Provide altered context to callbacks to hide UNSET values as None

[kdeldycke]

PR to fix:

• Sentinel available in context during option callbacks #3136
• Test failures with click 8.3.1 flask#5836

This highlight a side-effect introduced in:

• Fix default handling to defer UNSET normalization #3079
• default=True on feature flags is order-sensitive #3071

CC @dotlambda

[kdeldycke]

Ok I found a solution to reconcile the 2 issues. It's a bit dirty, but it works without side-effects.

[mgorny]

Thanks! I can confirm that this fixes the issues I've seen in black.

[Rowlando13]

The tests look good.

[Rowlando13]

@davidism Can you review this?

[Rowlando13]

@kdeldycke Also add change entry.

[davidism]

A ridiculous fix 😅, but I'm fine with it.

Maybe in the next release we can figure out some internal API separate from the external one, rather than this bit of magic.

[kdeldycke]

A ridiculous fix 😅, but I'm fine with it.

Oh yes. A bit ashamed by that. That's why I tried to be very explicit in delimiting that fix. Anyone reaching that implementation will understand that this part needs some refactor.

Maybe in the next release we can figure out some internal API separate from the external one, rather than this bit of magic.

Oh yes. You initiated that direction by helping me identify private methods in the previous months, with :meta private: tags in docstrings. Maybe we can go further and start prefixing functions, methods and properties with underscore _, as a hint for stuff you are not supposed to mess with. Let's discuss that once things settle down.

[kdeldycke]

@kdeldycke Also add change entry.

Ah yes, good call. Done.

[kdeldycke]

Also, just for reference, this PR pass all my tricky hacks in Click Extra. 😇

[kdeldycke]

Maybe in the next release we can figure out some internal API separate from the external one, rather than this bit of magic.

Oh yes. You initiated that direction by helping me identify private methods in the previous months, with :meta private: tags in docstrings. Maybe we can go further and start prefixing functions, methods and properties with underscore _, as a hint for stuff you are not supposed to mess with. Let's discuss that once things settle down.

Also, the advantage of all that UNSET saga is that we can now easily find where in the code base of Click there is expectation of value normalization. Just grep on UNSET! 😅🫣