README.md

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title: Rust Language Server Provider Sample Reference description: Language server provider that runs the rust analyzer when a matching document is opened. date: 2023-10-31

Walkthrough: Rust Language Server Provider Sample

This sample creates a Rust Language Server Provider extension that serves intellisense and tooltips when a rust file is opened in Visual Studio.

Prerequisites

This sample requires installing Rust and copying rust-analyzer.exe found under releases named "rust-analyzer-x86_64-pc-windows-msvc.zip" into the project folder.

Language Server Provider definition

The extension contains a code file that defines a language server provider and its properties starting with the VisualStudioContribution class attribute which makes the server available to Visual Studio:

[VisualStudioContribution]
internal class RustLanguageServerProvider : LanguageServerProvider
{

The LanguageServerProviderConfiguration property defines information about the server that is available to Visual Studio even before the extension is loaded:

public override LanguageServerProviderConfiguration LanguageServerProviderConfiguration => new(
    "%RustLspExtension.RustLanguageServerProvider.DisplayName%",
    new[] 
    { 
        DocumentFilter.FromDocumentType(RustDocumentType) 
    });

This configuration object allows setting the display name for the server and specifying one or more document filters. You can also specify a localized string as a display name from string-resoures.json:

{
    "RustLspExtension.RustLanguageServerProvider.DisplayName": "Rust Analyzer LSP server"
}

Activating the Language Server

Once a document that has a matching document type is opened, Visual Studio calls into CreateServerConnectionAsync and requests an IDuplexPipe that will be used to communicate with the language server.

In our sample, the rust-analyzer executable is launched and a duplex pipe is used to communicate with the process.

public override Task<IDuplexPipe?> CreateServerConnectionAsync(CancellationToken cancellationToken)
{
    ProcessStartInfo info = new ProcessStartInfo();
    info.FileName = Path.Combine(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location)!, @"rust-analyzer.exe");
    info.RedirectStandardInput = true;
    info.RedirectStandardOutput = true;
    info.UseShellExecute = false;
    info.CreateNoWindow = true;

    Process process = new Process();
    process.StartInfo = info;

    if (process.Start())
    {
        return Task.FromResult<IDuplexPipe?>(new DuplexPipe(
            PipeReader.Create(process.StandardOutput.BaseStream),
            PipeWriter.Create(process.StandardInput.BaseStream)));
    }

    return Task.FromResult<IDuplexPipe?>(null);
}

Disabling the server

LanguageServerProvider contains a public Boolean property Enabled, which is set to true by default. This property defines if Visual Studio should activate your server when a matching document type is opened. When Enabled is set to False, all currently running servers will be stopped and no new instances will be activated until re-enabled.

Capturing and handling activation failures

After CreateServerConnectionAsync completes, Visual Studio will attempt to initialize the server via the provided duplex pipe following standard LSP protocol. Once this step is done, OnServerInitializationResultAsync is called where ServerInitializationResult denotes if the server succeeded or failed to initialize, and if it failed LanguageServerInitializationFailureInfo will contain the exception and message provided by the language server.

public override Task OnServerInitializationResultAsync(ServerInitializationResult serverInitializationResult, LanguageServerInitializationFailureInfo? initializationFailureInfo, CancellationToken cancellationToken)
{
    if (serverInitializationResult == ServerInitializationResult.Failed)
    {
        // Log telemetry for failure and disable the server from being activated again.
        this.Enabled = false;
    }

    return base.OnServerInitializationResultAsync(serverInitializationResult, initializationFailureInfo, cancellationToken);
}

Usage

Once deployed, the language server will automatically start once an applicable document type is opened.