Invalid short optional option values

Currently it is not possible to specify -oval optional option value syntax, where it forbids the spaced -o val syntax because the value is ambiguous as it could be a following positional argument instead. In clap, require_equals handles the long form case, i.e. --option=val, but specifying it errs the -oval form since it affects the short form too, requiring -o=val which is not what we want. This is documented in https://github.com/clap-rs/clap/issues/3030.

In summary, clap by default supports the following optional option value forms:

• --long
• --long=value
• --long value
• -s
• -s value
• -s=value
• -svalue

With requires_equals(true):

• --long
• --long=value
• -s
• -s=value

What we actually want:

• --long
• --long=value
• -s
• -svalue ‼️

This affects several coreutils (non-exhaustive, please comment if more):

• date -I (#6387)
• pr -e/-i/-n/-s/-S (#10302)
• od -w (#10725)

I have tried to PR clap a new feature require_no_space to support the last form, but it has been rejected because 'we have not fully decided on a direction for this'. As it is currently, the issues are unfixable.

Start by reviewing the referenced clap issue #3030 and rejected PR #6247 to understand the unresolved option-parsing direction. Then inspect the affected coreutils issues, including #6387, #10302, and #10725; the work is done when the desired -svalue behavior is supported without allowing the spaced short-option form.