Fix panics when resizing (#1408)

* Change buffer.get & buffer.get_mut to return Option, Implement Trait Index & IndexMut to panic

* Prevent FilePicker from drawing outside buffer (rust panics)

* apply suggestion

* add function in_bounds to avoid useless calculations

Co-authored-by: mathis <mathis.brossier@universite-paris-saclay.fr>

4 files changed, 81 insertions, 31 deletions

diff --git a/helix-tui/src/backend/test.rs b/helix-tui/src/backend/test.rs
index 3f56b49c..52474148 100644
--- a/helix-tui/src/backend/test.rs
+++ b/helix-tui/src/backend/test.rs
@@ -111,8 +111,7 @@ impl Backend for TestBackend {
         I: Iterator<Item = (u16, u16, &'a Cell)>,
     {
         for (x, y, c) in content {
-            let cell = self.buffer.get_mut(x, y);
-            *cell = c.clone();
+            self.buffer[(x, y)] = c.clone();
         }
         Ok(())
     }
diff --git a/helix-tui/src/buffer.rs b/helix-tui/src/buffer.rs
index c49a0200..3c5e09ac 100644
--- a/helix-tui/src/buffer.rs
+++ b/helix-tui/src/buffer.rs
@@ -90,17 +90,17 @@ impl Default for Cell {
 /// use helix_view::graphics::{Rect, Color, Style, Modifier};
 ///
 /// let mut buf = Buffer::empty(Rect{x: 0, y: 0, width: 10, height: 5});
-/// buf.get_mut(0, 2).set_symbol("x");
-/// assert_eq!(buf.get(0, 2).symbol, "x");
+/// buf[(0, 2)].set_symbol("x");
+/// assert_eq!(buf[(0, 2)].symbol, "x");
 /// buf.set_string(3, 0, "string", Style::default().fg(Color::Red).bg(Color::White));
-/// assert_eq!(buf.get(5, 0), &Cell{
+/// assert_eq!(buf[(5, 0)], Cell{
 ///     symbol: String::from("r"),
 ///     fg: Color::Red,
 ///     bg: Color::White,
 ///     modifier: Modifier::empty()
 /// });
-/// buf.get_mut(5, 0).set_char('x');
-/// assert_eq!(buf.get(5, 0).symbol, "x");
+/// buf[(5, 0)].set_char('x');
+/// assert_eq!(buf[(5, 0)].symbol, "x");
 /// ```
 #[derive(Debug, Default, Clone, PartialEq)]
 pub struct Buffer {
@@ -162,15 +162,38 @@ impl Buffer {
     }
 
     /// Returns a reference to Cell at the given coordinates
-    pub fn get(&self, x: u16, y: u16) -> &Cell {
-        let i = self.index_of(x, y);
-        &self.content[i]
+    pub fn get(&self, x: u16, y: u16) -> Option<&Cell> {
+        self.index_of_opt(x, y).map(|i| &self.content[i])
     }
 
     /// Returns a mutable reference to Cell at the given coordinates
-    pub fn get_mut(&mut self, x: u16, y: u16) -> &mut Cell {
-        let i = self.index_of(x, y);
-        &mut self.content[i]
+    pub fn get_mut(&mut self, x: u16, y: u16) -> Option<&mut Cell> {
+        self.index_of_opt(x, y).map(|i| &mut self.content[i])
+    }
+
+    /// Tells whether the global (x, y) coordinates are inside the Buffer's area.
+    ///
+    /// Global coordinates are offset by the Buffer's area offset (`x`/`y`).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use helix_tui::buffer::Buffer;
+    /// # use helix_view::graphics::Rect;
+    /// let rect = Rect::new(200, 100, 10, 10);
+    /// let buffer = Buffer::empty(rect);
+    /// // Global coordinates inside the Buffer's area
+    /// assert!(buffer.in_bounds(209, 100));
+    /// // Global coordinates outside the Buffer's area
+    /// assert!(!buffer.in_bounds(210, 100));
+    /// ```
+    ///
+    /// Global coordinates are offset by the Buffer's area offset (`x`/`y`).
+    pub fn in_bounds(&self, x: u16, y: u16) -> bool {
+        x >= self.area.left()
+            && x < self.area.right()
+            && y >= self.area.top()
+            && y < self.area.bottom()
     }
 
     /// Returns the index in the Vec<Cell> for the given global (x, y) coordinates.
@@ -184,7 +207,7 @@ impl Buffer {
     /// # use helix_view::graphics::Rect;
     /// let rect = Rect::new(200, 100, 10, 10);
     /// let buffer = Buffer::empty(rect);
-    /// // Global coordinates to the top corner of this buffer's area
+    /// // Global coordinates to the top corner of this Buffer's area
     /// assert_eq!(buffer.index_of(200, 100), 0);
     /// ```
     ///
@@ -193,10 +216,7 @@ impl Buffer {
     /// Panics when given an coordinate that is outside of this Buffer's area.
     pub fn index_of(&self, x: u16, y: u16) -> usize {
         debug_assert!(
-            x >= self.area.left()
-                && x < self.area.right()
-                && y >= self.area.top()
-                && y < self.area.bottom(),
+            self.in_bounds(x, y),
             "Trying to access position outside the buffer: x={}, y={}, area={:?}",
             x,
             y,
@@ -205,6 +225,16 @@ impl Buffer {
         ((y - self.area.y) * self.area.width + (x - self.area.x)) as usize
     }
 
+    /// Returns the index in the Vec<Cell> for the given global (x, y) coordinates,
+    /// or `None` if the coordinates are outside the buffer's area.
+    fn index_of_opt(&self, x: u16, y: u16) -> Option<usize> {
+        if self.in_bounds(x, y) {
+            Some(self.index_of(x, y))
+        } else {
+            None
+        }
+    }
+
     /// Returns the (global) coordinates of a cell given its index
     ///
     /// Global coordinates are offset by the Buffer's area offset (`x`/`y`).
@@ -278,6 +308,11 @@ impl Buffer {
     where
         S: AsRef<str>,
     {
+        // prevent panic if out of range
+        if !self.in_bounds(x, y) || width == 0 {
+            return (x, y);
+        }
+
         let mut index = self.index_of(x, y);
         let mut x_offset = x as usize;
         let width = if ellipsis { width - 1 } else { width };
@@ -372,7 +407,7 @@ impl Buffer {
     pub fn set_background(&mut self, area: Rect, color: Color) {
         for y in area.top()..area.bottom() {
             for x in area.left()..area.right() {
-                self.get_mut(x, y).set_bg(color);
+                self[(x, y)].set_bg(color);
             }
         }
     }
@@ -380,7 +415,7 @@ impl Buffer {
     pub fn set_style(&mut self, area: Rect, style: Style) {
         for y in area.top()..area.bottom() {
             for x in area.left()..area.right() {
-                self.get_mut(x, y).set_style(style);
+                self[(x, y)].set_style(style);
             }
         }
     }
@@ -408,7 +443,7 @@ impl Buffer {
     pub fn clear(&mut self, area: Rect) {
         for x in area.left()..area.right() {
             for y in area.top()..area.bottom() {
-                self.get_mut(x, y).reset();
+                self[(x, y)].reset();
             }
         }
     }
@@ -417,7 +452,7 @@ impl Buffer {
     pub fn clear_with(&mut self, area: Rect, style: Style) {
         for x in area.left()..area.right() {
             for y in area.top()..area.bottom() {
-                let cell = self.get_mut(x, y);
+                let cell = &mut self[(x, y)];
                 cell.reset();
                 cell.set_style(style);
             }
@@ -509,6 +544,22 @@ impl Buffer {
     }
 }
 
+impl std::ops::Index<(u16, u16)> for Buffer {
+    type Output = Cell;
+
+    fn index(&self, (x, y): (u16, u16)) -> &Self::Output {
+        let i = self.index_of(x, y);
+        &self.content[i]
+    }
+}
+
+impl std::ops::IndexMut<(u16, u16)> for Buffer {
+    fn index_mut(&mut self, (x, y): (u16, u16)) -> &mut Self::Output {
+        let i = self.index_of(x, y);
+        &mut self.content[i]
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/helix-tui/src/widgets/block.rs b/helix-tui/src/widgets/block.rs
index 648c2d7e..d43ad41d 100644
--- a/helix-tui/src/widgets/block.rs
+++ b/helix-tui/src/widgets/block.rs
@@ -140,14 +140,14 @@ impl<'a> Widget for Block<'a> {
         // Sides
         if self.borders.intersects(Borders::LEFT) {
             for y in area.top()..area.bottom() {
-                buf.get_mut(area.left(), y)
+                buf[(area.left(), y)]
                     .set_symbol(symbols.vertical)
                     .set_style(self.border_style);
             }
         }
         if self.borders.intersects(Borders::TOP) {
             for x in area.left()..area.right() {
-                buf.get_mut(x, area.top())
+                buf[(x, area.top())]
                     .set_symbol(symbols.horizontal)
                     .set_style(self.border_style);
             }
@@ -155,7 +155,7 @@ impl<'a> Widget for Block<'a> {
         if self.borders.intersects(Borders::RIGHT) {
             let x = area.right() - 1;
             for y in area.top()..area.bottom() {
-                buf.get_mut(x, y)
+                buf[(x, y)]
                     .set_symbol(symbols.vertical)
                     .set_style(self.border_style);
             }
@@ -163,7 +163,7 @@ impl<'a> Widget for Block<'a> {
         if self.borders.intersects(Borders::BOTTOM) {
             let y = area.bottom() - 1;
             for x in area.left()..area.right() {
-                buf.get_mut(x, y)
+                buf[(x, y)]
                     .set_symbol(symbols.horizontal)
                     .set_style(self.border_style);
             }
@@ -171,22 +171,22 @@ impl<'a> Widget for Block<'a> {
 
         // Corners
         if self.borders.contains(Borders::RIGHT | Borders::BOTTOM) {
-            buf.get_mut(area.right() - 1, area.bottom() - 1)
+            buf[(area.right() - 1, area.bottom() - 1)]
                 .set_symbol(symbols.bottom_right)
                 .set_style(self.border_style);
         }
         if self.borders.contains(Borders::RIGHT | Borders::TOP) {
-            buf.get_mut(area.right() - 1, area.top())
+            buf[(area.right() - 1, area.top())]
                 .set_symbol(symbols.top_right)
                 .set_style(self.border_style);
         }
         if self.borders.contains(Borders::LEFT | Borders::BOTTOM) {
-            buf.get_mut(area.left(), area.bottom() - 1)
+            buf[(area.left(), area.bottom() - 1)]
                 .set_symbol(symbols.bottom_left)
                 .set_style(self.border_style);
         }
         if self.borders.contains(Borders::LEFT | Borders::TOP) {
-            buf.get_mut(area.left(), area.top())
+            buf[(area.left(), area.top())]
                 .set_symbol(symbols.top_left)
                 .set_style(self.border_style);
         }
diff --git a/helix-tui/src/widgets/paragraph.rs b/helix-tui/src/widgets/paragraph.rs
index fee35d25..8bafbb9a 100644
--- a/helix-tui/src/widgets/paragraph.rs
+++ b/helix-tui/src/widgets/paragraph.rs
@@ -176,7 +176,7 @@ impl<'a> Widget for Paragraph<'a> {
             if y >= self.scroll.0 {
                 let mut x = get_line_offset(current_line_width, text_area.width, self.alignment);
                 for StyledGrapheme { symbol, style } in current_line {
-                    buf.get_mut(text_area.left() + x, text_area.top() + y - self.scroll.0)
+                    buf[(text_area.left() + x, text_area.top() + y - self.scroll.0)]
                         .set_symbol(if symbol.is_empty() {
                             // If the symbol is empty, the last char which rendered last time will
                             // leave on the line. It's a quick fix.