Add support for setting allowed file-name characters

Add support for customising the allowed characters (through passing
a `string` or `RegExp`).

Closes GH-63.

Author: wooorm

doc/rules.md

@@ -797,6 +797,14 @@ Options: `boolean`, default: `false`.
   Warn when file names contain irregular characters: characters other
   than alpha-numericals, dashes, and dots (full-stops).
 
+  Options: `RegExp` or `string`, default: `'\\.a-zA-Z0-9-'`.
+
+  If a string is given, it will be wrapped in
+  `new RegExp('[^' + preferred + ']')`.
+
+  Any match by the wrapped or given expressions triggers a
+  warning.
+
 ### no-file-name-mixed-case
 
 ```md

lib/rules/no-file-name-irregular-characters.js

@@ -6,6 +6,14 @@
  * @fileoverview
  *   Warn when file names contain irregular characters: characters other
  *   than alpha-numericals, dashes, and dots (full-stops).
+ *
+ *   Options: `RegExp` or `string`, default: `'\\.a-zA-Z0-9-'`.
+ *
+ *   If a string is given, it will be wrapped in
+ *   `new RegExp('[^' + preferred + ']')`.
+ *
+ *   Any match by the wrapped or given expressions triggers a
+ *   warning.
  * @example
  *   Invalid: plug_ins.md, plug ins.md.
  *   Valid: plug-ins.md, plugins.md.
@@ -25,7 +33,14 @@
  * @param {Function} done - Callback.
  */
 function noFileNameIrregularCharacters(ast, file, preferred, done) {
-    var match = file.filename && file.filename.match(/[^.a-zA-Z0-9-]/);
+    var expression = preferred || /[^\\.a-zA-Z0-9-]/;
+    var match;
+
+    if (typeof expression === 'string') {
+        expression = new RegExp('[^' + expression + ']');
+    }
+
+    match = file.filename && file.filename.match(expression);
 
     if (match) {
         file.warn('Do not use `' + match[0] + '` in a file name');

test/index.js

@@ -432,6 +432,18 @@ describe('Rules', function () {
                 'file-name characters.md:1:1: Do not use ` ` in a file name'
             ]);
         });
+
+        describeSetting(/[^\\.aeiou]/, function () {
+            assertFile('empty.md', [
+                'empty.md:1:1: Do not use `m` in a file name'
+            ]);
+        });
+
+        describeSetting('aeiou', function () {
+            assertFile('empty.md', [
+                'empty.md:1:1: Do not use `m` in a file name'
+            ]);
+        });
     });
 
     describeRule('no-file-name-consecutive-dashes', function () {