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

[Robert Pluim]

Andy Moreton <address@hidden> writes:

> On Tue 24 Oct 2017, Robert Pluim wrote:
>> Like thus? Very lightly tested on GNU/Linux only. Might need a NEWS
>> entry.
>>
> Works for me on a 64bit MinGW64/MSYS2 build of emacs-26 on Windows 10.

OK.

> I don't think you need to remove the HAVE_LIBXML2 conditionals, as lisp
> code can check (fboundp 'libxml-available-p) before calling it, and it
> may break builds without libxml2 support.

I'm following the gnutls model, where gnutls-available-p is always
available, so you don't have to do

(and (fboundp 'libxml-available-p) (libxml-available-p))

If a build without libxml2 support breaks, then we fix the code in
emacs. Actually, my patch breaks --without-xml2 :-)

> Also, the libxml-available-p doc string claims it returns a list of
> capabilities (which is true for gnutls-available-p), but it only returns
> nil or t.

Ah yes, too much cut & paste. Revised version attached. Compile and
run-tested with and without xml2 on GNU/Linux.

>From 10fe04edc5adf942c2bf9806eea5dd81edd2c9a5 Mon Sep 17 00:00:00 2001
From: Robert Pluim <address@hidden>
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

* doc/lispref/text.texi (Parsing HTML/XML): Document libxml-available-p
---
 doc/lispref/text.texi |  5 +++++
 src/emacs.c           |  2 --
 src/lisp.h            |  2 +-
 src/xml.c             | 37 ++++++++++++++++++++++++++++++++-----
 4 files changed, 38 insertions(+), 8 deletions(-)

diff --git a/doc/lispref/text.texi b/doc/lispref/text.texi
index baa3c708e9..565d098069 100644
--- a/doc/lispref/text.texi
+++ b/doc/lispref/text.texi
@@ -4723,6 +4723,11 @@ Parsing HTML/XML
 @section Parsing HTML and XML
 @cindex parsing html
 
address@hidden libxml-available-p
+This function returns address@hidden if built-in libxml2 support is
+available.
address@hidden defun
+
 When Emacs is compiled with libxml2 support, the following functions
 are available to parse HTML or XML text into Lisp object trees.
 
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..7afaa63c42 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 */
-- 
2.15.0.rc1