fix(linky): throw error if input is not a string

BREAKING CHANGE:

Before this change, the filter assumed that the input (if not undefined/null) was of type 'string'
and that certain methods (such as `.match()`) would be available on it. Passing a non-string value
would most likely result in a not-very-useful error being thrown (trying to call a method that does
not exist) or in unexpected behavior (if the input happened to have the assumed methods).

After this change, a proper (informative) error will be thrown. If you want to pass non-string
values through `linky`, you need to explicitly convert them to strings first.
Since input values could be initialized asynchronously, `undefined` or `null` will still be
returned unchanged (without throwing an error).

Closes #13547

Closes #13693

docs/content/error/linky/notstring.ngdoc

@@ -0,0 +1,16 @@
+@ngdoc error
+@name linky:notstring
+@fullName Not a string
+@description
+
+This error occurs when {@link ngSanitize.linky linky} is used with a non-empty, non-string value:
+```html
+<div ng-bind-html="42 | linky"></div>
+```
+
+`linky` is supposed to be used with string values only, and therefore assumes that several methods
+(such as `.match()`) are available on the passed in value.
+The value can be initialized asynchronously and therefore null or undefined won't throw this error.
+
+If you want to pass non-string values to `linky` (e.g. Objects whose `.toString()` should be
+utilized), you need to manually convert them to strings.

src/ngSanitize/filter/linky.js

@@ -134,8 +134,13 @@ angular.module('ngSanitize').filter('linky', ['$sanitize', function($sanitize) {
         /((ftp|https?):\/\/|(www\.)|(mailto:)?[A-Za-z0-9._%+-]+@)\S*[^\s.;,(){}<>"\u201d\u2019]/i,
       MAILTO_REGEXP = /^mailto:/i;
 
+  var linkyMinErr = angular.$$minErr('linky');
+  var isString = angular.isString;
+
   return function(text, target, attributes) {
-    if (!text) return text;
+    if (text == null || text === '') return text;
+    if (!isString(text)) throw linkyMinErr('notstring', 'Expected string but received: {0}', text);
+
     var match;
     var raw = text;
     var html = [];

test/ngSanitize/filter/linkySpec.js

@@ -20,6 +20,37 @@ describe('linky', function() {
     expect(linky(undefined)).not.toBeDefined();
   });
 
+  it('should return `undefined`/`null`/`""` values unchanged', function() {
+    expect(linky(undefined)).toBe(undefined);
+    expect(linky(null)).toBe(null);
+    expect(linky('')).toBe('');
+  });
+
+  it('should throw an error when used with a non-string value (other than `undefined`/`null`)',
+    function() {
+      expect(function() { linky(false); }).
+        toThrowMinErr('linky', 'notstring', 'Expected string but received: false');
+
+      expect(function() { linky(true); }).
+        toThrowMinErr('linky', 'notstring', 'Expected string but received: true');
+
+      expect(function() { linky(0); }).
+        toThrowMinErr('linky', 'notstring', 'Expected string but received: 0');
+
+      expect(function() { linky(42); }).
+        toThrowMinErr('linky', 'notstring', 'Expected string but received: 42');
+
+      expect(function() { linky({}); }).
+        toThrowMinErr('linky', 'notstring', 'Expected string but received: {}');
+
+      expect(function() { linky([]); }).
+        toThrowMinErr('linky', 'notstring', 'Expected string but received: []');
+
+      expect(function() { linky(noop); }).
+        toThrowMinErr('linky', 'notstring', 'Expected string but received: function noop()');
+    }
+  );
+
   it('should be case-insensitive', function() {
     expect(linky('WWW.example.com')).toEqual('<a href="http://WWW.example.com">WWW.example.com</a>');
     expect(linky('WWW.EXAMPLE.COM')).toEqual('<a href="http://WWW.EXAMPLE.COM">WWW.EXAMPLE.COM</a>');