fix: end quietly when a reader leaves the pipe early

src/output.rs

@@ -1,3 +1,6 @@
+use std::fmt::Arguments;
+use std::io::{self, Write};
+
 // progress, on stderr and only when it was asked for
 macro_rules! note {
     ($ctx:expr, $($arg:tt)*) => {
@@ -12,4 +15,29 @@ macro_rules! warning {
     ($($arg:tt)*) => { eprintln!("warning: {}", format_args!($($arg)*)) };
 }
 
-pub(crate) use {note, warning};
+// what a command was asked for, on stdout
+macro_rules! line {
+    ($($arg:tt)*) => { $crate::output::write_line(format_args!($($arg)*)) };
+}
+
+// the same, for a caller that terminates its own entries
+macro_rules! text {
+    ($($arg:tt)*) => { $crate::output::write_text(format_args!($($arg)*)) };
+}
+
+pub(crate) fn write_line(args: Arguments) {
+    finish(writeln!(io::stdout(), "{args}"));
+}
+
+pub(crate) fn write_text(args: Arguments) {
+    finish(write!(io::stdout(), "{args}"));
+}
+
+// a reader leaving early ends the pipe; println! would panic instead
+fn finish(written: io::Result<()>) {
+    if written.is_err() {
+        std::process::exit(0);
+    }
+}
+
+pub(crate) use {line, note, text, warning};