src/vs/workbench/contrib/customEditor/browser/customEditors.ts/CustomEditorService/withActiveCustomEditor
class CustomEditorService:	private withActiveCustomEditor(f: (editor: CustomEditorInput) => void | Promise<void>): boolean | Promise<void> {
		const activeEditor = this.editorService.activeEditor;
		if (activeEditor instanceof CustomEditorInput) {
			const result = f(activeEditor);
			if (result) {
				return result;
			}
			return true;
		}
		return false;
	}