Sealed Windows FileTypeExt extensible trait broke FileTypeExt in wasi-common

[pinkforest]

EDIT: So Sealing happened via 2nd commit on: #98583 - which I had originally traced down here but didn't have PR ref

Unknowns / TODO

Note: I can't find windows_file_type_ext feature from unstable book or it's tracking issue ?

So the Sealed trait was designed to prevent people rolling own trait impl's ?

I suspect that cap-primitives may need to deal with the Sealed trait instead of rolling own trait / impl like it's done now ?

But I think that may be troublematic.. going by guessing what was intended in cap-primitives

Don't know yet enough about the sealed feature (yet) as it doesn't seem to have much docs around and I need to dig deeper on this.

Issue

On Windows builds that rely on wasi-common on which we rely on at lunatic:

wasi-common v0.40.0
├── cap-std v0.25.2
    ├── cap-primitives v0.25.2

We now get via cap-primitives this in 1.66.0-nightly (4a14677 2022-09-23):

    error[E0277]: the trait bound file_type::FileType: std::sealed::Sealed is not satisfied
    <snip>
        |
    134 | impl std::os::windows::fs::FileTypeExt for FileType {
        |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait std::sealed::Sealed is not implemented for file_type::FileType
        |
    <snip>
    error: could not compile cap-primitives due to previous error
    warning: build failed, waiting for other jobs to finish...
    error: failed to compile lunatic-runtime v0.10.0, intermediate artifacts can be found at <snip>

Now this was probably very intentional but

Sealed

So Sealed acts as some kind of guard for the ecosystem not to mess with it ?

mod sealed {
    /// This trait being unreachable from outside the crate
    /// prevents outside implementations of our extension traits.
    /// This allows adding more trait methods in the future.
    #[unstable(feature = "sealed", issue = "none")]
    pub trait Sealed {}
}

Related earlier changes

I see the below changes re: stabilisation related to feature windows_file_type_ext

commits a4cb0b9 and e374c91

library/std/src/os/windows/fs.rs      2022-06-27 09:57:56 -0700  10) use crate::sealed::Sealed;
library/std/src/os/windows/fs.rs      2022-06-27 09:41:12 -0700 506) #[stable(feature = "windows_file_type_ext", since = "1.64.0")]
library/std/src/os/windows/fs.rs      2022-06-27 09:57:56 -0700 507) pub trait FileTypeExt: Sealed {

wasi/cap-primitives Related

This works okay in OSX, Linux but Windows builds are now broken with this where the error comes from:

cap-primitives/src/fs/file_type.rs - https://docs.rs/cap-primitives/latest/src/cap_primitives/fs/file_type.rs.html#125-147

/// Windows-specific extensions for [`FileType`].                                                                                                                                         
///                                                                                                                                                                                       
/// This corresponds to [`std::os::windows::fs::FileTypeExt`].                                                                                                                            
#[cfg(all(windows, windows_file_type_ext))]
pub trait FileTypeExt {
    /// Returns `true` if this file type is a symbolic link that is also a directory.                                                                                                     
    fn is_symlink_dir(&self) -> bool;
    /// Returns `true` if this file type is a symbolic link that is also a file.                                                                                                          
    fn is_symlink_file(&self) -> bool;
}

#[cfg(all(windows, windows_file_type_ext))]
impl FileTypeExt for FileType {
    #[inline]
    fn is_symlink_dir(&self) -> bool {
	self.0 == Inner::Ext(ImplFileTypeExt::symlink_dir())
    }

    #[inline]
    fn is_symlink_file(&self) -> bool {
	self.0 == Inner::Ext(ImplFileTypeExt::symlink_file())
    }
}

git b

0a96e089bade library/std/src/sys/windows/ext/fs.rs (Prabakaran Kumaresshan 2020-08-16 22:28:45 +0530 503) /// Windows-specific extensions to [`fs::FileType`].
182d99cfd1a5 src/libstd/sys/windows/ext/fs.rs      (Dylan MacKenzie        2018-04-09 17:44:28 -0700 504) ///
182d99cfd1a5 src/libstd/sys/windows/ext/fs.rs      (Dylan MacKenzie        2018-04-09 17:44:28 -0700 505) /// On Windows, a symbolic link knows whether it is a file or directory.
e374c911af9a library/std/src/os/windows/fs.rs      (Josh Triplett          2022-06-27 09:41:12 -0700 506) #[stable(feature = "windows_file_type_ext", since = "1.64.0")]
a4cb0b90c049 library/std/src/os/windows/fs.rs      (Josh Triplett          2022-06-27 09:57:56 -0700 507) pub trait FileTypeExt: Sealed {
99ed06eb8864 src/libstd/sys/windows/ext/fs.rs      (Alexander Regueiro     2019-02-09 22:16:58 +0000 508)     /// Returns `true` if this file type is a symbolic link that is also a directory.
e374c911af9a library/std/src/os/windows/fs.rs      (Josh Triplett          2022-06-27 09:41:12 -0700 509)     #[stable(feature = "windows_file_type_ext", since = "1.64.0")]
9269e83b37e8 src/libstd/sys/windows/ext/fs.rs      (Peter Atashian         2018-02-11 13:40:46 -0500 510)     fn is_symlink_dir(&self) -> bool;
99ed06eb8864 src/libstd/sys/windows/ext/fs.rs      (Alexander Regueiro     2019-02-09 22:16:58 +0000 511)     /// Returns `true` if this file type is a symbolic link that is also a file.
e374c911af9a library/std/src/os/windows/fs.rs      (Josh Triplett          2022-06-27 09:41:12 -0700 512)     #[stable(feature = "windows_file_type_ext", since = "1.64.0")]
9269e83b37e8 src/libstd/sys/windows/ext/fs.rs      (Peter Atashian         2018-02-11 13:40:46 -0500 513)     fn is_symlink_file(&self) -> bool;
9269e83b37e8 src/libstd/sys/windows/ext/fs.rs      (Peter Atashian         2018-02-11 13:40:46 -0500 514) }
9269e83b37e8 src/libstd/sys/windows/ext/fs.rs      (Peter Atashian         2018-02-11 13:40:46 -0500 515) 
a4cb0b90c049 library/std/src/os/windows/fs.rs      (Josh Triplett          2022-06-27 09:57:56 -0700 516) #[stable(feature = "windows_file_type_ext", since = "1.64.0")]
a4cb0b90c049 library/std/src/os/windows/fs.rs      (Josh Triplett          2022-06-27 09:57:56 -0700 517) impl Sealed for fs::FileType {}
a4cb0b90c049 library/std/src/os/windows/fs.rs      (Josh Triplett          2022-06-27 09:57:56 -0700 518) 
e374c911af9a library/std/src/os/windows/fs.rs      (Josh Triplett          2022-06-27 09:41:12 -0700 519) #[stable(feature = "windows_file_type_ext", since = "1.64.0")]
9269e83b37e8 src/libstd/sys/windows/ext/fs.rs      (Peter Atashian         2018-02-11 13:40:46 -0500 520) impl FileTypeExt for fs::FileType {
c34fbfaad38c src/libstd/sys/windows/ext/fs.rs      (David Tolnay           2019-11-27 10:28:39 -0800 521)     fn is_symlink_dir(&self) -> bool {
c34fbfaad38c src/libstd/sys/windows/ext/fs.rs      (David Tolnay           2019-11-27 10:28:39 -0800 522)         self.as_inner().is_symlink_dir()
c34fbfaad38c src/libstd/sys/windows/ext/fs.rs      (David Tolnay           2019-11-27 10:28:39 -0800 523)     }
c34fbfaad38c src/libstd/sys/windows/ext/fs.rs      (David Tolnay           2019-11-27 10:28:39 -0800 524)     fn is_symlink_file(&self) -> bool {
c34fbfaad38c src/libstd/sys/windows/ext/fs.rs      (David Tolnay           2019-11-27 10:28:39 -0800 525)         self.as_inner().is_symlink_file()
c34fbfaad38c src/libstd/sys/windows/ext/fs.rs      (David Tolnay           2019-11-27 10:28:39 -0800 526)     }
9269e83b37e8 src/libstd/sys/windows/ext/fs.rs      (Peter Atashian         2018-02-11 13:40:46 -0500 527) }

Refs

https://docs.rs/cap-primitives/latest/src/cap_primitives/fs/file_type.rs.html#125-147
https://github.com/bytecodealliance/cap-std
https://doc.rust-lang.org/std/os/windows/fs/trait.FileTypeExt.html
https://stdrs.dev/nightly/x86_64-unknown-linux-gnu/std/sealed/trait.Sealed.html
https://stdrs.dev/nightly/x86_64-unknown-linux-gnu/std/sealed/trait.Sealed.html
lunatic-solutions/lunatic#136

[pinkforest]

So there is now wasmtime 0.40 which will break when / if this will into stable release

bytecodealliance/wasmtime#4957
bytecodealliance/cap-std#270 (comment)

I'll try to get a point release there so it continues to work under 0.40 at least

I also asked re: process about sealing traits that were previously not sealed
https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/.23102260.20Sealed.20Windows.20FileTypeExt/near/300660648

[pinkforest]

I'll see what wasmtime can provide to support 0.40 users. The sealed is working as intended - wasmtime was relying on unstable feature so no issue here.