bug#21904: date->string duff ISO 8601 format for non-4-digit years

[Mark H Weaver <mhw@netris.org>]

Mark H Weaver <mhw@netris.org> writes:
> Another question is whether or not we should raise an exception when
> attempting to print a year that cannot be represented in the requested
> year format.

I thought about it some more, and I'm now inclined to think that the
approach in your patches is reasonable, or at least it's the least bad
thing we can do when asked to print a year that doesn't fit within the
standard format, given the existing SRFI-19 API.

I also just noticed that the SRFI-19's reference implementation's
formatting of negative years is very badly broken (e.g. it prints "00-2"
when the year field is -2) and Guile had the same behavior after I
applied the fix from upstream to pad the year to 4 digits.

So, for now, I went ahead and implemented the behavior that you
recommended, with one difference: where you hardcode the padding
character to #\0 when formatting years, I use the padding character
specified by the user, following the SRFI-19 reference implementation.

What do you think?

      Mark