Detect debug mode in VSCode Extension

Question

I am developing a VSCode Extension and I would like to write a simple logging utility that only logs to the console during debugging, otherwise, it's a no-op.

Is there a flag or value somewhere available in an extension that indicated debugging is currently ongoing?

Answer 1

In case someone still needs it, one solution is to use custom environment variable when starting a client in a debug mode.

In your launch.json file:

{
    "type": "extensionHost",
    "request": "launch",
    "name": "Launch Client",
    "runtimeExecutable": "${execPath}",
    "args": ["--extensionDevelopmentPath=${workspaceRoot}"],
    "outFiles": ["${workspaceRoot}/client/out/**/*.js"],
    "env": {
        "VSCODE_DEBUG_MODE": "true"
    }
}

Then, you can check it in your code like this:

const isDebugMode = () => process.env.VSCODE_DEBUG_MODE === "true";

export function activate(context: ExtensionContext) {
  if (isDebugMode()) {
    // Debug ...
  } else {
    // Else ...
  }
}

Answer 2

This is now officially supported:

https://github.com/Microsoft/vscode/blob/master/src/vs/vscode.d.ts#L6431

export namespace debug {

    /**
     * The currently active [debug session](#DebugSession) or `undefined`. The active debug session is the one
     * represented by the debug action floating window or the one currently shown in the drop down menu of the debug action floating window.
     * If no debug session is active, the value is `undefined`.
     */
    export let activeDebugSession: DebugSession | undefined;

    /**
     * The currently active [debug console](#DebugConsole).
     */
    export let activeDebugConsole: DebugConsole;

    /**
     * List of breakpoints.
     */
    export let breakpoints: Breakpoint[];


    /**
     * An [event](#Event) which fires when the [active debug session](#debug.activeDebugSession)
     * has changed. *Note* that the event also fires when the active debug session changes
     * to `undefined`.
     */
    export const onDidChangeActiveDebugSession: Event<DebugSession | undefined>;

    /**
     * An [event](#Event) which fires when a new [debug session](#DebugSession) has been started.
     */
    export const onDidStartDebugSession: Event<DebugSession>;

    /**
     * An [event](#Event) which fires when a custom DAP event is received from the [debug session](#DebugSession).
     */
    export const onDidReceiveDebugSessionCustomEvent: Event<DebugSessionCustomEvent>;

    /**
     * An [event](#Event) which fires when a [debug session](#DebugSession) has terminated.
     */
    export const onDidTerminateDebugSession: Event<DebugSession>;

    /**
     * An [event](#Event) that is emitted when the set of breakpoints is added, removed, or changed.
     */
    export const onDidChangeBreakpoints: Event<BreakpointsChangeEvent>;


    /**
     * Register a [debug configuration provider](#DebugConfigurationProvider) for a specifc debug type.
     * More than one provider can be registered for the same type.
     *
     * @param type The debug type for which the provider is registered.
     * @param provider The [debug configuration provider](#DebugConfigurationProvider) to register.
     * @return A [disposable](#Disposable) that unregisters this provider when being disposed.
     */
    export function registerDebugConfigurationProvider(debugType: string, provider: DebugConfigurationProvider): Disposable;

    /**
     * Start debugging by using either a named launch or named compound configuration,
     * or by directly passing a [DebugConfiguration](#DebugConfiguration).
     * The named configurations are looked up in '.vscode/launch.json' found in the given folder.
     * Before debugging starts, all unsaved files are saved and the launch configurations are brought up-to-date.
     * Folder specific variables used in the configuration (e.g. '${workspaceFolder}') are resolved against the given folder.
     * @param folder The [workspace folder](#WorkspaceFolder) for looking up named configurations and resolving variables or `undefined` for a non-folder setup.
     * @param nameOrConfiguration Either the name of a debug or compound configuration or a [DebugConfiguration](#DebugConfiguration) object.
     * @return A thenable that resolves when debugging could be successfully started.
     */
    export function startDebugging(folder: WorkspaceFolder | undefined, nameOrConfiguration: string | DebugConfiguration): Thenable<boolean>;

    /**
     * Add breakpoints.
     * @param breakpoints The breakpoints to add.
    */
    export function addBreakpoints(breakpoints: Breakpoint[]): void;

    /**
     * Remove breakpoints.
     * @param breakpoints The breakpoints to remove.
     */
    export function removeBreakpoints(breakpoints: Breakpoint[]): void;
}