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 the 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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Configuration in `initializationOptions`

Upstream Issue: https://github.com/microsoft/language-server-protocol/issues/567

The initializationOptions field of the InitializeParams of the initialization request should contain the "rust-analyzer" section of the configuration.

rust-analyzer normally sends a "workspace/configuration" request with { "items": ["rust-analyzer"] } payload. However, the server can't do this during initialization. At the same time some essential configuration parameters are needed early on, before servicing requests. For this reason, we ask that initializationOptions contains the configuration, as if the server did make a "workspace/configuration" request.

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
Sending "initializationOptions": null
Sending "initializationOptions": {}

Snippet `TextEdit`

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

Experimental Client Capability: { "snippetTextEdit": boolean }

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

interface SnippetTextEdit extends TextEdit {
    insertTextFormat?: InsertTextFormat;
    annotationId?: ChangeAnnotationIdentifier;
}

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

When applying such code action or text edit, 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

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

Experimental Client Capability: { "codeActionGroup": boolean }

If this capability is set, CodeActions 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

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

Experimental 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 taking. 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 overridden function, the behavior with single “gotoSuper” request is surprising.

Join Lines

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

Experimental 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

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

Experimental Server Capability: { "onEnter": boolean }

This request is sent from client to server to handle the Enter key press.

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)

Experimental 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: boolean,
    /// The current text document. This and `position` will be used to determine in what scope
    /// paths in `query` should be resolved.
    textDocument: TextDocumentIdentifier;
    /// Position where SSR was invoked.
    position: Position;
    /// Current selections. Search/replace will be restricted to these if non-empty.
    selections: Range[];
}

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

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

Experimental 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 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

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

Experimental 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 the client to the server to obtain web and local URL(s) for documentation related to the symbol under the cursor, if available.

Method: experimental/externalDocs

Request: TextDocumentPositionParams

Response: string | null

Local Documentation

Experimental Client Capability: { "localDocs": boolean }

If this capability is set, the Open External Documentation request returned from the server will have the following structure:

interface ExternalDocsResponse {
    web?: string;
    local?: string;
}

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).

Rebuild proc-macros

Method: rust-analyzer/rebuildProcMacros

Request: null

Response: null

Rebuilds build scripts and proc-macros, and runs the build scripts to reseed the build data.

Server Status

Experimental Client Capability: { "serverStatusNotification": boolean }

Method: experimental/serverStatus

Notification:

interface ServerStatusParams {
    /// `ok` means that the server is completely functional.
    ///
    /// `warning` means that the server is partially functional.
    /// It can answer correctly to most requests, but some results
    /// might be wrong due to, for example, some missing dependencies.
    ///
    /// `error` means that the server is not functional. For example,
    /// there's a fatal build configuration problem. The server might
    /// still give correct answers to simple requests, but most results
    /// will be incomplete or wrong.
    health: "ok" | "warning" | "error",
    /// Is there any pending background work which might change the status?
    /// For example, are dependencies being downloaded?
    quiescent: boolean,
    /// Explanatory message to show on hover.
    message?: string,
}

This notification is sent from server to client. The client can use it to display persistent status to the user (in modline). It is similar to the showMessage, but is intended for stares rather than point-in-time events.

Note that this functionality is intended primarily to inform the end user about the state of the server. In particular, it‘s valid for the client to completely ignore this extension. Clients are discouraged from but are allowed to use the health status to decide if it’s worth sending a request to the server.

Controlling Flycheck

The flycheck/checkOnSave feature can be controlled via notifications sent by the client to the server.

Method: rust-analyzer/runFlycheck

Notification:

interface RunFlycheckParams {
    /// The text document whose cargo workspace flycheck process should be started.
    /// If the document is null or does not belong to a cargo workspace all flycheck processes will be started.
    textDocument: lc.TextDocumentIdentifier | null;
}

Triggers the flycheck processes.

Method: rust-analyzer/clearFlycheck

Notification:

interface ClearFlycheckParams {}

Clears the flycheck diagnostics.

Method: rust-analyzer/cancelFlycheck

Notification:

interface CancelFlycheckParams {}

Cancels all running flycheck processes.

Syntax Tree

Method: rust-analyzer/syntaxTree

Request:

interface SyntaxTreeParams {
    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.

View Mir

Method: rust-analyzer/viewMir

Request: TextDocumentPositionParams

Response: string

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

Interpret Function

Method: rust-analyzer/interpretFunction

Request: TextDocumentPositionParams

Response: string

Tries to evaluate the function using internal rust analyzer knowledge, without compiling the code. Currently evaluates the function under cursor, but will give a runnable in future. Highly experimental.

View File Text

Method: rust-analyzer/viewFileText

Request: TextDocumentIdentifier

Response: string

Returns the text of a file as seen by the server. This is for debugging file sync problems.

View ItemTree

Method: rust-analyzer/viewItemTree

Request:

interface ViewItemTreeParams {
    textDocument: TextDocumentIdentifier,
}

Response: string

Returns a textual representation of the ItemTree of the currently open file, for debugging.

View Crate Graph

Method: rust-analyzer/viewCrateGraph

Request:

interface ViewCrateGraphParams {
    full: boolean,
}

Response: string

Renders rust-analyzer's crate graph as an SVG image.

If full is true, the graph includes non-workspace crates (crates.io dependencies as well as sysroot crates).

Shuffle Crate Graph

Method: rust-analyzer/shuffleCrateGraph

Request: null

Shuffles the crate IDs in the crate graph, for debugging purposes.

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.

Hover Actions

Experimental 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

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

Experimental Server Capability: { "openCargoToml": boolean }

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.

Related tests

This request is sent from client to server to get the list of tests for the specified position.

Method: rust-analyzer/relatedTests

Request: TextDocumentPositionParams

Response: TestInfo[]

interface TestInfo {
    runnable: Runnable;
}

Hover Range

Upstream Issue: https://github.com/microsoft/language-server-protocol/issues/377

Experimental Server Capability: { “hoverRange”: boolean }

This extension allows passing a Range as a position field of HoverParams. The primary use-case is to use the hover request to show the type of the expression currently selected.

interface HoverParams extends WorkDoneProgressParams {
    textDocument: TextDocumentIdentifier;
    position: Range | Position;
}

Whenever the client sends a Range, it is understood as the current selection and any hover included in the range will show the type of the expression if possible.

Example

fn main() {
    let expression = $01 + 2 * 3$0;
}

Triggering a hover inside the selection above will show a result of i32.

Move Item

Upstream Issue: https://github.com/rust-lang/rust-analyzer/issues/6823

This request is sent from client to server to move item under cursor or selection in some direction.

Method: experimental/moveItem

Request: MoveItemParams

Response: SnippetTextEdit[]

export interface MoveItemParams {
    textDocument: TextDocumentIdentifier,
    range: Range,
    direction: Direction
}

export const enum Direction {
    Up = "Up",
    Down = "Down"
}

Workspace Symbols Filtering

Upstream Issue: https://github.com/microsoft/language-server-protocol/issues/941

Experimental Server Capability: { "workspaceSymbolScopeKindFiltering": boolean }

Extends the existing workspace/symbol request with ability to filter symbols by broad scope and kind of symbol. If this capability is set, workspace/symbol parameter gains two new optional fields:

interface WorkspaceSymbolParams {
    /**
     * Return only the symbols defined in the specified scope.
     */
    searchScope?: WorkspaceSymbolSearchScope;
    /**
     * Return only the symbols of specified kinds.
     */
    searchKind?: WorkspaceSymbolSearchKind;
    ...
}

const enum WorkspaceSymbolSearchScope {
    Workspace = "workspace",
    WorkspaceAndDependencies = "workspaceAndDependencies"
}

const enum WorkspaceSymbolSearchKind {
    OnlyTypes = "onlyTypes",
    AllSymbols = "allSymbols"
}

Client Commands

Upstream Issue: https://github.com/microsoft/language-server-protocol/issues/642

Experimental Client Capability: { "commands?": ClientCommandOptions }

Certain LSP types originating on the server, notably code lenses, embed commands. Commands can be serviced either by the server or by the client. However, the server doesn't know which commands are available on the client.

This extensions allows the client to communicate this info.

export interface ClientCommandOptions {
    /**
     * The commands to be executed on the client
     */
    commands: string[];
}

Colored Diagnostic Output

Experimental Client Capability: { "colorDiagnosticOutput": boolean }

If this capability is set, the “full compiler diagnostics” provided by checkOnSave will include ANSI color and style codes to render the diagnostic in a similar manner as cargo. This is translated into --message-format=json-diagnostic-rendered-ansi when flycheck is run, instead of the default --message-format=json.

The full compiler rendered diagnostics are included in the server response regardless of this capability:

// https://microsoft.github.io/language-server-protocol/specifications/specification-current#diagnostic
export interface Diagnostic {
    ...
    data?: {
        /**
         * The human-readable compiler output as it would be printed to a terminal.
         * Includes ANSI color and style codes if the client has set the experimental
         * `colorDiagnosticOutput` capability.
         */
        rendered?: string;
    };
}

Dependency Tree

Method: rust-analyzer/fetchDependencyList

Request:

export interface FetchDependencyListParams {}

Response:

export interface FetchDependencyListResult {
    crates: {
        name: string;
        version: string;
        path: string;
    }[];
}

Returns all crates from this workspace, so it can be used create a viewTree to help navigate the dependency tree.

View Recursive Memory Layout

Method: rust-analyzer/viewRecursiveMemoryLayout

Request: TextDocumentPositionParams

Response:

export interface RecursiveMemoryLayoutNode = {
    /// Name of the item, or [ROOT], `.n` for tuples
    item_name: string;
    /// Full name of the type (type aliases are ignored)
    typename: string;
    /// Size of the type in bytes
    size: number;
    /// Alignment of the type in bytes
    alignment: number;
    /// Offset of the type relative to its parent (or 0 if its the root)
    offset: number;
    /// Index of the node's parent (or -1 if its the root)
    parent_idx: number;
    /// Index of the node's children (or -1 if it does not have children)
    children_start: number;
    /// Number of child nodes (unspecified it does not have children)
    children_len: number;
};

export interface RecursiveMemoryLayout = {
    nodes: RecursiveMemoryLayoutNode[];
};

Returns a vector of nodes representing items in the datatype as a tree, RecursiveMemoryLayout::nodes[0] is the root node.

If RecursiveMemoryLayout::nodes::length == 0 we could not find a suitable type.

Generic Types do not give anything because they are incomplete. Fully specified generic types do not give anything if they are selected directly but do work when a child of other types this is consistent with other behavior.

Unresolved questions:

How should enums/unions be represented? currently they do not produce any children because they have multiple distinct sets of children.
Should niches be represented? currently they are not reported.
A visual representation of the memory layout is not specified, see the provided implementation for an example, however it may not translate well to terminal based editors or other such things.

LSP Extensions

Configuration in 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

Local Documentation

Analyzer Status

Reload Workspace

Rebuild proc-macros

Server Status

Controlling Flycheck

Syntax Tree

View Hir

View Mir

Interpret Function

View File Text

View ItemTree

View Crate Graph

Shuffle Crate Graph

Expand Macro

Hover Actions

Open Cargo.toml

Example

Related tests

Hover Range

Example

Move Item

Workspace Symbols Filtering

Client Commands

Colored Diagnostic Output

Dependency Tree

View Recursive Memory Layout

Unresolved questions:

Configuration in `initializationOptions`

Snippet `TextEdit`

`CodeAction` Groups