Implement Term::erase_chars

Fixes last known issue with htop. I think this implementation might not
be correct, but I don't yet understand the difference between erasing
and deleting (I imagine it's the difference between graphics state vs
grid state). Will probably need to circle back here.

Adds all range indexing operations to rows. Some were needed for the
erase_chars impl, and the rest are there for fully generality.

src/grid.rs

@@ -14,7 +14,7 @@
 //
 //! Functions for computing properties of the terminal grid
 
-use std::ops::{Index, IndexMut, Deref, DerefMut, Range, RangeTo, RangeFrom};
+use std::ops::{Index, IndexMut, Deref, DerefMut, Range, RangeTo, RangeFrom, RangeFull};
 use std::cmp::Ordering;
 use std::slice::{Iter, IterMut};
 
@@ -262,35 +262,29 @@ impl IndexMut<usize> for Row {
     }
 }
 
-impl Index<RangeFrom<usize>> for Row {
-    type Output = [Cell];
-    #[inline]
-    fn index<'a>(&'a self, index: RangeFrom<usize>) -> &'a [Cell] {
-        &self.0[index]
+macro_rules! row_index_range {
+    ($range:ty) => {
+        impl Index<$range> for Row {
+            type Output = [Cell];
+            #[inline]
+            fn index<'a>(&'a self, index: $range) -> &'a [Cell] {
+                &self.0[index]
+            }
+        }
+
+        impl IndexMut<$range> for Row {
+            #[inline]
+            fn index_mut<'a>(&'a mut self, index: $range) -> &'a mut [Cell] {
+                &mut self.0[index]
+            }
+        }
     }
 }
 
-impl IndexMut<RangeFrom<usize>> for Row {
-    #[inline]
-    fn index_mut<'a>(&'a mut self, index: RangeFrom<usize>) -> &'a mut [Cell] {
-        &mut self.0[index]
-    }
-}
-
-impl Index<RangeTo<usize>> for Row {
-    type Output = [Cell];
-    #[inline]
-    fn index<'a>(&'a self, index: RangeTo<usize>) -> &'a [Cell] {
-        &self.0[index]
-    }
-}
-
-impl IndexMut<RangeTo<usize>> for Row {
-    #[inline]
-    fn index_mut<'a>(&'a mut self, index: RangeTo<usize>) -> &'a mut [Cell] {
-        &mut self.0[index]
-    }
-}
+row_index_range!(Range<usize>);
+row_index_range!(RangeTo<usize>);
+row_index_range!(RangeFrom<usize>);
+row_index_range!(RangeFull);
 
 pub trait ClearRegion<T> {
     fn clear_region(&mut self, region: T);

src/term.rs

@@ -483,7 +483,17 @@ impl ansi::Handler for Term {
             self.scroll(count as isize);
         }
     }
-    fn erase_chars(&mut self, count: i64) { println!("erase_chars: {}", count); }
+    fn erase_chars(&mut self, count: i64) {
+        println!("erase_chars: {}", count);
+        let row_index = self.cursor.y as usize;
+        let col_index = self.cursor.x as usize;
+        let count = count as usize;
+
+        let row = &mut self.grid[row_index];
+        for c in &mut row[col_index..(count + col_index)] {
+            c.reset();
+        }
+    }
     fn delete_chars(&mut self, count: i64) { println!("delete_chars: {}", count); }
     fn move_backward_tabs(&mut self, count: i64) { println!("move_backward_tabs: {}", count); }
     fn move_forward_tabs(&mut self, count: i64) { println!("move_forward_tabs: {}", count); }