Auto merge of rust-lang#75772 - tmiasko:io-maybe-no, r=dtolnay

Remove unused `Maybe` wrapper around raw standard streams

* Remove result type from raw standard streams constructors
* Make raw standard stream constructors const
* Remove wrapper type handling absent raw standard streams

cargo checked with:

```shell
env CC=true ./x.py check library/std/ \
  --target i686-unknown-linux-gnu \
  --target wasm32-unknown-emscripten \
  --target wasm32-wasi \
  --target x86_64-fortanix-unknown-sgx \
  --target x86_64-pc-windows-gnu \
  --target x86_64-unknown-cloudabi \
  --target x86_64-unknown-hermit \
  --target x86_64-unknown-linux-gnu \
  --target x86_64-uwp-windows-gnu \
  --target x86_64-wrs-vxworks
```

Note: Last target doesn't compile currently.

library/std/src/io/stdio.rs

@@ -50,8 +50,9 @@ struct StderrRaw(stdio::Stderr);
 /// handles is **not** available to raw handles returned from this function.
 ///
 /// The returned handle has no external synchronization or buffering.
-fn stdin_raw() -> io::Result<StdinRaw> {
-    stdio::Stdin::new().map(StdinRaw)
+#[unstable(feature = "libstd_sys_internals", issue = "none")]
+const fn stdin_raw() -> StdinRaw {
+    StdinRaw(stdio::Stdin::new())
 }
 
 /// Constructs a new raw handle to the standard output stream of this process.
@@ -63,8 +64,9 @@ fn stdin_raw() -> io::Result<StdinRaw> {
 ///
 /// The returned handle has no external synchronization or buffering layered on
 /// top.
-fn stdout_raw() -> io::Result<StdoutRaw> {
-    stdio::Stdout::new().map(StdoutRaw)
+#[unstable(feature = "libstd_sys_internals", issue = "none")]
+const fn stdout_raw() -> StdoutRaw {
+    StdoutRaw(stdio::Stdout::new())
 }
 
 /// Constructs a new raw handle to the standard error stream of this process.
@@ -74,17 +76,18 @@ fn stdout_raw() -> io::Result<StdoutRaw> {
 ///
 /// The returned handle has no external synchronization or buffering layered on
 /// top.
-fn stderr_raw() -> io::Result<StderrRaw> {
-    stdio::Stderr::new().map(StderrRaw)
+#[unstable(feature = "libstd_sys_internals", issue = "none")]
+const fn stderr_raw() -> StderrRaw {
+    StderrRaw(stdio::Stderr::new())
 }
 
 impl Read for StdinRaw {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
-        self.0.read(buf)
+        handle_ebadf(self.0.read(buf), 0)
     }
 
     fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
-        self.0.read_vectored(bufs)
+        handle_ebadf(self.0.read_vectored(bufs), 0)
     }
 
     #[inline]
@@ -98,25 +101,22 @@ impl Read for StdinRaw {
     }
 
     fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
-        self.0.read_to_end(buf)
+        handle_ebadf(self.0.read_to_end(buf), 0)
     }
 
     fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
-        self.0.read_to_string(buf)
-    }
-
-    fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
-        self.0.read_exact(buf)
+        handle_ebadf(self.0.read_to_string(buf), 0)
     }
 }
 
 impl Write for StdoutRaw {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
-        self.0.write(buf)
+        handle_ebadf(self.0.write(buf), buf.len())
     }
 
     fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
-        self.0.write_vectored(bufs)
+        let total = bufs.iter().map(|b| b.len()).sum();
+        handle_ebadf(self.0.write_vectored(bufs), total)
     }
 
     #[inline]
@@ -125,29 +125,30 @@ impl Write for StdoutRaw {
     }
 
     fn flush(&mut self) -> io::Result<()> {
-        self.0.flush()
+        handle_ebadf(self.0.flush(), ())
     }
 
     fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
-        self.0.write_all(buf)
+        handle_ebadf(self.0.write_all(buf), ())
     }
 
     fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> io::Result<()> {
-        self.0.write_all_vectored(bufs)
+        handle_ebadf(self.0.write_all_vectored(bufs), ())
     }
 
     fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> io::Result<()> {
-        self.0.write_fmt(fmt)
+        handle_ebadf(self.0.write_fmt(fmt), ())
     }
 }
 
 impl Write for StderrRaw {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
-        self.0.write(buf)
+        handle_ebadf(self.0.write(buf), buf.len())
     }
 
     fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
-        self.0.write_vectored(bufs)
+        let total = bufs.iter().map(|b| b.len()).sum();
+        handle_ebadf(self.0.write_vectored(bufs), total)
     }
 
     #[inline]
@@ -156,80 +157,19 @@ impl Write for StderrRaw {
     }
 
     fn flush(&mut self) -> io::Result<()> {
-        self.0.flush()
+        handle_ebadf(self.0.flush(), ())
     }
 
     fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
-        self.0.write_all(buf)
+        handle_ebadf(self.0.write_all(buf), ())
     }
 
     fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> io::Result<()> {
-        self.0.write_all_vectored(bufs)
+        handle_ebadf(self.0.write_all_vectored(bufs), ())
     }
 
     fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> io::Result<()> {
-        self.0.write_fmt(fmt)
-    }
-}
-
-enum Maybe<T> {
-    Real(T),
-    Fake,
-}
-
-impl<W: io::Write> io::Write for Maybe<W> {
-    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
-        match *self {
-            Maybe::Real(ref mut w) => handle_ebadf(w.write(buf), buf.len()),
-            Maybe::Fake => Ok(buf.len()),
-        }
-    }
-
-    fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
-        let total = bufs.iter().map(|b| b.len()).sum();
-        match self {
-            Maybe::Real(w) => handle_ebadf(w.write_vectored(bufs), total),
-            Maybe::Fake => Ok(total),
-        }
-    }
-
-    #[inline]
-    fn is_write_vectored(&self) -> bool {
-        match self {
-            Maybe::Real(w) => w.is_write_vectored(),
-            Maybe::Fake => true,
-        }
-    }
-
-    fn flush(&mut self) -> io::Result<()> {
-        match *self {
-            Maybe::Real(ref mut w) => handle_ebadf(w.flush(), ()),
-            Maybe::Fake => Ok(()),
-        }
-    }
-}
-
-impl<R: io::Read> io::Read for Maybe<R> {
-    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
-        match *self {
-            Maybe::Real(ref mut r) => handle_ebadf(r.read(buf), 0),
-            Maybe::Fake => Ok(0),
-        }
-    }
-
-    fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
-        match self {
-            Maybe::Real(r) => handle_ebadf(r.read_vectored(bufs), 0),
-            Maybe::Fake => Ok(0),
-        }
-    }
-
-    #[inline]
-    fn is_read_vectored(&self) -> bool {
-        match self {
-            Maybe::Real(w) => w.is_read_vectored(),
-            Maybe::Fake => true,
-        }
+        handle_ebadf(self.0.write_fmt(fmt), ())
     }
 }
 
@@ -274,7 +214,7 @@ fn handle_ebadf<T>(r: io::Result<T>, default: T) -> io::Result<T> {
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Stdin {
-    inner: Arc<Mutex<BufReader<Maybe<StdinRaw>>>>,
+    inner: Arc<Mutex<BufReader<StdinRaw>>>,
 }
 
 /// A locked reference to the `Stdin` handle.
@@ -305,7 +245,7 @@ pub struct Stdin {
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct StdinLock<'a> {
-    inner: MutexGuard<'a, BufReader<Maybe<StdinRaw>>>,
+    inner: MutexGuard<'a, BufReader<StdinRaw>>,
 }
 
 /// Constructs a new handle to the standard input of the current process.
@@ -349,18 +289,14 @@ pub struct StdinLock<'a> {
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn stdin() -> Stdin {
-    static INSTANCE: Lazy<Mutex<BufReader<Maybe<StdinRaw>>>> = Lazy::new();
+    static INSTANCE: Lazy<Mutex<BufReader<StdinRaw>>> = Lazy::new();
     return Stdin {
         inner: unsafe { INSTANCE.get(stdin_init).expect("cannot access stdin during shutdown") },
     };
 
-    fn stdin_init() -> Arc<Mutex<BufReader<Maybe<StdinRaw>>>> {
+    fn stdin_init() -> Arc<Mutex<BufReader<StdinRaw>>> {
         // This must not reentrantly access `INSTANCE`
-        let stdin = match stdin_raw() {
-            Ok(stdin) => Maybe::Real(stdin),
-            _ => Maybe::Fake,
-        };
-
+        let stdin = stdin_raw();
         Arc::new(Mutex::new(BufReader::with_capacity(stdio::STDIN_BUF_SIZE, stdin)))
     }
 }
@@ -537,7 +473,7 @@ pub struct Stdout {
     // FIXME: this should be LineWriter or BufWriter depending on the state of
     //        stdout (tty or not). Note that if this is not line buffered it
     //        should also flush-on-panic or some form of flush-on-abort.
-    inner: Arc<ReentrantMutex<RefCell<LineWriter<Maybe<StdoutRaw>>>>>,
+    inner: Arc<ReentrantMutex<RefCell<LineWriter<StdoutRaw>>>>,
 }
 
 /// A locked reference to the `Stdout` handle.
@@ -551,7 +487,7 @@ pub struct Stdout {
 /// an error.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct StdoutLock<'a> {
-    inner: ReentrantMutexGuard<'a, RefCell<LineWriter<Maybe<StdoutRaw>>>>,
+    inner: ReentrantMutexGuard<'a, RefCell<LineWriter<StdoutRaw>>>,
 }
 
 /// Constructs a new handle to the standard output of the current process.
@@ -595,17 +531,14 @@ pub struct StdoutLock<'a> {
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn stdout() -> Stdout {
-    static INSTANCE: Lazy<ReentrantMutex<RefCell<LineWriter<Maybe<StdoutRaw>>>>> = Lazy::new();
+    static INSTANCE: Lazy<ReentrantMutex<RefCell<LineWriter<StdoutRaw>>>> = Lazy::new();
     return Stdout {
         inner: unsafe { INSTANCE.get(stdout_init).expect("cannot access stdout during shutdown") },
     };
 
-    fn stdout_init() -> Arc<ReentrantMutex<RefCell<LineWriter<Maybe<StdoutRaw>>>>> {
+    fn stdout_init() -> Arc<ReentrantMutex<RefCell<LineWriter<StdoutRaw>>>> {
         // This must not reentrantly access `INSTANCE`
-        let stdout = match stdout_raw() {
-            Ok(stdout) => Maybe::Real(stdout),
-            _ => Maybe::Fake,
-        };
+        let stdout = stdout_raw();
         unsafe {
             let ret = Arc::new(ReentrantMutex::new(RefCell::new(LineWriter::new(stdout))));
             ret.init();
@@ -715,7 +648,7 @@ impl fmt::Debug for StdoutLock<'_> {
 /// an error.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Stderr {
-    inner: &'static ReentrantMutex<RefCell<Maybe<StderrRaw>>>,
+    inner: &'static ReentrantMutex<RefCell<StderrRaw>>,
 }
 
 /// A locked reference to the `Stderr` handle.
@@ -729,7 +662,7 @@ pub struct Stderr {
 /// an error.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct StderrLock<'a> {
-    inner: ReentrantMutexGuard<'a, RefCell<Maybe<StderrRaw>>>,
+    inner: ReentrantMutexGuard<'a, RefCell<StderrRaw>>,
 }
 
 /// Constructs a new handle to the standard error of the current process.
@@ -778,19 +711,14 @@ pub fn stderr() -> Stderr {
     //
     // This has the added benefit of allowing `stderr` to be usable during
     // process shutdown as well!
-    static INSTANCE: ReentrantMutex<RefCell<Maybe<StderrRaw>>> =
-        unsafe { ReentrantMutex::new(RefCell::new(Maybe::Fake)) };
+    static INSTANCE: ReentrantMutex<RefCell<StderrRaw>> =
+        unsafe { ReentrantMutex::new(RefCell::new(stderr_raw())) };
 
     // When accessing stderr we need one-time initialization of the reentrant
-    // mutex, followed by one-time detection of whether we actually have a
-    // stderr handle or not. Afterwards we can just always use the now-filled-in
-    // `INSTANCE` value.
+    // mutex. Afterwards we can just always use the now-filled-in `INSTANCE` value.
     static INIT: Once = Once::new();
     INIT.call_once(|| unsafe {
         INSTANCE.init();
-        if let Ok(stderr) = stderr_raw() {
-            *INSTANCE.lock().borrow_mut() = Maybe::Real(stderr);
-        }
     });
     Stderr { inner: &INSTANCE }
 }

library/std/src/sys/cloudabi/stdio.rs

@@ -6,8 +6,8 @@ pub struct Stdout(());
 pub struct Stderr(());
 
 impl Stdin {
-    pub fn new() -> io::Result<Stdin> {
-        Ok(Stdin(()))
+    pub const fn new() -> Stdin {
+        Stdin(())
     }
 }
 
@@ -18,8 +18,8 @@ impl io::Read for Stdin {
 }
 
 impl Stdout {
-    pub fn new() -> io::Result<Stdout> {
-        Ok(Stdout(()))
+    pub const fn new() -> Stdout {
+        Stdout(())
     }
 }
 
@@ -37,8 +37,8 @@ impl io::Write for Stdout {
 }
 
 impl Stderr {
-    pub fn new() -> io::Result<Stderr> {
-        Ok(Stderr(()))
+    pub const fn new() -> Stderr {
+        Stderr(())
     }
 }
 
@@ -62,5 +62,5 @@ pub fn is_ebadf(err: &io::Error) -> bool {
 pub const STDIN_BUF_SIZE: usize = crate::sys_common::io::DEFAULT_BUF_SIZE;
 
 pub fn panic_output() -> Option<impl io::Write> {
-    Stderr::new().ok()
+    Some(Stderr::new())
 }

library/std/src/sys/hermit/stdio.rs

@@ -7,8 +7,8 @@ pub struct Stdout;
 pub struct Stderr;
 
 impl Stdin {
-    pub fn new() -> io::Result<Stdin> {
-        Ok(Stdin)
+    pub const fn new() -> Stdin {
+        Stdin
     }
 }
 
@@ -28,8 +28,8 @@ impl io::Read for Stdin {
 }
 
 impl Stdout {
-    pub fn new() -> io::Result<Stdout> {
-        Ok(Stdout)
+    pub const fn new() -> Stdout {
+        Stdout
     }
 }
 
@@ -69,8 +69,8 @@ impl io::Write for Stdout {
 }
 
 impl Stderr {
-    pub fn new() -> io::Result<Stderr> {
-        Ok(Stderr)
+    pub const fn new() -> Stderr {
+        Stderr
     }
 }
 
@@ -116,5 +116,5 @@ pub fn is_ebadf(_err: &io::Error) -> bool {
 }
 
 pub fn panic_output() -> Option<impl io::Write> {
-    Stderr::new().ok()
+    Some(Stderr::new())
 }