Misleading diagnostic from ambiguous reference to class template

[rjmccall]

Bugzilla Link	13393
Version	trunk
OS	All
CC	@DougGregor,@zygoloid

Extended Description

jeweloflife:clang$ cat /tmp/red.cpp

template <class T> class A;
namespace inner {
  template <class T> class A;
}
using namespace inner;

class B : A<B> {};

jeweloflife:clang$ clang /tmp/red.cpp

/tmp/red.cpp:7:11: error: unknown template name 'A'
class B : A<B> {};
          ^
1 error generated.

jeweloflife:clang$ cat << EOF > /dev/null

Obviously this diagnostic should say something about an ambiguous template reference, not an unknown one.

[philnik777]

Fixed in Clang 9: https://godbolt.org/z/M181KjTra