Exclude the error messages from the count of inline panel elements (#4957)

Ref #4304 ; explicitly identify and count inline-panel-child elements as per https://github.com/wagtail/wagtail/pull/4304#discussion_r169149310

CHANGELOG.txt

@@ -4,7 +4,8 @@ Changelog
 2.5 (xx.xx.xxxx) - IN DEVELOPMENT
 ~~~~~~~~~~~~~~~~
 
-* Fix: Set `SERVER_PORT` to 443 in `Page.dummy_request()` for HTTPS sites (Sergey Fedoseev)
+ * Fix: Set `SERVER_PORT` to 443 in `Page.dummy_request()` for HTTPS sites (Sergey Fedoseev)
+ * Fix: Validation error messages in `InlinePanel` no longer count towards `max_num` when disabling the 'add' button (Todd Dembrey, Thibaud Colas)
 
 
 2.4 (xx.xx.xxxx) - IN DEVELOPMENT

docs/releases/2.5.rst

@@ -19,6 +19,7 @@ Bug fixes
 ~~~~~~~~~
 
  * Set ``SERVER_PORT`` to 443 in ``Page.dummy_request()`` for HTTPS sites (Sergey Fedoseev)
+ * Validation error messages in ``InlinePanel`` no longer count towards ``max_num`` when disabling the 'add' button (Todd Dembrey, Thibaud Colas)
 
 
 Upgrade considerations

wagtail/admin/static_src/wagtailadmin/js/page-editor.js

@@ -176,7 +176,7 @@ function InlinePanel(opts) {
 
     self.updateAddButtonState = function() {
         if (opts.maxForms) {
-            var forms = $('> li', self.formsUl).not('.deleted');
+            var forms = $('> [data-inline-panel-child]', self.formsUl).not('.deleted');
             var addButton = $('#' + opts.formsetPrefix + '-ADD');
 
             if (forms.length >= opts.maxForms) {

wagtail/admin/templates/wagtailadmin/edit_handlers/inline_panel_child.html

@@ -1,5 +1,5 @@
 {% load i18n %}
-<li id="inline_child_{{ child.form.prefix }}">
+<li data-inline-panel-child id="inline_child_{{ child.form.prefix }}">
     <ul class="controls">
         {% if can_order %}
             <li><button type="button" class="button icon text-replace white icon-order-up inline-child-move-up" id="{{ child.form.prefix }}-move-up" title="{% trans 'Move up' %}">{% trans "Move up" %}</button></li>