src/vs/workbench/services/workingCopy/common/fileWorkingCopyManager.ts/FileWorkingCopyManager/doSave
class FileWorkingCopyManager:	private async doSave(resource: URI, options?: ISaveOptions): Promise<IStoredFileWorkingCopy<S> | undefined> {

		// Save is only possible with stored file working copies,
		// any other have to go via `saveAs` flow.
		const storedFileWorkingCopy = this.stored.get(resource);
		if (storedFileWorkingCopy) {
			const success = await storedFileWorkingCopy.save(options);
			if (success) {
				return storedFileWorkingCopy;
			}
		}

		return undefined;
	}