Rollup merge of #81975 - Amanieu:seal2, r=m-ou-se

Seal the CommandExt, OsStrExt and OsStringExt traits

A crater run (https://github.com/rust-lang/rust/pull/81213#issuecomment-767651811) has shown that this does not break any existing code.

This also unblocks #77728.

Based on #81213.

r? ````@m-ou-se````
cc ````@lygstate````

library/std/src/ffi/os_str.rs

@@ -76,6 +76,10 @@ pub struct OsString {
     inner: Buf,
 }
 
+/// Allows extension traits within `std`.
+#[unstable(feature = "sealed", issue = "none")]
+impl crate::sealed::Sealed for OsString {}
+
 /// Borrowed reference to an OS string (see [`OsString`]).
 ///
 /// This type represents a borrowed reference to a string in the operating system's preferred
@@ -100,6 +104,10 @@ pub struct OsStr {
     inner: Slice,
 }
 
+/// Allows extension traits within `std`.
+#[unstable(feature = "sealed", issue = "none")]
+impl crate::sealed::Sealed for OsStr {}
+
 impl OsString {
     /// Constructs a new empty `OsString`.
     ///

library/std/src/lib.rs

@@ -582,3 +582,11 @@ pub mod task {
 // is unconditional, so the unstable feature needs to be defined somewhere.
 #[unstable(feature = "restricted_std", issue = "none")]
 mod __restricted_std_workaround {}
+
+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 {}
+}

library/std/src/process.rs

@@ -498,6 +498,10 @@ pub struct Command {
     inner: imp::Command,
 }
 
+/// Allows extension traits within `std`.
+#[unstable(feature = "sealed", issue = "none")]
+impl crate::sealed::Sealed for Command {}
+
 impl Command {
     /// Constructs a new `Command` for launching the program at
     /// path `program`, with the following default configuration:
@@ -1375,6 +1379,10 @@ fn from(file: fs::File) -> Stdio {
 #[stable(feature = "process", since = "1.0.0")]
 pub struct ExitStatus(imp::ExitStatus);
 
+/// Allows extension traits within `std`.
+#[unstable(feature = "sealed", issue = "none")]
+impl crate::sealed::Sealed for ExitStatus {}
+
 impl ExitStatus {
     /// Was termination successful? Signal termination is not considered a
     /// success, and success is defined as a zero exit status.

library/std/src/sys/unix/ext/process.rs

@@ -6,20 +6,16 @@
 use crate::io;
 use crate::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
 use crate::process;
+use crate::sealed::Sealed;
 use crate::sys;
 use crate::sys_common::{AsInner, AsInnerMut, FromInner, IntoInner};
 
-mod private {
-    /// This trait being unreachable from outside the crate
-    /// prevents other implementations of the `ExitStatusExt` trait,
-    /// which allows potentially adding more trait methods in the future.
-    #[stable(feature = "none", since = "1.51.0")]
-    pub trait Sealed {}
-}
-
 /// Unix-specific extensions to the [`process::Command`] builder.
+///
+/// This trait is sealed: it cannot be implemented outside the standard library.
+/// This is so that future additional methods are not breaking changes.
 #[stable(feature = "rust1", since = "1.0.0")]
-pub trait CommandExt {
+pub trait CommandExt: Sealed {
     /// Sets the child process's user ID. This translates to a
     /// `setuid` call in the child process. Failure in the `setuid`
     /// call will cause the spawn to fail.
@@ -193,7 +189,7 @@ fn arg0<S>(&mut self, arg: S) -> &mut process::Command
 /// This trait is sealed: it cannot be implemented outside the standard library.
 /// This is so that future additional methods are not breaking changes.
 #[stable(feature = "rust1", since = "1.0.0")]
-pub trait ExitStatusExt: private::Sealed {
+pub trait ExitStatusExt: Sealed {
     /// Creates a new `ExitStatus` from the raw underlying `i32` return value of
     /// a process.
     #[stable(feature = "exit_status_from", since = "1.12.0")]
@@ -228,9 +224,6 @@ pub trait ExitStatusExt: private::Sealed {
     fn into_raw(self) -> i32;
 }
 
-#[stable(feature = "none", since = "1.51.0")]
-impl private::Sealed for process::ExitStatus {}
-
 #[stable(feature = "rust1", since = "1.0.0")]
 impl ExitStatusExt for process::ExitStatus {
     fn from_raw(raw: i32) -> Self {

library/std/src/sys/windows/ext/ffi.rs

@@ -53,6 +53,7 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 use crate::ffi::{OsStr, OsString};
+use crate::sealed::Sealed;
 use crate::sys::os_str::Buf;
 use crate::sys_common::wtf8::Wtf8Buf;
 use crate::sys_common::{AsInner, FromInner};
@@ -61,8 +62,11 @@
 pub use crate::sys_common::wtf8::EncodeWide;
 
 /// Windows-specific extensions to [`OsString`].
+///
+/// This trait is sealed: it cannot be implemented outside the standard library.
+/// This is so that future additional methods are not breaking changes.
 #[stable(feature = "rust1", since = "1.0.0")]
-pub trait OsStringExt {
+pub trait OsStringExt: Sealed {
     /// Creates an `OsString` from a potentially ill-formed UTF-16 slice of
     /// 16-bit code units.
     ///
@@ -92,8 +96,11 @@ fn from_wide(wide: &[u16]) -> OsString {
 }
 
 /// Windows-specific extensions to [`OsStr`].
+///
+/// This trait is sealed: it cannot be implemented outside the standard library.
+/// This is so that future additional methods are not breaking changes.
 #[stable(feature = "rust1", since = "1.0.0")]
-pub trait OsStrExt {
+pub trait OsStrExt: Sealed {
     /// Re-encodes an `OsStr` as a wide character sequence, i.e., potentially
     /// ill-formed UTF-16.
     ///

library/std/src/sys/windows/ext/process.rs

@@ -4,17 +4,10 @@
 
 use crate::os::windows::io::{AsRawHandle, FromRawHandle, IntoRawHandle, RawHandle};
 use crate::process;
+use crate::sealed::Sealed;
 use crate::sys;
 use crate::sys_common::{AsInner, AsInnerMut, FromInner, IntoInner};
 
-mod private {
-    /// This trait being unreachable from outside the crate
-    /// prevents other implementations of the `ExitStatusExt` trait,
-    /// which allows potentially adding more trait methods in the future.
-    #[stable(feature = "none", since = "1.51.0")]
-    pub trait Sealed {}
-}
-
 #[stable(feature = "process_extensions", since = "1.2.0")]
 impl FromRawHandle for process::Stdio {
     unsafe fn from_raw_handle(handle: RawHandle) -> process::Stdio {
@@ -85,7 +78,7 @@ fn into_raw_handle(self) -> RawHandle {
 /// This trait is sealed: it cannot be implemented outside the standard library.
 /// This is so that future additional methods are not breaking changes.
 #[stable(feature = "exit_status_from", since = "1.12.0")]
-pub trait ExitStatusExt: private::Sealed {
+pub trait ExitStatusExt: Sealed {
     /// Creates a new `ExitStatus` from the raw underlying `u32` return value of
     /// a process.
     #[stable(feature = "exit_status_from", since = "1.12.0")]
@@ -99,12 +92,12 @@ fn from_raw(raw: u32) -> Self {
     }
 }
 
-#[stable(feature = "none", since = "1.51.0")]
-impl private::Sealed for process::ExitStatus {}
-
 /// Windows-specific extensions to the [`process::Command`] builder.
+///
+/// This trait is sealed: it cannot be implemented outside the standard library.
+/// This is so that future additional methods are not breaking changes.
 #[stable(feature = "windows_process_extensions", since = "1.16.0")]
-pub trait CommandExt {
+pub trait CommandExt: Sealed {
     /// Sets the [process creation flags][1] to be passed to `CreateProcess`.
     ///
     /// These will always be ORed with `CREATE_UNICODE_ENVIRONMENT`.

library/std/src/sys_common/os_str_bytes.rs

@@ -6,6 +6,7 @@
 use crate::fmt;
 use crate::mem;
 use crate::rc::Rc;
+use crate::sealed::Sealed;
 use crate::str;
 use crate::sync::Arc;
 use crate::sys_common::bytestring::debug_fmt_bytestring;
@@ -232,8 +233,11 @@ pub fn eq_ignore_ascii_case(&self, other: &Self) -> bool {
 }
 
 /// Platform-specific extensions to [`OsString`].
+///
+/// This trait is sealed: it cannot be implemented outside the standard library.
+/// This is so that future additional methods are not breaking changes.
 #[stable(feature = "rust1", since = "1.0.0")]
-pub trait OsStringExt {
+pub trait OsStringExt: Sealed {
     /// Creates an [`OsString`] from a byte vector.
     ///
     /// See the module documentation for an example.
@@ -258,8 +262,11 @@ fn into_vec(self) -> Vec<u8> {
 }
 
 /// Platform-specific extensions to [`OsStr`].
+///
+/// This trait is sealed: it cannot be implemented outside the standard library.
+/// This is so that future additional methods are not breaking changes.
 #[stable(feature = "rust1", since = "1.0.0")]
-pub trait OsStrExt {
+pub trait OsStrExt: Sealed {
     #[stable(feature = "rust1", since = "1.0.0")]
     /// Creates an [`OsStr`] from a byte slice.
     ///