Hi,

the xref backend for etags can be annoying at times, especially in
combination with other backends. This patch should improve the
situation, by allowing the user to configure how and when the etags
backend is activated. The new user option etags-query-file would allow
the backend to never query a TAGS file, or conditionally, depending on
the existence of a TAGS file (in which case it can also be automatically
loaded).

I could imagine this might be extended to allow an auto-generate option,
but that feature seems out of scope of this patch, and probably would
require some interoperation with project.el.

-- 
	Philip K.