LSP Extensions

This document describes LSP extensions used by rust-analyzer. It's a best effort document, when in doubt, consult the source (and send a PR with clarification ;-) ). We aim to upstream all non Rust-specific extensions to the protocol, but this is not a top priority. All capabilities are enabled via experimental field of ClientCapabilities or ServerCapabilities. Requests which we hope to upstream live under experimental/ namespace. Requests, which are likely to always remain specific to rust-analyzer are under rust-analyzer/ namespace.

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UTF-8 offsets

rust-analyzer supports clangd's extension for opting into UTF-8 as the coordinate space for offsets (by default, LSP uses UTF-16 offsets).

https://clangd.llvm.org/extensions.html#utf-8-offsets

`initializationOptions`

For initializationOptions, rust-analyzer expects "rust-analyzer" section of the configuration. That is, rust-analyzer usually sends "workspace/configuration" request with { "items": ["rust-analyzer"] } payload. initializationOptions should contain the same data that would be in the first item of the result. If a language client does not know about rust-analyzer's configuration options it can get sensible defaults by doing any of the following:

Not sending initializationOptions
Send "initializationOptions": null
Send "initializationOptions": {}

Snippet `TextEdit`

Issue: https://github.com/microsoft/language-server-protocol/issues/724

Client Capability: { "snippetTextEdit": boolean }

If this capability is set, WorkspaceEdits returned from codeAction requests might contain SnippetTextEdits instead of usual TextEdits:

interface SnippetTextEdit extends TextEdit {
    insertTextFormat?: InsertTextFormat;
}

export interface TextDocumentEdit {
	textDocument: OptionalVersionedTextDocumentIdentifier;
	edits: (TextEdit | SnippetTextEdit)[];
}

When applying such code action, the editor should insert snippet, with tab stops and placeholder. At the moment, rust-analyzer guarantees that only a single edit will have InsertTextFormat.Snippet.

Example

“Add derive” code action transforms struct S; into #[derive($0)] struct S;

Unresolved Questions

Where exactly are SnippetTextEdits allowed (only in code actions at the moment)?
Can snippets span multiple files (so far, no)?

`CodeAction` Groups

Issue: https://github.com/microsoft/language-server-protocol/issues/994

Client Capability: { "codeActionGroup": boolean }

If this capability is set, CodeAction returned from the server contain an additional field, group:

interface CodeAction {
    title: string;
    group?: string;
    ...
}

All code-actions with the same group should be grouped under single (extendable) entry in lightbulb menu. The set of actions [ { title: "foo" }, { group: "frobnicate", title: "bar" }, { group: "frobnicate", title: "baz" }] should be rendered as

💡
  +-------------+
  | foo         |
  +-------------+-----+
  | frobnicate >| bar |
  +-------------+-----+
                | baz |
                +-----+

Alternatively, selecting frobnicate could present a user with an additional menu to choose between bar and baz.

Example

fn main() {
    let x: Entry/*cursor here*/ = todo!();
}

Invoking code action at this position will yield two code actions for importing Entry from either collections::HashMap or collection::BTreeMap, grouped under a single “import” group.

Unresolved Questions

Is a fixed two-level structure enough?
Should we devise a general way to encode custom interaction protocols for GUI refactorings?

Parent Module

Issue: https://github.com/microsoft/language-server-protocol/issues/1002

Server Capability: { "parentModule": boolean }

This request is sent from client to server to handle “Goto Parent Module” editor action.

Method: experimental/parentModule

Request: TextDocumentPositionParams

Response: Location | Location[] | LocationLink[] | null

Example

// src/main.rs
mod foo;
// src/foo.rs

/* cursor here*/

experimental/parentModule returns a single Link to the mod foo; declaration.

Unresolved Question

An alternative would be to use a more general “gotoSuper” request, which would work for super methods, super classes and super modules. This is the approach IntelliJ Rust is takeing. However, experience shows that super module (which generally has a feeling of navigation between files) should be separate. If you want super module, but the cursor happens to be inside an overriden function, the behavior with single “gotoSuper” request is surprising.

Join Lines

Issue: https://github.com/microsoft/language-server-protocol/issues/992

Server Capability: { "joinLines": boolean }

This request is sent from client to server to handle “Join Lines” editor action.

Method: experimental/joinLines

Request:

interface JoinLinesParams {
    textDocument: TextDocumentIdentifier,
    /// Currently active selections/cursor offsets.
    /// This is an array to support multiple cursors.
    ranges: Range[],
}

Response: TextEdit[]

Example

fn main() {
    /*cursor here*/let x = {
        92
    };
}

experimental/joinLines yields (curly braces are automagically removed)

fn main() {
    let x = 92;
}

Unresolved Question

What is the position of the cursor after joinLines? Currently this is left to editor's discretion, but it might be useful to specify on the server via snippets. However, it then becomes unclear how it works with multi cursor.

On Enter

Issue: https://github.com/microsoft/language-server-protocol/issues/1001

Server Capability: { "onEnter": boolean }

This request is sent from client to server to handle Enter keypress.

Method: experimental/onEnter

Request:: TextDocumentPositionParams

Response:

SnippetTextEdit[]

Example

fn main() {
    // Some /*cursor here*/ docs
    let x = 92;
}

experimental/onEnter returns the following snippet

fn main() {
    // Some
    // $0 docs
    let x = 92;
}

The primary goal of onEnter is to handle automatic indentation when opening a new line. This is not yet implemented. The secondary goal is to handle fixing up syntax, like continuing doc strings and comments, and escaping \n in string literals.

As proper cursor positioning is raison-d'etat for onEnter, it uses SnippetTextEdit.

Unresolved Question

How to deal with synchronicity of the request? One option is to require the client to block until the server returns the response. Another option is to do a OT-style merging of edits from client and server. A third option is to do a record-replay: client applies heuristic on enter immediately, then applies all user's keypresses. When the server is ready with the response, the client rollbacks all the changes and applies the recorded actions on top of the correct response.
How to deal with multiple carets?
Should we extend this to arbitrary typed events and not just onEnter?

Structural Search Replace (SSR)

Server Capability: { "ssr": boolean }

This request is sent from client to server to handle structural search replace -- automated syntax tree based transformation of the source.

Method: experimental/ssr

Request:

interface SsrParams {
    /// Search query.
    /// The specific syntax is specified outside of the protocol.
    query: string,
    /// If true, only check the syntax of the query and don't compute the actual edit.
    parseOnly: bool,
    /// The current text document. This and `position` will be used to determine in what scope
    /// paths in `query` should be resolved.
    textDocument: lc.TextDocumentIdentifier;
    /// Position where SSR was invoked.
    position: lc.Position;
}

Response:

WorkspaceEdit

Example

SSR with query foo($a, $b) ==>> ($a).foo($b) will transform, eg foo(y + 5, z) into (y + 5).foo(z).

Unresolved Question

Probably needs search without replace mode
Needs a way to limit the scope to certain files.

Matching Brace

Issue: https://github.com/microsoft/language-server-protocol/issues/999

Server Capability: { "matchingBrace": boolean }

This request is sent from client to server to handle “Matching Brace” editor action.

Method: experimental/matchingBrace

Request:

interface MatchingBraceParams {
    textDocument: TextDocumentIdentifier,
    /// Position for each cursor
    positions: Position[],
}

Response:

Position[]

Example

fn main() {
    let x: Vec<()>/*cursor here*/ = vec![]
}

experimental/matchingBrace yields the position of <. In many cases, matching braces can be handled by the editor. However, some cases (like disambiguating between generics and comparison operations) need a real parser. Moreover, it would be cool if editors didn't need to implement even basic language parsing

Unresolved Question

Should we return a a nested brace structure, to allow paredit-like actions of jump out of the current brace pair? This is how SelectionRange request works.
Alternatively, should we perhaps flag certain SelectionRanges as being brace pairs?

Runnables

Issue: https://github.com/microsoft/language-server-protocol/issues/944

Server Capability: { "runnables": { "kinds": string[] } }

This request is sent from client to server to get the list of things that can be run (tests, binaries, cargo check -p).

Method: experimental/runnables

Request:

interface RunnablesParams {
    textDocument: TextDocumentIdentifier;
    /// If null, compute runnables for the whole file.
    position?: Position;
}

Response: Runnable[]

interface Runnable {
    label: string;
    /// If this Runnable is associated with a specific function/module, etc, the location of this item
    location?: LocationLink;
    /// Running things is necessary technology specific, `kind` needs to be advertised via server capabilities,
    // the type of `args` is specific to `kind`. The actual running is handled by the client.
    kind: string;
    args: any;
}

rust-analyzer supports only one kind, "cargo". The args for "cargo" look like this:

{
    workspaceRoot?: string;
    cargoArgs: string[];
    cargoExtraArgs: string[];
    executableArgs: string[];
    expectTest?: boolean;
    overrideCargo?: string;
}

Open External Documentation

This request is sent from client to server to get a URL to documentation for the symbol under the cursor, if available.

Method experimental/externalDocs

Request:: TextDocumentPositionParams

Response string | null

Analyzer Status

Method: rust-analyzer/analyzerStatus

Request:

interface AnalyzerStatusParams {
    /// If specified, show dependencies of the current file.
    textDocument?: TextDocumentIdentifier;
}

Response: string

Returns internal status message, mostly for debugging purposes.

Reload Workspace

Method: rust-analyzer/reloadWorkspace

Request: null

Response: null

Reloads project information (that is, re-executes cargo metadata).

Status Notification

Client Capability: { "statusNotification": boolean }

Method: rust-analyzer/status

Notification:

interface StatusParams {
    status: "loading" | "readyPartial" | "ready" | "invalid" | "needsReload",
}

This notification is sent from server to client. The client can use it to display persistent status to the user (in modline). For needsReload state, the client can provide a context-menu action to run rust-analyzer/reloadWorkspace request.

Syntax Tree

Method: rust-analyzer/syntaxTree

Request:

interface SyntaxTeeParams {
    textDocument: TextDocumentIdentifier,
    range?: Range,
}

Response: string

Returns textual representation of a parse tree for the file/selected region. Primarily for debugging, but very useful for all people working on rust-analyzer itself.

View Hir

Method: rust-analyzer/viewHir

Request: TextDocumentPositionParams

Response: string

Returns a textual representation of the HIR of the function containing the cursor. For debugging or when working on rust-analyzer itself.

Expand Macro

Method: rust-analyzer/expandMacro

Request:

interface ExpandMacroParams {
    textDocument: TextDocumentIdentifier,
    position: Position,
}

Response:

interface ExpandedMacro {
    name: string,
    expansion: string,
}

Expands macro call at a given position.

Inlay Hints

Method: rust-analyzer/inlayHints

This request is sent from client to server to render “inlay hints” -- virtual text inserted into editor to show things like inferred types. Generally, the client should re-query inlay hints after every modification. Note that we plan to move this request to experimental/inlayHints, as it is not really Rust-specific, but the current API is not necessary the right one. Upstream issue: https://github.com/microsoft/language-server-protocol/issues/956

Request:

interface InlayHintsParams {
    textDocument: TextDocumentIdentifier,
}

Response: InlayHint[]

interface InlayHint {
    kind: "TypeHint" | "ParameterHint" | "ChainingHint",
    range: Range,
    label: string,
}

Hover Actions

Client Capability: { "hoverActions": boolean }

If this capability is set, Hover request returned from the server might contain an additional field, actions:

interface Hover {
    ...
    actions?: CommandLinkGroup[];
}

interface CommandLink extends Command {
    /**
     * A tooltip for the command, when represented in the UI.
     */
    tooltip?: string;
}

interface CommandLinkGroup {
    title?: string;
    commands: CommandLink[];
}

Such actions on the client side are appended to a hover bottom as command links:

  +-----------------------------+
  | Hover content               |
  |                             |
  +-----------------------------+
  | _Action1_ | _Action2_       |  <- first group, no TITLE
  +-----------------------------+
  | TITLE _Action1_ | _Action2_ |  <- second group
  +-----------------------------+
  ...

Open Cargo.toml

Issue: https://github.com/rust-analyzer/rust-analyzer/issues/6462

This request is sent from client to server to open the current project's Cargo.toml

Method: experimental/openCargoToml

Request: OpenCargoTomlParams

Response: Location | null

Example

// Cargo.toml
[package]
// src/main.rs

/* cursor here*/

experimental/openCargoToml returns a single Link to the start of the [package] keyword.

LSP Extensions

UTF-8 offsets

initializationOptions

Snippet TextEdit

Example

Unresolved Questions

CodeAction Groups

Example

Unresolved Questions

Parent Module

Example

Unresolved Question

Join Lines

Example

Unresolved Question

On Enter

Example

Unresolved Question

Structural Search Replace (SSR)

Example

Unresolved Question

Matching Brace

Example

Unresolved Question

Runnables

Open External Documentation

Analyzer Status

Reload Workspace

Status Notification

Syntax Tree

View Hir

Expand Macro

Inlay Hints

Hover Actions

Open Cargo.toml

Example

`initializationOptions`

Snippet `TextEdit`

`CodeAction` Groups