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The Language Server

The Deno CLI comes with a built in language server that can provide an intelligent editing experience, as well as a way to easily access the other tools that come built in with Deno. For most users, using the language server would be via an editor such as Visual Studio Code or other editors.

This page is designed for those creating integrations to the language server or providing a package registry for Deno that integrates intelligently.

The Deno Language Server provides a server implementation of the Language Server Protocol which is specifically tailored to provide a Deno view of code. It is integrated into the command line and can be started via the lsp sub-command.

Structure Jump to heading

When the language server is started, a LanguageServer instance is created which holds all of the state of the language server. It also defines all of the methods that the client calls via the Language Server RPC protocol.

Settings Jump to heading

The language server supports a number of settings for a workspace:

  • deno.enable
  • deno.enablePaths
  • deno.cache
  • deno.certificateStores
  • deno.config
  • deno.importMap
  • deno.internalDebug
  • deno.codeLens.implementations
  • deno.codeLens.references
  • deno.codeLens.referencesAllFunctions
  • deno.codeLens.test
  • deno.suggest.completeFunctionCalls
  • deno.suggest.names
  • deno.suggest.paths
  • deno.suggest.autoImports
  • deno.suggest.imports.autoDiscover
  • deno.suggest.imports.hosts
  • deno.lint
  • deno.tlsCertificate
  • deno.unsafelyIgnoreCertificateErrors
  • deno.unstable

And there are settings that are supported on a per resource basis by the language server:

  • deno.enable
  • deno.enablePaths
  • deno.codeLens.test

Deno analyzes these settings at multiple points in the language server process. First, when the initialize request arrives from the client, the initializationOptions will be assumed to be an object that represents the deno namespace of options. For example, the following value will enable Deno with the unstable APIs for this instance of the language server.

{
  "enable": true,
  "unstable": true
}

When the language server receives a workspace/didChangeConfiguration notification, it will assess if the client has indicated if it has a workspaceConfiguration capability. If it does, it will send a workspace/configuration request which will include a request for the workspace configuration as well as the configuration of all URIs that the language server is currently tracking.

If the client has the workspaceConfiguration capability, the language server will send a configuration request for the URI when it received the textDocument/didOpen notification in order to get the resources specific settings.

If the client does not have the workspaceConfiguration capability, the language server will assume the workspace setting applies to all resources.

Commands Jump to heading

There are several commands that might be issued by the language server to the client, which the client is expected to implement:

cache Jump to heading

deno.cache is sent as a resolution code action when there is an un-cached module specifier that is being imported into a module. It will be sent with and argument that contains the resolved specifier as a string to be cached.

showReferences Jump to heading

deno.showReferences is sent as the command on some code lenses to show locations of references. The arguments contain the specifier that is the subject of the command, the start position of the target and the locations of the references to show.

test Jump to heading

deno.test is sent as part of a test code lens to, of which the client is expected to run a test based on the arguments, which are the specifier the test is contained in and the name of the test to filter the tests on.

Requests Jump to heading

The LSP currently supports the following custom requests. A client should implement these in order to have a fully functioning client that integrates well with Deno:

cache Jump to heading

deno/cache will instruct Deno to attempt to cache a module and all of its dependencies. If a referrer only is passed, then all dependencies for the module specifier will be loaded. If there are values in the uris, then only those uris will be cached.

It expects parameters of:

interface CacheParams {
  referrer: TextDocumentIdentifier;
  uris: TextDocumentIdentifier[];
}

performance Jump to heading

deno/performance requests the return of the timing averages for the internal instrumentation of Deno. It does not expect any parameters.

reloadImportRegistries Jump to heading

deno/reloadImportRegistries reloads any cached responses from import registries. It does not expect any parameters.

virtualTextDocument Jump to heading

deno/virtualTextDocument requests a virtual text document from the LSP, which is a read only document that can be displayed in the client. This allows clients to access documents in the Deno cache, like remote modules and TypeScript library files built into Deno. The Deno language server will encode all internal files under the custom schema deno:, so clients should route all requests for the deno: schema back to the deno/virtualTextDocument API.

It also supports a special URL of deno:/status.md which provides a markdown formatted text document that contains details about the status of the LSP for display to a user.

It expects parameters of:

interface VirtualTextDocumentParams {
  textDocument: TextDocumentIdentifier;
}

task Jump to heading

deno/task requests the return of available deno tasks, see task_runner. It does not expect any parameters.

Notifications Jump to heading

There is currently one custom notification that is sent from the server to the client, deno/registryState. When deno.suggest.imports.autoDiscover is true and an origin for an import being added to a document is not explicitly set in deno.suggest.imports.hosts, the origin will be checked and the notification will be sent to the client of the status.

When receiving the notification, if the param suggestion is true, the client should offer the user the choice to enable the origin and add it to the configuration for deno.suggest.imports.hosts. If suggestion is false the client should add it to the configuration of as false to stop the language server from attempting to detect if suggestions are supported.

The params for the notification are:

interface RegistryStatusNotificationParams {
  origin: string;
  suggestions: boolean;
}

Language IDs Jump to heading

The language server supports diagnostics and formatting for the following text document language IDs:

  • "javascript"
  • "javascriptreact"
  • "jsx" non standard, same as javascriptreact
  • "typescript"
  • "typescriptreact"
  • "tsx" non standard, same as typescriptreact

The language server supports only formatting for the following language IDs:

  • "json"
  • "jsonc"
  • "markdown"

Testing Jump to heading

The Deno language server supports a custom set of APIs to enable testing. These are built around providing information to enable the vscode's Testing API but can be used by other language server clients to provide a similar interface.

Both the client and the server should support the experimental testingApi capability:

interface ClientCapabilities {
  experimental?: {
    testingApi: boolean;
  };
}

interface ServerCapabilities {
  experimental?: {
    testingApi: boolean;
  };
}

When a version of Deno that supports the testing API encounters a client which supports the capability, it will initialize the code which handles the test detection and will start providing the notifications which enable it.

It should also be noted that when the testing API capabilities are enabled, the testing code lenses will no longer be sent to the client.

Testing settings Jump to heading

There are specific settings which change the behavior of the language server:

Arguments Jump to heading

deno.testing.args is an array of strings which will be provided as arguments when executing tests. This works in the same fashion as the deno test subcommand.

Enable/Diable Jump to heading

deno.testing.enable is a binary flag that enables or disables the testing server

Testing notifications Jump to heading

The server will send notifications to the client under certain conditions.

deno/testModule Jump to heading

When a module containing tests is discovered by the server, it will notify the client by sending a deno/testModule notification along with a payload of TestModuleParams.

Deno structures in this fashion:

  • A module can contain n tests.
  • A test can contain n steps.
  • A step can contain n steps.

When Deno does static analysis of a test module, it attempts to identify any tests and test steps. Because of the dynamic way tests can be declared in Deno, they cannot always be statically identified and can only be identified when the module is executed. The notification is designed to handle both of these situations when updating the client. When tests are discovered statically, the notification kind will be "replace", when tests or steps are discovered at execution time, the notification kind will be "insert".

As a test document is edited in the editor, and textDocument/didChange notifications are received from the client, the static analysis of those changes will be performed server side and if the tests have changed, the client will receive a notification.

When a client receives a "replace" notification, it can safely "replace" a test module representation, where when an "insert" it received, it should recursively try to add to existing representations.

For test modules the textDocument.uri should be used as the unique ID for any representation (as it the string URL to the unique module). TestData items contain a unique id string. This id string is a SHA-256 hash of identifying information that the server tracks for a test.

interface TestData {
  /** The unique ID for this test/step. */
  id: string;

  /** The display label for the test/step. */
  label: string;

  /** Any test steps that are associated with this test/step */
  steps?: TestData[];

  /** The range of the owning text document that applies to the test. */
  range?: Range;
}

interface TestModuleParams {
  /** The text document identifier that the tests are related to. */
  textDocument: TextDocumentIdentifier;

  /** A indication if tests described are _newly_ discovered and should be
   * _inserted_ or if the tests associated are a replacement for any existing
   * tests. */
  kind: "insert" | "replace";

  /** The text label for the test module. */
  label: string;

  /** An array of tests that are owned by this test module. */
  tests: TestData[];
}

deno/testModuleDelete Jump to heading

When a test module is deleted that the server is observing, the server will issue a deno/testModuleDelete notification. When receiving the notification the client should remove the representation of the test module and all of its children tests and test steps.

interface TestModuleDeleteParams {
  /** The text document identifier that has been removed. */
  textDocument: TextDocumentIdentifier;
}

deno/testRunProgress Jump to heading

When a deno/testRun is requested from the client, the server will support progress of that test run via the deno/testRunProgress notification.

The client should process these messages and update any UI representation.

The state change is represented in the .message.kind property of the TestRunProgressParams. The states are:

  • "enqueued" - A test or test step has been enqueued for testing.
  • "skipped" - A test or test step was skipped. This occurs when the Deno test has the ignore option set to true.
  • "started" - A test or test step has started.
  • "passed" - A test or test step has passed.
  • "failed" - A test or test step has failed. This is intended to indicate an error with the test harness instead of the test itself, but Deno currently does not support this distinction.
  • "errored" - The test or test step has errored. Additional information about the error will be in the .message.messages property.
  • "end" - The test run has ended.
interface TestIdentifier {
  /** The test module the message is related to. */
  textDocument: TextDocumentIdentifier;

  /** The optional ID of the test. If not present, then the message applies to
   * all tests in the test module. */
  id?: string;

  /** The optional ID of the step. If not present, then the message only applies
   * to the test. */
  stepId?: string;
}

interface TestMessage {
  /** The content of the message. */
  message: MarkupContent;

  /** An optional string which represents the expected output. */
  expectedOutput?: string;

  /** An optional string which represents the actual output. */
  actualOutput?: string;

  /** An optional location related to the message. */
  location?: Location;
}

interface TestEnqueuedStartedSkipped {
  /** The state change that has occurred to a specific test or test step.
   *
   * - `"enqueued"` - the test is now enqueued to be tested
   * - `"started"` - the test has started
   * - `"skipped"` - the test was skipped
   */
  type: "enqueued" | "started" | "skipped";

  /** The test or test step relating to the state change. */
  test: TestIdentifier;
}

interface TestFailedErrored {
  /** The state change that has occurred to a specific test or test step.
   *
   * - `"failed"` - The test failed to run properly, versus the test erroring.
   *   currently the Deno language server does not support this.
   * - `"errored"` - The test errored.
   */
  type: "failed" | "errored";

  /** The test or test step relating to the state change. */
  test: TestIdentifier;

  /** Messages related to the state change. */
  messages: TestMessage[];

  /** An optional duration, in milliseconds from the start to the current
   * state. */
  duration?: number;
}

interface TestPassed {
  /** The state change that has occurred to a specific test or test step. */
  type: "passed";

  /** The test or test step relating to the state change. */
  test: TestIdentifier;

  /** An optional duration, in milliseconds from the start to the current
   * state. */
  duration?: number;
}

interface TestOutput {
  /** The test or test step has output information / logged information. */
  type: "output";

  /** The value of the output. */
  value: string;

  /** The associated test or test step if there was one. */
  test?: TestIdentifier;

  /** An optional location associated with the output. */
  location?: Location;
}

interface TestEnd {
  /** The test run has ended. */
  type: "end";
}

type TestRunProgressMessage =
  | TestEnqueuedStartedSkipped
  | TestFailedErrored
  | TestPassed
  | TestOutput
  | TestEnd;

interface TestRunProgressParams {
  /** The test run ID that the progress message applies to. */
  id: number;

  /** The message*/
  message: TestRunProgressMessage;
}

Testing requests Jump to heading

The server handles two different requests:

deno/testRun Jump to heading

To request the language server to perform a set of tests, the client sends a deno/testRun request, which includes that ID of the test run to be used in future responses to the client, the type of the test run, and any test modules or tests to include or exclude.

Currently Deno only supports the "run" kind of test run. Both "debug" and "coverage" are planned to be supported in the future.

When there are no test modules or tests that are included, it implies that all discovered tests modules and tests should be executed. When a test module is included, but not any test ids, it implies that all tests within that test module should be included. Once all the tests are identified, any excluded tests are removed and the resolved set of tests are returned in the response as "enqueued".

It is not possible to include or exclude test steps via this API, because of the dynamic nature of how test steps are declared and run.

interface TestRunRequestParams {
  /** The id of the test run to be used for future messages. */
  id: number;

  /** The run kind. Currently Deno only supports `"run"` */
  kind: "run" | "coverage" | "debug";

  /** Test modules or tests to exclude from the test run. */
  exclude?: TestIdentifier[];

  /** Test modules or tests to include in the test run. */
  include?: TestIdentifier[];
}

interface EnqueuedTestModule {
  /** The test module the enqueued test IDs relate to */
  textDocument: TextDocumentIdentifier;

  /** The test IDs which are now enqueued for testing */
  ids: string[];
}

interface TestRunResponseParams {
  /** Test modules and test IDs that are now enqueued for testing. */
  enqueued: EnqueuedTestModule[];
}

deno/testRunCancel Jump to heading

If a client wishes to cancel a currently running test run, it sends a deno/testRunCancel request with the test ID to cancel. The response back will be a boolean of true if the test is cancelled or false if it was not possible. Appropriate test progress notifications will still be sent as the test is being cancelled.

interface TestRunCancelParams {
  /** The test id to be cancelled. */
  id: number;
}