fix(widgets/block): allow Block to render on small areas

src/widgets/block.rs

@@ -135,13 +135,12 @@ impl<'a> Block<'a> {
 
 impl<'a> Widget for Block<'a> {
     fn render(self, area: Rect, buf: &mut Buffer) {
-        buf.set_style(area, self.style);
-
-        if area.width < 2 || area.height < 2 {
+        if area.area() == 0 {
             return;
         }
-
+        buf.set_style(area, self.style);
         let symbols = BorderType::line_symbols(self.border_type);
+
         // Sides
         if self.borders.intersects(Borders::LEFT) {
             for y in area.top()..area.bottom() {
@@ -175,9 +174,9 @@ impl<'a> Widget for Block<'a> {
         }
 
         // Corners
-        if self.borders.contains(Borders::LEFT | Borders::TOP) {
-            buf.get_mut(area.left(), area.top())
-                .set_symbol(symbols.top_left)
+        if self.borders.contains(Borders::RIGHT | Borders::BOTTOM) {
+            buf.get_mut(area.right() - 1, area.bottom() - 1)
+                .set_symbol(symbols.bottom_right)
                 .set_style(self.border_style);
         }
         if self.borders.contains(Borders::RIGHT | Borders::TOP) {
@@ -190,9 +189,9 @@ impl<'a> Widget for Block<'a> {
                 .set_symbol(symbols.bottom_left)
                 .set_style(self.border_style);
         }
-        if self.borders.contains(Borders::RIGHT | Borders::BOTTOM) {
-            buf.get_mut(area.right() - 1, area.bottom() - 1)
-                .set_symbol(symbols.bottom_right)
+        if self.borders.contains(Borders::LEFT | Borders::TOP) {
+            buf.get_mut(area.left(), area.top())
+                .set_symbol(symbols.top_left)
                 .set_style(self.border_style);
         }
 
@@ -207,7 +206,7 @@ impl<'a> Widget for Block<'a> {
             } else {
                 0
             };
-            let width = area.width - lx - rx;
+            let width = area.width.saturating_sub(lx).saturating_sub(rx);
             buf.set_spans(area.left() + lx, area.top(), &title, width);
         }
     }

tests/widgets_block.rs

@@ -45,3 +45,169 @@ fn widgets_block_renders() {
     }
     terminal.backend().assert_buffer(&expected);
 }
+
+#[test]
+fn widgets_block_renders_on_small_areas() {
+    let test_case = |block, area: Rect, expected| {
+        let backend = TestBackend::new(area.width, area.height);
+        let mut terminal = Terminal::new(backend).unwrap();
+        terminal
+            .draw(|f| {
+                f.render_widget(block, area);
+            })
+            .unwrap();
+        terminal.backend().assert_buffer(&expected);
+    };
+
+    let one_cell_test_cases = [
+        (Borders::NONE, "T"),
+        (Borders::LEFT, "│"),
+        (Borders::TOP, "T"),
+        (Borders::RIGHT, "│"),
+        (Borders::BOTTOM, "T"),
+        (Borders::ALL, "┌"),
+    ];
+    for (borders, symbol) in one_cell_test_cases.iter().cloned() {
+        test_case(
+            Block::default().title("Test").borders(borders),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 0,
+                height: 0,
+            },
+            Buffer::empty(Rect {
+                x: 0,
+                y: 0,
+                width: 0,
+                height: 0,
+            }),
+        );
+        test_case(
+            Block::default().title("Test").borders(borders),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 0,
+            },
+            Buffer::empty(Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 0,
+            }),
+        );
+        test_case(
+            Block::default().title("Test").borders(borders),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 0,
+                height: 1,
+            },
+            Buffer::empty(Rect {
+                x: 0,
+                y: 0,
+                width: 0,
+                height: 1,
+            }),
+        );
+        test_case(
+            Block::default().title("Test").borders(borders),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 1,
+            },
+            Buffer::with_lines(vec![symbol]),
+        );
+    }
+    test_case(
+        Block::default().title("Test").borders(Borders::LEFT),
+        Rect {
+            x: 0,
+            y: 0,
+            width: 4,
+            height: 1,
+        },
+        Buffer::with_lines(vec!["│Tes"]),
+    );
+    test_case(
+        Block::default().title("Test").borders(Borders::RIGHT),
+        Rect {
+            x: 0,
+            y: 0,
+            width: 4,
+            height: 1,
+        },
+        Buffer::with_lines(vec!["Tes│"]),
+    );
+    test_case(
+        Block::default().title("Test").borders(Borders::RIGHT),
+        Rect {
+            x: 0,
+            y: 0,
+            width: 4,
+            height: 1,
+        },
+        Buffer::with_lines(vec!["Tes│"]),
+    );
+    test_case(
+        Block::default()
+            .title("Test")
+            .borders(Borders::LEFT | Borders::RIGHT),
+        Rect {
+            x: 0,
+            y: 0,
+            width: 4,
+            height: 1,
+        },
+        Buffer::with_lines(vec!["│Te│"]),
+    );
+    test_case(
+        Block::default().title("Test").borders(Borders::TOP),
+        Rect {
+            x: 0,
+            y: 0,
+            width: 4,
+            height: 1,
+        },
+        Buffer::with_lines(vec!["Test"]),
+    );
+    test_case(
+        Block::default().title("Test").borders(Borders::TOP),
+        Rect {
+            x: 0,
+            y: 0,
+            width: 5,
+            height: 1,
+        },
+        Buffer::with_lines(vec!["Test─"]),
+    );
+    test_case(
+        Block::default()
+            .title("Test")
+            .borders(Borders::LEFT | Borders::TOP),
+        Rect {
+            x: 0,
+            y: 0,
+            width: 5,
+            height: 1,
+        },
+        Buffer::with_lines(vec!["┌Test"]),
+    );
+    test_case(
+        Block::default()
+            .title("Test")
+            .borders(Borders::LEFT | Borders::TOP),
+        Rect {
+            x: 0,
+            y: 0,
+            width: 6,
+            height: 1,
+        },
+        Buffer::with_lines(vec!["┌Test─"]),
+    );
+}