stdio: Document no support for writing to non-blocking stdio/stderr

Printing to stdio/stderr that have been opened with non-blocking
(O_NONBLOCK in linux) can result in an error, which is not handled
by std::io module causing a panic.

Signed-off-by: Usama Arif <[email protected]>

library/std/src/io/stdio.rs

@@ -992,6 +992,9 @@ pub fn set_output_capture(sink: Option<LocalStream>) -> Option<LocalStream> {
 /// the global stream.
 ///
 /// However, if the actual I/O causes an error, this function does panic.
+///
+/// Writing to non-blocking stdout/stderr can cause an error, which will lead
+/// this function to panic.
 fn print_to<T>(args: fmt::Arguments<'_>, global_s: fn() -> T, label: &str)
 where
     T: Write,

library/std/src/macros.rs

@@ -49,6 +49,9 @@ macro_rules! panic {
 ///
 /// Panics if writing to `io::stdout()` fails.
 ///
+/// Writing to non-blocking stdout can cause an error, which will lead
+/// this macro to panic.
+///
 /// # Examples
 ///
 /// ```
@@ -107,6 +110,9 @@ macro_rules! print {
 ///
 /// Panics if writing to [`io::stdout`] fails.
 ///
+/// Writing to non-blocking stdout can cause an error, which will lead
+/// this macro to panic.
+///
 /// [`io::stdout`]: crate::io::stdout
 ///
 /// # Examples
@@ -147,6 +153,9 @@ macro_rules! println {
 ///
 /// Panics if writing to `io::stderr` fails.
 ///
+/// Writing to non-blocking stdout can cause an error, which will lead
+/// this macro to panic.
+///
 /// # Examples
 ///
 /// ```
@@ -179,6 +188,9 @@ macro_rules! eprint {
 ///
 /// Panics if writing to `io::stderr` fails.
 ///
+/// Writing to non-blocking stdout can cause an error, which will lead
+/// this macro to panic.
+///
 /// # Examples
 ///
 /// ```