From 94e31c990b6ae60e5afbda5e3c8f301ba79df0a8 Mon Sep 17 00:00:00 2001
From: matt rice <ratmice@gmail.com>
Date: Tue, 1 Feb 2022 15:14:04 -0800
Subject: [PATCH 1/2] impl Try for ExitStatus

Currently just sys/unix is implemented.
---
 library/std/src/lib.rs                        |  1 +
 library/std/src/process.rs                    | 28 +++++++++++++++++++
 .../std/src/sys/unix/process/process_unix.rs  | 19 +++++++++++++
 3 files changed, 48 insertions(+)

diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index 6dc3fd9858451..8f6e86dbc3a44 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -300,6 +300,7 @@
 #![feature(thin_box)]
 #![feature(toowned_clone_into)]
 #![feature(try_reserve_kind)]
+#![feature(try_trait_v2)]
 #![feature(vec_into_raw_parts)]
 //
 // Library features (unwind):
diff --git a/library/std/src/process.rs b/library/std/src/process.rs
index 771461a59089b..0d3c3de566593 100644
--- a/library/std/src/process.rs
+++ b/library/std/src/process.rs
@@ -112,10 +112,12 @@ use crate::fmt;
 use crate::fs;
 use crate::io::{self, IoSlice, IoSliceMut};
 use crate::num::NonZeroI32;
+use crate::ops::{ControlFlow, FromResidual, Try};
 use crate::path::Path;
 use crate::str;
 use crate::sys::pipe::{read2, AnonPipe};
 use crate::sys::process as imp;
+
 #[stable(feature = "command_access", since = "1.57.0")]
 pub use crate::sys_common::process::CommandEnvs;
 use crate::sys_common::{AsInner, AsInnerMut, FromInner, IntoInner};
@@ -1542,6 +1544,29 @@ impl fmt::Display for ExitStatus {
     }
 }
 
+#[unstable(feature = "exit_status_error", issue = "84908")]
+impl Try for ExitStatus {
+    type Output = ();
+    type Residual = Result<Infallible, ExitStatusError>;
+
+    fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
+        self.0.try_branch()
+    }
+
+    fn from_output((): ()) -> Self {
+        Self(imp::ExitStatus::zero_status())
+    }
+}
+
+#[unstable(feature = "exit_status_error", issue = "84908")]
+impl FromResidual<Result<Infallible, ExitStatusError>> for ExitStatus {
+    fn from_residual(residual: Result<Infallible, ExitStatusError>) -> Self {
+        match residual {
+            Err(exit_status_error) => exit_status_error.into(),
+        }
+    }
+}
+
 /// Allows extension traits within `std`.
 #[unstable(feature = "sealed", issue = "none")]
 impl crate::sealed::Sealed for ExitStatusError {}
@@ -1574,6 +1599,9 @@ pub struct ExitStatusError(imp::ExitStatusError);
 
 #[unstable(feature = "exit_status_error", issue = "84908")]
 impl ExitStatusError {
+    pub(crate) fn new(exit_status_error: imp::ExitStatusError) -> Self {
+        ExitStatusError(exit_status_error)
+    }
     /// Reports the exit code, if applicable, from an `ExitStatusError`.
     ///
     /// In Unix terms the return value is the **exit status**: the value passed to `exit`, if the
diff --git a/library/std/src/sys/unix/process/process_unix.rs b/library/std/src/sys/unix/process/process_unix.rs
index 23bb6d6c15f63..61c178a78acea 100644
--- a/library/std/src/sys/unix/process/process_unix.rs
+++ b/library/std/src/sys/unix/process/process_unix.rs
@@ -1,7 +1,9 @@
+use crate::convert::Infallible;
 use crate::fmt;
 use crate::io::{self, Error, ErrorKind};
 use crate::mem;
 use crate::num::NonZeroI32;
+use crate::ops::ControlFlow;
 use crate::ptr;
 use crate::sys;
 use crate::sys::cvt;
@@ -647,6 +649,12 @@ impl ExitStatus {
         ExitStatus(status)
     }
 
+    // Returns a new 0 status, to avoid hard coding zero
+    // in crate::process::ExitStatus.
+    pub fn zero_status() -> ExitStatus {
+        ExitStatus(0)
+    }
+
     fn exited(&self) -> bool {
         libc::WIFEXITED(self.0)
     }
@@ -663,6 +671,17 @@ impl ExitStatus {
         }
     }
 
+    pub fn try_branch(
+        self,
+    ) -> ControlFlow<Result<Infallible, crate::process::ExitStatusError>, ()> {
+        match NonZero_c_int::try_from(self.0) {
+            Ok(failure) => ControlFlow::Break(Err(crate::process::ExitStatusError::new(
+                ExitStatusError(failure),
+            ))),
+            Err(_) => ControlFlow::Continue(()),
+        }
+    }
+
     pub fn code(&self) -> Option<i32> {
         self.exited().then(|| libc::WEXITSTATUS(self.0))
     }

From f64d80843ce7d9a8171bca37a7031e707d4f2064 Mon Sep 17 00:00:00 2001
From: matt rice <ratmice@gmail.com>
Date: Wed, 2 Feb 2022 03:55:51 -0800
Subject: [PATCH 2/2] windows implementation of impl Try for ExitStatus.

Signed-off-by: matt rice <ratmice@gmail.com>
---
 library/std/src/sys/windows/process.rs | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/library/std/src/sys/windows/process.rs b/library/std/src/sys/windows/process.rs
index 8e5325b80e4a5..66cd42fb31fd9 100644
--- a/library/std/src/sys/windows/process.rs
+++ b/library/std/src/sys/windows/process.rs
@@ -5,6 +5,7 @@ mod tests;
 
 use crate::cmp;
 use crate::collections::BTreeMap;
+use crate::convert::Infallible;
 use crate::env;
 use crate::env::consts::{EXE_EXTENSION, EXE_SUFFIX};
 use crate::ffi::{OsStr, OsString};
@@ -12,6 +13,7 @@ use crate::fmt;
 use crate::io::{self, Error, ErrorKind};
 use crate::mem;
 use crate::num::NonZeroI32;
+use crate::ops::ControlFlow;
 use crate::os::windows::ffi::{OsStrExt, OsStringExt};
 use crate::os::windows::io::{AsHandle, AsRawHandle, BorrowedHandle, FromRawHandle, IntoRawHandle};
 use crate::path::{Path, PathBuf};
@@ -675,6 +677,21 @@ impl ExitStatus {
     pub fn code(&self) -> Option<i32> {
         Some(self.0 as i32)
     }
+
+    pub fn try_branch(
+        self,
+    ) -> ControlFlow<Result<Infallible, crate::process::ExitStatusError>, ()> {
+        match NonZeroDWORD::try_from(self.0) {
+            Ok(failure) => ControlFlow::Break(Err(crate::process::ExitStatusError::new(
+                ExitStatusError(failure),
+            ))),
+            Err(_) => ControlFlow::Continue(()),
+        }
+    }
+
+    pub fn zero_status() -> ExitStatus {
+        ExitStatus(0)
+    }
 }
 
 /// Converts a raw `c::DWORD` to a type-safe `ExitStatus` by wrapping it without copying.