What's the right way to detect libxml2?

[Clément Pit-Claudel]

Hi emacs-devel,

In Flycheck we use ``libxml-parse-region`` if available, and fall back to 
``xml-parse-region`` otherwise.  We recently realized that our libxml detection 
code was wrong, however.

We used to write ``(if (fboundp 'libxml-parse-region) (libxml-parse-region …) 
(xml-parse-region …))``, but this isn't sufficient on Windows, where 
``fboundp`` succeeds if Emacs was compiled with libxml support, even if the 
appropriate DLL isn't installed on the user's system.

What's the proper way to autodetect libxml? We're thinking of doing this 
instead::

   (if (and (fboundp 'libxml-parse-region)
            (with-temp-buffer
              (insert "<xml/>")
              (libxml-parse-region (point-min) (point-max))))
       (libxml-parse-region …)
     (xml-parse-region …))

Do we have better options?

Thanks!
Clément.