Add alternate file support for coffeescript.

Author: BrentWheeldon

autoload/rails.vim

@@ -3258,13 +3258,27 @@ function! s:readable_alternate_candidates(...) dict abort
     return ['app/helpers/application_helper.rb']
   elseif f =~# 'spec\.js$'
     return [s:sub(s:sub(f, 'spec/javascripts', 'app/assets/javascripts'), '_spec.js', '.js')."\n"]
+  elseif f =~# 'spec\.coffee$'
+    return [s:sub(s:sub(f, 'spec/javascripts', 'app/assets/javascripts'), '_spec.coffee', '.coffee')."\n"]
+  elseif f =~# 'spec\.js\.coffee$'
+    return [s:sub(s:sub(f, 'spec/javascripts', 'app/assets/javascripts'), '_spec.js.coffee', '.js.coffee')."\n"]
   elseif self.type_name('javascript')
     if f =~ 'public/javascripts'
       let to_replace = 'public/javascripts'
     else
       let to_replace = 'app/assets/javascripts'
     endif
-    return [s:sub(s:sub(f, to_replace, 'spec/javascripts'), '.js', '_spec.js')."\n"]
+    if f =~ '.coffee.js$'
+      let suffix = '.coffee.js'
+      let suffix_replacement = '_spec.coffee.js'
+    elseif f =~ '.coffee$'
+      let suffix = '.coffee'
+      let suffix_replacement = '_spec.coffee'
+    else
+      let suffix = '.js'
+      let suffix_replacement = '_spec.js'
+    endif
+    return [s:sub(s:sub(f, to_replace, 'spec/javascripts'), suffix, suffix_replacement)."\n"]
   elseif self.type_name('db-schema') || f =~# '^db/\w*structure.sql$'
     return ['db/seeds.rb']
   elseif f ==# 'db/seeds.rb'