SI-4425 do some validity checking on unapplies.

Filter out unapplies which can't be called (such as those with
a second non-implicit parameter list) and report the error in a
meaningful fashion.

2 files changed, 14 insertions, 3 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/ContextErrors.scala b/src/compiler/scala/tools/nsc/typechecker/ContextErrors.scala
index 81f5545695..7f4bf0dfbc 100644
--- a/src/compiler/scala/tools/nsc/typechecker/ContextErrors.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/ContextErrors.scala
@@ -593,7 +593,12 @@ trait ContextErrors {
       }
 
       def CaseClassConstructorError(tree: Tree) = {
-        issueNormalTypeError(tree, tree.symbol + " is not a case class constructor, nor does it have an unapply/unapplySeq method")
+        val baseMessage = tree.symbol + " is not a case class constructor, nor does it have an unapply/unapplySeq method"
+        val addendum = directUnapplyMember(tree.symbol.info) match {
+          case sym if hasMultipleNonImplicitParamLists(sym) => s"\nNote: ${sym.defString} exists in ${tree.symbol}, but it cannot be used as an extractor due to its second non-implicit parameter list"
+          case _                                            => ""
+        }
+        issueNormalTypeError(tree, baseMessage + addendum)
         setError(tree)
       }
 
diff --git a/src/compiler/scala/tools/nsc/typechecker/Unapplies.scala b/src/compiler/scala/tools/nsc/typechecker/Unapplies.scala
index 0e2c836860..18b8f8a9ce 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Unapplies.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Unapplies.scala
@@ -46,8 +46,14 @@ trait Unapplies extends ast.TreeDSL {
     }
   }
 
-  /** returns unapply or unapplySeq if available */
-  def unapplyMember(tp: Type): Symbol = (tp member nme.unapply) orElse (tp member nme.unapplySeq)
+  /** Returns unapply or unapplySeq if available, without further checks.
+   */
+  def directUnapplyMember(tp: Type): Symbol = (tp member nme.unapply) orElse (tp member nme.unapplySeq)
+
+  /** Filters out unapplies with multiple (non-implicit) parameter lists,
+   *  as they cannot be used as extractors
+   */
+  def unapplyMember(tp: Type): Symbol = directUnapplyMember(tp) filter (sym => !hasMultipleNonImplicitParamLists(sym))
 
   object ExtractorType {
     def unapply(tp: Type): Option[Symbol] = unapplyMember(tp).toOption