Fix Typeable for inner classes

Fixes #748
milessabin · Dec 24, 2019 · fe4bbe0 · fe4bbe0
1 parent 8ce40d1
commit fe4bbe0
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Showing 2 changed files with 25 additions and 1 deletion.
diff --git a/core/src/main/scala/shapeless/typeable.scala b/core/src/main/scala/shapeless/typeable.scala
@@ -119,6 +119,14 @@ object Typeable extends TupleTypeableInstances with LowPriorityTypeable {
       def describe = name
     }
 
+  /** Typeable instance defined by a partial function and given an explicit name */
+  def partialFunctionTypeable[T](pf: PartialFunction[Any, T], name: => String): Typeable[T] =
+    new Typeable[T] {
+      val caster = pf.lift
+      def cast(t: Any) = caster(t)
+      def describe = name
+    }
+
   /** Typeable instance for singleton value types */
   def valueSingletonTypeable[T](value: T, name: String): Typeable[T] =
     new Typeable[T] {
@@ -454,8 +462,11 @@ class TypeableMacros(val c: blackbox.Context) extends SingletonTypeUtils {
           } else {
             c.abort(c.enclosingPosition, s"No default Typeable for type $tpe capturing an outer type variable")
           }
+        } else if (tsym.isStatic || tsym.isFinal || (tsym.isClass && tsym.asClass.isTrait)) {
+          // scala/bug#4440 Final inner classes and traits have no outer accessor.
+          q"_root_.shapeless.Typeable.namedSimpleTypeable(classOf[$tpe], ${nameOf(tsym)})"
         } else {
-          q"""_root_.shapeless.Typeable.namedSimpleTypeable(_root_.scala.Predef.classOf[$tpe], ${nameOf(tsym)})"""
+          q"_root_.shapeless.Typeable.partialFunctionTypeable({ case x: $tpe => x }, ${nameOf(tsym)})"
         }
     }
   }

diff --git a/core/src/test/scala/shapeless/typeable.scala b/core/src/test/scala/shapeless/typeable.scala
@@ -25,6 +25,11 @@ class TypeableTests {
   import syntax.typeable._
   import test._
 
+  class Outer {
+    class Inner
+    val inner = new Inner
+  }
+
   @Test
   def testPrimitives: Unit = {
     val b: Any = 23.toByte
@@ -684,4 +689,12 @@ class TypeableTests {
     assertEquals("|+|.type", Typeable[|+|.type].describe)
     assertEquals("Symbol('witness)", Typeable[witness.T].describe)
   }
+
+  @Test
+  def testInnerClasses(): Unit = {
+    val outer1 = new Outer
+    val outer2 = new Outer
+    assertEquals(None, outer1.inner.cast[outer2.Inner])
+    assertEquals(Some(outer1.inner), outer1.inner.cast[outer1.Inner])
+  }
 }