Admit @volatile on accessor in trait

There's no other place to squirrel away the annotation
until we create a field in a subclass.

The test documents the idea, but does not capture the
regression seen in the wild, as explained in a comment.

1 files changed, 13 insertions, 0 deletions

diff --git a/test/files/pos/trait_fields_volatile.scala b/test/files/pos/trait_fields_volatile.scala
new file mode 100644
index 0000000000..030b24f187
--- /dev/null
+++ b/test/files/pos/trait_fields_volatile.scala
@@ -0,0 +1,13 @@
+// This test illustrates the intent of what should work (but didn't for a while during the fields refactoring),
+// but it does not actually defend against the regression seen in twitter-util's Scheduler, which I cannot reproduce
+// outside the project. The whole project consistently fails to build before, and compiles after the commit
+// that includes this test, but this single test file (as well as Scheduler.scala with external dependencies removed)
+// compiles both before and after....
+// (https://github.com/twitter/util/blob/6398a56923/util-core/src/main/scala/com/twitter/concurrent/Scheduler.scala#L260-L265)
+// There's also a run test that checks that the field in C is actually volatile.
+trait Vola {
+  @volatile private[this] var _vola = "tile"
+  @volatile var vola = "tile"
+}
+
+class C extends Vola