[FIX] web: display error dialog when onchanges fails

When the onchange returns a dictionary with a 'warning' key, it is
supposed to fail and display a dialog with the content of the warning.

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

@@ -951,7 +951,8 @@ var Model = AbstractModel.extend({
      *
      * @param {Object} record
      * @param {string[]} fields changed fields
-     * @returns
+     * @returns {Deferred} The returned deferred can fail, in which case the
+     *   fail value will be the warning message received from the server
      */
     _applyOnChange: function (record, fields) {
         var self = this;
@@ -980,6 +981,9 @@ var Model = AbstractModel.extend({
         return this.mutex.exec(function () {
             var args = [idList, currentData, fields, onchange_spec, context];
             return self.performModelRPC(record.model, 'onchange', args, {}).then(function (result) {
+                if (result.warning) {
+                    return $.Deferred().reject(result.warning);
+                }
                 var defs = [];
                 _.each(result.value, function (val, name) {
                     var field = record.fields[name];

addons/web/static/src/js/views/field_manager_mixin.js

@@ -9,6 +9,10 @@ odoo.define('web.FieldManagerMixin', function (require) {
  */
 
 var BasicModel = require('web.BasicModel');
+var Dialog = require('web.Dialog');
+var core = require('web.core');
+
+var qweb = core.qweb;
 
 return {
     custom_events: {
@@ -84,6 +88,12 @@ return {
             } else {
                 self._confirmChange(dataPointID, result, event);
             }
+        }).fail(function (warning) {
+            new Dialog(self, {
+                size: 'medium',
+                title: warning.title,
+                $content: qweb.render("CrashManager.warning", warning)
+            }).open();
         });
     },
     /**

addons/web/static/test/views/form_tests.js

@@ -1554,6 +1554,42 @@ QUnit.module('Views', {
         assert.strictEqual(form.$('.o_priority .fa-star').length, 2,
             'priority widget should have correct value');
     });
-});
 
-});
+    QUnit.test('display a dialog if onchange result is a warning', function (assert) {
+        assert.expect(2);
+
+        this.data.partner.onchanges = { foo: true };
+
+        var form = createView({
+            View: FormView,
+            model: 'partner',
+            data: this.data,
+            arch: '<form string="Partners">' +
+                    '<group><field name="foo"/><field name="int_field"/></group>' +
+                '</form>',
+            res_id: 2,
+            mockRPC: function (route, args) {
+                if (args.method === 'onchange') {
+                    return $.when({
+                        valu: {},
+                        warning: {
+                            title: "Warning",
+                            message: "You must first select a partner"
+                        }
+                    });
+                }
+                return this._super.apply(this, arguments);
+            },
+        });
+
+        form.$buttons.find('.o_form_button_edit').click();
+
+        form.$('input').first().val("tralala").trigger('input');
+
+        assert.strictEqual($('.modal .modal-title:contains(Warning)').length, 1,
+            "should have rendered a modal dialog with correct title");
+        assert.strictEqual($('.modal .modal-body:contains(You must first select a partner)').length, 1,
+            "should have rendered a modal dialog with correct content");
+    });
+
+});});