src/vs/workbench/services/workingCopy/common/workingCopyHistoryService.ts/WorkingCopyHistoryModel/doAddEntry
class WorkingCopyHistoryModel:	private async doAddEntry(source: SaveSource, timestamp: number, token: CancellationToken): Promise<IWorkingCopyHistoryEntry> {
		const workingCopyResource = assertIsDefined(this.workingCopyResource);
		const workingCopyName = assertIsDefined(this.workingCopyName);
		const historyEntriesFolder = assertIsDefined(this.historyEntriesFolder);

		// Perform a fast clone operation with minimal overhead to a new random location
		const id = `${randomPath(undefined, undefined, 4)}${extname(workingCopyResource)}`;
		const location = joinPath(historyEntriesFolder, id);
		await this.fileService.cloneFile(workingCopyResource, location);

		// Add to list of entries
		const entry: IWorkingCopyHistoryEntry = {
			id,
			workingCopy: { resource: workingCopyResource, name: workingCopyName },
			location,
			timestamp,
			source
		};
		this.entries.push(entry);

		// Update version ID of model to use for storing later
		this.versionId++;

		// Events
		this.entryAddedEmitter.fire({ entry });

		return entry;
	}