Improve error message on attempt to use instance member in static context

[valeriyvan]

Resolves #62909

[xedin]

I don't think that "in static context" brings any clarify because everybody has a different idea what "static context" means, but I'm biased. @hborla WDYT?

[AnthonyLatsis]

I’m probably biased too, but I read this as "you cannot use this at all in a static function". Regrettably, the best alternative I can currently think of is instance member cannot be used on type object.

[AnthonyLatsis]

However, maybe it does make sense to say "static context" specifically when self. is implicit, keep the current wording for T., and say "metatype" for meta..

[xedin]

"you cannot use this at all in a static function".

This is exactly what I'm afraid of happening.

[valeriyvan]

Guys, how should we proceed with this fix?

[AnthonyLatsis]

The primary goal is to tailor the message for implicit accesses on self specifically. The current message reads well when applied to an explicit access on a type identifier as in T.member(). As for how exactly we want to tailor it, we need to come up with a better idea than what was voiced in the issue.

[xedin]

Maybe a good start would be to limit this diagnostic to situations when self. is implicit (that's what "in static context" means for a lot of people IMHO).

[AnthonyLatsis]

Putting in my two cents: instance member %1 cannot be used on static 'self'

[tysun]

@AnthonyLatsis @xedin

That alternative error message, instance member %1 cannot be used on static 'self', is a bit confusing. It indicates that there's a static 'self' you're trying to use. Swift doesn't have a concept of a static 'self' as self refers to an instance of the type, while static properties and methods belong to the type itself, not an instance.

Perhaps a more accurate alternative error message could be: Instance member %1 cannot be accessed directly from a static method of the same type. I think this error message makes it clear that you are trying to access an instance member from a static method, which is not allowed in Swift.

[AnthonyLatsis]

Swift doesn't have a concept of a static 'self' as self refers to an instance of the type

Not really. In a static context, self refers to Self.self (this is usually just the parent type object or metatype), not an instance. We can definitely do better than the alternative I suggested though.

Perhaps a more accurate alternative error message could be: Instance member %1 cannot be accessed directly from a static method of the same type

I think this message has the same problem as the synonymous cannot be used in static context discussed earlier. It can easily be interpreted as "you cannot access this inside a static method".

[xavgru12]

Swift doesn't have a concept of a static 'self' as self refers to an instance of the type

Not really. In a static context, self refers to Self.self (this is usually just the parent type object or metatype), not an instance. We can definitely do better than the alternative I suggested though.

Perhaps a more accurate alternative error message could be: Instance member %1 cannot be accessed directly from a static method of the same type

I think this message has the same problem as the synonymous cannot be used in static context discussed earlier. It can easily be interpreted as "you cannot access this inside a static method".

What @tysun said really nails it down for me. What do others think?

Instance member %1 cannot be accessed directly from a static method of the same type