Idiomatic type for reader_readline nchars argument

src/builtins/read.rs

@@ -28,6 +28,7 @@
 use crate::wutil::encoding::zero_mbstate;
 use crate::wutil::perror;
 use libc::SEEK_CUR;
+use std::num::NonZeroUsize;
 use std::os::fd::RawFd;
 use std::sync::atomic::Ordering;
 
@@ -244,7 +245,7 @@ fn read_interactive(
 
     let mline = {
         let _interactive = parser.push_scope(|s| s.is_interactive = true);
-        reader_readline(parser, nchars)
+        reader_readline(parser, NonZeroUsize::try_from(nchars).ok())
     };
     terminal_protocols_disable_ifn();
     if let Some(line) = mline {

src/reader.rs

@@ -1060,12 +1060,11 @@ pub fn reader_reading_interrupted(data: &mut ReaderData) -> i32 {
 }
 
 /// Read one line of input. Before calling this function, reader_push() must have been called in
-/// order to set up a valid reader environment. If nchars > 0, return after reading that many
+/// order to set up a valid reader environment. If nchars is given, return after reading that many
 /// characters even if a full line has not yet been read. Note: the returned value may be longer
 /// than nchars if a single keypress resulted in multiple characters being inserted into the
 /// commandline.
-pub fn reader_readline(parser: &Parser, nchars: usize) -> Option<WString> {
-    let nchars = NonZeroUsize::try_from(nchars).ok();
+pub fn reader_readline(parser: &Parser, nchars: Option<NonZeroUsize>) -> Option<WString> {
     let data = current_data().unwrap();
     let mut reader = Reader { parser, data };
     reader.readline(nchars)