fix(text): truncate based on alignment (#1432)

This is a follow-up PR to https://github.com/ratatui/ratatui/pull/987,
which implemented alignment-aware truncation for the `Line` widget.
However, the truncation only checked the `Line::alignment` field, and
any alignment inherited from a parent's `Text::alignment` field would
not be used.

This commit updates the truncation of `Line` to depend both on the
individual `Line::alignment`, and on any alignment inherited from the
parent's `Text::alignment`.

Co-authored-by: Josh McKinney <joshka@users.noreply.github.com>

src/text/line.rs

@@ -687,6 +687,21 @@ impl Widget for Line<'_> {
 
 impl WidgetRef for Line<'_> {
     fn render_ref(&self, area: Rect, buf: &mut Buffer) {
+        self.render_with_alignment(area, buf, None);
+    }
+}
+
+impl Line<'_> {
+    /// An internal implementation method for `WidgetRef::render_ref`
+    ///
+    /// Allows the parent widget to define a default alignment, to be
+    /// used if `Line::alignment` is `None`.
+    pub(crate) fn render_with_alignment(
+        &self,
+        area: Rect,
+        buf: &mut Buffer,
+        parent_alignment: Option<Alignment>,
+    ) {
         let area = area.intersection(buf.area);
         if area.is_empty() {
             return;
@@ -699,10 +714,12 @@ impl WidgetRef for Line<'_> {
 
         buf.set_style(area, self.style);
 
+        let alignment = self.alignment.or(parent_alignment);
+
         let area_width = usize::from(area.width);
         let can_render_complete_line = line_width <= area_width;
         if can_render_complete_line {
-            let indent_width = match self.alignment {
+            let indent_width = match alignment {
                 Some(Alignment::Center) => (area_width.saturating_sub(line_width)) / 2,
                 Some(Alignment::Right) => area_width.saturating_sub(line_width),
                 Some(Alignment::Left) | None => 0,
@@ -713,7 +730,7 @@ impl WidgetRef for Line<'_> {
         } else {
             // There is not enough space to render the whole line. As the right side is truncated by
             // the area width, only truncate the left.
-            let skip_width = match self.alignment {
+            let skip_width = match alignment {
                 Some(Alignment::Center) => (line_width.saturating_sub(area_width)) / 2,
                 Some(Alignment::Right) => line_width.saturating_sub(area_width),
                 Some(Alignment::Left) | None => 0,

src/text/text.rs

@@ -735,23 +735,8 @@ impl WidgetRef for Text<'_> {
     fn render_ref(&self, area: Rect, buf: &mut Buffer) {
         let area = area.intersection(buf.area);
         buf.set_style(area, self.style);
-        for (line, row) in self.iter().zip(area.rows()) {
-            let line_width = line.width() as u16;
-
-            let x_offset = match (self.alignment, line.alignment) {
-                (Some(Alignment::Center), None) => area.width.saturating_sub(line_width) / 2,
-                (Some(Alignment::Right), None) => area.width.saturating_sub(line_width),
-                _ => 0,
-            };
-
-            let line_area = Rect {
-                x: area.x + x_offset,
-                y: row.y,
-                width: area.width - x_offset,
-                height: 1,
-            };
-
-            line.render(line_area, buf);
+        for (line, line_area) in self.iter().zip(area.rows()) {
+            line.render_with_alignment(line_area, buf, self.alignment);
         }
     }
 }
@@ -1196,6 +1181,33 @@ mod tests {
             assert_eq!(buf, Buffer::with_lines([" foo  "]));
         }
 
+        #[test]
+        fn render_right_aligned_with_truncation() {
+            let text = Text::from("123456789").alignment(Alignment::Right);
+            let area = Rect::new(0, 0, 5, 1);
+            let mut buf = Buffer::empty(area);
+            text.render(area, &mut buf);
+            assert_eq!(buf, Buffer::with_lines(["56789"]));
+        }
+
+        #[test]
+        fn render_centered_odd_with_truncation() {
+            let text = Text::from("123456789").alignment(Alignment::Center);
+            let area = Rect::new(0, 0, 5, 1);
+            let mut buf = Buffer::empty(area);
+            text.render(area, &mut buf);
+            assert_eq!(buf, Buffer::with_lines(["34567"]));
+        }
+
+        #[test]
+        fn render_centered_even_with_truncation() {
+            let text = Text::from("123456789").alignment(Alignment::Center);
+            let area = Rect::new(0, 0, 6, 1);
+            let mut buf = Buffer::empty(area);
+            text.render(area, &mut buf);
+            assert_eq!(buf, Buffer::with_lines(["234567"]));
+        }
+
         #[test]
         fn render_one_line_right() {
             let text = Text::from(vec![