Auto merge of #85746 - m-ou-se:io-error-other, r=joshtriplett

Redefine `ErrorKind::Other` and stop using it in std.

This implements the idea I shared yesterday in the libs meeting when we were discussing how to handle adding new `ErrorKind`s to the standard library: This redefines `Other` to be for *user defined errors only*, and changes all uses of `Other` in the standard library to a `#[doc(hidden)]` and permanently `#[unstable]` `ErrorKind` that users can not match on. This ensures that adding `ErrorKind`s at a later point in time is not a breaking change, since the user couldn't match on these errors anyway. This way, we use the `#[non_exhaustive]` property of the enum in a more effective way.

Open questions:
- How do we check this change doesn't cause too much breakage? Will a crate run help and be enough?
- How do we ensure we don't accidentally start using `Other` again in the standard library? We don't have a `pub(not crate)` or `#[deprecated(in this crate only)]`.

cc #79965

cc `@rust-lang/libs` `@ijackson`

r? `@dtolnay`

library/std/src/fs.rs

@@ -880,8 +880,7 @@ impl OpenOptions {
     /// This function will return an error under a number of different
     /// circumstances. Some of these error conditions are listed here, together
     /// with their [`io::ErrorKind`]. The mapping to [`io::ErrorKind`]s is not
-    /// part of the compatibility contract of the function, especially the
-    /// [`Other`] kind might change to more specific kinds in the future.
+    /// part of the compatibility contract of the function.
     ///
     /// * [`NotFound`]: The specified file does not exist and neither `create`
     ///   or `create_new` is set.
@@ -895,9 +894,11 @@ impl OpenOptions {
     ///   exists.
     /// * [`InvalidInput`]: Invalid combinations of open options (truncate
     ///   without write access, no access mode set, etc.).
-    /// * [`Other`]: One of the directory components of the specified file path
+    ///
+    /// The following errors don't match any existing [`io::ErrorKind`] at the moment:
+    /// * One of the directory components of the specified file path
     ///   was not, in fact, a directory.
-    /// * [`Other`]: Filesystem-level errors: full disk, write permission
+    /// * Filesystem-level errors: full disk, write permission
     ///   requested on a read-only file system, exceeded disk quota, too many
     ///   open files, too long filename, too many symbolic links in the
     ///   specified path (Unix-like systems only), etc.
@@ -913,7 +914,6 @@ impl OpenOptions {
     /// [`AlreadyExists`]: io::ErrorKind::AlreadyExists
     /// [`InvalidInput`]: io::ErrorKind::InvalidInput
     /// [`NotFound`]: io::ErrorKind::NotFound
-    /// [`Other`]: io::ErrorKind::Other
     /// [`PermissionDenied`]: io::ErrorKind::PermissionDenied
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn open<P: AsRef<Path>>(&self, path: P) -> io::Result<File> {
@@ -2216,7 +2216,7 @@ impl DirBuilder {
             Some(p) => self.create_dir_all(p)?,
             None => {
                 return Err(io::Error::new_const(
-                    io::ErrorKind::Other,
+                    io::ErrorKind::Uncategorized,
                     &"failed to create whole tree",
                 ));
             }

library/std/src/fs/tests.rs

@@ -1329,7 +1329,8 @@ fn metadata_access_times() {
         match (a.created(), b.created()) {
             (Ok(t1), Ok(t2)) => assert!(t1 <= t2),
             (Err(e1), Err(e2))
-                if e1.kind() == ErrorKind::Other && e2.kind() == ErrorKind::Other
+                if e1.kind() == ErrorKind::Uncategorized
+                    && e2.kind() == ErrorKind::Uncategorized
                     || e1.kind() == ErrorKind::Unsupported
                         && e2.kind() == ErrorKind::Unsupported => {}
             (a, b) => {

library/std/src/io/error.rs

@@ -163,12 +163,17 @@ pub enum ErrorKind {
     /// Interrupted operations can typically be retried.
     #[stable(feature = "rust1", since = "1.0.0")]
     Interrupted,
-    /// Any I/O error not part of this list.
+
+    /// A custom error that does not fall under any other I/O error kind.
     ///
-    /// Errors that are `Other` now may move to a different or a new
-    /// [`ErrorKind`] variant in the future. It is not recommended to match
-    /// an error against `Other` and to expect any additional characteristics,
-    /// e.g., a specific [`Error::raw_os_error`] return value.
+    /// This can be used to construct your own [`Error`]s 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,
 
@@ -191,6 +196,15 @@ pub enum ErrorKind {
     /// to allocate enough memory.
     #[stable(feature = "out_of_memory_error", since = "1.54.0")]
     OutOfMemory,
+
+    /// 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 {
@@ -212,10 +226,11 @@ impl ErrorKind {
             ErrorKind::TimedOut => "timed out",
             ErrorKind::WriteZero => "write zero",
             ErrorKind::Interrupted => "operation interrupted",
-            ErrorKind::Other => "other os error",
             ErrorKind::UnexpectedEof => "unexpected end of file",
             ErrorKind::Unsupported => "unsupported",
             ErrorKind::OutOfMemory => "out of memory",
+            ErrorKind::Other => "other error",
+            ErrorKind::Uncategorized => "uncategorized error",
         }
     }
 }
@@ -538,7 +553,7 @@ impl Error {
     /// }
     ///
     /// fn main() {
-    ///     // Will print "Other".
+    ///     // Will print "Uncategorized".
     ///     print_error(Error::last_os_error());
     ///     // Will print "AddrInUse".
     ///     print_error(Error::new(ErrorKind::AddrInUse, "oh no!"));

library/std/src/io/mod.rs

@@ -1644,7 +1644,7 @@ pub trait Write {
                 if output.error.is_err() {
                     output.error
                 } else {
-                    Err(Error::new_const(ErrorKind::Other, &"formatter error"))
+                    Err(Error::new_const(ErrorKind::Uncategorized, &"formatter error"))
                 }
             }
         }

library/std/src/net/tcp/tests.rs

@@ -342,7 +342,7 @@ fn double_bind() {
             Err(e) => {
                 assert!(
                     e.kind() == ErrorKind::ConnectionRefused
-                        || e.kind() == ErrorKind::Other
+                        || e.kind() == ErrorKind::Uncategorized
                         || e.kind() == ErrorKind::AddrInUse,
                     "unknown error: {} {:?}",
                     e,

library/std/src/os/wasi/fs.rs

@@ -532,5 +532,6 @@ pub fn symlink_path<P: AsRef<Path>, U: AsRef<Path>>(old_path: P, new_path: U) ->
 }
 
 fn osstr2str(f: &OsStr) -> io::Result<&str> {
-    f.to_str().ok_or_else(|| io::Error::new_const(io::ErrorKind::Other, &"input must be utf-8"))
+    f.to_str()
+        .ok_or_else(|| io::Error::new_const(io::ErrorKind::Uncategorized, &"input must be utf-8"))
 }

library/std/src/process.rs

@@ -1658,8 +1658,7 @@ impl Child {
     /// Forces the child process to exit. If the child has already exited, an [`InvalidInput`]
     /// error is returned.
     ///
-    /// The mapping to [`ErrorKind`]s is not part of the compatibility contract of the function,
-    /// especially the [`Other`] kind might change to more specific kinds in the future.
+    /// The mapping to [`ErrorKind`]s is not part of the compatibility contract of the function.
     ///
     /// This is equivalent to sending a SIGKILL on Unix platforms.
     ///
@@ -1680,7 +1679,6 @@ impl Child {
     ///
     /// [`ErrorKind`]: io::ErrorKind
     /// [`InvalidInput`]: io::ErrorKind::InvalidInput
-    /// [`Other`]: io::ErrorKind::Other
     #[stable(feature = "process", since = "1.0.0")]
     pub fn kill(&mut self) -> io::Result<()> {
         self.handle.kill()

library/std/src/sys/hermit/mod.rs

@@ -149,7 +149,7 @@ pub fn decode_error_kind(errno: i32) -> ErrorKind {
         x if x == 1 as i32 => ErrorKind::PermissionDenied,
         x if x == 32 as i32 => ErrorKind::BrokenPipe,
         x if x == 110 as i32 => ErrorKind::TimedOut,
-        _ => ErrorKind::Other,
+        _ => ErrorKind::Uncategorized,
     }
 }
 

library/std/src/sys/hermit/net.rs

@@ -15,7 +15,7 @@ use crate::time::Duration;
 pub fn init() -> io::Result<()> {
     if abi::network_init() < 0 {
         return Err(io::Error::new_const(
-            ErrorKind::Other,
+            ErrorKind::Uncategorized,
             &"Unable to initialize network interface",
         ));
     }
@@ -51,7 +51,7 @@ impl TcpStream {
         match abi::tcpstream::connect(addr.ip().to_string().as_bytes(), addr.port(), None) {
             Ok(handle) => Ok(TcpStream(Arc::new(Socket(handle)))),
             _ => Err(io::Error::new_const(
-                ErrorKind::Other,
+                ErrorKind::Uncategorized,
                 &"Unable to initiate a connection on a socket",
             )),
         }
@@ -65,44 +65,46 @@ impl TcpStream {
         ) {
             Ok(handle) => Ok(TcpStream(Arc::new(Socket(handle)))),
             _ => Err(io::Error::new_const(
-                ErrorKind::Other,
+                ErrorKind::Uncategorized,
                 &"Unable to initiate a connection on a socket",
             )),
         }
     }
 
     pub fn set_read_timeout(&self, duration: Option<Duration>) -> io::Result<()> {
         abi::tcpstream::set_read_timeout(*self.0.as_inner(), duration.map(|d| d.as_millis() as u64))
-            .map_err(|_| io::Error::new_const(ErrorKind::Other, &"Unable to set timeout value"))
+            .map_err(|_| {
+                io::Error::new_const(ErrorKind::Uncategorized, &"Unable to set timeout value")
+            })
     }
 
     pub fn set_write_timeout(&self, duration: Option<Duration>) -> io::Result<()> {
         abi::tcpstream::set_write_timeout(
             *self.0.as_inner(),
             duration.map(|d| d.as_millis() as u64),
         )
-        .map_err(|_| io::Error::new_const(ErrorKind::Other, &"Unable to set timeout value"))
+        .map_err(|_| io::Error::new_const(ErrorKind::Uncategorized, &"Unable to set timeout value"))
     }
 
     pub fn read_timeout(&self) -> io::Result<Option<Duration>> {
         let duration = abi::tcpstream::get_read_timeout(*self.0.as_inner()).map_err(|_| {
-            io::Error::new_const(ErrorKind::Other, &"Unable to determine timeout value")
+            io::Error::new_const(ErrorKind::Uncategorized, &"Unable to determine timeout value")
         })?;
 
         Ok(duration.map(|d| Duration::from_millis(d)))
     }
 
     pub fn write_timeout(&self) -> io::Result<Option<Duration>> {
         let duration = abi::tcpstream::get_write_timeout(*self.0.as_inner()).map_err(|_| {
-            io::Error::new_const(ErrorKind::Other, &"Unable to determine timeout value")
+            io::Error::new_const(ErrorKind::Uncategorized, &"Unable to determine timeout value")
         })?;
 
         Ok(duration.map(|d| Duration::from_millis(d)))
     }
 
     pub fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
         abi::tcpstream::peek(*self.0.as_inner(), buf)
-            .map_err(|_| io::Error::new_const(ErrorKind::Other, &"set_nodelay failed"))
+            .map_err(|_| io::Error::new_const(ErrorKind::Uncategorized, &"peek failed"))
     }
 
     pub fn read(&self, buffer: &mut [u8]) -> io::Result<usize> {
@@ -113,8 +115,9 @@ impl TcpStream {
         let mut size: usize = 0;
 
         for i in ioslice.iter_mut() {
-            let ret = abi::tcpstream::read(*self.0.as_inner(), &mut i[0..])
-                .map_err(|_| io::Error::new_const(ErrorKind::Other, &"Unable to read on socket"))?;
+            let ret = abi::tcpstream::read(*self.0.as_inner(), &mut i[0..]).map_err(|_| {
+                io::Error::new_const(ErrorKind::Uncategorized, &"Unable to read on socket")
+            })?;
 
             if ret != 0 {
                 size += ret;
@@ -138,7 +141,7 @@ impl TcpStream {
 
         for i in ioslice.iter() {
             size += abi::tcpstream::write(*self.0.as_inner(), i).map_err(|_| {
-                io::Error::new_const(ErrorKind::Other, &"Unable to write on socket")
+                io::Error::new_const(ErrorKind::Uncategorized, &"Unable to write on socket")
             })?;
         }
 
@@ -152,13 +155,13 @@ impl TcpStream {
 
     pub fn peer_addr(&self) -> io::Result<SocketAddr> {
         let (ipaddr, port) = abi::tcpstream::peer_addr(*self.0.as_inner())
-            .map_err(|_| io::Error::new_const(ErrorKind::Other, &"peer_addr failed"))?;
+            .map_err(|_| io::Error::new_const(ErrorKind::Uncategorized, &"peer_addr failed"))?;
 
         let saddr = match ipaddr {
             Ipv4(ref addr) => SocketAddr::new(IpAddr::V4(Ipv4Addr::from(addr.0)), port),
             Ipv6(ref addr) => SocketAddr::new(IpAddr::V6(Ipv6Addr::from(addr.0)), port),
             _ => {
-                return Err(io::Error::new_const(ErrorKind::Other, &"peer_addr failed"));
+                return Err(io::Error::new_const(ErrorKind::Uncategorized, &"peer_addr failed"));
             }
         };
 
@@ -170,8 +173,9 @@ impl TcpStream {
     }
 
     pub fn shutdown(&self, how: Shutdown) -> io::Result<()> {
-        abi::tcpstream::shutdown(*self.0.as_inner(), how as i32)
-            .map_err(|_| io::Error::new_const(ErrorKind::Other, &"unable to shutdown socket"))
+        abi::tcpstream::shutdown(*self.0.as_inner(), how as i32).map_err(|_| {
+            io::Error::new_const(ErrorKind::Uncategorized, &"unable to shutdown socket")
+        })
     }
 
     pub fn duplicate(&self) -> io::Result<TcpStream> {
@@ -180,31 +184,32 @@ impl TcpStream {
 
     pub fn set_nodelay(&self, mode: bool) -> io::Result<()> {
         abi::tcpstream::set_nodelay(*self.0.as_inner(), mode)
-            .map_err(|_| io::Error::new_const(ErrorKind::Other, &"set_nodelay failed"))
+            .map_err(|_| io::Error::new_const(ErrorKind::Uncategorized, &"set_nodelay failed"))
     }
 
     pub fn nodelay(&self) -> io::Result<bool> {
         abi::tcpstream::nodelay(*self.0.as_inner())
-            .map_err(|_| io::Error::new_const(ErrorKind::Other, &"nodelay failed"))
+            .map_err(|_| io::Error::new_const(ErrorKind::Uncategorized, &"nodelay failed"))
     }
 
     pub fn set_ttl(&self, tll: u32) -> io::Result<()> {
         abi::tcpstream::set_tll(*self.0.as_inner(), tll)
-            .map_err(|_| io::Error::new_const(ErrorKind::Other, &"unable to set TTL"))
+            .map_err(|_| io::Error::new_const(ErrorKind::Uncategorized, &"unable to set TTL"))
     }
 
     pub fn ttl(&self) -> io::Result<u32> {
         abi::tcpstream::get_tll(*self.0.as_inner())
-            .map_err(|_| io::Error::new_const(ErrorKind::Other, &"unable to get TTL"))
+            .map_err(|_| io::Error::new_const(ErrorKind::Uncategorized, &"unable to get TTL"))
     }
 
     pub fn take_error(&self) -> io::Result<Option<io::Error>> {
         unsupported()
     }
 
     pub fn set_nonblocking(&self, mode: bool) -> io::Result<()> {
-        abi::tcpstream::set_nonblocking(*self.0.as_inner(), mode)
-            .map_err(|_| io::Error::new_const(ErrorKind::Other, &"unable to set blocking mode"))
+        abi::tcpstream::set_nonblocking(*self.0.as_inner(), mode).map_err(|_| {
+            io::Error::new_const(ErrorKind::Uncategorized, &"unable to set blocking mode")
+        })
     }
 }
 
@@ -230,12 +235,12 @@ impl TcpListener {
 
     pub fn accept(&self) -> io::Result<(TcpStream, SocketAddr)> {
         let (handle, ipaddr, port) = abi::tcplistener::accept(self.0.port())
-            .map_err(|_| io::Error::new_const(ErrorKind::Other, &"accept failed"))?;
+            .map_err(|_| io::Error::new_const(ErrorKind::Uncategorized, &"accept failed"))?;
         let saddr = match ipaddr {
             Ipv4(ref addr) => SocketAddr::new(IpAddr::V4(Ipv4Addr::from(addr.0)), port),
             Ipv6(ref addr) => SocketAddr::new(IpAddr::V6(Ipv6Addr::from(addr.0)), port),
             _ => {
-                return Err(io::Error::new_const(ErrorKind::Other, &"accept failed"));
+                return Err(io::Error::new_const(ErrorKind::Uncategorized, &"accept failed"));
             }
         };
 

library/std/src/sys/hermit/stdio.rs

@@ -40,7 +40,7 @@ impl io::Write for Stdout {
         unsafe { len = abi::write(1, data.as_ptr() as *const u8, data.len()) }
 
         if len < 0 {
-            Err(io::Error::new_const(io::ErrorKind::Other, &"Stdout is not able to print"))
+            Err(io::Error::new_const(io::ErrorKind::Uncategorized, &"Stdout is not able to print"))
         } else {
             Ok(len as usize)
         }
@@ -52,7 +52,7 @@ impl io::Write for Stdout {
         unsafe { len = abi::write(1, data.as_ptr() as *const u8, data.len()) }
 
         if len < 0 {
-            Err(io::Error::new_const(io::ErrorKind::Other, &"Stdout is not able to print"))
+            Err(io::Error::new_const(io::ErrorKind::Uncategorized, &"Stdout is not able to print"))
         } else {
             Ok(len as usize)
         }
@@ -81,7 +81,7 @@ impl io::Write for Stderr {
         unsafe { len = abi::write(2, data.as_ptr() as *const u8, data.len()) }
 
         if len < 0 {
-            Err(io::Error::new_const(io::ErrorKind::Other, &"Stderr is not able to print"))
+            Err(io::Error::new_const(io::ErrorKind::Uncategorized, &"Stderr is not able to print"))
         } else {
             Ok(len as usize)
         }
@@ -93,7 +93,7 @@ impl io::Write for Stderr {
         unsafe { len = abi::write(2, data.as_ptr() as *const u8, data.len()) }
 
         if len < 0 {
-            Err(io::Error::new_const(io::ErrorKind::Other, &"Stderr is not able to print"))
+            Err(io::Error::new_const(io::ErrorKind::Uncategorized, &"Stderr is not able to print"))
         } else {
             Ok(len as usize)
         }

library/std/src/sys/hermit/thread.rs

@@ -39,7 +39,7 @@ impl Thread {
             // The thread failed to start and as a result p was not consumed. Therefore, it is
             // safe to reconstruct the box so that it gets deallocated.
             drop(Box::from_raw(p));
-            Err(io::Error::new_const(io::ErrorKind::Other, &"Unable to create thread!"))
+            Err(io::Error::new_const(io::ErrorKind::Uncategorized, &"Unable to create thread!"))
         } else {
             Ok(Thread { tid: tid })
         };