bug#33679: Emacs uses APIs deprecated in WebKitGTK 2.21.1

[Paul Eggert <eggert@cs.ucla.edu>]

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I hadn't built Emacs lately with xwidgets support. When I tried it on Fedora 29 
via './configure --with-xwidgets --enable-gcc-warnings' the build failed with 
the diagnostics at the end of this message. Apparently WebKitGTK has mutated and 
Emacs hasn't kept up. Although I plan to work around the immediate problem by 
installing the attached patch on master, could an xwidgets expert please fix 
this the "right" way by using the JavaScriptCore GLib API instead? Thanks.

   CC       xwidget.o
xwidget.c: In function ‘webkit_javascript_finished_cb’:
xwidget.c:393:2: error: ‘webkit_javascript_result_get_global_context’ is 
deprecated [-Werror=deprecated-declarations]
   context = webkit_javascript_result_get_global_context (js_result);
   ^~~~~~~
In file included from /usr/include/webkitgtk-4.0/webkit2/webkit2.h:54,
                  from xwidget.c:30:
/usr/include/webkitgtk-4.0/webkit2/WebKitJavascriptResult.h:49:1: note: declared 
here
  webkit_javascript_result_get_global_context (WebKitJavascriptResult *js_result);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
xwidget.c:394:2: error: ‘webkit_javascript_result_get_value’ is deprecated: Use 
'webkit_javascript_result_get_js_value' instead [-Werror=deprecated-declarations]
   value = webkit_javascript_result_get_value (js_result);
   ^~~~~
In file included from /usr/include/webkitgtk-4.0/webkit2/webkit2.h:54,
                  from xwidget.c:30:
/usr/include/webkitgtk-4.0/webkit2/WebKitJavascriptResult.h:52:1: note: declared 
here
  webkit_javascript_result_get_value          (WebKitJavascriptResult *js_result);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[1]: *** [Makefile:384: xwidget.o] Error 1
make[1]: Leaving directory '/home/eggert/src/gnu/emacs/master-tmp/src'
make: *** [Makefile:421: src] Error 2

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From bcdda254cb249950812a6b7122278a4d63761194 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Sat, 8 Dec 2018 15:29:07 -0800
Subject: [PATCH] Suppress WebKitGTK+ 2.21.1 diagnostics

* src/xwidget.c: Suppress deprecation warnings.
---
 src/xwidget.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/xwidget.c b/src/xwidget.c
index 6da7a0bb3f..24f7d39077 100644
--- a/src/xwidget.c
+++ b/src/xwidget.c
@@ -30,6 +30,14 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #include <webkit2/webkit2.h>
 #include <JavaScriptCore/JavaScript.h>
 
+/* Suppress GCC deprecation warnings starting in WebKitGTK+ 2.21.1 for
+   webkit_javascript_result_get_global_context and
+   webkit_javascript_result_get_value.
+   FIXME: Use the JavaScriptCore GLib API instead, and remove this hack.  */
+#if WEBKIT_CHECK_VERSION (2, 21, 1) && GNUC_PREREQ (4, 2, 0)
+# pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+#endif
+
 static struct xwidget *
 allocate_xwidget (void)
 {
-- 
2.19.2