Exclude empty columns on the right from the prerender cache

tests/components/backlog.rs

@@ -89,12 +89,72 @@ fn test_single_item_cached() {
     text: Text::raw("hello"),
     prerender: &prerender,
   };
+  let mut buf = Buffer::empty(rect(0, 0, 18, 8));
   bl.draw_items(&mut buf, area, vec![item].into_iter())
     .context("Failed to draw")
     .unwrap();
   assert_eq!(buf, expected);
 }
 
+/// Checks that the prerender cache does not store empty columns to the right
+#[test]
+fn test_only_necessary_width() {
+  let mut bl = Backlog::default();
+  let prerender1 = Prerender::new();
+  let prerender2 = Prerender::new();
+  let item1 = BufferItem {
+    text: Text::raw("hi\nworld"),
+    prerender: &prerender1,
+  };
+  let item2 = BufferItem {
+    text: Text::raw(":)"),
+    prerender: &prerender2,
+  };
+  let mut cell = ratatui::buffer::Cell::default();
+  cell.set_char('.');
+  let mut buf = Buffer::filled(rect(0, 0, 18, 7), &cell); // poisoned buffer
+  let area = rect(3, 1, 12, 5);
+  bl.draw_items(&mut buf, area, vec![item2, item1].into_iter())
+    .context("Failed to draw")
+    .unwrap();
+
+  let expected = Buffer::with_lines(vec![
+    "..................",
+    "...┌──────────┐...",
+    "...│hi........│...",
+    "...│world.....│...",
+    "...│:)........│...",
+    "...└──────────┘...",
+    "..................",
+  ]);
+  assert_eq!(buf, expected);
+
+  assert_eq!(prerender1.key(), Some(10));
+
+  let item1 = BufferItem {
+    text: Text::raw("hi\nworld"),
+    prerender: &prerender1,
+  };
+  let item2 = BufferItem {
+    text: Text::raw(":)"),
+    prerender: &prerender2,
+  };
+  let mut buf = Buffer::empty(rect(0, 0, 18, 7));
+  bl.draw_items(&mut buf, area, vec![item2, item1].into_iter())
+    .context("Failed to draw")
+    .unwrap();
+  let expected = Buffer::with_lines(vec![
+    "                  ",
+    "   ┌──────────┐   ",
+    "   │hi...     │   ", // dots are leftover from the poisoned buffer above
+    "   │world     │   ",
+    "   │:)        │   ",
+    "   └──────────┘   ",
+    "                  ",
+  ]);
+  assert_eq!(buf, expected);
+}
+
 #[test]
 fn test_single_item_tight() {
   let mut bl = Backlog::default();