fix(widgets/table): improve computation of table column widths

src/layout.rs

@@ -63,6 +63,9 @@ pub struct Layout {
     direction: Direction,
     margin: Margin,
     constraints: Vec<Constraint>,
+    /// Whether the last chunk of the computed layout should be expanded to fill the available
+    /// space.
+    expand_to_fill: bool,
 }
 
 thread_local! {
@@ -78,6 +81,7 @@ impl Default for Layout {
                 vertical: 0,
             },
             constraints: Vec::new(),
+            expand_to_fill: true,
         }
     }
 }
@@ -114,6 +118,11 @@ impl Layout {
         self
     }
 
+    pub(crate) fn expand_to_fill(mut self, expand_to_fill: bool) -> Layout {
+        self.expand_to_fill = expand_to_fill;
+        self
+    }
+
     /// Wrapper function around the cassowary-rs solver to be able to split a given
     /// area into smaller ones based on the preferred widths or heights and the direction.
     ///
@@ -222,11 +231,13 @@ fn split(area: Rect, layout: &Layout) -> Vec<Rect> {
             Direction::Vertical => first.top() | EQ(REQUIRED) | f64::from(dest_area.top()),
         });
     }
-    if let Some(last) = elements.last() {
-        ccs.push(match layout.direction {
-            Direction::Horizontal => last.right() | EQ(REQUIRED) | f64::from(dest_area.right()),
-            Direction::Vertical => last.bottom() | EQ(REQUIRED) | f64::from(dest_area.bottom()),
-        });
+    if layout.expand_to_fill {
+        if let Some(last) = elements.last() {
+            ccs.push(match layout.direction {
+                Direction::Horizontal => last.right() | EQ(REQUIRED) | f64::from(dest_area.right()),
+                Direction::Vertical => last.bottom() | EQ(REQUIRED) | f64::from(dest_area.bottom()),
+            });
+        }
     }
     match layout.direction {
         Direction::Horizontal => {
@@ -299,14 +310,16 @@ fn split(area: Rect, layout: &Layout) -> Vec<Rect> {
         }
     }
 
-    // Fix imprecision by extending the last item a bit if necessary
-    if let Some(last) = results.last_mut() {
-        match layout.direction {
-            Direction::Vertical => {
-                last.height = dest_area.bottom() - last.y;
-            }
-            Direction::Horizontal => {
-                last.width = dest_area.right() - last.x;
+    if layout.expand_to_fill {
+        // Fix imprecision by extending the last item a bit if necessary
+        if let Some(last) = results.last_mut() {
+            match layout.direction {
+                Direction::Vertical => {
+                    last.height = dest_area.bottom() - last.y;
+                }
+                Direction::Horizontal => {
+                    last.width = dest_area.right() - last.x;
+                }
             }
         }
     }

src/widgets/table.rs

@@ -1,16 +1,10 @@
 use crate::{
     buffer::Buffer,
-    layout::{Constraint, Rect},
+    layout::{Constraint, Direction, Layout, Rect},
     style::Style,
     text::Text,
     widgets::{Block, StatefulWidget, Widget},
 };
-use cassowary::{
-    strength::{MEDIUM, REQUIRED, WEAK},
-    WeightedRelation::*,
-    {Expression, Solver},
-};
-use std::collections::HashMap;
 use unicode_width::UnicodeWidthStr;
 
 /// A [`Cell`] contains the [`Text`] to be displayed in a [`Row`] of a [`Table`].
@@ -273,69 +267,33 @@ impl<'a> Table<'a> {
     }
 
     fn get_columns_widths(&self, max_width: u16, has_selection: bool) -> Vec<u16> {
-        let mut solver = Solver::new();
-        let mut var_indices = HashMap::new();
-        let mut ccs = Vec::new();
-        let mut variables = Vec::new();
-        for i in 0..self.widths.len() {
-            let var = cassowary::Variable::new();
-            variables.push(var);
-            var_indices.insert(var, i);
-        }
-        let spacing_width = (variables.len() as u16).saturating_sub(1) * self.column_spacing;
-        let mut available_width = max_width.saturating_sub(spacing_width);
+        let mut constraints = Vec::with_capacity(self.widths.len() * 2 + 1);
         if has_selection {
             let highlight_symbol_width =
                 self.highlight_symbol.map(|s| s.width() as u16).unwrap_or(0);
-            available_width = available_width.saturating_sub(highlight_symbol_width);
+            constraints.push(Constraint::Length(highlight_symbol_width));
         }
-        for (i, constraint) in self.widths.iter().enumerate() {
-            ccs.push(variables[i] | GE(WEAK) | 0.);
-            ccs.push(match *constraint {
-                Constraint::Length(v) => variables[i] | EQ(MEDIUM) | f64::from(v),
-                Constraint::Percentage(v) => {
-                    variables[i] | EQ(WEAK) | (f64::from(v * available_width) / 100.0)
-                }
-                Constraint::Ratio(n, d) => {
-                    variables[i]
-                        | EQ(WEAK)
-                        | (f64::from(available_width) * f64::from(n) / f64::from(d))
-                }
-                Constraint::Min(v) => variables[i] | GE(WEAK) | f64::from(v),
-                Constraint::Max(v) => variables[i] | LE(WEAK) | f64::from(v),
-            })
+        for constraint in self.widths {
+            constraints.push(*constraint);
+            constraints.push(Constraint::Length(self.column_spacing));
         }
-        solver
-            .add_constraint(
-                variables
-                    .iter()
-                    .fold(Expression::from_constant(0.), |acc, v| acc + *v)
-                    | LE(REQUIRED)
-                    | f64::from(available_width),
-            )
-            .unwrap();
-        solver.add_constraints(&ccs).unwrap();
-        let mut widths = vec![0; variables.len()];
-        for &(var, value) in solver.fetch_changes() {
-            let index = var_indices[&var];
-            let value = if value.is_sign_negative() {
-                0
-            } else {
-                value.round() as u16
-            };
-            widths[index] = value;
+        if !self.widths.is_empty() {
+            constraints.pop();
         }
-        // Cassowary could still return columns widths greater than the max width when there are
-        // fixed length constraints that cannot be satisfied. Therefore, we clamp the widths from
-        // left to right.
-        let mut available_width = max_width;
-        for w in &mut widths {
-            *w = available_width.min(*w);
-            available_width = available_width
-                .saturating_sub(*w)
-                .saturating_sub(self.column_spacing);
+        let mut chunks = Layout::default()
+            .direction(Direction::Horizontal)
+            .constraints(constraints)
+            .expand_to_fill(false)
+            .split(Rect {
+                x: 0,
+                y: 0,
+                width: max_width,
+                height: 1,
+            });
+        if has_selection {
+            chunks.remove(0);
         }
-        widths
+        chunks.iter().step_by(2).map(|c| c.width).collect()
     }
 
     fn get_row_bounds(

tests/widgets_table.rs

@@ -354,12 +354,12 @@ fn widgets_table_columns_widths_can_use_mixed_constraints() {
         ],
         Buffer::with_lines(vec![
             "┌────────────────────────────┐",
-            "│Hea Head2                Hea│",
+            "│Hea Head2                He │",
             "│                            │",
-            "│Row Row12                Row│",
-            "│Row Row22                Row│",
-            "│Row Row32                Row│",
-            "│Row Row42                Row│",
+            "│Row Row12                Ro │",
+            "│Row Row22                Ro │",
+            "│Row Row32                Ro │",
+            "│Row Row42                Ro │",
             "│                            │",
             "│                            │",
             "└────────────────────────────┘",
@@ -715,3 +715,37 @@ fn widgets_table_should_render_even_if_empty() {
 
     terminal.backend().assert_buffer(&expected);
 }
+
+#[test]
+fn widgets_table_columns_dont_panic() {
+    let test_case = |state: &mut TableState, table: Table, width: u16| {
+        let backend = TestBackend::new(width, 8);
+        let mut terminal = Terminal::new(backend).unwrap();
+        terminal
+            .draw(|f| {
+                let size = f.size();
+                f.render_stateful_widget(table, size, state);
+            })
+            .unwrap();
+    };
+
+    // based on https://github.com/fdehau/tui-rs/issues/470#issuecomment-852562848
+    let table1_width = 98;
+    let table1 = Table::new(vec![Row::new(vec!["r1", "r2", "r3", "r4"])])
+        .header(Row::new(vec!["h1", "h2", "h3", "h4"]))
+        .block(Block::default().borders(Borders::ALL))
+        .highlight_symbol(">> ")
+        .column_spacing(1)
+        .widths(&[
+            Constraint::Percentage(15),
+            Constraint::Percentage(15),
+            Constraint::Percentage(25),
+            Constraint::Percentage(45),
+        ]);
+
+    let mut state = TableState::default();
+
+    // select first, which would cause a panic before fix
+    state.select(Some(0));
+    test_case(&mut state, table1.clone(), table1_width);
+}