Thanks Stefan, I've revised the patch according to your suggestions (see attached). I also revised the docstring.

Thanks!
Colin

On Tue, 25 May 2021, at 14:29, Stefan Monnier wrote:
> > That regex was borrowed directly from `string-trim`, to which I added
> > a `.`. You're right that the main motivation was to allow the caller to pass
> > either `.foo` or `foo` as the extension and have either case work (many
> > languages do this). Leaving the other characters in the regex seemed like
> > a sanitary thing to do, just in case they pass something bogus.
> 
> File names can be used in different ways for different purposes.
> We don't have any good reason to think that a space or a newline at the
> end of a file name (or beginning of an extension) is "bogus".
> 
> If such things occurred somewhat often and always in ways where they are
> indeed undesirable, we could consider removing them (the tradeoff
> between occasional harm and frequent error-avoidance would be
> favorable), but here this is just asking for trouble with no benefit.
> 
> > 1. Simplifying the regex to just include dots (and perhaps whitespace) (i.e. trust the caller), or;
> 
> Please do that.
> 
> > 2. Expanding the logic to sanitize both ends of both arguments, (i.e. don't trust the caller), or;
> 
> I don't think we have any reason to think we should "sanitize" it.
> 
> > 3. Adding error-throwing logic if malformed files or extensions are given (i.e. warn the user).
> 
> "Malformed" according to which standard?
> 
> 
>         Stefan
> 
>