Move std::io::ErrorKind to core::io::ErrorKind

* Contributing to #154046
* Generally useful for `no_std` interop since `std::io::Error` implements `From<ErrorKind>`
* Low friction as `ErrorKind` is not platform dependent or otherwise dependent on `std`

Author: bushrat011899

library/core/src/io/error_kind.rs

@@ -0,0 +1,307 @@
+#![unstable(feature = "core_io_error_kind", issue = "154046")]
+
+use crate::fmt;
+
+/// A list specifying general categories of I/O error.
+///
+/// This list is intended to grow over time and it is not recommended to
+/// exhaustively match against it.
+///
+/// # Handling errors and matching on `ErrorKind`
+///
+/// In application code, use `match` for the `ErrorKind` values you are
+/// expecting; use `_` to match "all other errors".
+///
+/// In comprehensive and thorough tests that want to verify that a test doesn't
+/// return any known incorrect error kind, you may want to cut-and-paste the
+/// current full list of errors from here into your test code, and then match
+/// `_` as the correct case. This seems counterintuitive, but it will make your
+/// tests more robust. In particular, if you want to verify that your code does
+/// produce an unrecognized error kind, the robust solution is to check for all
+/// the recognized error kinds and fail in those cases.
+#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "io_errorkind")]
+#[allow(deprecated)]
+#[non_exhaustive]
+pub enum ErrorKind {
+    /// An entity was not found, often a file.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    NotFound,
+    /// The operation lacked the necessary privileges to complete.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    PermissionDenied,
+    /// The connection was refused by the remote server.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    ConnectionRefused,
+    /// The connection was reset by the remote server.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    ConnectionReset,
+    /// The remote host is not reachable.
+    #[stable(feature = "io_error_a_bit_more", since = "1.83.0")]
+    HostUnreachable,
+    /// The network containing the remote host is not reachable.
+    #[stable(feature = "io_error_a_bit_more", since = "1.83.0")]
+    NetworkUnreachable,
+    /// The connection was aborted (terminated) by the remote server.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    ConnectionAborted,
+    /// The network operation failed because it was not connected yet.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    NotConnected,
+    /// A socket address could not be bound because the address is already in
+    /// use elsewhere.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    AddrInUse,
+    /// A nonexistent interface was requested or the requested address was not
+    /// local.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    AddrNotAvailable,
+    /// The system's networking is down.
+    #[stable(feature = "io_error_a_bit_more", since = "1.83.0")]
+    NetworkDown,
+    /// The operation failed because a pipe was closed.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    BrokenPipe,
+    /// An entity already exists, often a file.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    AlreadyExists,
+    /// The operation needs to block to complete, but the blocking operation was
+    /// requested to not occur.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    WouldBlock,
+    /// A filesystem object is, unexpectedly, not a directory.
+    ///
+    /// For example, a filesystem path was specified where one of the intermediate directory
+    /// components was, in fact, a plain file.
+    #[stable(feature = "io_error_a_bit_more", since = "1.83.0")]
+    NotADirectory,
+    /// The filesystem object is, unexpectedly, a directory.
+    ///
+    /// A directory was specified when a non-directory was expected.
+    #[stable(feature = "io_error_a_bit_more", since = "1.83.0")]
+    IsADirectory,
+    /// A non-empty directory was specified where an empty directory was expected.
+    #[stable(feature = "io_error_a_bit_more", since = "1.83.0")]
+    DirectoryNotEmpty,
+    /// The filesystem or storage medium is read-only, but a write operation was attempted.
+    #[stable(feature = "io_error_a_bit_more", since = "1.83.0")]
+    ReadOnlyFilesystem,
+    /// Loop in the filesystem or IO subsystem; often, too many levels of symbolic links.
+    ///
+    /// There was a loop (or excessively long chain) resolving a filesystem object
+    /// or file IO object.
+    ///
+    /// On Unix this is usually the result of a symbolic link loop; or, of exceeding the
+    /// system-specific limit on the depth of symlink traversal.
+    #[unstable(feature = "io_error_more", issue = "86442")]
+    FilesystemLoop,
+    /// Stale network file handle.
+    ///
+    /// With some network filesystems, notably NFS, an open file (or directory) can be invalidated
+    /// by problems with the network or server.
+    #[stable(feature = "io_error_a_bit_more", since = "1.83.0")]
+    StaleNetworkFileHandle,
+    /// A parameter was incorrect.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    InvalidInput,
+    /// Data not valid for the operation were encountered.
+    ///
+    /// Unlike [`InvalidInput`], this typically means that the operation
+    /// parameters were valid, however the error was caused by malformed
+    /// input data.
+    ///
+    /// For example, a function that reads a file into a string will error with
+    /// `InvalidData` if the file's contents are not valid UTF-8.
+    ///
+    /// [`InvalidInput`]: ErrorKind::InvalidInput
+    #[stable(feature = "io_invalid_data", since = "1.2.0")]
+    InvalidData,
+    /// The I/O operation's timeout expired, causing it to be canceled.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    TimedOut,
+    /// An error returned when an operation could not be completed because a
+    /// call to an underlying writer returned [`Ok(0)`].
+    ///
+    /// This typically means that an operation could only succeed if it wrote a
+    /// particular number of bytes but only a smaller number of bytes could be
+    /// written.
+    ///
+    /// [`Ok(0)`]: Ok
+    #[stable(feature = "rust1", since = "1.0.0")]
+    WriteZero,
+    /// The underlying storage (typically, a filesystem) is full.
+    ///
+    /// This does not include out of quota errors.
+    #[stable(feature = "io_error_a_bit_more", since = "1.83.0")]
+    StorageFull,
+    /// Seek on unseekable file.
+    ///
+    /// Seeking was attempted on an open file handle which is not suitable for seeking - for
+    /// example, on Unix, a named pipe opened with `File::open`.
+    #[stable(feature = "io_error_a_bit_more", since = "1.83.0")]
+    NotSeekable,
+    /// Filesystem quota or some other kind of quota was exceeded.
+    #[stable(feature = "io_error_quota_exceeded", since = "1.85.0")]
+    QuotaExceeded,
+    /// File larger than allowed or supported.
+    ///
+    /// This might arise from a hard limit of the underlying filesystem or file access API, or from
+    /// an administratively imposed resource limitation.  Simple disk full, and out of quota, have
+    /// their own errors.
+    #[stable(feature = "io_error_a_bit_more", since = "1.83.0")]
+    FileTooLarge,
+    /// Resource is busy.
+    #[stable(feature = "io_error_a_bit_more", since = "1.83.0")]
+    ResourceBusy,
+    /// Executable file is busy.
+    ///
+    /// An attempt was made to write to a file which is also in use as a running program.  (Not all
+    /// operating systems detect this situation.)
+    #[stable(feature = "io_error_a_bit_more", since = "1.83.0")]
+    ExecutableFileBusy,
+    /// Deadlock (avoided).
+    ///
+    /// A file locking operation would result in deadlock.  This situation is typically detected, if
+    /// at all, on a best-effort basis.
+    #[stable(feature = "io_error_a_bit_more", since = "1.83.0")]
+    Deadlock,
+    /// Cross-device or cross-filesystem (hard) link or rename.
+    #[stable(feature = "io_error_crosses_devices", since = "1.85.0")]
+    CrossesDevices,
+    /// Too many (hard) links to the same filesystem object.
+    ///
+    /// The filesystem does not support making so many hardlinks to the same file.
+    #[stable(feature = "io_error_a_bit_more", since = "1.83.0")]
+    TooManyLinks,
+    /// A filename was invalid.
+    ///
+    /// This error can also occur if a length limit for a name was exceeded.
+    #[stable(feature = "io_error_invalid_filename", since = "1.87.0")]
+    InvalidFilename,
+    /// Program argument list too long.
+    ///
+    /// When trying to run an external program, a system or process limit on the size of the
+    /// arguments would have been exceeded.
+    #[stable(feature = "io_error_a_bit_more", since = "1.83.0")]
+    ArgumentListTooLong,
+    /// This operation was interrupted.
+    ///
+    /// Interrupted operations can typically be retried.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    Interrupted,
+
+    /// This operation is unsupported on this platform.
+    ///
+    /// This means that the operation can never succeed.
+    #[stable(feature = "unsupported_error", since = "1.53.0")]
+    Unsupported,
+
+    // ErrorKinds which are primarily categorisations for OS error
+    // codes should be added above.
+    //
+    /// An error returned when an operation could not be completed because an
+    /// "end of file" was reached prematurely.
+    ///
+    /// This typically means that an operation could only succeed if it read a
+    /// particular number of bytes but only a smaller number of bytes could be
+    /// read.
+    #[stable(feature = "read_exact", since = "1.6.0")]
+    UnexpectedEof,
+
+    /// An operation could not be completed, because it failed
+    /// to allocate enough memory.
+    #[stable(feature = "out_of_memory_error", since = "1.54.0")]
+    OutOfMemory,
+
+    /// The operation was partially successful and needs to be checked
+    /// later on due to not blocking.
+    #[unstable(feature = "io_error_inprogress", issue = "130840")]
+    InProgress,
+
+    // "Unusual" error kinds which do not correspond simply to (sets
+    // of) OS error codes, should be added just above this comment.
+    // `Other` and `Uncategorized` should remain at the end:
+    //
+    /// A custom error that does not fall under any other I/O error kind.
+    ///
+    /// This can be used to construct your own errors that do not match any
+    /// [`ErrorKind`].
+    ///
+    /// This [`ErrorKind`] is not used by the standard library.
+    ///
+    /// Errors from the standard library that do not fall under any of the I/O
+    /// error kinds cannot be `match`ed on, and will only match a wildcard (`_`) pattern.
+    /// New [`ErrorKind`]s might be added in the future for some of those.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    Other,
+
+    /// Any I/O error from the standard library that's not part of this list.
+    ///
+    /// Errors that are `Uncategorized` now may move to a different or a new
+    /// [`ErrorKind`] variant in the future. It is not recommended to match
+    /// an error against `Uncategorized`; use a wildcard match (`_`) instead.
+    #[unstable(feature = "io_error_uncategorized", issue = "none")]
+    #[doc(hidden)]
+    Uncategorized,
+}
+
+impl ErrorKind {
+    pub(crate) const fn as_str(&self) -> &'static str {
+        use ErrorKind::*;
+        match *self {
+            // tidy-alphabetical-start
+            AddrInUse => "address in use",
+            AddrNotAvailable => "address not available",
+            AlreadyExists => "entity already exists",
+            ArgumentListTooLong => "argument list too long",
+            BrokenPipe => "broken pipe",
+            ConnectionAborted => "connection aborted",
+            ConnectionRefused => "connection refused",
+            ConnectionReset => "connection reset",
+            CrossesDevices => "cross-device link or rename",
+            Deadlock => "deadlock",
+            DirectoryNotEmpty => "directory not empty",
+            ExecutableFileBusy => "executable file busy",
+            FileTooLarge => "file too large",
+            FilesystemLoop => "filesystem loop or indirection limit (e.g. symlink loop)",
+            HostUnreachable => "host unreachable",
+            InProgress => "in progress",
+            Interrupted => "operation interrupted",
+            InvalidData => "invalid data",
+            InvalidFilename => "invalid filename",
+            InvalidInput => "invalid input parameter",
+            IsADirectory => "is a directory",
+            NetworkDown => "network down",
+            NetworkUnreachable => "network unreachable",
+            NotADirectory => "not a directory",
+            NotConnected => "not connected",
+            NotFound => "entity not found",
+            NotSeekable => "seek on unseekable file",
+            Other => "other error",
+            OutOfMemory => "out of memory",
+            PermissionDenied => "permission denied",
+            QuotaExceeded => "quota exceeded",
+            ReadOnlyFilesystem => "read-only filesystem or storage medium",
+            ResourceBusy => "resource busy",
+            StaleNetworkFileHandle => "stale network file handle",
+            StorageFull => "no storage space",
+            TimedOut => "timed out",
+            TooManyLinks => "too many links",
+            Uncategorized => "uncategorized error",
+            UnexpectedEof => "unexpected end of file",
+            Unsupported => "unsupported",
+            WouldBlock => "operation would block",
+            WriteZero => "write zero",
+            // tidy-alphabetical-end
+        }
+    }
+}
+
+#[stable(feature = "io_errorkind_display", since = "1.60.0")]
+impl fmt::Display for ErrorKind {
+    /// Shows a human-readable description of the `ErrorKind`.
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.write_str(self.as_str())
+    }
+}

library/core/src/io/mod.rs

@@ -1,6 +1,11 @@
 //! Traits, helpers, and type definitions for core I/O functionality.
 
+use crate::fmt;
+
 mod borrowed_buf;
+mod error_kind;
 
 #[unstable(feature = "core_io_borrowed_buf", issue = "117693")]
 pub use self::borrowed_buf::{BorrowedBuf, BorrowedCursor};
+#[unstable(feature = "core_io_error_kind", issue = "154046")]
+pub use self::error_kind::ErrorKind;