[FIX] web: BasicModel: discard changes when reloading

... from a new record.

Steps to reproduce the issue:
  - go to a multi-record view (e.g. list) of basically any model
  - click on 'Create' -> it opens a form view in edit mode
  - click on 'Discard' -> it goes back to the list
  - click on an existing record -> it should open the selected
    record in readonly.
However, it didn't display the data of the selected record, but
the default data of a new record (the result of a default_get).

This was because the changes weren't properly discarded when
reloading from a new record (it rather restored the record to its
initial state, i.e. to the result of the default_get).

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

@@ -228,7 +228,7 @@ var BasicModel = AbstractModel.extend({
         options = options || {};
         var element = this.localData[id];
         var isNew = this.isNew(id);
-        var rollback = options.rollback || isNew;
+        var rollback = 'rollback' in options ? options.rollback : isNew;
         this._visitChildren(element, function (elem) {
             if (rollback && elem._savePoint) {
                 if (elem._savePoint instanceof Array) {
@@ -644,7 +644,7 @@ var BasicModel = AbstractModel.extend({
                 return this._makeDefaultRecord(element.model, params);
             }
             if (!options.keepChanges) {
-                this.discardChanges(id);
+                this.discardChanges(id, {rollback: false});
             }
         }
 

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

@@ -1371,4 +1371,37 @@ QUnit.module('Views', {
 
         model.destroy();
     });
+
+    QUnit.test('changes are discarded when reloading from a new record', function (assert) {
+        // practical use case: click on 'Create' to open a form view in edit
+        // mode (new record), click on 'Discard', then open an existing record
+        assert.expect(2);
+
+        this.data.partner.fields.foo.default = 'default';
+        var model = createModel({
+            Model: BasicModel,
+            data: this.data,
+        });
+
+        // load a new record (default_get)
+        var params = _.extend(this.params, {
+            res_id: undefined,
+            type: 'record',
+            fieldNames: ['foo'],
+        });
+        model.load(params).then(function (resultID) {
+            var record = model.get(resultID);
+            assert.strictEqual(record.data.foo, 'default',
+                "should be the default value");
+
+            // reload with id 2
+            model.reload(record.id, {currentId: 2}).then(function (resultID) {
+                var record = model.get(resultID);
+                assert.strictEqual(record.data.foo, 'gnap',
+                    "should be the value of record 2");
+            });
+        });
+
+        model.destroy();
+    });
 });});