🐛 Fix: disallow need variants for list type fields

[chrisjsewell]

The variant processing was turning these into strings, rather than list of strings, which does not make sense and breaks the need item schema.

Since this is the case, and has not been noticed before, it is doubtful that variants are ever used in this context.

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 88.66%. Comparing base (4e10030) to head (a7f6ee6).
⚠️ Report is 147 commits behind head on master.

Files with missing lines	Patch %	Lines
sphinx_needs/functions/functions.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1489      +/-   ##
==========================================
+ Coverage   86.87%   88.66%   +1.78%     
==========================================
  Files          56       68      +12     
  Lines        6532     8451    +1919     
==========================================
+ Hits         5675     7493    +1818     
- Misses        857      958     +101     

Flag	Coverage Δ
pytests	88.66% <66.66%> (+1.78%)	⬆️

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[ubmarco]

So this is a good observation. Really seems like it was only working for options as match_variants returns str | None, so you have a fair point. I will approve this as it makes SN safer.
However I think variant handling is a powerful feature, also for links.
I am ok for disabling this for now and listen to user's feedback whether link variants are a thing.
@danwos marking you so you are aware of this

[danwos]

I have seen once a use case, where variant management was needed for links, as the user wanted to link a spec to 2 different requirements, which were coming from 2 OEMs.
This was a platform project, used by multiple customers, which all delivered their own list of requirements. And it's a valid, often told use case for platform projects.

Would it cost much time to fix it instead of deactivating it?
It's one feature less for Sphinx-Needs :(

[chrisjsewell]

Would it cost much time to fix it instead of deactivating it?

The question is; what does this syntax even mean, in terms of a list of strings?

For example here; :links: [tag]:some|thing, other|wise,
are some|thing / other|wise single link references,
or a list of references; ["some", "thing"], and how does these even integrate with the initial parsing of these strings.

The idea of variants is not necessarily bad, but the implementation is a complete ill-though out mess.

I will be disabling this for now,
but a next step is to move the initial identification/parsing of dynamic functions and variants to the need item creation phase (e.g. when a directive is parsed),
and then we will better be able to implement/orchestrate the parsing of string lists / dynamic functions / variant functions and how they interact together