[FIX] web: list: keep header checkbox selected

... when toggling an optional field.

This bug wasn't really important until now, but with the new
selection mechanism, it could lead to weird situations (e.g. the
selection box says that all records are selected, but the thead
checkbox isn't checked).

Part of task 2185145

addons/web/static/src/js/views/list/list_renderer.js

@@ -989,6 +989,9 @@ var ListRenderer = BasicRenderer.extend({
                     return _.contains(self.selection, $(el).data('id'));
                 });
                 $checked_rows.find('.o_list_record_selector input').prop('checked', true);
+                if ($checked_rows.length === self.$('.o_data_row').length) { // all rows are checked
+                    self.$('thead .o_list_record_selector input').prop('checked', true);
+                }
             }
         });
         return Promise.all([this._super.apply(this, arguments), prom]);

addons/web/static/tests/views/list_tests.js

@@ -8839,6 +8839,55 @@ QUnit.module('Views', {
         list.destroy();
     });
 
+    QUnit.test('selection is kept when optional fields are toggled', async function (assert) {
+        assert.expect(7);
+
+        var RamStorageService = AbstractStorageService.extend({
+            storage: new RamStorage(),
+        });
+
+        var list = await createView({
+            View: ListView,
+            model: 'foo',
+            data: this.data,
+            arch: '<tree>' +
+                    '<field name="foo"/>' +
+                    '<field name="m2o" optional="hide"/>' +
+                '</tree>',
+            services: {
+                local_storage: RamStorageService,
+            },
+        });
+
+        assert.containsN(list, 'th', 2);
+
+        // select a record
+        await testUtils.dom.click(list.$('.o_data_row .o_list_record_selector input:first'));
+
+        assert.containsOnce(list, '.o_list_record_selector input:checked');
+
+        // add an optional field
+        await testUtils.dom.click(list.$('table .o_optional_columns_dropdown_toggle'));
+        await testUtils.dom.click(list.$('div.o_optional_columns div.dropdown-item:first input'));
+        assert.containsN(list, 'th', 3);
+
+        assert.containsOnce(list, '.o_list_record_selector input:checked');
+
+        // select all records
+        await testUtils.dom.click(list.$('thead .o_list_record_selector input'));
+
+        assert.containsN(list, '.o_list_record_selector input:checked', 5);
+
+        // remove an optional field
+        await testUtils.dom.click(list.$('table .o_optional_columns_dropdown_toggle'));
+        await testUtils.dom.click(list.$('div.o_optional_columns div.dropdown-item:first input'));
+        assert.containsN(list, 'th', 2);
+
+        assert.containsN(list, '.o_list_record_selector input:checked', 5);
+
+        list.destroy();
+    });
+
     QUnit.test('change the viewType of the current action', async function (assert) {
         assert.expect(25);