2 files changed, 30 insertions, 2 deletions

diff --git a/addons/web/static/src/js/fields/abstract_field.js b/addons/web/static/src/js/fields/abstract_field.js
index 47802d5d8c7..6eac12a2dba 100644
--- a/addons/web/static/src/js/fields/abstract_field.js
+++ b/addons/web/static/src/js/fields/abstract_field.js
@@ -153,7 +153,7 @@ var AbstractField = Widget.extend({
 
         // the 'required' flag is basically only needed to determine if the widget
         // is in a valid state (not valid if empty and required)
-        this.required = options.required || false;
+        this.required = options.required || this.field.required;
 
         // the 'idForLabel' is the (html) id that should be set to the relevent
         // dom entity.  If done correctly, clicking on the corresponding label
@@ -202,7 +202,13 @@ var AbstractField = Widget.extend({
      * a field widget is valid if its value is valid and if there is a value when
      * it is required.  This is checked before saving a record, by the form view.
      *
-     * @returns {boolean}
+     * Note: the return value may be a boolean.  It is necessary for some fields
+     * (x2many) to sometimes ask confirmation to the user if the current dirty
+     * invalid line can be discarded.  This is an asynchronous operation, so we
+     * need the expressivity of something like a deferred.
+     *
+     * @returns {boolean|Deferred} true/false if the widget is valid, or a
+     *   deferred which resolves to true/false if the widget is valid or not
      */
     isValid: function () {
         var is_required = this.required;
diff --git a/addons/web/static/src/js/fields/relational_fields.js b/addons/web/static/src/js/fields/relational_fields.js
index c29f958cc06..4ae30264ff0 100644
--- a/addons/web/static/src/js/fields/relational_fields.js
+++ b/addons/web/static/src/js/fields/relational_fields.js
@@ -560,6 +560,28 @@ var FieldX2Many = AbstractField.extend({
     isSet: function () {
         return true;
     },
+    /**
+     * This is a tricky override.  For relational fields, we don't just need to
+     * know if the field is valid.  We also need to discard some invalid lines,
+     * if the user is ok with it (or automatically if the invalid line is not
+     * dirty). This is the reason why we need to change the signature of the
+     * AbstractField isValid method to optionally return a deferred.
+     *
+     * @override
+     * @returns {boolean|Deferred} if there is a renderer (sub list or kanban
+     *   view), we may need to ask the user => it will return a deferred.
+     *   Otherwise, it returns a boolean
+     */
+    isValid: function () {
+        if (!this.renderer) {
+            return this._super.apply(this, arguments);
+        }
+        var def = $.Deferred();
+        this.renderer.canBeSaved()
+            .then(def.resolve.bind(def, true))
+            .fail(def.resolve.bind(def, false));
+        return def;
+    },
 
     //--------------------------------------------------------------------------
     // Private