Fix bug in counting slashes in a regexp.

Fixes rubocop#391.

CHANGELOG.md

@@ -7,6 +7,7 @@
 * [#374](https://github.com/bbatsov/rubocop/issues/374) - Fixed error at post condition loop (`begin-end-while`, `begin-end-until`) in `UnusedLocalVariable` and `ShadowingOuterLocalVariable`
 * [#373](https://github.com/bbatsov/rubocop/issues/373) and [#376](https://github.com/bbatsov/rubocop/issues/376) - allow braces around multi-line blocks if `do`-`end` would change the meaning of the code
 * `RedundantSelf` now allows `self.` followed by any ruby keyword
+* [#391](https://github.com/bbatsov/rubocop/issues/391) - Fix bug in counting slashes in a regexp.
 
 ## 0.10.0 (17/07/2013)
 

lib/rubocop/cop/style/regexp_literal.rb

@@ -8,9 +8,10 @@ module Style
       # value of the configuration parameter MaxSlashes.
       class RegexpLiteral < Cop
         def on_regexp(node)
-          slashes = node.loc.expression.source[1...-1].scan(/\//).size
+          slashes = node.loc.expression.source.count('/')
           max = RegexpLiteral.max_slashes
           msg = if node.loc.begin.is?('/')
+                  slashes -= 2 # subtract delimiters
                   error_message('') if slashes > max
                 else
                   error_message('only ') if slashes <= max

spec/rubocop/cops/style/regexp_literal_spec.rb

@@ -22,6 +22,7 @@ module Style
             it 'accepts zero or one slash in regexp' do
               inspect_source(rl, ['x =~ /\/home/',
                                   'y =~ /\//',
+                                  'w =~ /\//m',
                                   'z =~ /a/'])
               expect(rl.offences).to be_empty
             end