src/vs/workbench/contrib/format/browser/formatActionsMultiple.ts/logFormatterTelemetry
function logFormatterTelemetry<T extends { extensionId?: ExtensionIdentifier }>(telemetryService: ITelemetryService, mode: 'document' | 'range', options: T[], pick?: T) {

	function extKey(obj: T): string {
		return obj.extensionId ? ExtensionIdentifier.toKey(obj.extensionId) : 'unknown';
	}
	/*
	 * __GDPR__
		"formatterpick" : {
			"mode" : { "classification": "SystemMetaData", "purpose": "FeatureInsight" },
			"extensions" : { "classification": "SystemMetaData", "purpose": "FeatureInsight" },
			"pick" : { "classification": "SystemMetaData", "purpose": "FeatureInsight" }
		}
	 */
	telemetryService.publicLog('formatterpick', {
		mode,
		extensions: options.map(extKey),
		pick: pick ? extKey(pick) : 'none'
	});
}