a11y: Consistently use list type for errormessage relation

This more closely matches the spec. This is an API break, however the
atspi backend already assumed that this was a list, and would throw
criticals whenever this relation was set. Therefore it can be assumed
that this relation was not previously in active use.

demos/gtk-demo/errorstates.c

@@ -55,7 +55,7 @@ mode_switch_state_set (GtkSwitch *sw,
     {
       gtk_widget_set_visible (label, TRUE);
       gtk_accessible_update_relation (GTK_ACCESSIBLE (sw),
-                                      GTK_ACCESSIBLE_RELATION_ERROR_MESSAGE, label,
+                                      GTK_ACCESSIBLE_RELATION_ERROR_MESSAGE, label, NULL,
                                       -1);
       gtk_accessible_update_state (GTK_ACCESSIBLE (sw),
                                    GTK_ACCESSIBLE_STATE_INVALID, GTK_ACCESSIBLE_INVALID_TRUE,

docs/reference/gtk/section-accessibility.md

@@ -171,7 +171,7 @@ Each relation name is part of the `GtkAccessibleRelation` enumeration.
 | %GTK_ACCESSIBLE_RELATION_CONTROLS | “aria-controls” | a list of `GtkAccessible` |
 | %GTK_ACCESSIBLE_RELATION_DESCRIBED_BY | “aria-describedby” | a list of `GtkAccessible` |
 | %GTK_ACCESSIBLE_RELATION_DETAILS | “aria-details” | a list of `GtkAccessible` |
-| %GTK_ACCESSIBLE_RELATION_ERROR_MESSAGE | “aria-errormessage” | `GtkAccessible` |
+| %GTK_ACCESSIBLE_RELATION_ERROR_MESSAGE | “aria-errormessage” | a list of `GtkAccessible` |
 | %GTK_ACCESSIBLE_RELATION_FLOW_TO | “aria-flowto” | a list of `GtkAccessible` |
 | %GTK_ACCESSIBLE_RELATION_LABELLED_BY | “aria-labelledby” | a list of `GtkAccessible` |
 | %GTK_ACCESSIBLE_RELATION_OWNS | “aria-owns” | a list of `GtkAccessible` |

gtk/gtkaccessiblevalue.c

@@ -859,7 +859,7 @@ static const GtkAccessibleCollect collect_rels[] = {
   },
   [GTK_ACCESSIBLE_RELATION_ERROR_MESSAGE] = {
     .value = GTK_ACCESSIBLE_RELATION_ERROR_MESSAGE,
-    .ctype = GTK_ACCESSIBLE_COLLECT_REFERENCE,
+    .ctype = GTK_ACCESSIBLE_COLLECT_REFERENCE_LIST,
     .name = "errormessage"
   },
   [GTK_ACCESSIBLE_RELATION_FLOW_TO] = {

gtk/gtkenums.h

@@ -1684,8 +1684,8 @@ typedef enum {
  *    that describes the object. Value type: reference
  * @GTK_ACCESSIBLE_RELATION_DETAILS: Identifies the element (or elements) that
  *    provide additional information related to the object. Value type: reference
- * @GTK_ACCESSIBLE_RELATION_ERROR_MESSAGE: Identifies the element that provides
+ * @GTK_ACCESSIBLE_RELATION_ERROR_MESSAGE: Identifies the element (or elements) that
- *    an error message for an object. Value type: reference
+ *    provide an error message for an object. Value type: reference
  * @GTK_ACCESSIBLE_RELATION_FLOW_TO: Identifies the next element (or elements)
  *    in an alternate reading order of content which, at the user's discretion,
  *    allows assistive technology to override the general default of reading in

testsuite/a11y/accessible.c

@@ -661,7 +661,7 @@ main (int argc, char *argv[])
   g_test_add_data_func ("/a11y/relation/controls", GUINT_TO_POINTER (GTK_ACCESSIBLE_RELATION_CONTROLS), test_reflist_relation);
   g_test_add_data_func ("/a11y/relation/described-by", GUINT_TO_POINTER (GTK_ACCESSIBLE_RELATION_DESCRIBED_BY), test_reflist_relation);
   g_test_add_data_func ("/a11y/relation/details", GUINT_TO_POINTER (GTK_ACCESSIBLE_RELATION_DETAILS), test_reflist_relation);
-  g_test_add_data_func ("/a11y/relation/error-message", GUINT_TO_POINTER (GTK_ACCESSIBLE_RELATION_ERROR_MESSAGE), test_ref_relation);
+  g_test_add_data_func ("/a11y/relation/error-message", GUINT_TO_POINTER (GTK_ACCESSIBLE_RELATION_ERROR_MESSAGE), test_reflist_relation);
   g_test_add_data_func ("/a11y/relation/flow-to", GUINT_TO_POINTER (GTK_ACCESSIBLE_RELATION_FLOW_TO), test_reflist_relation);
   g_test_add_data_func ("/a11y/relation/labelled-by", GUINT_TO_POINTER (GTK_ACCESSIBLE_RELATION_LABELLED_BY), test_reflist_relation);
   g_test_add_data_func ("/a11y/relation/owns", GUINT_TO_POINTER (GTK_ACCESSIBLE_RELATION_OWNS), test_reflist_relation);