Seal MetadataExt on all platforms

[ChrisDenton]

The Windows flavour of MetadataExt is currently unimplementable on stable because of unstable methods. Therefore anyone making a cross-platform library that implements MetadataExt will fail on Windows. So let's see if we can seal it for all platforms.

Last time this was tried, sealing MetadataExt only caused a problem for one old version of one crate.

[rustbot]

r? @Mark-Simulacrum

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[ChrisDenton]

@bors try

[bors]

⌛ Trying commit a0572b3 with merge 3d5258f...

[bors]

☀️ Try build successful - checks-actions
Build commit: 3d5258f (3d5258f568a4b4970d455e4e29f39fd691b5a41a)

[bors]

☀️ Try build successful - checks-actions
Build commit: 3d5258f (3d5258f568a4b4970d455e4e29f39fd691b5a41a)

[ChrisDenton]

@craterbot check

[craterbot]

👌 Experiment pr-118916 created and queued.
🤖 Automatically detected try build 3d5258f
🔍 You can check out the queue and this experiment's details.

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[craterbot]

🚧 Experiment pr-118916 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🎉 Experiment pr-118916 is completed!
📊 133 regressed and 0 fixed (399389 total)
📰 Open the full report.

⚠️ If you notice any spurious failure please add them to the blacklist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[ChrisDenton]

So the bad news is that cap-primitives has regressed again. Last time it was only one old version of cap-primitives that was affected so I wrongly assumed it would have remained fixed. The good news is that cap-primitives appears to be the only crate affected (the other failures are spurious: "No space left on device").

[INFO] [stdout] error[E0277]: the trait bound `metadata_ext::MetadataExt: std::sealed::Sealed` is not satisfied
[INFO] [stdout]    --> /opt/rustwide/cargo-home/registry/src/index.crates.io-6f17d22bba15001f/cap-primitives-2.0.0/src/rustix/fs/metadata_ext.rs:277:34
[INFO] [stdout]     |
[INFO] [stdout] 277 | impl rustix::fs::MetadataExt for MetadataExt {
[INFO] [stdout]     |                                  ^^^^^^^^^^^ the trait `std::sealed::Sealed` is not implemented for `metadata_ext::MetadataExt`
[INFO] [stdout]     |
[INFO] [stdout]     = help: the following other types implement trait `std::sealed::Sealed`:
[INFO] [stdout]               OsString
[INFO] [stdout]               OsStr
[INFO] [stdout]               File
[INFO] [stdout]               std::fs::DirEntry
[INFO] [stdout]               Stdin
[INFO] [stdout]               StdinLock<'_>
[INFO] [stdout]               Stdout
[INFO] [stdout]               StdoutLock<'_>
[INFO] [stdout]             and 15 others
[INFO] [stdout] note: required by a bound in `rustix::fs::MetadataExt`
[INFO] [stdout]    --> /rustc/3d5258f568a4b4970d455e4e29f39fd691b5a41a/library/std/src/os/unix/fs.rs:432:1
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] error[E0277]: the trait bound `metadata::Metadata: std::sealed::Sealed` is not satisfied
[INFO] [stdout]    --> /opt/rustwide/cargo-home/registry/src/index.crates.io-6f17d22bba15001f/cap-primitives-2.0.0/src/fs/metadata.rs:202:41
[INFO] [stdout]     |
[INFO] [stdout] 202 | impl std::os::unix::fs::MetadataExt for Metadata {
[INFO] [stdout]     |                                         ^^^^^^^^ the trait `std::sealed::Sealed` is not implemented for `metadata::Metadata`
[INFO] [stdout]     |
[INFO] [stdout]     = help: the following other types implement trait `std::sealed::Sealed`:
[INFO] [stdout]               OsString
[INFO] [stdout]               OsStr
[INFO] [stdout]               File
[INFO] [stdout]               std::fs::DirEntry
[INFO] [stdout]               Stdin
[INFO] [stdout]               StdinLock<'_>
[INFO] [stdout]               Stdout
[INFO] [stdout]               StdoutLock<'_>
[INFO] [stdout]             and 15 others
[INFO] [stdout] note: required by a bound in `rustix::fs::MetadataExt`
[INFO] [stdout]    --> /rustc/3d5258f568a4b4970d455e4e29f39fd691b5a41a/library/std/src/os/unix/fs.rs:432:1

[ChrisDenton]

cc @sunfishcode, maybe changes could be made to cap-primitives. Though I'm now thinking we can't do this on Unix. If we ever do have a need to extend Metadata further on Unix platforms we can always create MetadataExt2.

[sunfishcode]

Yeah. I can change cap-primitives to avoid using MetadataExt, and a few more *Ext traits too.

[Mark-Simulacrum]

@rustbot author

[ChrisDenton]

I think I'll close this for now. Even if cap-primitives is updated today there's going to be a long tale of crates relying on older versions so it'd be best to revisit this later. I might open another PR for specific platforms where MetadataExt can be sealed.

[sunfishcode]

@ChrisDenton I've now remove all implementations of all std::os::* traits from cap-std, and released it as cap-std 3.0. As you say, it'll likely be some time before all users are updated.