Deprecate function and mixin names beginning with --

[nex3]

See #2197
See sass/sass#3854
See sass/sass-spec#1982
[skip sass-embedded]

[WebMechanic]

Hello,

I updated to 1.77.0 and noticed this also affects mixins starting with double underscores such as @mixin __fubar() and their @include __fubar().

If this is intended it should probably be mentioned in the documentation

We only had a couple of old mixins using the __ prefix to mark them as "private". No big deal as the warning in the console was very helpful.

Bye.

[Goodwine]

It was intended. Underscores and hyphens are equivalent in Sass identifiers. We assume users are familiar with that fact, but I understand it may not be obvious.

From the docs:

Mixin names, like all Sass identifiers, treat hyphens and underscores as identical. This means that reset-list and reset_list both refer to the same mixin.

https://sass-lang.com/documentation/at-rules/mixin/

[WebMechanic]

Thanks, indeed not so obvious :-)
From this example with the inline hyphens and underscores, I had never deduced that this also applies to prefixes which most languages handle very differently -- except CSS and as I learned now, Sass.
It's always these "little things" that cause confusion :-)

[nex3]

I think @WebMechanic is right that this is a bug. The spec is ambiguous here, and there's not a strong reason for us to forbid functions from being written and referenced with double leading underscores.