[FIX] web: only call name_get when necessary

For many2one fields, 'default_get' only returns the id, whereas
'onchange' (like 'read') returns an array with id and display_name.

Before this rev., when creating a new record, we always called
'name_get' for all many2ones, whether or not their value was
obtained by 'default_get' or 'onchange', i.e. even if their
display_name was already known.

It may just look like unnecessary RPCs, but those RPCs could
actually cause a crash when the user has access to the main model
(and thus can access the display_name of the many2one thanks to
related sudo), but doesn't have access to the many2one comodel.

closes odoo/odoo#30892

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

@@ -2400,7 +2400,7 @@ var BasicModel = AbstractModel.extend({
             if (field.type === 'many2one' && !record.fieldsInfo[record.viewType][name].__no_fetch) {
                 var localId = (record._changes && record._changes[name]) || record.data[name];
                 var relatedRecord = self.localData[localId];
-                if (!relatedRecord) {
+                if (!relatedRecord || relatedRecord.data.display_name) {
                     return;
                 }
                 toBeFetched.push({

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

@@ -2644,6 +2644,42 @@ QUnit.module('relational_fields', {
         form.destroy();
     });
 
+    QUnit.test('do not call name_get if display_name already known', function (assert) {
+        // default_get only returns the id for many2one fields
+        // onchange returns an array with the id and the display_name
+        // thus, when an onchange is performed, there is no need to call
+        // name_get as the display_name is alreay available
+        assert.expect(6);
+
+        this.data.partner.fields.product_id.default = 37;
+        this.data.partner.onchanges = {
+            trululu: function (obj) {
+                obj.trululu = [1, 'first record'];
+            },
+        };
+
+        var form = createView({
+            View: FormView,
+            model: 'partner',
+            data: this.data,
+            arch: '<form><field name="trululu"/><field name="product_id"/></form>',
+            mockRPC: function (route, args) {
+                assert.step(args.method + ' on ' + args.model);
+                return this._super.apply(this, arguments);
+            },
+        });
+
+        assert.strictEqual(form.$('.o_field_widget[name=trululu] input').val(), 'first record');
+        assert.strictEqual(form.$('.o_field_widget[name=product_id] input').val(), 'xphone');
+        assert.verifySteps([
+            'default_get on partner',
+            'onchange on partner',
+            'name_get on product',
+        ]);
+
+        form.destroy();
+    });
+
     QUnit.test('many2one in one2many: domain updated by an onchange', function (assert) {
         assert.expect(3);