Unreachable at IdentifierResolver.cpp:78 when friend-ing a using declaration

Hi,

I'm new to clang development but I think I've managed to find
and patch a small issue. I'm not sure what SOP is for this is, so I'm
sending a message here; if this is unnecessary in the future let me
know.

The code below crashes because Sema::CheckOverload assumes that a
function declaration is in the same semantic scope as the current
lexical scope whenever the latter is a record and tries to use member
using hiding rules:

struct A
{
    void delete_foo();
};

struct B : public A
{
    using A::delete_foo;
};

struct Foo { friend void B::delete_foo(); private: ~Foo() { } };

Similar results are obtained when "friend"-ing a using declaration
declared at namespace scope.

I added a small check to verify that the new function declaration is
actually in the same semantic scope as the current (record) scope: as
far as I can tell this can only affect "friend" declarations. The code
above now triggers an error "declaration conflicts with target of
using declaration already in scope" (I believe this is correct, g++
errors as well) rather than a crash, and added a test for this case.

Bug report at http://llvm.org/bugs/show_bug.cgi?id=15485 with patch attached.

Let me know if there's anything else I can do to help with this issue.

Thanks,
Stephen

Apologies, not sure why I didn't notice before but the patch I
attached seems to break a test (namespace.udecl/p12.cpp), so ignore
it.

I updated the patch to check specifically for friend decls, rather
than basing the check on semantic scope (didn't realize that using
decls also belonged to the semantic scope of their original class;
build environment was in a different state than what I thought when I
ran the tests originally so didn't catch it)...all tests passed now
(including the new one to test this particular issue).

I just realized there's a separate cfe-commits list: should I submit
the patch there? Sorry for my unfamiliarity with procedures.

Thanks,
Stephen