Prohibit views targeting AnyVal

Library changes in Scala 2.10 mean that we are left with the
unfortunate situation of admitting:

    scala> "": AnyVal
    res0: AnyVal =

 We already have explicit checks in place to prevent views
 targeting `AnyRef`. This commit balances this out by prohibiting
 `AnyVal`, as well.

The enclosed test shows that this case is now prevented. If multiple
implicits views are applicable, the ambiguity error is still raised;
these check comes right at the end. Maybe that ought to be changed,
but I don't think it matters too much.

I've also disabled this prohibition under -Xsource:2.10.

1 files changed, 33 insertions, 0 deletions

diff --git a/test/files/neg/no-implicit-to-anyref-any-val.scala b/test/files/neg/no-implicit-to-anyref-any-val.scala
new file mode 100644
index 0000000000..f5daf541af
--- /dev/null
+++ b/test/files/neg/no-implicit-to-anyref-any-val.scala
@@ -0,0 +1,33 @@
+// Checks that the state of standard implicits in Predef._ and scala._
+// doesn't allow us to unambiguously and implicitly convert AnyVal
+// and subtypes to AnyRef.
+//
+// In the days before value classes, this was precariously held be
+// the competing implicits Any => StringAdd and Any => StringFormat.
+// Since then, these have both become value classes, but seeing as
+// this happened simultaneously, we're still okay.
+object Test {
+  locally {
+    1: AnyRef
+  }
+
+  locally {
+    // before this test case was added and ContextErrors was tweaked, this
+    // emitted: "Note that Any extends Any, not AnyRef."
+    (null: Any): AnyRef
+  }
+
+  locally {
+    (0: AnyVal): AnyRef
+  }
+
+  class AV(val a: Int) extends AnyVal
+
+  locally {
+    new AV(0): AnyRef
+  }
+
+  "": AnyVal
+
+  new Object() : AnyVal
+}