Refs can now generate default even when found

Fixes #749.

Author: Marsup

API.md

@@ -1545,6 +1545,7 @@ References support the following arguments:
 - `options` - optional settings:
     - `separator` - overrides the default `.` hierarchy separator.
     - `contextPrefix` - overrides the default `$` context prefix signifier.
+    - `defaultFor` - optional array defining what should be considered as candidate for default in addition to not finding the reference.
 
 Note that references can only be used where explicitly supported such as in `valid()` or `invalid()` rules. If upwards
 (parents) references are needed, use [`object.assert()`](#objectassertref-schema-message).

lib/ref.js

@@ -16,16 +16,34 @@ exports.create = function (key, options) {
 
     const settings = Hoek.clone(options);         // options can be reused and modified
 
-    const ref = function (value, validationOptions) {
+    let ref = function (value, validationOptions) {
 
         return Hoek.reach(ref.isContext ? validationOptions.context : value, ref.key, settings);
     };
 
+    if (options && options.defaultFor) {
+        Hoek.assert(Array.isArray(options.defaultFor), 'defaultFor must be an array');
+
+        const oldRef = ref;
+
+        ref = function (value, validationOptions) {
+
+            const result = oldRef(value, validationOptions);
+
+            if (result !== settings.default && settings.defaultFor.indexOf(result) !== -1) {
+                return Hoek.clone(settings.default);
+            }
+
+            return result;
+        };
+    }
+
     ref.isContext = (key[0] === ((settings && settings.contextPrefix) || '$'));
     ref.key = (ref.isContext ? key.slice(1) : key);
     ref.path = ref.key.split((settings && settings.separator) || '.');
     ref.depth = ref.path.length;
     ref.root = ref.path[0];
+    ref.settings = settings;
     ref.isJoi = true;
 
     ref.toString = function () {

test/ref.js

@@ -440,6 +440,38 @@ describe('ref', () => {
         done();
     });
 
+    it('uses ref default', (done) => {
+
+        const schema = Joi.object({
+            a: Joi.number().min(Joi.ref('b', { default: 2 })),
+            b: Joi.any()
+        });
+
+        Helper.validate(schema, [
+            [{ a: 5 }, true],
+            [{ b: 5 }, true],
+            [{ a: 1 }, false, null, 'child "a" fails because ["a" must be larger than or equal to 2]'],
+            [{ a: 0, b: 1 }, false, null, 'child "a" fails because ["a" must be larger than or equal to 1]']
+        ], done);
+    });
+
+    it('uses ref default with defaultFor', (done) => {
+
+        const schema = Joi.object({
+            a: Joi.number().min(Joi.ref('b', { default: 2, defaultFor: ['', 3] })),
+            b: Joi.any()
+        });
+
+        Helper.validate(schema, [
+            [{ a: 5 }, true],
+            [{ b: 5 }, true],
+            [{ a: 1 }, false, null, 'child "a" fails because ["a" must be larger than or equal to 2]'],
+            [{ a: 0, b: 1 }, false, null, 'child "a" fails because ["a" must be larger than or equal to 1]'],
+            [{ a: 1, b: '' }, false, null, 'child "a" fails because ["a" must be larger than or equal to 2]'],
+            [{ a: 1, b: 3 }, false, null, 'child "a" fails because ["a" must be larger than or equal to 2]']
+        ], done);
+    });
+
     describe('create()', () => {
 
         it('throws when key is missing', (done) => {