fix(widgets/chart): remove overflow when dataset if empty (#274)

* docs: Fix missing code block fence
* use slice::windows to deal with underflow issue
* add test for empty dataset and lines

src/widgets/chart.rs

@@ -304,6 +304,7 @@ where
     /// // or if its height is greater than 25% of the total widget height.
     /// let _chart: Chart<String, String> = Chart::default()
     ///     .hidden_legend_constraints(constraints);
+    /// ```
     pub fn hidden_legend_constraints(
         mut self,
         constraints: (Constraint, Constraint),
@@ -499,12 +500,12 @@ where
                         color: dataset.style.fg,
                     });
                     if let GraphType::Line = dataset.graph_type {
-                        for i in 0..dataset.data.len() - 1 {
+                        for data in dataset.data.windows(2) {
                             ctx.draw(&Line {
-                                x1: dataset.data[i].0,
+                                x1: data[0].0,
-                                y1: dataset.data[i].1,
+                                y1: data[0].1,
-                                x2: dataset.data[i + 1].0,
+                                x2: data[1].0,
-                                y2: dataset.data[i + 1].1,
+                                y2: data[1].1,
                                 color: dataset.style.fg,
                             })
                         }

tests/chart.rs

@@ -3,7 +3,7 @@ use tui::{
     layout::Rect,
     style::{Color, Style},
     symbols,
-    widgets::{Axis, Block, Borders, Chart, Dataset},
+    widgets::{Axis, Block, Borders, Chart, Dataset, GraphType::Line},
     Terminal,
 };
 
@@ -72,3 +72,33 @@ fn handles_overflow() {
         })
         .unwrap();
 }
+
+#[test]
+fn empty_dataset_line_test() {
+    let backend = TestBackend::new(100, 100);
+    let mut terminal = Terminal::new(backend).unwrap();
+
+    terminal
+        .draw(|mut f| {
+            let datasets = [Dataset::default().data(&[]).graph_type(Line)];
+            let chart = Chart::default()
+                .block(
+                    Block::default()
+                        .title("Empty Dataset With Line")
+                        .borders(Borders::ALL),
+                )
+                .x_axis(Axis::default().bounds([0.0, 0.0]).labels(&["0.0", "1.0"]))
+                .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: 100,
+                    height: 100,
+                },
+            );
+        })
+        .unwrap();
+}