ChildContext: Add command_boxed (#37)

This lets us make the `ChildContext` fields private, making it possible
for users to implement (e.g.) `ChildExt`.

Author: 9999years

src/child_context.rs

@@ -18,8 +18,8 @@ use crate::OutputContext;
 ///
 /// See: [`OutputContext`].
 pub struct ChildContext<C> {
-    pub(crate) child: C,
-    pub(crate) command: Box<dyn CommandDisplay + Send + Sync>,
+    child: C,
+    command: Box<dyn CommandDisplay + Send + Sync>,
 }
 
 impl<C> ChildContext<C> {
@@ -47,6 +47,19 @@ impl<C> ChildContext<C> {
     pub fn command(&self) -> &(dyn CommandDisplay + Send + Sync + 'static) {
         self.command.borrow()
     }
+
+    /// Get a reference to the [`Box`] containing the command which produced this child process.
+    ///
+    /// This value, unlike the return value from [`ChildContext::command`], can be [`Clone`]d.
+    #[expect(clippy::borrowed_box)]
+    pub fn command_boxed(&self) -> &Box<dyn CommandDisplay + Send + Sync> {
+        &self.command
+    }
+
+    /// Get the child and command which produced the child.
+    pub fn into_child_and_command(self) -> (C, Box<dyn CommandDisplay + Send + Sync>) {
+        (self.child, self.command)
+    }
 }
 
 impl<C> Debug for ChildContext<C>

src/child_ext.rs

@@ -1,4 +1,3 @@
-use std::borrow::Borrow;
 use std::fmt::Debug;
 use std::fmt::Display;
 use std::process::Child;
@@ -234,8 +233,8 @@ impl ChildExt for ChildContext<Child> {
         E: From<Self::Error>,
     {
         self.log()?;
-        let command = dyn_clone::clone_box(self.command.borrow());
-        match self.child.wait_with_output() {
+        let (child, command) = self.into_child_and_command();
+        match child.wait_with_output() {
             Ok(output) => match output.try_into() {
                 Ok(output) => succeeded(OutputContext::new(output, command)),
                 Err(error) => {
@@ -253,8 +252,8 @@ impl ChildExt for ChildContext<Child> {
     where
         E: From<Self::Error>,
     {
-        let command = dyn_clone::clone_box(self.command.borrow());
-        match self.child.try_wait() {
+        let command = self.command_boxed().clone();
+        match self.child_mut().try_wait() {
             Ok(status) => succeeded(TryWaitContext::new(status, command)),
             Err(inner) => Err(Error::from(WaitError::new(command, inner)).into()),
         }
@@ -268,8 +267,8 @@ impl ChildExt for ChildContext<Child> {
         E: From<Self::Error>,
     {
         self.log()?;
-        let command = dyn_clone::clone_box(self.command.borrow());
-        match self.child.wait() {
+        let command = self.command_boxed().clone();
+        match self.child_mut().wait() {
             Ok(status) => succeeded(OutputContext::new(status, command)),
             Err(inner) => Err(Error::from(ExecError::new(command, inner)).into()),
         }