Automated tag generation and syntax highlighting in Vim

Vim has long been my favorite text editor and combined with Exuberant Ctags it has the potential to provide most of what I expect from an integrated development environment. Exuberant Ctags is the latest incarnation of a family of computer programs that scan source code files to create an index of identifiers (tags) and where they are defined. Vim uses this index (a so-called tags file) to enable you to jump to the definition of any identifier using the Ctrl-] mapping.

When you’re familiar with integrated development environments you may recognize this feature as “Go-to definition”. One advantage of the combination of Vim and Exuberant Ctags over integrated development environments is that Vim supports syntax highlighting for over 500 file types (!) and Exuberant Ctags can generate tags for over 40 file types as well…

There’s just one problem: You have to manually keep your tags files up-to-date and this turns out to be a royal pain in the ass! So I set out to write a Vim plug-in that would do this boring work for me. When I finished the plug-in’s basic functionality (one automatic command and a call to system()) I became interested in dynamic syntax highlighting, so I added that as well to see if it would work — surprisingly well I’m happy to report!

Install & first use

Unzip the most recent ZIP archive file inside your Vim profile directory (usually this is ~/.vim on UNIX and %USERPROFILE%\vimfiles on Windows), restart Vim and try it out: Edit any file type supported by Exuberant Ctags and within ten seconds the plug-in should create/update your tags file (~/.vimtags on UNIX, ~/_vimtags on Windows) with the tags defined in the file you just edited! This means that whatever file you’re editing in Vim (as long as its on the local file system), tags will always be available by the time you need them!

Additionally if the file you just opened is a C, Lua, PHP, Python or Vim source file you should also notice that the function and type names defined in the file have been syntax highlighted.

If the plug-in warns you that ctags isn’t installed you can download it from its homepage, or if you’re running Debian/Ubuntu you can install it by executing the following shell command:

sudo apt-get install exuberant-ctags

Configuration

The plug-in is intended to work without configuration but can be customized by changing the following options:

The easytags_cmd option

The plug-in will try to determine the location where Exuberant Ctags is installed on its own but this might not always work because any given executable named ctags in your $PATH might not in fact be Exuberant Ctags but some older, more primitive ctags implementation which doesn’t support the same command-line options and thus breaks the easytags.vim plug-in. If this is the case you can set the global variable g:easytags_cmd to the location where you’ve installed Exuberant Ctags, e.g.:

:let g:easytags_cmd = '/usr/local/bin/ctags'

The easytags_file option

As mentioned above the plug-in will store your tags in ~/.vimtags on UNIX and ~/_vimtags on Windows. To change the location of this file, set the global variable easytags_file, e.g.:

:let g:easytags_file = '~/.vim/tags'

A leading ~ in the easytags_file variable is expanded to your current home directory ($HOME on UNIX, %USERPROFILE% on Windows).

The easytags_always_enabled option

By default the plug-in automatically generates and highlights tags when you stop typing for a few seconds. This means that when you edit a file, the dynamic highlighting won’t appear until you pause for a moment. If you don’t want this you can configure the plug-in to always enable dynamic highlighting:

:let g:easytags_always_enabled = 1

Be warned that after setting this option you’ll probably notice why it’s disabled by default: Every time you edit a file in Vim, the plug-in will first run Exuberant Ctags and then highlight the tags, which slows Vim down quite a lot. I have some ideas on how to improve this latency by executing Exuberant Ctags in the background, so stay tuned!

Note: If you change this option it won’t apply until you restart Vim, so you’ll have to set this option in your ~/.vimrc script (~/_vimrc on Windows).

The easytags_on_cursorhold option

As I explained above the plug-in by default doesn’t update or highlight your tags until you stop typing for a moment. The plug-in tries hard to do the least amount of work possible in this break but it might still interrupt your workflow. If it does you can disable the periodic update:

:let g:easytags_on_cursorhold = 0

Note: Like the easytags_always_enabled option, if you change this option it won’t apply until you restart Vim, so you’ll have to set this option in your ~/.vimrc script (~/_vimrc on Windows).

The easytags_resolve_links option

UNIX has symbolic links and hard links, both of which conflict with the concept of having one unique location for every identifier. With regards to hard links there’s not much anyone can do, but because I use symbolic links quite a lot I’ve added this option. It’s disabled by default since it has a small performance impact and might not do what unknowing users expect it to: When you enable this option the plug-in will resolve symbolic links in pathnames, which means your tags file will only contain entries with canonical pathnames. To enable this option (which I strongly suggest doing when you run UNIX and use symbolic links) execute the following Vim command:

:let g:easytags_resolve_links = 1

Troubleshooting

The plug-in complains that Exuberant Ctags isn’t installed

After a Mac OS X user found out the hard way that the ctags executable isn’t always Exuberant Ctags and we spend a few hours debugging the problem I added proper version detection: The plug-in executes ctags --version when Vim is started to verify that Exuberant Ctags 5.5 or newer is installed. If it isn’t Vim will show the following message on startup:

easytags.vim: Plug-in not loaded because Exuberant Ctags isn't installed!
Please download & install Exuberant Ctags from http://ctags.sf.net

If the installed Exuberant Ctags version is too old the plug-in will complain:

easytags.vim: Plug-in not loaded because Exuberant Ctags 5.5
or newer is required while you have version %s installed!

If you have the right version of Exuberant Ctags installed but the plug-in still complains, try executing the following command from inside Vim:

:!which ctags

If this doesn’t print the location where you installed Exuberant Ctags it means your system already had a ctags executable but it isn’t compatible with Exuberant Ctags 5.5 and you’ll need to set the g:easytags_cmd option (see above) so the plug-in knows which ctags to run.

Vim locks up while the plug-in is running

Once or twice now in several years I’ve experienced Exuberant Ctags getting into an infinite loop when given garbage input. In my case this happened by accident a few days ago :-|. Because my plug-in executes ctags in the foreground this will block Vim indefinitely! If this happens you might be able to kill ctags by pressing Ctrl-C but if that doesn’t work you can also kill it without stopping Vim using a task manager or the pkill command:

pkill -KILL ctags

If Vim seems very slow and you suspect this plug-in might be the one to blame, increase Vim’s verbosity level:

:set vbs=1

Every time the plug-in executes it will time how long the execution takes and add the results to Vim’s message history, which you can view by executing the :messages command.

Contact

If you have questions, bug reports, suggestions, etc. the author can be contacted at peter@peterodding.com. The latest version is available at http://peterodding.com/code/vim/easytags and http://github.com/xolox/vim-easytags. If you like this plug-in please vote for it on www.vim.org.

License

This software is licensed under the MIT license.
© 2010 Peter Odding <peter@peterodding.com>.