Fix Dir.glob when readdir doesn't report file type

[straight-shoota]

Dir.next_entry was missing a validation for d_type value. In case it is DT_UNKNOWN, we can't determine wether it's a directory or not. Entry#dir is an internal API currently only used by Dir.glob so changing its type to Bool | Nil to signal unknown is fine.
Fixes #9876

[bcardiff]

It works as a charm! 🎉
Thanks! ⚡

It usually itches me to use Bool?, because there are two falsey values in that type.

[asterite]

I would use an enum with File, Dir and Unknown instead of a Bool?. That way you don't even need to document that "if it's nil it means it's unknown".

[straight-shoota]

This is just an internal ivar for optimizing Dir. glob, not anything near a public API. I'd prefer to keep it that simple. At least for now. We can revisit when considering to use more info from readdir for other purposes.

[asterite]

I'd prefer to keep it that simple

In my mind, an enum is simpler than Bool?. Specially when it comes to understanding what each of those values is.

[straight-shoota]

Alternatively, Entry could just hold the d_type value...

[bcardiff]

Since the entry type is internal i'm fine with the current state.

But having an enum with all the values of https://www.gnu.org/software/libc/manual/html_node/Directory-Entries.html, or at least the one we use today sounds like a path that can evolve smoothly. All unmapped d_type can default to the enum equivalent to unknown. That way there is no need to do the full mapping today if not wanted.

I would not assign directly the d_type value to abstraction leak.

[bcardiff]

Given the discussion after the approval, should this PR expect more work or is good to go since the discussion is about non public design?

[asterite]

Looks good to me, the internal implementation details can be changed later on 👍