Fix crash when vi cursor in history during clear

Fixes #5544.

CHANGELOG.md

@@ -30,6 +30,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Vi mode search starting in the line below the vi cursor
 - Invisible cursor with matching foreground/background colors
 - Crash when hovering over a match emptied by post-processing
+- Crash when the vi cursor is on the scrollback and viewport clear is invoked
+- Freeze when the vi cursor is on the scrollback and scrollback clear is invoked
 
 ### Removed
 

alacritty_terminal/src/grid/mod.rs

@@ -376,6 +376,9 @@ impl<T> Grid<T> {
     pub fn clear_history(&mut self) {
         // Explicitly purge all lines from history.
         self.raw.shrink_lines(self.history_size());
+
+        // Reset display offset.
+        self.display_offset = 0;
     }
 
     /// This is used only for initializing after loading ref-tests.

alacritty_terminal/src/term/mod.rs

@@ -1424,6 +1424,9 @@ impl<T: EventListener> Handler for Term<T> {
                     self.grid.reset_region(..);
                 } else {
                     self.grid.clear_viewport();
+
+                    self.vi_mode_cursor.point.line =
+                        self.vi_mode_cursor.point.line.grid_clamp(self, Boundary::Cursor);
                 }
 
                 self.selection = None;
@@ -1431,6 +1434,9 @@ impl<T: EventListener> Handler for Term<T> {
             ansi::ClearMode::Saved if self.history_size() > 0 => {
                 self.grid.clear_history();
 
+                self.vi_mode_cursor.point.line =
+                    self.vi_mode_cursor.point.line.grid_clamp(self, Boundary::Cursor);
+
                 self.selection = self.selection.take().filter(|s| !s.intersects_range(..Line(0)));
             },
             // We have no history to clear.
@@ -2118,6 +2124,50 @@ mod tests {
         assert_eq!(term.grid()[cursor].c, '▒');
     }
 
+    #[test]
+    fn clear_viewport_set_vi_cursor_into_viewport() {
+        let size = SizeInfo::new(10.0, 20.0, 1.0, 1.0, 0.0, 0.0, false);
+        let mut term = Term::new(&Config::default(), size, ());
+
+        // Create 10 lines of scrollback.
+        for _ in 0..29 {
+            term.newline();
+        }
+
+        // Change the display area and the vi cursor position.
+        term.scroll_display(Scroll::Top);
+        term.vi_mode_cursor.point = Point::new(Line(-5), Column(3));
+
+        // Clear the viewport.
+        term.clear_screen(ansi::ClearMode::All);
+
+        assert_eq!(term.grid.display_offset(), 0);
+        assert_eq!(term.vi_mode_cursor.point.line.0, 0);
+        assert_eq!(term.vi_mode_cursor.point.column.0, 3);
+    }
+
+    #[test]
+    fn clear_scrollback_set_vi_cursor_into_viewport() {
+        let size = SizeInfo::new(10.0, 20.0, 1.0, 1.0, 0.0, 0.0, false);
+        let mut term = Term::new(&Config::default(), size, ());
+
+        // Create 10 lines of scrollback.
+        for _ in 0..29 {
+            term.newline();
+        }
+
+        // Change the display area and the vi cursor position.
+        term.scroll_display(Scroll::Top);
+        term.vi_mode_cursor.point = Point::new(Line(-5), Column(3));
+
+        // Clear the scrollback buffer.
+        term.clear_screen(ansi::ClearMode::Saved);
+
+        assert_eq!(term.grid.display_offset(), 0);
+        assert_eq!(term.vi_mode_cursor.point.line.0, 0);
+        assert_eq!(term.vi_mode_cursor.point.column.0, 3);
+    }
+
     #[test]
     fn clear_saved_lines() {
         let size = SizeInfo::new(21.0, 51.0, 3.0, 3.0, 0.0, 0.0, false);