Allow for partial application of the message context

addon/messages.js

@@ -54,19 +54,52 @@ export default {
   },
 
   /**
-   * Regex replace all placeholders with their given context
+   * Finds the placeholders and replace them with values
+   * from context depending on the availability requirements.
    * @method formatMessage
    * @param  {String} message
    * @param  {Object} context
+   * @param  {Boolean} applyAll
    * @return {String}
+   * @private
    */
-  formatMessage(message, context = {}) {
+  _formatMessage(message, context = {}, applyAll = true) {
     let m = message;
 
     if (isNone(m) || typeof m !== 'string') {
       m = get(this, 'invalid');
     }
-    return m.replace(get(this, '_regex'), (s, attr) => get(context, attr));
+    return m.replace(get(this, '_regex'), (s, attr) => {
+      let hasActualValue = typeof context === 'object' && context.hasOwnProperty(attr);
+      if (hasActualValue || applyAll) {
+        return get(context, attr);
+      }
+      return s;
+    });
+  },
+
+  /**
+   * Regex replace all placeholders with their given context
+   * @method formatMessage
+   * @param  {String} message
+   * @param  {Object} context
+   * @return {String}
+   */
+  formatMessage(message, context = {}) {
+    return this._formatMessage(message, context, true);
+  },
+
+  /**
+   * Regex replace placeholders with their given context
+   * for the keys provided by the the context. Leaves the
+   * unavailable keys untouched.
+   * @method formatMessage
+   * @param  {String} message
+   * @param  {Object} context
+   * @return {String}
+   */
+  formatPartialMessage(message, context = {}) {
+    return this._formatMessage(message, context, false);
   },
 
   /**

tests/unit/validators/messages-test.js

@@ -24,6 +24,16 @@ test('formatMessage', function(assert) {
   assert.equal(messages.formatMessage('{foo} {foo} {bar} {baz}', { foo: 'a', bar: 1, baz: 'abc' }), 'a a 1 abc');
 });
 
+test('formatPartialMessage', function(assert) {
+  assert.expect(3);
+  let context = {
+    description: 'This field'
+  };
+  assert.equal(messages.formatPartialMessage(undefined, context), 'This field is invalid');
+  assert.equal(messages.formatPartialMessage('{foo} is undefined'), '{foo} is undefined');
+  assert.equal(messages.formatPartialMessage('{foo} {foo} {bar} {baz}', { foo: 'a', bar: 1 }), 'a a 1 {baz}');
+});
+
 test('getMessageFor', function(assert) {
   assert.expect(2);
   let context = {