New function '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.

* doc/lispref/text.texi (Parsing HTML/XML): Document libxml-available-p.
(GnuTLS Cryptography, Format of GnuTLS Cryptography Inputs)
(Document Object Model): Fix indentation of the first paragraph.

* etc/NEWS (libxml-available-p): Mention libxml-available-p.

3 files changed, 33 insertions, 8 deletions

diff --git a/src/emacs.c b/src/emacs.c
index 0fe7d9113b4..808abcd9aa2 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 78843483edc..1ce32f33420 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4391,9 +4391,9 @@ 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 d087a34a5e0..7afaa63c421 100644
--- a/src/xml.c
+++ b/src/xml.c
@@ -18,15 +18,15 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 
 #include <config.h>
 
+#include "lisp.h"
+#include "buffer.h"
+
 #ifdef HAVE_LIBXML2
 
 #include <libxml/tree.h>
 #include <libxml/parser.h>
 #include <libxml/HTMLparser.h>
 
-#include "lisp.h"
-#include "buffer.h"
-
 
 #ifdef WINDOWSNT
 
@@ -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 */
 
 
+
+DEFUN ("libxml-available-p", Flibxml_available_p, Slibxml_available_p, 0, 0, 0,
+       doc: /* Return t if libxml2 support 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 */