constant-typed final val in trait should yield impl method

Author: adriaanm

src/compiler/scala/tools/nsc/transform/AddInterfaces.scala

@@ -58,7 +58,7 @@ abstract class AddInterfaces extends InfoTransform { self: Erasure =>
   def needsImplMethod(sym: Symbol) = (
        sym.isMethod
     && isInterfaceMember(sym)
-    && (!sym.isAccessor || sym.isLazy) // We no longer do the implclass-dance for accessors -- they are mixed in directly into their implementing classes during the fields phase
+    && (!(sym hasFlag ACCESSOR) || sym.isLazy || !(sym hasFlag SYNTHESIZE_IMPL_IN_SUBCLASS)) // SYNTHESIZE_IMPL_IN_SUBCLASS accessors are mixed in by the fields phase, but others should be treated as regulars methods (constant-typed getters)
 // so that constructors populates the init method in the impl class
     && (!sym.hasFlag(DEFERRED | SUPERACCESSOR) || (sym hasFlag lateDEFERRED))
   )

src/compiler/scala/tools/nsc/transform/Fields.scala

@@ -138,18 +138,19 @@ abstract class Fields extends InfoTransform with ast.TreeDSL with TypingTransfor
 
         // strict, memoized accessors will receive an implementation in first real class to extend this trait
         decls.foreach {
-          case accessor if (accessor hasFlag ACCESSOR) && !(accessor hasFlag (DEFERRED | LAZY))
-                        && fieldMemoizationIn(accessor, clazz).needsField =>
+          case accessor if accessor hasFlag ACCESSOR =>
             // only affects private symbols, with a destructive update of their name, also sets flags
             // required for private vals in traits
             accessor.makeNotPrivate(clazz)
 
-            // in a trait, a memoized accessor becomes deferred
-            // (it'll receive an implementation in the first real class to extend this trait)
-            markAccessorImplementedInSubclass(accessor)
+            if (!(accessor hasFlag (DEFERRED | LAZY)) && fieldMemoizationIn(accessor, clazz).needsField) {
+              // in a trait, a memoized accessor becomes deferred
+              // (it'll receive an implementation in the first real class to extend this trait)
+              markAccessorImplementedInSubclass(accessor)
 
-            if ((accessor hasFlag STABLE) && accessor.isGetter) // TODO: isGetter is probably redundant?
-              newSetters += newTraitSetter(accessor, clazz)
+              if ((accessor hasFlag STABLE) && accessor.isGetter) // TODO: isGetter is probably redundant?
+                newSetters += newTraitSetter(accessor, clazz)
+            }
 
           case _ =>
         }

src/compiler/scala/tools/nsc/transform/Mixin.scala

@@ -46,7 +46,7 @@ abstract class Mixin extends InfoTransform with ast.TreeDSL {
        sym.owner.isImplClass
     && sym.isMethod
     && (!sym.isModule || sym.hasFlag(PRIVATE | LIFTED))
-    && (!(sym hasFlag (ACCESSOR | SUPERACCESSOR)) || sym.isLazy)
+    && (!(sym hasFlag (ACCESSOR | SUPERACCESSOR)) || sym.isLazy || !(sym hasFlag SYNTHESIZE_IMPL_IN_SUBCLASS))
   )
 
   /** A member of a trait is static only if it belongs only to the

test/files/trait-defaults/fields.scala

@@ -1,3 +1,7 @@
+trait T { final val C = "S" }
+// there should be a C method in `T$class`!
+class C extends T { println(C) }
+
 trait T {
   type Res
   val x: Res = ???