closes 2462. better implicit error messages.

@implicitNotFound(msg="Custom error message that may refer to type parameters ${T} and ${U}")
trait Constraint[T, U]

whenever an implicit argument of type Constraint[A, B] cannot be found,
the custom error message will be used, where the type arguments are
interpolated in the obvious way

note: if the msg in the annotation references non-existing type params,
a warning is emitted

the patch also cleans up annotation argument retrieval (moved it to
AnnotationInfo from Symbol)

review by odersky

1 files changed, 1 insertions, 0 deletions

diff --git a/src/compiler/scala/tools/nsc/symtab/Definitions.scala b/src/compiler/scala/tools/nsc/symtab/Definitions.scala
index d9e453291f..dbf95f9ac2 100644
--- a/src/compiler/scala/tools/nsc/symtab/Definitions.scala
+++ b/src/compiler/scala/tools/nsc/symtab/Definitions.scala
@@ -124,6 +124,7 @@ trait Definitions extends reflect.generic.StandardDefinitions {
     lazy val TailrecClass               = getClass("scala.annotation.tailrec")
     lazy val SwitchClass                = getClass("scala.annotation.switch")
     lazy val ElidableMethodClass        = getClass("scala.annotation.elidable")
+    lazy val ImplicitNotFoundClass      = getClass("scala.annotation.implicitNotFound")
     lazy val FieldTargetClass           = getClass("scala.annotation.target.field")
     lazy val GetterTargetClass          = getClass("scala.annotation.target.getter")
     lazy val SetterTargetClass          = getClass("scala.annotation.target.setter")