Add new rule no-empty-url

Closes GH-109.

doc/rules.md

@@ -2,7 +2,7 @@
 
 # List of Rules
 
-This document describes all (60)
+This document describes all (61)
 available rules, what they check for, examples of
 what they warn for, and how to fix their warnings.
 
@@ -96,6 +96,7 @@ For example, as follows:
 -   [no-duplicate-headings-in-section](#no-duplicate-headings-in-section)
 -   [no-duplicate-headings](#no-duplicate-headings)
 -   [no-emphasis-as-heading](#no-emphasis-as-heading)
+-   [no-empty-url](#no-empty-url)
 -   [no-file-name-articles](#no-file-name-articles)
 -   [no-file-name-consecutive-dashes](#no-file-name-consecutive-dashes)
 -   [no-file-name-irregular-characters](#no-file-name-irregular-characters)
@@ -1492,6 +1493,33 @@ Bar.
 1:1-1:6: Don’t use emphasis to introduce a section, use a heading
 ```
 
+## `no-empty-url`
+
+Warn for empty URLs in links and images.
+
+When this rule is turned on, the following file
+`valid.md` is ok:
+
+```markdown
+[alpha](http://bravo.com).
+
+![charlie](http://delta.com/echo.png "foxtrott").
+```
+
+When this rule is turned on, the following file
+`invalid.md` is **not** ok:
+
+```markdown
+[golf]().
+
+![hotel]().
+```
+
+```text
+1:1-1:9: Don’t use links without URL
+3:1-3:11: Don’t use images without URL
+```
+
 ## `no-file-name-articles`
 
 Warn when file name start with an article.

packages/remark-lint/lib/rules.js

@@ -31,6 +31,7 @@ module.exports = {
   'no-duplicate-headings-in-section': require('./rules/no-duplicate-headings-in-section.js'),
   'no-duplicate-headings': require('./rules/no-duplicate-headings.js'),
   'no-emphasis-as-heading': require('./rules/no-emphasis-as-heading.js'),
+  'no-empty-url': require('./rules/no-empty-url.js'),
   'no-file-name-articles': require('./rules/no-file-name-articles.js'),
   'no-file-name-consecutive-dashes': require('./rules/no-file-name-consecutive-dashes.js'),
   'no-file-name-irregular-characters': require('./rules/no-file-name-irregular-characters.js'),

packages/remark-lint/lib/rules/no-empty-url.js

@@ -0,0 +1,44 @@
+/**
+ * @author Titus Wormer
+ * @copyright 2015 Titus Wormer
+ * @license MIT
+ * @module no-empty-url
+ * @fileoverview
+ *   Warn for empty URLs in links and images.
+ *
+ * @example {"name": "valid.md"}
+ *
+ *   [alpha](http://bravo.com).
+ *
+ *   ![charlie](http://delta.com/echo.png "foxtrott").
+*
+ * @example {"name": "invalid.md", "label": "input"}
+ *
+ *   [golf]().
+ *
+ *   ![hotel]().
+ *
+ * @example {"name": "invalid.md", "label": "output"}
+ *
+ *   1:1-1:9: Don’t use links without URL
+ *   3:1-3:11: Don’t use images without URL
+ */
+
+'use strict';
+
+var visit = require('unist-util-visit');
+var generated = require('unist-util-generated');
+
+module.exports = noEmptyLinkURL;
+
+var types = ['link', 'image'];
+
+function noEmptyLinkURL(tree, file) {
+  visit(tree, visitor);
+
+  function visitor(node) {
+    if (types.indexOf(node.type) !== -1 && !generated(node) && !node.url) {
+      file.message('Don’t use ' + node.type + 's without URL', node);
+    }
+  }
+}