943e73..db54f76 100644
--- a/build.sbt
+++ b/build.sbt
@@ -48,7 +48,7 @@ lazy val buildSettings = Seq(
   organization := "com.propensive",
   scalaVersion := "2.12.2",
   name := "magnolia",
-  version := "0.1.0",
+  version := "0.2.0",
   scalacOptions ++= Seq("-deprecation", "-feature", "-Ywarn-value-discard", "-Ywarn-dead-code", "-Ywarn-nullary-unit", "-Ywarn-numeric-widen", "-Ywarn-inaccessible", "-Ywarn-adapted-args"),
   crossScalaVersions := Seq("2.10.6", "2.11.11", "2.12.2"),
   scmInfo := Some(ScmInfo(url("https://github.com/propensive/magnolia"),
diff --git a/core/src/main/scala/magnolia.scala b/core/src/main/scala/magnolia.scala
index 22beec4..d2978b5 100644
--- a/core/src/main/scala/magnolia.scala
+++ b/core/src/main/scala/magnolia.scala
@@ -134,6 +134,11 @@ class Macros(val c: whitebox.Context) {
     } else if(isSealedTrait) {
 
       val subtypes = classType.get.knownDirectSubclasses.to[List]
+
+      if(subtypes.isEmpty) {
+        c.info(c.enclosingPosition, s"could not find any direct subtypes of $typeSymbol", true)
+        c.abort(c.enclosingPosition, "")
+      }
       
       Some {
         val components = subtypes.map(_.asType.toType).map { searchType =>
@@ -167,20 +172,14 @@ class Macros(val c: whitebox.Context) {
 
     construct.map { const =>
       val impl = derivationImplicit.merge
-      val res = q"""{
+      q"""{
         def $assignedName: $resultType = $impl.construct { sourceParameter => $const }
         $assignedName
       }"""
-
-      try c.typecheck(res) catch {
-        case e: Exception =>
-          e.printStackTrace()
-      }
-      res
     }
   }
   
-  def magnolia[T: WeakTypeTag, Typeclass: WeakTypeTag]: Tree = try {
+  def magnolia[T: WeakTypeTag, Typeclass: WeakTypeTag]: Tree = {
 
     val genericType: Type = weakTypeOf[T]
     val currentStack: Stack = recursionStack.get(c.enclosingPosition).getOrElse(Stack(List(), List()))
@@ -196,7 +195,14 @@ class Macros(val c: whitebox.Context) {
       Left(c.untypecheck(c.inferImplicitValue(coDerivationType, false, false)))
     } catch {
       case e: Exception =>
-        Right(c.untypecheck(c.inferImplicitValue(contraDerivationType)))
+        try Right(c.untypecheck(c.inferImplicitValue(contraDerivationType, false, false))) catch {
+          case e: Exception =>
+            c.info(c.enclosingPosition, s"could not find an implicit instance of "+
+                s"CovariantDerivation[$typeConstructor] or "+
+                s"ContravariantDerivation[$typeConstructor]", true)
+
+            throw e
+        }
     }
     
     if(directlyReentrant) throw DirectlyReentrantException()
@@ -235,9 +241,6 @@ class Macros(val c: whitebox.Context) {
       c.abort(c.enclosingPosition, "could not infer typeclass for type $genericType")
     }
 
-  } catch {
-    case DirectlyReentrantException() => ???
-    case e: Exception => e.printStackTrace(); ???
   }
 }
 
diff --git a/examples/src/main/scala/example.scala b/examples/src/main/scala/example.scala
index 7199b13..e649b88 100644
--- a/examples/src/main/scala/example.scala
+++ b/examples/src/main/scala/example.scala
@@ -16,9 +16,11 @@ object `package` {
   implicit def showSet[T: Show]: Show[Set[T]] = s => "set"
 }
 
+sealed trait EmptyType
+
 sealed trait Tree
 case class Branch(left: Tree, right: Tree) extends Tree
-case class Leaf(value: Int) extends Tree
+case class Leaf(value: Int, no: EmptyType) extends Tree
 
 sealed trait Entity
 case class Person(name: String, address: Address) extends Entity
diff --git a/tests/shared/src/main/scala/magnolia/main.scala b/tests/shared/src/main/scala/magnolia/main.scala
index 727eb1f..014ec33 100644
--- a/tests/shared/src/main/scala/magnolia/main.scala
+++ b/tests/shared/src/main/scala/magnolia/main.scala
@@ -4,7 +4,7 @@ import examples._
 
 object Main {
   def main(args: Array[String]): Unit = {
-    println(Branch(Branch(Leaf(1), Leaf(2)), Leaf(3)).show)
+    println(Branch(Branch(Leaf(1, null), Leaf(2, null)), Leaf(3, null)).show)
     println(List[Entity](Person("John Smith",
         Address(List("1 High Street", "London", "SW1A 1AA"),
         Country("UK", "GBR", false)))).show)