Unify the grid line indexing types

Previously Alacritty was using two different ways to reference lines in
the terminal. Either a `usize`, or a `Line(usize)`. These indexing
systems both served different purposes, but made it difficult to reason
about logic involving these systems because of its inconsistency.

To resolve this issue, a single new `Line(i32)` type has been
introduced.  All existing references to lines and points now rely on
this definition of a line.

The indexing starts at the top of the terminal region with the line 0,
which matches the line 1 used by escape sequences. Each line in the
history becomes increasingly negative and the bottommost line is equal
to the number of visible lines minus one.

Having a system which goes into the negatives allows following the
escape sequence's indexing system closely, while at the same time making
it trivial to implement `Ord` for points.

The Alacritty UI crate is the only place which has a different indexing
system, since rendering and input puts the zero line at the top of the
viewport, rather than the top of the terminal region.

All instances which refer to a number of lines/columns instead of just a
single Line/Column have also been changed to use a `usize` instead. This
way a Line/Column will always refer to a specific place in the grid and
no confusion is created by having a count of lines as a possible index
into the grid storage.

2 files changed, 8 insertions, 6 deletions

diff --git a/alacritty_terminal/src/tty/unix.rs b/alacritty_terminal/src/tty/unix.rs
index 9cce1983..ba59bb66 100644
--- a/alacritty_terminal/src/tty/unix.rs
+++ b/alacritty_terminal/src/tty/unix.rs
@@ -25,6 +25,7 @@ use signal_hook::{self as sighook, iterator::Signals};
 
 use crate::config::{Config, Program};
 use crate::event::OnResize;
+use crate::grid::Dimensions;
 use crate::term::SizeInfo;
 use crate::tty::{ChildEvent, EventedPty, EventedReadWrite};
 
@@ -357,8 +358,8 @@ pub trait ToWinsize {
 impl<'a> ToWinsize for &'a SizeInfo {
     fn to_winsize(&self) -> winsize {
         winsize {
-            ws_row: self.screen_lines().0 as libc::c_ushort,
-            ws_col: self.cols().0 as libc::c_ushort,
+            ws_row: self.screen_lines() as libc::c_ushort,
+            ws_col: self.columns() as libc::c_ushort,
             ws_xpixel: self.width() as libc::c_ushort,
             ws_ypixel: self.height() as libc::c_ushort,
         }
diff --git a/alacritty_terminal/src/tty/windows/conpty.rs b/alacritty_terminal/src/tty/windows/conpty.rs
index de3d8d4e..919bd00f 100644
--- a/alacritty_terminal/src/tty/windows/conpty.rs
+++ b/alacritty_terminal/src/tty/windows/conpty.rs
@@ -19,6 +19,7 @@ use winapi::um::wincontypes::{COORD, HPCON};
 
 use crate::config::Config;
 use crate::event::OnResize;
+use crate::grid::Dimensions;
 use crate::term::SizeInfo;
 use crate::tty::windows::child::ChildExitWatcher;
 use crate::tty::windows::{cmdline, win32_string, Pty};
@@ -185,11 +186,11 @@ impl OnResize for Conpty {
 
 /// Helper to build a COORD from a SizeInfo, returning None in overflow cases.
 fn coord_from_sizeinfo(size: &SizeInfo) -> Option<COORD> {
-    let cols = size.cols().0;
-    let lines = size.screen_lines().0;
+    let lines = size.screen_lines();
+    let columns = size.columns();
 
-    if cols <= i16::MAX as usize && lines <= i16::MAX as usize {
-        Some(COORD { X: cols as i16, Y: lines as i16 })
+    if columns <= i16::MAX as usize && lines <= i16::MAX as usize {
+        Some(COORD { X: columns as i16, Y: lines as i16 })
     } else {
         None
     }