Language features with language servers

As explained in Language features, Vem purposely avoids providing actions that are associated to any programming language in particular. However, you can add this kind of features for your preferred programming languages in a variety of ways. One of them is using a Language Server. Language Servers are programs that contain the expert knowledge about that programming language and communicate with the editor using a standard protocol known as LSP (Language Server Protocol). Since the protocol is standard, the same language server can be used by multiple editors such as Vim/Vem, VSCode or Emacs. That way, the development efforts of the community for a given language server benefit all the editors simultaneously. You can have language servers for different languages installed simultaneously too, and they will be used depending on the files that you have open at the moment.

Language servers have been popularized by Visual Code, which uses them as its means of integration with different programming languages, and represent an one-stop solution for many different features.

Not all language servers offer all possibilities. Which capabilities are supported depend on the language they are created for and their particular implementation. However, the most common supported actions are:

  • Code completion (eg. offering methods of a class after typing .)

  • Go to definition (go to the location where a symbol is first defined)

  • Find references (show a list of all usages of a symbol)

  • Diagnostics (show list of all syntax errors, warnings and hints)

  • Information on hover (show documentation about the current symbol)

  • Signature help (show current function/method signature)

  • Format code (format the whole document or a section of it automatically)

  • Rename (rename symbol across project)

  • Folding (fold code based on the language syntax)

To get a list of all available options you can check the official specification.

How to use a Language Server

To make use of a Language Server you need to go through the following steps:

Install a LSP plugin for Vim

To give Vim the ability to talk to a language server, a plugin is necessary. There are many available:

Despite their names all are available for both Vim and Neovim. However, most of them make use of features that are only available in the latest versions of these editors, therefore make sure you use the newest version possible of either one.

Sometimes, the LSP plugins may have dependencies themselves. For example, Coc.nvim depends on NodeJS being installed on the system, while LanguageClient-neovim has no dependencies. Depending on which plugin you decide to use, you may need to install the required ones.

Install a Language Server

There are Language servers available for most programming languages. Check or for a complete list.

Configure the LSP plugin to use your Language Server

Once you have your Language Sever installed, you have to configure the LSP plugin so it can access it. Usually the information that you have to provide is:

  • The name of the server.

  • If it is accessed as an executable file or as an open socket (and the command line or network address to access it).

  • Some extra configuration that you can pass to the Language Server itself when connecting to it.

Some LSP plugins allow you to pass this information as a dictionary in your vemrc file, others provide already preconfigured set-ups for most popular Language Servers and others allow you to install an additional plugin with the configuration you need for popular ones too. Follow the instructions of your LSP plugin to know how to do this in your case.

Set the key mappings to use the LSP features

Most LSP plugins don't define specific key mappings for the LSP features so they don't clash with mappings that are already defined by the user. Instead, they define <Plug> actions or command-line commands that you can use to define your own key mappings. For example, if your LSP plugin defines <Plug>(lsp-definition) as the action for Go to definition, you can create your own mapping in your vemrc like:

nmap <silent> Cd <Plug>(lsp-definition)

Vem doesn't create mappings for those features neither but reserves all key mappings starting with C for them. The following is a list of recommended mappings (you don't have to necessarily define them like this, but you can use this list as a starting point):

C i:

Show identifier information

C s:

Show signature information

C d:

Go to definition

C t:

Go to type definition

C p:

Go to implementation

C r:

Find references of identifier

C u:

Highlight usages of identifier

C a:

Show possible code actions

C w:

List symbols in workspace

C b:

List symbols in buffer

C F:

Format document

C R:

Rename identifier