[FIX] web: x2m in x2m with different fields in different views

Use case: a x2m (ex: attribute values) displayed in a x2m (ex: attributes on
product) using different fields in different views (ex: tags in product form view
and list in product attribute form view). When opening the x2m record (in a
wizard) then going back on the form view, the tags are empty because the
`display_name` value has been lost when fetching x2m for the second time.

In this case, the list `fieldsInfo` needs to be updated with the existing
(default for tags) one so all the fields will be correctly loaded.

Task 1916891

closes odoo/odoo#29598

addons/web/static/src/js/views/basic/basic_view.js

@@ -107,6 +107,21 @@ var BasicView = AbstractView.extend({
                             if (_.difference(fieldViewTypes, recordViewTypes).length) {
                                 fieldNames.push(name);
                             }
+
+                            if (record.data[name].viewType === 'default') {
+                                // Use case: x2many (tags) in x2many list views
+                                // When opening the x2many record form view, the
+                                // x2many will be reloaded but it may not have
+                                // the same fields (ex: tags in list and list in
+                                // form) so we need to merge the fieldsInfo to
+                                // avoid losing the initial fields (display_name)
+                                var defaultFieldInfo = record.data[name].fieldsInfo.default;
+                                _.each(fieldViews, function (fieldView) {
+                                    _.each(fieldView.fieldsInfo, function (x2mFieldInfo) {
+                                        _.defaults(x2mFieldInfo, defaultFieldInfo);
+                                    });
+                                });
+                            }
                         }
                     }
                     // Many2one: context is not the same between the different views

addons/web/static/tests/fields/relational_fields_tests.js

@@ -2852,7 +2852,7 @@ QUnit.module('relational_fields', {
         $modal.find('thead input[type=checkbox]').click();
 
         $modal.find('.btn.btn-sm.btn-primary.o_select_button').click();
-        
+
         pager_limit = form.$('.o_field_many2many.o_field_widget.o_field_x2many.o_field_x2many_list .o_pager_limit');
         assert.equal(pager_limit.text(), '51',
             'We should have 51 records in the m2m field');
@@ -11801,6 +11801,53 @@ QUnit.module('relational_fields', {
         form.destroy();
     });
 
+    QUnit.test('widget many2many_tags in one2many with display_name', function (assert) {
+        assert.expect(4);
+        this.data.turtle.records[0].partner_ids = [2];
+
+        var form = createView({
+            View: FormView,
+            model: 'partner',
+            data: this.data,
+            arch: '<form string="Partners">' +
+                    '<sheet>' +
+                        '<field name="turtles">' +
+                            '<tree>' +
+                                '<field name="partner_ids" widget="many2many_tags"/>' +  // will use display_name
+                            '</tree>' +
+                            '<form>' +
+                                '<sheet>' +
+                                    '<field name="partner_ids"/>' +
+                                '</sheet>' +
+                            '</form>' +
+                        '</field>' +
+                    '</sheet>' +
+                '</form>',
+            archs: {
+                'partner,false,list': '<tree><field name="foo"/></tree>',
+            },
+            res_id: 1,
+        });
+
+        assert.strictEqual(form.$('.o_field_one2many[name="turtles"] .o_list_view .o_field_many2manytags[name="partner_ids"]').text().replace(/\s/g, ''),
+            "secondrecordaaa", "the tags should be correctly rendered");
+
+        // open the x2m form view
+        form.$('.o_field_one2many[name="turtles"] .o_list_view td.o_data_cell:first').click();
+        assert.strictEqual($('.modal .o_form_view .o_field_many2many[name="partner_ids"] .o_list_view .o_data_cell').text(),
+            "blipMy little Foo Value", "the list view should be correctly rendered with foo");
+
+        $('.modal button.o_form_button_cancel').click();
+        assert.strictEqual(form.$('.o_field_one2many[name="turtles"] .o_list_view .o_field_many2manytags[name="partner_ids"]').text().replace(/\s/g, ''),
+            "secondrecordaaa", "the tags should still be correctly rendered");
+
+        form.$buttons.find('.o_form_button_edit').click();
+        assert.strictEqual(form.$('.o_field_one2many[name="turtles"] .o_list_view .o_field_many2manytags[name="partner_ids"]').text().replace(/\s/g, ''),
+            "secondrecordaaa", "the tags should still be correctly rendered");
+
+        form.destroy();
+    });
+
     QUnit.module('FieldRadio');
 
     QUnit.test('fieldradio widget on a many2one in a new record', function (assert) {