a11y: Add dummy AT-SPI context

Does not do anything, at the moment, but it's going to get filled out
soon.

The backend is selected depending on the platform being compiled in;
since we're using AT-SPI on X11 and Wayland, and we don't have other
accessibility implementations, we currently don't care about run time
selection, but we're going to have to deal with that.

gtk/a11y/gtkatspicontext.c

@@ -0,0 +1,85 @@
+/* gtkatspicontext.c: AT-SPI GtkATContext implementation
+ *
+ * Copyright 2020  GNOME Foundation
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "gtkatspicontextprivate.h"
+
+struct _GtkAtSpiContext
+{
+  GtkATContext parent_instance;
+};
+
+G_DEFINE_TYPE (GtkAtSpiContext, gtk_at_spi_context, GTK_TYPE_AT_CONTEXT)
+
+static void
+gtk_at_spi_context_state_change (GtkATContext                *self,
+                                 GtkAccessibleStateChange     changed_states,
+                                 GtkAccessiblePropertyChange  changed_properties,
+                                 GtkAccessibleRelationChange  changed_relations,
+                                 GtkAccessibleAttributeSet   *states,
+                                 GtkAccessibleAttributeSet   *properties,
+                                 GtkAccessibleAttributeSet   *relations)
+{
+}
+
+static void
+gtk_at_spi_context_constructed (GObject *gobject)
+{
+  G_OBJECT_CLASS (gtk_at_spi_context_parent_class)->constructed (gobject);
+}
+
+static void
+gtk_at_spi_context_class_init (GtkAtSpiContextClass *klass)
+{
+  GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
+  GtkATContextClass *context_class = GTK_AT_CONTEXT_CLASS (klass);
+
+  gobject_class->constructed = gtk_at_spi_context_constructed;
+
+  context_class->state_change = gtk_at_spi_context_state_change;
+}
+
+static void
+gtk_at_spi_context_init (GtkAtSpiContext *self)
+{
+}
+
+/*< private >
+ * gtk_at_spi_context_new:
+ * @accessible_role: the accessible role for the AT context
+ * @accessible: the #GtkAccessible instance which owns the context
+ *
+ * Creates a new #GtkAtSpiContext instance for @accessible, using the
+ * given @accessible_role.
+ *
+ * Returns: (transfer full): the newly created #GtkAtSpiContext
+ */
+GtkATContext *
+gtk_at_spi_context_new (GtkAccessibleRole  accessible_role,
+                        GtkAccessible *    accessible)
+{
+  g_return_val_if_fail (GTK_IS_ACCESSIBLE (accessible), NULL);
+
+  return g_object_new (GTK_TYPE_AT_SPI_CONTEXT,
+                       "accessible-role", accessible_role,
+                       "accessible", accessible,
+                       NULL);
+}

gtk/a11y/gtkatspicontextprivate.h

@@ -0,0 +1,35 @@
+/* gtkatspicontextprivate.h: AT-SPI GtkATContext implementation
+ *
+ * Copyright 2020  GNOME Foundation
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "gtkatcontextprivate.h"
+
+G_BEGIN_DECLS
+
+#define GTK_TYPE_AT_SPI_CONTEXT (gtk_at_spi_context_get_type())
+
+G_DECLARE_FINAL_TYPE (GtkAtSpiContext, gtk_at_spi_context, GTK, AT_SPI_CONTEXT, GtkATContext)
+
+GtkATContext *
+gtk_at_spi_context_new (GtkAccessibleRole  accessible_role,
+                        GtkAccessible     *accessible);
+
+G_END_DECLS

gtk/a11y/meson.build

@@ -7,4 +7,8 @@ endif
 
 if gtk_a11y_backends.contains('atspi')
   subdir('atspi')
+
+  gtk_a11y_src += files([
+    'gtkatspicontext.c',
+  ])
 endif

gtk/gtkatcontext.c

@@ -36,9 +36,14 @@
 #include "gtkatcontextprivate.h"
 
 #include "gtkaccessiblevalueprivate.h"
+#include "gtkdebug.h"
 #include "gtktestatcontextprivate.h"
 #include "gtktypebuiltins.h"
 
+#if defined(GDK_WINDOWING_X11) || defined(GDK_WINDOWING_WAYLAND)
+#include "a11y/gtkatspicontextprivate.h"
+#endif
+
 G_DEFINE_ABSTRACT_TYPE (GtkATContext, gtk_at_context, G_TYPE_OBJECT)
 
 enum
@@ -354,6 +359,20 @@ gtk_at_context_get_accessible_role (GtkATContext *self)
   return self->accessible_role;
 }
 
+static const struct {
+  const char *name;
+  GtkATContext * (* create_context) (GtkAccessibleRole accessible_role,
+                                     GtkAccessible    *accessible);
+} a11y_backends[] = {
+#if defined(GDK_WINDOWING_WAYLAND)
+  { "AT-SPI", _gtk_at_spi_context_new },
+#endif
+#if defined(GDK_WINDOWING_X11)
+  { "AT-SPI", gtk_at_spi_context_new },
+#endif
+  { NULL, NULL },
+};
+
 /**
  * gtk_at_context_create: (constructor)
  * @accessible_role: the accessible role used by the #GtkATContext
@@ -401,8 +420,23 @@ gtk_at_context_create (GtkAccessibleRole  accessible_role,
   if (gtk_no_a11y[0] == '1')
     return NULL;
 
+  GtkATContext *res = NULL;
+
+  for (guint i = 0; i < G_N_ELEMENTS (a11y_backends); i++)
+    {
+      GTK_NOTE (A11Y, g_message ("Trying %s a11y backend", a11y_backends[i].name));
+      if (a11y_backends[i].create_context != NULL)
+        {
+          res = a11y_backends[i].create_context (accessible_role, accessible);
+          break;
+        }
+    }
+
+  if (res == NULL)
+    res = gtk_test_at_context_new (accessible_role, accessible);
+
   /* FIXME: Add GIOExtension for AT contexts */
-  return gtk_test_at_context_new (accessible_role, accessible);
+  return res;
 }
 
 /*< private >