Should we expose IShell.activeWidget, or short-circuit in IShell.activateById?

[krassowski]

Problem

Extensions may want to activate a widget if it is not active. This is because activating a widget may have side effects. In case of notebooks the side effect of ensuring focus can lead to problematic behaviour in CodeMirror editor extensions, such as jupyterlab-vim. In jupyterlab-contrib/jupyterlab-vim#85 I workaround it by comparing the widget with IShell.currentWidget but it feels like we should be comparing against IShell.activeWidget; however that is not exposed as public API.

Proposed Solution

a) expose IShell.activeWidget,
b) short-circuit in IShell.activateById if provided id is equal IShell.activeWidget.id

Downsides:

• (a) increases API surface
• (b) may break existing code if it is relying on side effects always being invoked

Additional context

Implementation has activateById, activeWidget, and currentWidget:

jupyterlab/packages/application/src/shell.ts

Lines 499 to 505 in e2cdaf1

	/**
	* The active widget in the shell's main area.
	*/
	get activeWidget(): Widget | null {
	return this._tracker.activeWidget;
	}

jupyterlab/packages/application/src/shell.ts

Lines 547 to 552 in e2cdaf1

	/**
	* The current widget in the shell's main area.
	*/
	get currentWidget(): Widget | null {
	return this._tracker.currentWidget;
	}

jupyterlab/packages/application/src/shell.ts

Lines 743 to 746 in e2cdaf1

	/**
	* Activate a widget in its area.
	*/
	activateById(id: string): void {

Public API only exposes activateById and currentWidget:

jupyterlab/packages/application/src/frontend.ts

Lines 242 to 251 in e2cdaf1

	/**
	* A minimal shell type for Jupyter front-end applications.
	*/
	export interface IShell extends Widget {
	/**
	* Activates a widget inside the application shell.
	*
	* @param id - The ID of the widget being activated.
	*/
	activateById(id: string): void;

jupyterlab/packages/application/src/frontend.ts

Lines 270 to 277 in e2cdaf1

	/**
	* The focused widget in the application shell.
	*
	* #### Notes
	* Different shell implementations have latitude to decide what "current"
	* or "focused" mean, depending on their user interface characteristics.
	*/
	readonly currentWidget: Widget | null;

[fcollonval]

I support you with this proposal.