don't try to create tags w/o scala-reflect.jar

Since recently type tags have relocated to scala-reflect.jar,
meaning that they are no longer always on library classpath.

In the compiler we do have code that generates type tags, and this code
is bound to fail if scala-reflect.jar isn't there.

I though this wouldn't be a problem, because type tag materialization
is only going to be triggered by users explicitly requesting a type tag.

That's generally true, but I overlooked a corner case. Since we provide
manifest <-> type tag compatibility, manifest lookup can sometimes trigger
tag lookup, which might result in tag synthesis, which blows up like this:
http://groups.google.com/group/scala-internals/browse_thread/thread/166ce4b71b7c46bb

This commit also ensures that type tag generation/interop doesnt sneak into the
code of the libraries that don't have scala-reflect.jar on their classpath.
For details refer to the discussion at scala-internals:
http://groups.google.com/group/scala-internals/browse_thread/thread/72f6ce3010f4d8

1 files changed, 3 insertions, 0 deletions

diff --git a/test/files/run/typetags_without_scala_reflect_typetag_lookup.check b/test/files/run/typetags_without_scala_reflect_typetag_lookup.check
new file mode 100644
index 0000000000..f6b82c33f6
--- /dev/null
+++ b/test/files/run/typetags_without_scala_reflect_typetag_lookup.check
@@ -0,0 +1,3 @@
+newSource1:9: error: could not find implicit value for evidence parameter of type reflect.runtime.package.universe.TypeTag[Int]

+      Library.foo[Int]

+                 ^