Re: What's the right way to detect libxml2?

[Robert Pluim <rpluim@gmail.com>]

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Andy Moreton <andrewjmoreton@gmail.com> writes:

> On Tue 24 Oct 2017, Clément Pit-Claudel wrote:
>
>> On 2017-10-24 09:38, Andy Moreton wrote:
>>> For libxml2, try using (shr-render-buffer) on an HTML/XML buffer to get
>>> the library loaded.
>>
>> Is that better than just calling libxml-parse-xml-region and checking for a
>> nil return value? It sounds like shr-render-buffer would do a lot more — do we
>> need that?
>
> No, it was just an example of doing something to force the library to be
> loaded. Your version is simpler, and having (libxml-available-p) would
> be even better.
>
>     AndyM

Like thus? Very lightly tested on GNU/Linux only. Might need a NEWS
entry.


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From e74de0a485009918d71d0643bc03195b5fd01761 Mon Sep 17 00:00:00 2001
From: Robert Pluim <rpluim@gmail.com>
Date: Tue, 24 Oct 2017 19:01:28 +0200
Subject: [PATCH] Provide libxml-available-p

* src/emacs.c (main): Call syms_of_xml unconditionally

* src/lisp.h: Provide syms_of_xml prototype even when
HAVE_LIBXML2 is not defined

* src/xml.c (Flibxml_available_p): New function, cloned from
Fgnutls_available_p
(syms_of_xml): Provide Slibxml_available_p
---
 src/emacs.c |  2 --
 src/lisp.h  |  2 +-
 src/xml.c   | 31 +++++++++++++++++++++++++++++--
 3 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/src/emacs.c b/src/emacs.c
index 0fe7d9113b..808abcd9aa 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -1542,9 +1542,7 @@ Using an Emacs configured with --with-x-toolkit=lucid does not have this problem
 #endif
 #endif /* HAVE_X_WINDOWS */
 
-#ifdef HAVE_LIBXML2
       syms_of_xml ();
-#endif
 
 #ifdef HAVE_LCMS2
       syms_of_lcms2 ();
diff --git a/src/lisp.h b/src/lisp.h
index 266370333f..cc8d90cbf1 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4399,9 +4399,9 @@ extern void syms_of_xterm (void);
 extern char *x_get_keysym_name (int);
 #endif /* HAVE_WINDOW_SYSTEM */
 
-#ifdef HAVE_LIBXML2
 /* Defined in xml.c.  */
 extern void syms_of_xml (void);
+#ifdef HAVE_LIBXML2
 extern void xml_cleanup_parser (void);
 #endif
 
diff --git a/src/xml.c b/src/xml.c
index d087a34a5e..825d5a0f64 100644
--- a/src/xml.c
+++ b/src/xml.c
@@ -291,16 +291,43 @@ If DISCARD-COMMENTS is non-nil, all HTML comments are discarded. */)
     return parse_region (start, end, base_url, discard_comments, false);
   return Qnil;
 }
+#endif /* HAVE_LIBXML2 */
 
 \f
+
+DEFUN ("libxml-available-p", Flibxml_available_p, Slibxml_available_p, 0, 0, 0,
+       doc: /* Return list of capabilities if LibXML2 is available in this instance of Emacs.*/)
+  (void)
+{
+#ifdef HAVE_LIBXML2
+# ifdef WINDOWSNT
+  Lisp_Object found = Fassq (Qlibxml2, Vlibrary_cache);
+  if (CONSP (found))
+    return XCDR (found);
+  else
+    {
+      Lisp_Object status;
+      status = init_libxml2_functions () ? Qt : Qnil;
+      Vlibrary_cache = Fcons (Fcons (Qlibxml2, status), Vlibrary_cache);
+      return status;
+    }
+# else
+  return Qt;
+# endif /* WINDOWSNT */
+#else
+  return Qnil;
+#endif	/* HAVE_LIBXML2 */
+}
+
 /***********************************************************************
 			    Initialization
  ***********************************************************************/
 void
 syms_of_xml (void)
 {
+#ifdef HAVE_LIBXML2
   defsubr (&Slibxml_parse_html_region);
   defsubr (&Slibxml_parse_xml_region);
+#endif
+  defsubr (&Slibxml_available_p);
 }
-
-#endif /* HAVE_LIBXML2 */
-- 
2.15.0.rc1