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.

1 files changed, 4 insertions, 4 deletions

diff --git a/alacritty_terminal/tests/ref.rs b/alacritty_terminal/tests/ref.rs
index a0a831d5..e229b6d2 100644
--- a/alacritty_terminal/tests/ref.rs
+++ b/alacritty_terminal/tests/ref.rs
@@ -9,7 +9,7 @@ use alacritty_terminal::ansi;
 use alacritty_terminal::config::MockConfig;
 use alacritty_terminal::event::{Event, EventListener};
 use alacritty_terminal::grid::{Dimensions, Grid};
-use alacritty_terminal::index::Column;
+use alacritty_terminal::index::{Column, Line};
 use alacritty_terminal::term::cell::Cell;
 use alacritty_terminal::term::{SizeInfo, Term};
 
@@ -118,9 +118,9 @@ fn ref_test(dir: &Path) {
 
     if grid != term_grid {
         for i in 0..grid.total_lines() {
-            for j in 0..grid.cols().0 {
-                let cell = &term_grid[i][Column(j)];
-                let original_cell = &grid[i][Column(j)];
+            for j in 0..grid.columns() {
+                let cell = &term_grid[Line(i as i32)][Column(j)];
+                let original_cell = &grid[Line(i as i32)][Column(j)];
                 if original_cell != cell {
                     println!(
                         "[{i}][{j}] {original:?} => {now:?}",