[PATCH 03/12] Keep track of position in getline()

[Rory Dudley <rory@xxxxxxx>]

Keep track of the cursor position in getline(), this way it is not
possible to backspace the prompt.
---
 src/buffer.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/buffer.rs b/src/buffer.rs
index 48e2d85..eedb694 100644
--- a/src/buffer.rs
+++ b/src/buffer.rs
@@ -24,6 +24,10 @@ fn getchar() -> u8 {
 /// that (ICANON and ECHO) are off. See the beginning of [crate::repl]
 /// for more details.
 pub fn getline(buffer: &mut Arc<Mutex<Vec<u8>>>) -> usize {
+    // Keep track of position for backspaces
+    let mut pos: usize = 0;
+
+    // Loop over characters until there is a newline
     loop {
         let c = getchar();
         match c {
@@ -32,6 +36,7 @@ pub fn getline(buffer: &mut Arc<Mutex<Vec<u8>>>) -> usize {
 
             // tab
             b'\t' => {
+                pos += 1;
                 print!(" ");
                 buffer.lock().unwrap().push(b' ');
             }
@@ -41,12 +46,17 @@ pub fn getline(buffer: &mut Arc<Mutex<Vec<u8>>>) -> usize {
 
             // backspace
             127 => {
+                if pos == 0 {
+                    continue;
+                }
+                pos -= 1;
                 buffer.lock().unwrap().pop();
                 print!("\u{8} \u{8}");
             }
 
             // everything else
             _ => {
+                pos += 1;
                 print!("{}", c as char);
                 buffer.lock().unwrap().push(c);
             }
-- 
2.46.2