fix(ngPluralize): generate a warning when using a not defined rule

When using `ng-pluralize` and a rule is missing, then generate a warning

Fix #10207

Author: marclaval

Diff for: src/ng/directive/ngPluralize.js

@@ -54,6 +54,9 @@
  * <span ng-non-bindable>`{{personCount}}`</span>. The closed braces `{}` is a placeholder
  * for <span ng-non-bindable>{{numberExpression}}</span>.
  *
+ * If no rule is defined for a category, then an empty string is displayed and a warning is generated.
+ * Note that some locales define more categories than `one` and `other`. For example, fr-fr defines `few` and `many`.
+ *
  * # Configuring ngPluralize with offset
  * The `offset` attribute allows further customization of pluralized text, which can result in
  * a better user experience. For example, instead of the message "4 people are viewing this document",
@@ -172,7 +175,7 @@
       </file>
     </example>
  */
-var ngPluralizeDirective = ['$locale', '$interpolate', function($locale, $interpolate) {
+var ngPluralizeDirective = ['$locale', '$interpolate', '$log', function($locale, $interpolate, $log) {
   var BRACE = /{}/g,
       IS_WHEN = /^when(Minus)?(.+)$/;
 
@@ -216,7 +219,14 @@ var ngPluralizeDirective = ['$locale', '$interpolate', function($locale, $interp
         // In JS `NaN !== NaN`, so we have to exlicitly check.
         if ((count !== lastCount) && !(countIsNaN && isNaN(lastCount))) {
           watchRemover();
-          watchRemover = scope.$watch(whensExpFns[count], updateElementText);
+          var whenExpFn = whensExpFns[count];
+          if (isUndefined(whenExpFn)) {
+            $log.debug("ngPluralize: no rule defined for '" + count + "' in " + whenExp);
+            watchRemover = noop;
+            updateElementText();
+          } else {
+            watchRemover = scope.$watch(whenExpFn, updateElementText);
+          }
           lastCount = count;
         }
       });

Diff for: test/ng/directive/ngPluralizeSpec.js

@@ -146,6 +146,57 @@ describe('ngPluralize', function() {
     }));
   });
 
+  describe('undefined rule cases', function() {
+    var $locale, $log;
+    beforeEach(inject(function(_$locale_, _$log_) {
+      $locale = _$locale_;
+      $log = _$log_;
+    }));
+    afterEach(inject(function($log) {
+      $log.reset();
+    }));
+
+    it('should generate a warning when being asked to use a rule that is not defined',
+      inject(function($rootScope, $compile) {
+      element = $compile(
+          '<ng:pluralize count="email"' +
+                         "when=\"{'0': 'Zero'," +
+                                 "'one': 'Some text'," +
+                                 "'other': 'Some text'}\">" +
+          '</ng:pluralize>')($rootScope);
+      $locale.pluralCat = function() {return "few";};
+
+      $rootScope.email = '3';
+      expect($log.debug.logs).toEqual([]);
+      $rootScope.$digest();
+      expect(element.text()).toBe('');
+      expect($log.debug.logs.shift())
+        .toEqual(["ngPluralize: no rule defined for 'few' in {'0': 'Zero','one': 'Some text','other': 'Some text'}"]);
+    }));
+
+    it('should empty the element content when using a rule that is not defined',
+      inject(function($rootScope, $compile) {
+      element = $compile(
+          '<ng:pluralize count="email"' +
+                         "when=\"{'0': 'Zero'," +
+                                 "'one': 'Some text'," +
+                                 "'other': 'Some text'}\">" +
+          '</ng:pluralize>')($rootScope);
+      $locale.pluralCat = function(count) {return count === 1 ? "one" : "few";};
+
+      $rootScope.email = '0';
+      $rootScope.$digest();
+      expect(element.text()).toBe('Zero');
+
+      $rootScope.email = '3';
+      $rootScope.$digest();
+      expect(element.text()).toBe('');
+
+      $rootScope.email = '1';
+      $rootScope.$digest();
+      expect(element.text()).toBe('Some text');
+    }));
+  });
 
   describe('deal with pluralized strings with offset', function() {
     it('should show single/plural strings with offset', inject(function($rootScope, $compile) {