Implemented a new builtin and improved error handling

src/fern.rs

@@ -11,6 +11,7 @@ pub mod signal;
 #[cfg(test)]
 pub mod tests;
 pub mod getopt;
+pub mod shopt;
 
 use std::collections::HashSet;
 
@@ -22,8 +23,25 @@ use state::{source_rc, write_meta};
 use termios::{LocalFlags, Termios};
 use crate::prelude::*;
 
-pub static mut SAVED_TERMIOS: Option<Option<Termios>> = None;
-
+/// The previous state of the terminal options.
+///
+/// This variable stores the terminal settings at the start of the program and restores them when the program exits.
+/// It is initialized exactly once at the start of the program and accessed exactly once at the end of the program.
+/// It will not be mutated or accessed under any other circumstances.
+///
+/// This ended up being necessary because wrapping Termios in a thread-safe way was unreasonably tricky.
+///
+/// The possible states of this variable are:
+/// - `None`: The terminal options have not been set yet (before initialization).
+/// - `Some(None)`: There were no terminal options to save (i.e., no terminal input detected).
+/// - `Some(Some(Termios))`: The terminal options (as `Termios`) have been saved.
+///
+/// **Important:** This static variable is mutable and accessed via unsafe code. It is only safe to use because:
+/// - It is set once during program startup and accessed once during program exit.
+/// - It is not mutated or accessed after the initial setup and final read.
+///
+/// **Caution:** Future changes to this code should respect these constraints to ensure safety. Modifying or accessing this variable outside the defined lifecycle could lead to undefined behavior.
+pub(crate) static mut SAVED_TERMIOS: Option<Option<Termios>> = None;
 
 pub fn save_termios() {
 	unsafe {
@@ -37,15 +55,15 @@ pub fn save_termios() {
 		});
 	}
 }
-
 #[allow(static_mut_refs)]
-pub fn get_saved_termios() -> Option<Termios> {
-	unsafe {
-		// This is only used when the shell exits so it's fine
-		// SAVED_TERMIOS is only mutated once at the start as well
-		SAVED_TERMIOS.clone().flatten()
-	}
+pub unsafe fn get_saved_termios() -> Option<Termios> {
+	// SAVED_TERMIOS should *only ever* be set once and accessed once
+	// Set at the start of the program, and accessed during the exit of the program to reset the termios.
+	// Do not use this variable anywhere else
+	SAVED_TERMIOS.clone().flatten()
 }
+
+/// Set termios to not echo control characters, like ^Z for instance
 fn set_termios() {
 	if isatty(std::io::stdin().as_raw_fd()).unwrap() {
 		let mut termios = termios::tcgetattr(std::io::stdin()).unwrap();
@@ -73,12 +91,24 @@ fn main() {
 		eprintln!("{e}");
 	}
 
-	loop {
+	const MAX_READLINE_ERRORS: u32 = 5;
+	let mut readline_err_count: u32 = 0;
+
+	loop { // Main loop
 		let input = match prompt::read_line() {
-			Ok(line) => line,
+			Ok(line) => {
+				readline_err_count = 0;
+				line
+			}
 			Err(e) => {
 				eprintln!("{e}");
-				continue
+				readline_err_count += 1;
+				if readline_err_count == MAX_READLINE_ERRORS {
+					eprintln!("reached maximum readline error count, exiting");
+					break
+				} else {
+					continue
+				}
 			}
 		};
 
@@ -86,4 +116,5 @@ fn main() {
 			eprintln!("{e}");
 		}
 	}
+	exit(1);
 }