Rollup merge of #105458 - Ayush1325:blocking_spawn, r=Mark-Simulacrum

Allow blocking `Command::output`

### Problem
Currently, `Command::output` is internally implemented using `Command::spawn`. This is problematic because some targets (like UEFI) do not actually support multitasking and thus block while the program is executing. This coupling does not make much sense as `Command::output` is supposed to block until the execution is complete anyway and thus does not need to rely on a non-blocking `Child` or any other intermediate.

### Solution
This PR moves the implementation of `Command::output` to `std::sys`. This means targets can choose to implement only `Command::output` without having to implement `Command::spawn`.

### Additional Information

This was originally conceived when working on https://github.com/rust-lang/rust/pull/100316. Currently, the only target I know about that will benefit from this change is UEFI.

This PR can also be used to implement more efficient `Command::output` since the intermediate `Process` is not actually needed anymore, but that is outside the scope of this PR.

Since this is not a public API change, I'm not sure if an RFC is needed or not.

9 files changed, 41 insertions, 1 deletions

diff --git a/library/std/src/sys/unix/pipe.rs b/library/std/src/sys/unix/pipe.rs
index a56c275c942..a744d0ab640 100644
--- a/library/std/src/sys/unix/pipe.rs
+++ b/library/std/src/sys/unix/pipe.rs
@@ -58,6 +58,10 @@ impl AnonPipe {
         self.0.is_read_vectored()
     }
 
+    pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
+        self.0.read_to_end(buf)
+    }
+
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
         self.0.write(buf)
     }
diff --git a/library/std/src/sys/unix/process/process_fuchsia.rs b/library/std/src/sys/unix/process/process_fuchsia.rs
index 66ea3db2015..4c99d758c93 100644
--- a/library/std/src/sys/unix/process/process_fuchsia.rs
+++ b/library/std/src/sys/unix/process/process_fuchsia.rs
@@ -35,6 +35,11 @@ impl Command {
         Ok((Process { handle: Handle::new(process_handle) }, ours))
     }
 
+    pub fn output(&mut self) -> io::Result<(ExitStatus, Vec<u8>, Vec<u8>)> {
+        let (proc, pipes) = self.spawn(Stdio::MakePipe, false)?;
+        crate::sys_common::process::wait_with_output(proc, pipes)
+    }
+
     pub fn exec(&mut self, default: Stdio) -> io::Error {
         if self.saw_nul() {
             return io::const_io_error!(
diff --git a/library/std/src/sys/unix/process/process_unix.rs b/library/std/src/sys/unix/process/process_unix.rs
index c0716a089bc..39d1c8b1d8e 100644
--- a/library/std/src/sys/unix/process/process_unix.rs
+++ b/library/std/src/sys/unix/process/process_unix.rs
@@ -133,6 +133,11 @@ impl Command {
         }
     }
 
+    pub fn output(&mut self) -> io::Result<(ExitStatus, Vec<u8>, Vec<u8>)> {
+        let (proc, pipes) = self.spawn(Stdio::MakePipe, false)?;
+        crate::sys_common::process::wait_with_output(proc, pipes)
+    }
+
     // Attempts to fork the process. If successful, returns Ok((0, -1))
     // in the child, and Ok((child_pid, -1)) in the parent.
     #[cfg(not(target_os = "linux"))]
diff --git a/library/std/src/sys/unix/process/process_unsupported.rs b/library/std/src/sys/unix/process/process_unsupported.rs
index 72f9f3f9ca7..f28ca58d020 100644
--- a/library/std/src/sys/unix/process/process_unsupported.rs
+++ b/library/std/src/sys/unix/process/process_unsupported.rs
@@ -20,6 +20,10 @@ impl Command {
         unsupported()
     }
 
+    pub fn output(&mut self) -> io::Result<(ExitStatus, Vec<u8>, Vec<u8>)> {
+        unsupported()
+    }
+
     pub fn exec(&mut self, _default: Stdio) -> io::Error {
         unsupported_err()
     }
diff --git a/library/std/src/sys/unix/process/process_vxworks.rs b/library/std/src/sys/unix/process/process_vxworks.rs
index 200ef671967..f549d37c301 100644
--- a/library/std/src/sys/unix/process/process_vxworks.rs
+++ b/library/std/src/sys/unix/process/process_vxworks.rs
@@ -108,6 +108,11 @@ impl Command {
         }
     }
 
+    pub fn output(&mut self) -> io::Result<(ExitStatus, Vec<u8>, Vec<u8>)> {
+        let (proc, pipes) = self.spawn(Stdio::MakePipe, false)?;
+        crate::sys_common::process::wait_with_output(proc, pipes)
+    }
+
     pub fn exec(&mut self, default: Stdio) -> io::Error {
         let ret = Command::spawn(self, default, false);
         match ret {
diff --git a/library/std/src/sys/unsupported/pipe.rs b/library/std/src/sys/unsupported/pipe.rs
index 25514c2322f..0bba673b458 100644
--- a/library/std/src/sys/unsupported/pipe.rs
+++ b/library/std/src/sys/unsupported/pipe.rs
@@ -15,6 +15,10 @@ impl AnonPipe {
         self.0
     }
 
+    pub fn read_to_end(&self, _buf: &mut Vec<u8>) -> io::Result<usize> {
+        self.0
+    }
+
     pub fn write(&self, _buf: &[u8]) -> io::Result<usize> {
         self.0
     }
diff --git a/library/std/src/sys/unsupported/process.rs b/library/std/src/sys/unsupported/process.rs
index 633f17c054b..a494f2d6b4c 100644
--- a/library/std/src/sys/unsupported/process.rs
+++ b/library/std/src/sys/unsupported/process.rs
@@ -75,6 +75,10 @@ impl Command {
     ) -> io::Result<(Process, StdioPipes)> {
         unsupported()
     }
+
+    pub fn output(&mut self) -> io::Result<(ExitStatus, Vec<u8>, Vec<u8>)> {
+        unsupported()
+    }
 }
 
 impl From<AnonPipe> for Stdio {
diff --git a/library/std/src/sys/windows/pipe.rs b/library/std/src/sys/windows/pipe.rs
index 9f26acc4520..7b25edaa556 100644
--- a/library/std/src/sys/windows/pipe.rs
+++ b/library/std/src/sys/windows/pipe.rs
@@ -1,7 +1,7 @@
 use crate::os::windows::prelude::*;
 
 use crate::ffi::OsStr;
-use crate::io::{self, IoSlice, IoSliceMut};
+use crate::io::{self, IoSlice, IoSliceMut, Read};
 use crate::mem;
 use crate::path::Path;
 use crate::ptr;
@@ -261,6 +261,10 @@ impl AnonPipe {
         self.inner.is_read_vectored()
     }
 
+    pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
+        self.handle().read_to_end(buf)
+    }
+
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
         unsafe {
             let len = crate::cmp::min(buf.len(), c::DWORD::MAX as usize) as c::DWORD;
diff --git a/library/std/src/sys/windows/process.rs b/library/std/src/sys/windows/process.rs
index 31e9b34fb9e..10bc949e1f4 100644
--- a/library/std/src/sys/windows/process.rs
+++ b/library/std/src/sys/windows/process.rs
@@ -351,6 +351,11 @@ impl Command {
             ))
         }
     }
+
+    pub fn output(&mut self) -> io::Result<(ExitStatus, Vec<u8>, Vec<u8>)> {
+        let (proc, pipes) = self.spawn(Stdio::MakePipe, false)?;
+        crate::sys_common::process::wait_with_output(proc, pipes)
+    }
 }
 
 impl fmt::Debug for Command {