Setting up LSP in Vim

In a previous article, I explained a little about how Language Server Protocol clients work. This time I’m going to explain how we can take advantage of this protocol in Vim.

Installing vim-lsp

Configuring vim-lsp is a little more complicated than installing other plugins, because it requires many pieces to be put together in order for it to work correctly.

Let’s start by installing vim-lsp:

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cd ~/.vim/pack/my-plugins/start
git clone https://github.com/prabirshrestha/vim-lsp.git

Before we can use the plugin, we need to do some configuration. More specifically, we need to tell the plugin where it can find the language server for a particular programming language.

Let’s try to get this to work with for Java. We can find instructions for downloading the Java Language Server binary in my Implementing a Language Server Protocol client article.

We can tell vim-lsp to use the our Java Language Server by adding something like this to our vimrc file:

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au User lsp_setup call lsp#register_server({
        \   'name': 'eclipse-jdt-ls',
        \   'cmd': {server_info->[
        \     'java',
        \     '-Declipse.application=org.eclipse.jdt.ls.core.id1',
        \     '-Dosgi.bundles.defaultStartLevel=4',
        \     '-Declipse.product=org.eclipse.jdt.ls.core.product',
        \     '-Dlog.level=ALL',
        \     '-noverify',
        \     '-Xmx1G',
        \     '-jar',
        \       expand('~/bin/jdt-server/plugins/org.eclipse.equinox.launcher_1.6.400.v20210924-0641.jar'),
        \     '-configuration',
        \       expand('~/bin/jdt-server/config_linux'),
        \     '-data',
        \       expand('~/bin/jdt-server/data'),
        \     '--add-modules=ALL-SYSTEM',
        \     '--add-opens',
        \       expand('~/bin/jdt-server/java.base/java.util=ALL-UNNAMED'),
        \     '--add-opens',
        \       expand('~/bin/jdt-server/java.base/java.lang=ALL-UNNAMED')
        \   ]},
        \   'allowlist': ['java'],
        \ })

This should be enough to get some functionality working. For example, when we are working on a java file, we can put our cursor on top of a type and use:

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:LspDefinition

To open the file where that type is defined. This is just one of the many commands that are available to us now.

Typing these commands can be time consuming, so we might want to create shortcuts for them. For example, we can make it so gd takes us to the declaration by adding this to our vimrc:

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nmap gd :LspDefinition<CR>

This can be done for any command we intend to use often.

Autocomplete

This is probably one of the most desired features in an IDE. Sadly, vim-lsp doesn’t provide code completion by itself.

To enable code completion in vim, we need asyncomplete.vim. This plugin takes care of listening to our keystrokes and showing auto-complete suggestions in a pop-up.

To install it:

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cd ~/.vim/pack/my-plugins/start
git clone https://github.com/prabirshrestha/asyncomplete.vim.git

To integrate with vim-lsp, we also need this other plugin:

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cd ~/.vim/pack/my-plugins/start
git clone https://github.com/prabirshrestha/asyncomplete-lsp.vim.git

This is all we need for autocomplete suggestions to start popping up as we type:

We can navigate the options with the arrow keys and select the one we want by pressing enter.

While in theory, this is all that’s needed, I found the performance of the automatic pop-up was really bad for me, so I decided to disable it by adding this to my ~/.vimrc:

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let g:asyncomplete_auto_popup = 0

To trigger the pop-up manually, we can type Ctrl+n. This combination also works to cycle forward through the options in the pop-up. We can use Ctrl+p to cycle backwards. Once we find the option we want, we can just continue typing and the highlighted option will be selected.

Automatically configure language servers

In the beginning of this article we downloaded the LSP for java and configured our .vimrc so vim knows how to use it. Configuring the LSP requires knowledge about the specific server options, so it can be complicated for some languages.

If we want to support multiple programming languages, configuring each of them manually can be a lot of work. For this reason vim-lsp-settings was created.

This plugin takes care of automatically installing and configuring LSP servers for different languages.

To install the plugin:

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cd ~/.vim/pack/my-plugins/start
git clone https://github.com/mattn/vim-lsp-settings.git

When we open a file with an extension supported by vim-lsp-settings, that we haven’t already installed, we’ll see a message like this one at the bottom of the screen:

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Please do :LspInstallServer to enable Language Server typescript-language-server

We can then use the :LspInstallServer command to have the server be automatically installed and configured for us.

Conclusion

Getting LSP to work on vim has been a struggle for me for a few years, so I’m really happy I finally achieved it.

The tests I have done look promising, but I did notice that the performance is not great. It takes some time for the server to load and to perform some actions. If I find any insights to improve the performance I’ll try to write about them.