Don't panic if the other end of std{out,err} is closed (#4179)

* fix #4161

println! and friends will panic on BrokenPipe. The solution is to use
writeln! instead, and ignore the error (or do we want to do something else?)

* test that nu doesn't panic in case of BrokenPipe error

* fixup! test that nu doesn't panic in case of BrokenPipe error

* make do_not_panic_if_broken_pipe only run on UNIX systems

crates/nu-protocol/src/macros.rs

@@ -6,7 +6,7 @@
 macro_rules! out {
     ($($tokens:tt)*) => {
         use std::io::Write;
-        print!($($tokens)*);
+        write!(std::io::stdout(), $($tokens)*).unwrap_or(());
         let _ = std::io::stdout().flush();
     }
 }
@@ -17,7 +17,12 @@ macro_rules! out {
 /// and stray printlns left by accident
 #[macro_export]
 macro_rules! outln {
-    ($($tokens:tt)*) => { println!($($tokens)*) }
+    ($($tokens:tt)*) => {
+        {
+            use std::io::Write;
+            writeln!(std::io::stdout(), $($tokens)*).unwrap_or(())
+        }
+    }
 }
 
 /// Outputs to standard error
@@ -26,7 +31,12 @@ macro_rules! outln {
 /// and stray printlns left by accident
 #[macro_export]
 macro_rules! errln {
-    ($($tokens:tt)*) => { eprintln!($($tokens)*) }
+    ($($tokens:tt)*) => {
+        {
+            use std::io::Write;
+            writeln!(std::io::stderr(), $($tokens)*).unwrap_or(())
+        }
+    }
 }
 
 #[macro_export]

tests/shell/mod.rs

@@ -53,3 +53,20 @@ fn plugins_are_declared_with_wix() {
 
     assert_eq!(actual.out, "0");
 }
+
+#[test]
+#[cfg(not(windows))]
+fn do_not_panic_if_broken_pipe() {
+    // `nu -h | false`
+    // used to panic with a BrokenPipe error
+    let child_output = std::process::Command::new("sh")
+        .arg("-c")
+        .arg(format!(
+            "{:?} -h | false",
+            nu_test_support::fs::executable_path()
+        ))
+        .output()
+        .expect("failed to execute process");
+
+    assert!(child_output.stderr.is_empty());
+}