[REF] web: label creation on form view rendering

The original goal of the commit was to implement a missing behavior
for label tags in form view. This finally need some deeper refactoring
for it to work so this commit does not introduce any change in behavior,
only comments explaining the problem.

addons/web/static/src/js/views/form/form_renderer.js

@@ -368,24 +368,11 @@ var FormRenderer = BasicRenderer.extend({
      * @returns {jQueryElement}
      */
     _renderInnerGroupField: function (node) {
-        var self = this;
         var widget = this._renderFieldWidget(node, this.state);
-        var fieldName = node.attrs.name;
         var $tds = $('<td/>').append(widget.$el);
 
         if (node.attrs.nolabel !== '1') {
-            var $labelTd = this._renderInnerGroupLabel(node, {
-                callback: function (element, modifiers, record) {
-                    var widgets = self.allFieldWidgets[record.id];
-                    element.$el.toggleClass('o_form_label_empty', !!( // FIXME condition is evaluated twice (label AND widget...)
-                        record.data.id
-                        && (modifiers.readonly || self.mode === 'readonly')
-                        // The widget could have been rerendered so we have to
-                        // search it in the list with the field name
-                        && !_.findWhere(widgets, {name: fieldName}).isSet()
-                    ));
-                },
-            });
+            var $labelTd = this._renderInnerGroupLabel(node);
             $tds = $labelTd.add($tds);
         }
 
@@ -394,12 +381,11 @@ var FormRenderer = BasicRenderer.extend({
     /**
      * @private
      * @param {string} label
-     * @param {Object} [modifiersOptions]
      * @returns {jQueryElement}
      */
-    _renderInnerGroupLabel: function (label, modifiersOptions) {
+    _renderInnerGroupLabel: function (label) {
         return $('<td/>', {class: 'o_td_label'})
-            .append(this._renderTagLabel(label, modifiersOptions));
+            .append(this._renderTagLabel(label));
     },
     /**
      * Render a node, from the arch of the view. It is a generic method, that
@@ -566,10 +552,10 @@ var FormRenderer = BasicRenderer.extend({
     /**
      * @private
      * @param {Object} node
-     * @param {Object} [modifiersOptions]
      * @returns {jQueryElement}
      */
-    _renderTagLabel: function (node, modifiersOptions) {
+    _renderTagLabel: function (node) {
+        var self = this;
         var text;
         var fieldName = node.tag === 'label' ? node.attrs.for : node.attrs.name;
         if ('string' in node.attrs) { // allow empty string
@@ -587,6 +573,31 @@ var FormRenderer = BasicRenderer.extend({
         if (node.tag === 'label') {
             this._handleAttributes($result, node);
         }
+        var modifiersOptions;
+        if (fieldName) {
+            modifiersOptions = {
+                callback: function (element, modifiers, record) {
+                    var widgets = self.allFieldWidgets[record.id];
+                    var widget = _.findWhere(widgets, {name: fieldName});
+                    if (!widget) {
+                        return; // FIXME this occurs if the widget is created
+                                // after the label (explicit <label/> tag in the
+                                // arch), so this won't work on first rendering
+                                // only on reevaluation
+                    }
+                    element.$el.toggleClass('o_form_label_empty', !!( // FIXME condition is evaluated twice (label AND widget...)
+                        record.data.id
+                        && (modifiers.readonly || self.mode === 'readonly')
+                        && !widget.isSet()
+                    ));
+                },
+            };
+        }
+        // FIXME if the function is called with a <label/> node, the registered
+        // modifiers will be those on this node. Maybe the desired behavior
+        // would be to merge them with associated field node if any... note:
+        // this worked in 10.0 for "o_form_label_empty" reevaluation but not for
+        // "o_invisible_modifier" reevaluation on labels...
         this._registerModifiers(node, this.state, $result, modifiersOptions);
         return $result;
     },