Programmatic Language Features

Programmatic Language Features is a set of smart-editing features powered by the vscode.languages.* API. There are two common ways to provide a dynamic language feature in Visual Studio Code. Let's take Hover as an example:

vscode.languages.registerHoverProvider('javascript', {
  provideHover(document, position, token) {
    return {
      contents: ['Hover Content']
    };
  }
});

As you see above, the vscode.languages.registerHoverProvider API provides an easy way to provide hover contents to JavaScript files. After this extension gets activated, whenever you hover over some JavaScript code, VS Code queries all HoverProvider for JavaScript and shows the result in a Hover widget. The Language Feature Listing and illustrated gif below provides an easy way for you to locate which VS Code API / LSP Method your extension needs.

An alternative approach is to implement a Language Server that speaks Language Server Protocol. The way it works is:

• An extension provides a Language Client and a Language Server for JavaScript.
• The Language Client is like any other VS Code extension, running in the Node.js Extension Host context. When it gets activated, it spawns the Language Server in another process and communicates with it through Language Server Protocol.
• You hover over JavaScript code in VS Code
• VS Code informs the Language Client of the hover
• The Language Client queries the Language Server for a hover result and sends it back to VS Code
• VS Code displays the hover result in a Hover widget

The process seems more complicated, but it provides two major benefits:

• The Language Server can be written in any language
• The Language Server can be reused to provide smart editing features for multiple editors

For a more in-depth guide, head over to the Language Server extension guide.

Language Features Listing

This listing includes the following items for each language feature:

• An illustration of the language feature in VS Code
• Related VS Code API
• Related LSP methods