fix(widgets/canvas): Add bounds check when drawing line high/low (#283)

* Add bounds check when drawing line high/low
* Add test to ensure codepath doesn't break

src/widgets/canvas/line.rs

@@ -64,7 +64,11 @@ fn draw_line_low(painter: &mut Painter, x1: usize, y1: usize, x2: usize, y2: usi
     for x in x1..=x2 {
         painter.paint(x, y, color);
         if d > 0 {
-            y = if y1 > y2 { y - 1 } else { y + 1 };
+            y = if y1 > y2 {
+                y.saturating_sub(1)
+            } else {
+                y.saturating_add(1)
+            };
             d -= 2 * dx;
         }
         d += 2 * dy;
@@ -79,7 +83,11 @@ fn draw_line_high(painter: &mut Painter, x1: usize, y1: usize, x2: usize, y2: us
     for y in y1..=y2 {
         painter.paint(x, y, color);
         if d > 0 {
-            x = if x1 > x2 { x - 1 } else { x + 1 };
+            x = if x1 > x2 {
+                x.saturating_sub(1)
+            } else {
+                x.saturating_add(1)
+            };
             d -= 2 * dy;
         }
         d += 2 * dx;

tests/chart.rs

@@ -35,3 +35,40 @@ fn zero_axes_ok() {
         })
         .unwrap();
 }
+
+#[test]
+fn handles_overflow() {
+    let backend = TestBackend::new(80, 30);
+    let mut terminal = Terminal::new(backend).unwrap();
+
+    terminal
+        .draw(|mut f| {
+            let datasets = [Dataset::default()
+                .marker(symbols::Marker::Braille)
+                .style(Style::default().fg(Color::Magenta))
+                .data(&[
+                    (1588298471.0, 1.0),
+                    (1588298473.0, 0.0),
+                    (1588298496.0, 1.0),
+                ])];
+            let chart = Chart::default()
+                .block(Block::default().title("Plot").borders(Borders::ALL))
+                .x_axis(
+                    Axis::default()
+                        .bounds([1588298471.0, 1588992600.0])
+                        .labels(&["1588298471.0", "1588992600.0"]),
+                )
+                .y_axis(Axis::default().bounds([0.0, 1.0]).labels(&["0.0", "1.0"]))
+                .datasets(&datasets);
+            f.render_widget(
+                chart,
+                Rect {
+                    x: 0,
+                    y: 0,
+                    width: 80,
+                    height: 30,
+                },
+            );
+        })
+        .unwrap();
+}