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.

5 files changed, 42 insertions, 22 deletions

diff --git a/test/files/neg/no-implicit-to-anyref-any-val.check b/test/files/neg/no-implicit-to-anyref-any-val.check
new file mode 100644
index 0000000000..5953e1bd6d
--- /dev/null
+++ b/test/files/neg/no-implicit-to-anyref-any-val.check
@@ -0,0 +1,34 @@
+no-implicit-to-anyref-any-val.scala:11: error: the result type of an implicit conversion must be more specific than AnyRef
+    1: AnyRef
+    ^
+no-implicit-to-anyref-any-val.scala:17: error: type mismatch;
+ found   : Any
+ required: AnyRef
+    (null: Any): AnyRef
+         ^
+no-implicit-to-anyref-any-val.scala:21: error: type mismatch;
+ found   : AnyVal
+ required: AnyRef
+    (0: AnyVal): AnyRef
+      ^
+no-implicit-to-anyref-any-val.scala:27: error: type mismatch;
+ found   : Test.AV
+ required: AnyRef
+Note that AV extends Any, not AnyRef.
+Such types can participate in value classes, but instances
+cannot appear in singleton types or in reference comparisons.
+    new AV(0): AnyRef
+    ^
+no-implicit-to-anyref-any-val.scala:30: error: the result type of an implicit conversion must be more specific than AnyVal
+  "": AnyVal
+  ^
+no-implicit-to-anyref-any-val.scala:32: error: type mismatch;
+ found   : Object
+ required: AnyVal
+Note that implicit conversions are not applicable because they are ambiguous:
+ both method ArrowAssoc in object Predef of type [A](self: A)ArrowAssoc[A]
+ and method Ensuring in object Predef of type [A](self: A)Ensuring[A]
+ are possible conversion functions from Object to AnyVal
+  new Object() : AnyVal
+  ^
+6 errors found
diff --git a/test/files/neg/no-implicit-to-anyref.scala b/test/files/neg/no-implicit-to-anyref-any-val.scala
index 3e3d373e38..f5daf541af 100644
--- a/test/files/neg/no-implicit-to-anyref.scala
+++ b/test/files/neg/no-implicit-to-anyref-any-val.scala
@@ -26,4 +26,8 @@ object Test {
   locally {
     new AV(0): AnyRef
   }
+
+  "": AnyVal
+
+  new Object() : AnyVal
 }
diff --git a/test/files/neg/no-implicit-to-anyref.check b/test/files/neg/no-implicit-to-anyref.check
deleted file mode 100644
index fe417ad8b0..0000000000
--- a/test/files/neg/no-implicit-to-anyref.check
+++ /dev/null
@@ -1,22 +0,0 @@
-no-implicit-to-anyref.scala:11: error: the result type of an implicit conversion must be more specific than AnyRef
-    1: AnyRef
-    ^
-no-implicit-to-anyref.scala:17: error: type mismatch;
- found   : Any
- required: AnyRef
-    (null: Any): AnyRef
-         ^
-no-implicit-to-anyref.scala:21: error: type mismatch;
- found   : AnyVal
- required: AnyRef
-    (0: AnyVal): AnyRef
-      ^
-no-implicit-to-anyref.scala:27: error: type mismatch;
- found   : Test.AV
- required: AnyRef
-Note that AV extends Any, not AnyRef.
-Such types can participate in value classes, but instances
-cannot appear in singleton types or in reference comparisons.
-    new AV(0): AnyRef
-    ^
-four errors found
diff --git a/test/files/pos/implicit-anyval-2.10.flags b/test/files/pos/implicit-anyval-2.10.flags
new file mode 100644
index 0000000000..94c8056747
--- /dev/null
+++ b/test/files/pos/implicit-anyval-2.10.flags
@@ -0,0 +1 @@
+-Xsource:2.10
diff --git a/test/files/pos/implicit-anyval-2.10.scala b/test/files/pos/implicit-anyval-2.10.scala
new file mode 100644
index 0000000000..3082af73b8
--- /dev/null
+++ b/test/files/pos/implicit-anyval-2.10.scala
@@ -0,0 +1,3 @@
+object Test {
+  "": AnyVal // newly prohibited in 2.11, allowed under -Xsourse:2.10
+}
\ No newline at end of file