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std: map ENOTSUP to ErrorKind::Unsupported #158580

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Merged
rust-bors merged 2 commits into from
Aug 18, 2026
+6 −2
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std: map ENOTSUP to ErrorKind::Unsupported #158580

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std: map ENOTSUP to ErrorKind::Unsupported
valentynkit Jun 29, 2026
aa49d14
std: move ENOSYS next to the other Unsupported arms
valentynkit Aug 16, 2026
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8 changes: 6 additions & 2 deletions library/std/src/sys/io/error/unix.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -158,7 +158,6 @@ pub fn decode_error_kind(errno: i32) -> io::ErrorKind {
libc::ENOENT => NotFound,
libc::ENOMEM => OutOfMemory,
libc::ENOSPC => StorageFull,
libc::ENOSYS => Unsupported,
libc::EMLINK => TooManyLinks,
libc::ENAMETOOLONG => InvalidFilename,
libc::ENETDOWN => NetworkDown,
Expand All @@ -176,11 +175,16 @@ pub fn decode_error_kind(errno: i32) -> io::ErrorKind {
libc::EXDEV => CrossesDevices,
libc::EINPROGRESS => InProgress,
libc::EMFILE | libc::ENFILE => TooManyOpenFiles,
libc::EOPNOTSUPP => Unsupported,
libc::EIO => InputOutputError,

libc::EACCES | libc::EPERM => PermissionDenied,

libc::ENOSYS => Unsupported,
// EOPNOTSUPP and ENOTSUP can have the same value on some systems,
// but different values on others (e.g. Apple), so we can't use a
// match clause
x if x == libc::EOPNOTSUPP || x == libc::ENOTSUP => Unsupported,

@RalfJung RalfJung Aug 15, 2026 •
edited by rustbot
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Note that there is also ENOSYS mapping to the same thing. Seems better to group all 3 together.

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@valentynkit valentynkit Aug 16, 2026

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Thanks for highlighting this, you are right ENOSYS maps to Unsupported as well.

Currently the guard was added because Linux libc defines ENOTSUP as EOPNOTSUPP (same value), so an or-pattern would be unreachable and dead code on Linux (95 | 95 => ...).
ENOSYS have distinct value, so it doesn't need a guard, and keeping it as pattern has some benefits (compiler could catch if it will collide with another arm).

I could add it, if you prefer to have 3 of them grouped together anyway, if not, i could just move ENOSYS arm right above this guard, so Unsupported case will be near each other.

@RalfJung RalfJung Aug 16, 2026

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IMO it'd be best to have them all next to each other -- whether as one arm or as two (one using the if ... || ...) doesn't matter much IMO.

@valentynkit valentynkit Aug 16, 2026

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Yeah agree, moved ENOSYS to have Unsupported cases next to each other.

@workingjubilee workingjubilee Aug 17, 2026

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Hm. Annoying feature of the pattern matching lint, that.


// These two constants can have the same value on some systems,
// but different values on others, so we can't use a match
// clause
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