Seal CommandExt trait

This is technically a breaking change, but we follow the standard
library's decision that sealing CommandExt is fine.
rust-lang/rust@bfd1ccf

Author: taiki-e

src/lib.rs

@@ -82,6 +82,10 @@ pub mod unix;
 #[cfg(windows)]
 pub mod windows;
 
+mod sealed {
+    pub trait Sealed {}
+}
+
 /// An event delivered every time the SIGCHLD signal occurs.
 static SIGCHLD: Event = Event::new();
 

src/unix.rs

@@ -7,7 +7,10 @@ use std::os::unix::process::CommandExt as _;
 use crate::Command;
 
 /// Unix-specific extensions to the [`Command`] builder.
-pub trait CommandExt {
+///
+/// This trait is sealed: it cannot be implemented outside `async-process`.
+/// This is so that future additional methods are not breaking changes.
+pub trait CommandExt: crate::sealed::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.
@@ -88,6 +91,7 @@ pub trait CommandExt {
         S: AsRef<OsStr>;
 }
 
+impl crate::sealed::Sealed for Command {}
 impl CommandExt for Command {
     fn uid(&mut self, id: u32) -> &mut Command {
         self.inner.uid(id);

src/windows.rs

@@ -6,7 +6,10 @@ use std::os::windows::process::CommandExt as _;
 use crate::{Child, Command};
 
 /// Windows-specific extensions to the [`Command`] builder.
-pub trait CommandExt {
+///
+/// This trait is sealed: it cannot be implemented outside `async-process`.
+/// This is so that future additional methods are not breaking changes.
+pub trait CommandExt: crate::sealed::Sealed {
     /// Sets the [process creation flags][1] to be passed to `CreateProcess`.
     ///
     /// These will always be ORed with `CREATE_UNICODE_ENVIRONMENT`.
@@ -15,6 +18,7 @@ pub trait CommandExt {
     fn creation_flags(&mut self, flags: u32) -> &mut Command;
 }
 
+impl crate::sealed::Sealed for Command {}
 impl CommandExt for Command {
     fn creation_flags(&mut self, flags: u32) -> &mut Command {
         self.inner.creation_flags(flags);