feat: add Block::title_top and Block::title_top_bottom (#940)

This adds the ability to add titles to the top and bottom of a block
without having to use the `Title` struct (which will be removed in a
future release - likely v0.28.0).

Fixes a subtle bug if the title was created from a right aligned Line
and was also right aligned. The title would be rendered one cell too far
to the right.

```rust
Block::bordered()
    .title_top(Line::raw("A").left_aligned())
    .title_top(Line::raw("B").centered())
    .title_top(Line::raw("C").right_aligned())
    .title_bottom(Line::raw("D").left_aligned())
    .title_bottom(Line::raw("E").centered())
    .title_bottom(Line::raw("F").right_aligned())
    .render(buffer.area, &mut buffer);
// renders
"┌A─────B─────C┐",
"│             │",
"└D─────E─────F┘",
```

Addresses part of #738

<!-- Please read CONTRIBUTING.md before submitting any pull request. -->

src/widgets/block.rs

@@ -22,6 +22,20 @@ pub use title::{Position, Title};
 /// [`Title`] using [`Block::title`]. It can also be [styled](Block::style) and
 /// [padded](Block::padding).
 ///
+/// You can call the title methods multiple times to add multiple titles. Each title will be
+/// rendered with a single space separating titles that are in the same position or alignment. When
+/// both centered and non-centered titles are rendered, the centered space is calculated based on
+/// the full width of the block, rather than the leftover width.
+///
+/// Titles are not rendered in the corners of the block unless there is no border on that edge.  
+/// If the block is too small and multiple titles overlap, the border may get cut off at a corner.
+///
+/// ```plain
+/// ┌With at least a left border───
+///
+/// Without left border───
+/// ```
+///
 /// # Examples
 ///
 /// ```
@@ -228,6 +242,62 @@ impl<'a> Block<'a> {
         self
     }
 
+    /// Adds a title to the top of the block.
+    ///
+    /// You can provide any type that can be converted into [`Line`] including: strings, string
+    /// slices (`&str`), borrowed strings (`Cow<str>`), [spans](crate::text::Span), or vectors of
+    /// [spans](crate::text::Span) (`Vec<Span>`).
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use ratatui::{ prelude::*, widgets::* };
+    /// Block::bordered()
+    ///     .title_top("Left1") // By default in the top left corner
+    ///     .title_top(Line::from("Left2").left_aligned())
+    ///     .title_top(Line::from("Right").right_aligned())
+    ///     .title_top(Line::from("Center").centered());
+    ///
+    /// // Renders
+    /// // ┌Left1─Left2───Center─────────Right┐
+    /// // │                                  │
+    /// // └──────────────────────────────────┘
+    /// ```
+    #[must_use = "method moves the value of self and returns the modified value"]
+    pub fn title_top<T: Into<Line<'a>>>(mut self, title: T) -> Self {
+        let title = Title::from(title).position(Position::Top);
+        self.titles.push(title);
+        self
+    }
+
+    /// Adds a title to the bottom of the block.
+    ///
+    /// You can provide any type that can be converted into [`Line`] including: strings, string
+    /// slices (`&str`), borrowed strings (`Cow<str>`), [spans](crate::text::Span), or vectors of
+    /// [spans](crate::text::Span) (`Vec<Span>`).
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use ratatui::{ prelude::*, widgets::* };
+    /// Block::bordered()
+    ///     .title_bottom("Left1") // By default in the top left corner
+    ///     .title_bottom(Line::from("Left2").left_aligned())
+    ///     .title_bottom(Line::from("Right").right_aligned())
+    ///     .title_bottom(Line::from("Center").centered());
+    ///
+    /// // Renders
+    /// // ┌──────────────────────────────────┐
+    /// // │                                  │
+    /// // └Left1─Left2───Center─────────Right┘
+    /// ```
+    #[must_use = "method moves the value of self and returns the modified value"]
+    pub fn title_bottom<T: Into<Line<'a>>>(mut self, title: T) -> Self {
+        let title = Title::from(title).position(Position::Bottom);
+        self.titles.push(title);
+        self
+    }
+
     /// Applies the style to all titles.
     ///
     /// `style` accepts any type that is convertible to [`Style`] (e.g. [`Style`], [`Color`], or
@@ -655,6 +725,7 @@ impl Block<'_> {
                     .right()
                     .saturating_sub(title_width)
                     .max(titles_area.left()),
+                width: title_width.min(titles_area.width),
                 ..titles_area
             };
             buf.set_style(title_area, self.titles_style);
@@ -1130,6 +1201,50 @@ mod tests {
         )
     }
 
+    #[test]
+    fn title() {
+        let mut buffer = Buffer::empty(Rect::new(0, 0, 15, 3));
+        use Alignment::*;
+        use Position::*;
+        Block::bordered()
+            .title(Title::from("A").position(Top).alignment(Left))
+            .title(Title::from("B").position(Top).alignment(Center))
+            .title(Title::from("C").position(Top).alignment(Right))
+            .title(Title::from("D").position(Bottom).alignment(Left))
+            .title(Title::from("E").position(Bottom).alignment(Center))
+            .title(Title::from("F").position(Bottom).alignment(Right))
+            .render(buffer.area, &mut buffer);
+        assert_buffer_eq!(
+            buffer,
+            Buffer::with_lines(vec![
+                "┌A─────B─────C┐",
+                "│             │",
+                "└D─────E─────F┘",
+            ])
+        );
+    }
+
+    #[test]
+    fn title_top_bottom() {
+        let mut buffer = Buffer::empty(Rect::new(0, 0, 15, 3));
+        Block::bordered()
+            .title_top(Line::raw("A").left_aligned())
+            .title_top(Line::raw("B").centered())
+            .title_top(Line::raw("C").right_aligned())
+            .title_bottom(Line::raw("D").left_aligned())
+            .title_bottom(Line::raw("E").centered())
+            .title_bottom(Line::raw("F").right_aligned())
+            .render(buffer.area, &mut buffer);
+        assert_buffer_eq!(
+            buffer,
+            Buffer::with_lines(vec![
+                "┌A─────B─────C┐",
+                "│             │",
+                "└D─────E─────F┘",
+            ])
+        );
+    }
+
     #[test]
     fn title_alignment() {
         let tests = vec![

src/widgets/block/title.rs

@@ -115,18 +115,25 @@ where
     T: Into<Line<'a>>,
 {
     fn from(value: T) -> Self {
-        Self::default().content(value.into())
+        let content = value.into();
+        let alignment = content.alignment;
+        Self {
+            content,
+            alignment,
+            position: None,
+        }
     }
 }
 
 #[cfg(test)]
 mod tests {
+    use rstest::rstest;
     use strum::ParseError;
 
     use super::*;
 
     #[test]
-    fn position_tostring() {
+    fn position_to_string() {
         assert_eq!(Position::Top.to_string(), "Top");
         assert_eq!(Position::Bottom.to_string(), "Bottom");
     }
@@ -137,4 +144,24 @@ mod tests {
         assert_eq!("Bottom".parse::<Position>(), Ok(Position::Bottom));
         assert_eq!("".parse::<Position>(), Err(ParseError::VariantNotFound));
     }
+
+    #[test]
+    fn title_from_line() {
+        let title = Title::from(Line::raw("Title"));
+        assert_eq!(title.content, Line::from("Title"));
+        assert_eq!(title.alignment, None);
+        assert_eq!(title.position, None);
+    }
+
+    #[rstest]
+    #[case::left(Alignment::Left)]
+    #[case::center(Alignment::Center)]
+    #[case::right(Alignment::Right)]
+    fn title_from_line_with_alignment(#[case] alignment: Alignment) {
+        let line = Line::raw("Title").alignment(alignment);
+        let title = Title::from(line.clone());
+        assert_eq!(title.content, line);
+        assert_eq!(title.alignment, Some(alignment));
+        assert_eq!(title.position, None);
+    }
 }