Fix element saving broken by unchecked-checkbox submission change

The previous commit stopped submitting empty values for unchecked
checkboxes. This broke element saving in ViewMapAddModify: the toggle_<attr>
checkboxes control whether an attribute overrides its inherited value, and
the PHP code used has_var('toggle_' . $attr) to detect whether a toggle was
rendered in the form at all (vs. the attribute being a must-field with no
toggle). With unchecked toggles no longer submitted, has_var returned false
for unchecked toggles too, causing all toggled-off attributes to be treated
as "no toggle = include unconditionally", which selected all elements.

Fix by rendering a hidden sentinel field (_has_toggle_<attr>) alongside each
toggle checkbox. has_var now checks the sentinel, which is always submitted
as a hidden field regardless of the checkbox state, so the distinction
between "toggle present but unchecked" and "no toggle rendered" is preserved.

Author: loocars

changelog.d/fix-element-saving-after-checkbox-submit-change.md

@@ -0,0 +1 @@
+FIX: Saving map elements incorrectly applied all attributes after the unchecked-checkbox submission fix

share/server/core/classes/ViewMapAddModify.php

@@ -79,7 +79,7 @@ private function filterMapAttrs()
 
             if (
                 (isset($attrDefs[$attr]['must']) && $attrDefs[$attr]['must'] == '1')
-                || !has_var('toggle_' . $attr)
+                || !has_var('_has_toggle_' . $attr)
                 || get_checkbox('toggle_' . $attr)
             ) {
                 if (isset($attrDefs[$attr]['array']) && $attrDefs[$attr]['array']) {
@@ -462,6 +462,12 @@ private function drawField($propname, $prop, $properties)
         // Add a checkbox to toggle the usage of an attribute. But only add it for
         // non-must attributes.
         if (!$prop['must'] && $fieldType != 'readonly') {
+            // Sentinel hidden field so the server can detect that this toggle exists
+            // in the form regardless of whether the checkbox is checked or not.
+            // Unchecked checkboxes are not submitted by the browser (or by getFormParams),
+            // so has_var('toggle_X') alone cannot distinguish "toggle rendered but unchecked"
+            // from "no toggle rendered at all".
+            hidden('_has_toggle_' . $propname, '1');
             checkbox(
                 'toggle_' . $propname,
                 $isInherited === false,