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Document the Termination trait's impls #96819

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Document the Termination trait's impls #96819

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26 changes: 26 additions & 0 deletions library/std/src/process.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2107,13 +2107,24 @@ pub trait Termination {
#[stable(feature = "termination_trait_lib", since = "1.61.0")]
impl Termination for () {
#[inline]
/// Returns `ExitCode::SUCCESS`.
fn report(self) -> ExitCode {
ExitCode::SUCCESS.report()
}
}

#[stable(feature = "termination_trait_lib", since = "1.61.0")]
impl<E: fmt::Debug> Termination for Result<(), E> {
/// Returns a meaningful exit code, and outputs an error message if
/// appropriate.
///
/// If the result is `Ok`, returns `ExitCode::SUCCESS`.
///
/// If the result is `Err`, writes the [`fmt::Debug`] representation of
/// the error value to [`io::stderr`] and returns `ExitCode::FAILURE`.
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I don't want to guarantee this behavior, because I expect us to change it in the future.

In particular, if we add the "generic member access" mechanism, we could then change this trait implementation to attempt to retrieve an ExitCode from E, and use that if available.

///
/// [`fmt::Debug`]: crate::fmt::Debug
/// [`io::stderr`]: crate::io::stderr
fn report(self) -> ExitCode {
match self {
Ok(()) => ().report(),
Expand All @@ -2131,6 +2142,13 @@ impl Termination for ! {

#[stable(feature = "termination_trait_lib", since = "1.61.0")]
impl<E: fmt::Debug> Termination for Result<!, E> {
/// Returns a meaningful exit code and outputs an error message.
///
/// Writes the [`fmt::Debug`] representation of the error value to
/// [`io::stderr`] and returns `ExitCode::FAILURE`.
Comment on lines +2147 to +2148
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As above, I expect us to change this in the future.

///
/// [`fmt::Debug`]: crate::fmt::Debug
/// [`io::stderr`]: crate::io::stderr
fn report(self) -> ExitCode {
let Err(err) = self;
eprintln!("Error: {err:?}");
Expand All @@ -2140,6 +2158,13 @@ impl<E: fmt::Debug> Termination for Result<!, E> {

#[stable(feature = "termination_trait_lib", since = "1.61.0")]
impl<E: fmt::Debug> Termination for Result<Infallible, E> {
/// Returns a meaningful exit code and outputs an error message.
///
/// Writes the [`fmt::Debug`] representation of the error value to
/// [`io::stderr`] and returns `ExitCode::FAILURE`.
Comment on lines +2163 to +2164
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As above, I expect us to change this in the future.

///
/// [`fmt::Debug`]: crate::fmt::Debug
/// [`io::stderr`]: crate::io::stderr
fn report(self) -> ExitCode {
let Err(err) = self;
Err::<!, _>(err).report()
Expand All @@ -2148,6 +2173,7 @@ impl<E: fmt::Debug> Termination for Result<Infallible, E> {

#[stable(feature = "termination_trait_lib", since = "1.61.0")]
impl Termination for ExitCode {
/// Returns the `ExitCode` unchanged.
#[inline]
fn report(self) -> ExitCode {
self
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