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commit f89a3e098dab68a5b94f99d6cadf2eceaaf31e8b
parent e18d4d8962776236f2afea0d57e6882071e396ae
Author: Daniel Moch <daniel@danielmoch.com>
Date:   Sun,  2 Dec 2018 18:31:12 -0500

Tags post

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Aposts/2018/12/you-should-be-using-tags-in-vim.rst | 235+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 235 insertions(+), 0 deletions(-)

diff --git a/posts/2018/12/you-should-be-using-tags-in-vim.rst b/posts/2018/12/you-should-be-using-tags-in-vim.rst @@ -0,0 +1,235 @@ +.. title: You Should Be Using Tags In Vim +.. slug: you-should-be-using-tags-in-vim +.. date: 2018-12-02 17:33:09 UTC-05:00 +.. category: technology +.. type: text + +*Note, this is a crosspost of an entry I wrote in the vimways.org_ +advent calendar this you. If you're interested in Vim, I recommend you +pop on over there and read the other articles too.* + + I love you; you complete me. + - Dr. Evil + +I first came to Vim by recommendation. I was looking for a good Python +IDE (at the time I was new to the language) and one recommendation was +to use Vim with a variety of plugins added on top. That Vim could do a +lot of the things I thought only an IDE could do came as a bit of a +shock. I spent a summer as an intern using Emacs at a Unix terminal, but +didn't have enough curiosity at the time to use it any differently from +``notepad.exe``. I spent that summer wishing I had automatic features for +completion, indentation, and all the things that made me appreciate +the IDE's I used in college. How naive I was! + +So how was I directed to achieve powerful programming completions in +Vim? By the use of a plugin called YouCompleteMe. My experience with it +was okay, at least to start with. It took a while to install and get +working, but that didn't bother me at the time since I was just playing +around with it at home and the stakes were low if it suddenly broke. I +did notice it slowed Vim down. Like a lot. But that was mainly when it +was starting up and I didn't know enough to find it frustrating. +Probably the first thing that really bothered me about the plugin was +that the embedded Jedi language server used more memory than Vim itself. +The other recommended plugins were similarly laggy, and I eventually +went in search of something better. + +What I found was Vim itself. + +Did you know that Vim has built-in facilities for completions? It works +admirably well out of the box too, but with a little bit of additional +setup it can be great. Let's take a look at what Vim has on offer +regarding completion and see what it takes to fully leverage it. + +Completion in Vim +----------------- + +Completion in Vim is powerful, but not necessarily straightforward. Read +`:h ins-completion`_ and you'll see what I mean: + +.. code:: txt + + Completion can be done for: + + 1. Whole lines |i_CTRL-X_CTRL-L| + 2. keywords in the current file |i_CTRL-X_CTRL-N| + 3. keywords in 'dictionary' |i_CTRL-X_CTRL-K| + 4. keywords in 'thesaurus', thesaurus-style |i_CTRL-X_CTRL-T| + 5. keywords in the current and included files |i_CTRL-X_CTRL-I| + 6. tags |i_CTRL-X_CTRL-]| + 7. file names |i_CTRL-X_CTRL-F| + 8. definitions or macros |i_CTRL-X_CTRL-D| + 9. Vim command-line |i_CTRL-X_CTRL-V| + 10. User defined completion |i_CTRL-X_CTRL-U| + 11. omni completion |i_CTRL-X_CTRL-O| + 12. Spelling suggestions |i_CTRL-X_s| + 13. keywords in 'complete' |i_CTRL-N| |i_CTRL-P| + +Vim is smart enough to pull completion data from a variety of sources, +but in turn expects users to know which source will provide the best +answer and to invoke the correct keymap to draw the desired completions. +It's not a huge hurdle in terms of a learning curve, but it's not as +simple as hitting tab either. + +The first thing one should do when trying to learn Vim's completion +system is to disable any completion plugins and learn these keymaps. +Getting comfortable with them will also help you learn and remember +where Vim can pull completion information from. You should also read `:h +'completefunc'`_ and `:h 'complete'` for more information on +user-defined completion and the ``complete`` option. + +Now that we have a cursory understanding of completion in Vim, let's +take a deeper look at tags and how they figure into completion. + +Introduction to ``tags`` in Vim +------------------------------- + +One source of completion in Vim is tag completion, which pulls from a +special file called–appropriately—a tags file. Tags files are collections +of identifiers (e.g., function names) that are compiled into a single +file along with references to their location in a source tree. Vim is +capable of using a (properly formatted) tags file for a variety of use +cases, among them navigating your source code à la Visual Studio and +completion. + +By default Vim doesn't do anything with a tags file except read it. See +`:h 'tags'`_ to learn how to configure where Vim looks for tags files. +Vimdoc also contains a very good introduction_ to tags more generally, +so I won't spend any more time here introducing them. Let's move on and +take a look at how we generate tags files. + +Introduction to ``ctags`` +------------------------- + +Tags files solve the problem of navigating and completing code in a +given project, but they also create a problem: how do we create the tags +file, and how do we keep it up to date? It would be a pain to manually +maintain the tags file even for a small project; it would be all but +impossible to do it for a large project like the Linux kernel. Luckily +no one has to maintain a tags file. There are plenty of utilities to do +that for you, usually bearing the name ctags, or some variant. One very +popular choice is called `Exuberant Ctags`_, which has the virtue of +being extendable via regular expressions placed into a ``.ctags`` file, +but the drawback of not having been updated since 2009. Another +increasingly popular option is `Universal Ctags`_, which functions as +a drop-in replacement for Exuberant Ctags and is actively maintained. +I've had good luck with both. + +Tags files and the tools that generate them have a long history +alongside advanced text editors. The history-of-computing nerd in me +likes knowing that I'm using the same tool programmers have used since +the early days of BSD Unix. It's also a testament to how strong of a +solution they provide that folks are still using them 40 years later. + +Generating ``tags`` Files +------------------------- + +Manually +~~~~~~~~ + +When we speak of manually generating tags files, we're talking about +using any one of the aforementioned tags utilities to generate the tags +file. If you're the type of person who takes pleasure in at least +understanding how to do things from the command line, you should consult +the manual page for your selected tags utility. Take special note of the +flags necessary to recurse through all of the subdirectories if you want +to generate a tags file for an entire project in one shot. + +Automatically +~~~~~~~~~~~~~ + +You can always use your ctags utility to generate your tags files from +the command line, but that's a heck of a lot of back and forth between +your text editor and your shell, and I doubt anyone who tries to do that +will enjoy the experience for long. So let's look at ways to generate +them automatically. + +If you only ever see yourself using tags files with Vim, then maybe a +plugin will interest you. I used `Gutentags`_ for a long time, and +found it "just works" as advertised. It has sane defaults, but lots of +opportunities to customize its behavior, which you'll see if you visit +the above link. + +In spite of that, I ended up moving in a different direction with +managing my tags files. There were several reasons, but the main one is +that I like to think of tags files as separate from Vim, something the +text editor consumes without having to manage. It's an opinionated view +of things, but I increasingly didn't like to configure my text editor to +manage my tags files. So I went in search of another method, and what I +found was the `Tim Pope`_ method, which I've since implemented myself. +Rather than using Vim itself to manage tags files, this method uses +local `Git hooks`_ to rebuild the tags whenever any of a handful of +common Git operations are performed. The result is a system that also +just works, but does so in a half-a-dozen lines of shell script rather +than a few *hundred* lines of Vimscript. Gotta keep that Vim config +tight. + +As a bonus, if you already use Tim Pope's `Fugitive Git +plugin`_ (and you should), this method handily places your tags +file where that plugin tells Vim to look for it—in the ``.git`` folder. +Of course the shell-script approach is infinitely configurable, so you +can ultimately place the tags file wherever you want. One could also +tailor this for other distributed SCM tools (e.g., Mercurial). + +Generically speaking, there are other options as well. You could set a +filesystem watcher to watch your project tree and run ctags any time a +file changes. A task runner like `Grunt` might be a viable option +too, especially for web developers. The goal is to automate the task of +(re)generating your tags file, so there is likely to be no shortage of +options. + +Tying It All Together +--------------------- + +That brings us back to where we started, to the issue of code completion +in Vim. Yes, Vim does offer native code completion (completing from tags +is done with ``C-x, C-]`` in insert mode). No, it's probably not as +powerful as what you could get with something like a Jedi plugin à la +YouCompleteMe, but I've found it satisfies my needs more often than not, +with ``:grep`` (or my own `:GrepJob`_ filling the gap nicely in a +more native fashion. + +There's more you can do here too. For instance, if you find yourself +instinctively reaching for the tab key in order to complete a word, +there is VimCompletesMe_, which takes advantage of all of Vim's +built-in completions through the clever use of an `omni completion +function`_. It works, but users do give up some control over selecting +what data source Vim uses for a particular completion. I used this +plugin for a while after I gave up on YouCompleteMe, but ultimately +removed it because it effectively made the tab key ambiguous in Insert +mode. Sometimes I wanted to insert an actual tab character, but got a +completion instead. + +With all of this in place, it's natural to ask whether a language server +is even necessary with Vim. I don't intend here to suggest an answer to +that question, but I will say that many of the solutions to date for +language server integration in Vim have seemed like more trouble than +they're worth. That said, with the advent of Vim 8 and its asynchronous +capabilities, there is headroom for these solutions to improve, and I +expect the best among them to become more compelling in the near future. + +I do not recommend coming to Vim with a mindset of creating an IDE in +your terminal. That said, Vim is a very powerful tool and if you invest +the time to learn how it works it will take you very far. In other +words, use Vim for all it's worth *before* looking for a plugin to help +you out. Anyone who (like me) jumps right to installing a bunch of +plugins—whether in a spree of grabbing anything that looks interesting +or just to copy someone else's configuration—will likely end up with an +unmaintainable mess of a tool that doesn't work consistently, may not +work at all, or works about as slow as the IDE you wanted to break free +of. + +.. _\:h ins-completion: http://vimdoc.sourceforge.net/htmldoc/insert.html#ins-completion +.. _Exuberant Ctags: http://ctags.sourceforge.net/ +.. _Universal Ctags: https://ctags.io/ +.. _Gutentags: https://bolt80.com/gutentags/ +.. _Tim Pope: https://tbaggery.com/2011/08/08/effortless-ctags-with-git.html +.. _Git hooks: https://git-scm.com/docs/githooks +.. _Fugitive Git plugin: https://github.com/tpope/vim-fugitive +.. _\:GrepJob: https://git.danielmoch.com/vim-makejob.git +.. _VimCompletesMe: https://github.com/ajh17/VimCompletesMe +.. _omni completion function: http://vimdoc.sourceforge.net/htmldoc/options.html#'omnifunc' +.. _\:h 'completefunc': http://vimdoc.sourceforge.net/htmldoc/options.html#'completefunc' +.. _\:h 'complete': http://vimdoc.sourceforge.net/htmldoc/options.html#'complete' +.. _\:h 'tags': http://vimdoc.sourceforge.net/htmldoc/options.html#'tags' +.. _introduction: http://vimdoc.sourceforge.net/htmldoc/usr_29.html#29.1 +.. _Grunt: https://gruntjs.com/