mirrors now support overriden fields and methods

Previously `checkMemberOf` was blocking base fields and methods
that are overriden in receiver.getClass. Now this is fixed.

The fix also uncovered an issue with field mirrors. Currently
their `get` and `set` methods don't respect overriding and always
return field values from a base class.

After discussing this on a reflection meeting, we decided that this
behavior is desirable and that for overriding people should use
reflectMethod and then apply on getters/setters. See the discussion at:
https://github.com/scala/scala/pull/1054.

2 files changed, 21 insertions, 1 deletions

diff --git a/src/reflect/scala/reflect/api/Mirrors.scala b/src/reflect/scala/reflect/api/Mirrors.scala
index 41acd73492..8f69ab526b 100644
--- a/src/reflect/scala/reflect/api/Mirrors.scala
+++ b/src/reflect/scala/reflect/api/Mirrors.scala
@@ -33,6 +33,14 @@ trait Mirrors { self: Universe =>
     /** Reflects against a field symbol and returns a mirror
      *  that can be used to get and, if appropriate, set the value of the field.
      *
+     *  FieldMirrors are the only way to get at private[this] vals and vars and
+     *  might be useful to inspect the data of underlying Java fields.
+     *  For all other uses, it's better to go through the fields accessor.
+     *
+     *  In particular, there should be no need to ever access a field mirror
+     *  when reflecting on just the public members of a class or trait.
+     *  Note also that only accessor MethodMirrors, but not FieldMirrors will accurately reflect overriding behavior.
+     *
      *  To get a field symbol by the name of the field you would like to reflect,
      *  use `<this mirror>.symbol.typeSignature.member(newTermName(<name of the field>)).asTerm.accessed`.
      *  For further information about member lookup refer to `Symbol.typeSignature`.
@@ -107,6 +115,10 @@ trait Mirrors { self: Universe =>
      *  Scala reflection uses reflection capabilities of the underlying platform,
      *  so `FieldMirror.get` might throw platform-specific exceptions associated
      *  with getting a field or invoking a getter method of the field.
+     *
+     *  If `symbol` represents a field of a base class with respect to the class of the receiver,
+     *  and this base field is overriden in the class of the receiver, then this method will retrieve
+     *  the value of the base field. To achieve overriding behavior, use reflectMethod on an accessor.
      */
     def get: Any
 
@@ -117,6 +129,10 @@ trait Mirrors { self: Universe =>
      *  Scala reflection uses reflection capabilities of the underlying platform,
      *  so `FieldMirror.get` might throw platform-specific exceptions associated
      *  with setting a field or invoking a setter method of the field.
+     *
+     *  If `symbol` represents a field of a base class with respect to the class of the receiver,
+     *  and this base field is overriden in the class of the receiver, then this method will set
+     *  the value of the base field. To achieve overriding behavior, use reflectMethod on an accessor.
      */
     def set(value: Any): Unit
   }
diff --git a/src/reflect/scala/reflect/runtime/JavaMirrors.scala b/src/reflect/scala/reflect/runtime/JavaMirrors.scala
index f9407d5b1b..d671225c37 100644
--- a/src/reflect/scala/reflect/runtime/JavaMirrors.scala
+++ b/src/reflect/scala/reflect/runtime/JavaMirrors.scala
@@ -161,7 +161,11 @@ trait JavaMirrors extends internal.SymbolTable with api.JavaUniverse { self: Sym
       } else if (wannabe.owner == AnyValClass) {
         if (!owner.isPrimitiveValueClass && !owner.isDerivedValueClass) ErrorNotMember(wannabe, owner)
       } else {
-        if (!owner.info.member(wannabe.name).alternatives.contains(wannabe)) ErrorNotMember(wannabe, owner)
+        def isMemberOf(wannabe: Symbol, owner: ClassSymbol): Boolean = {
+          val isNonShadowedMember = owner.info.member(wannabe.name).alternatives.contains(wannabe)
+          isNonShadowedMember || owner.info.baseClasses.tail.exists(base => isMemberOf(wannabe, base.asClass))
+        }
+        if (!isMemberOf(wannabe, owner)) ErrorNotMember(wannabe, owner)
       }
     }