fix(panes): show visual error when failing to resize panes (#2036)

* fix(panes): show visual error when failing to resize pane vertically/horizontally

* fix(resize): retry pane resize on rounding errors

* fix(resize): proper error when resizing other panes into fixed panes

* style(fmt): rustfmt

9 files changed, 415 insertions, 69 deletions

diff --git a/zellij-server/src/background_jobs.rs b/zellij-server/src/background_jobs.rs
index 3c89ed064..c612c9d57 100644
--- a/zellij-server/src/background_jobs.rs
+++ b/zellij-server/src/background_jobs.rs
@@ -10,7 +10,7 @@ use crate::thread_bus::Bus;
 
 #[derive(Debug, Clone, Eq, PartialEq, Hash)]
 pub enum BackgroundJob {
-    DisplayPaneError(PaneId, String),
+    DisplayPaneError(Vec<PaneId>, String),
     Exit,
 }
 
@@ -34,7 +34,7 @@ pub(crate) fn background_jobs_main(bus: Bus<BackgroundJob>) -> Result<()> {
         err_ctx.add_call(ContextType::BackgroundJob((&event).into()));
         let job = event.clone();
         match event {
-            BackgroundJob::DisplayPaneError(pane_id, text) => {
+            BackgroundJob::DisplayPaneError(pane_ids, text) => {
                 if job_already_running(job, &mut running_jobs) {
                     continue;
                 }
@@ -42,11 +42,14 @@ pub(crate) fn background_jobs_main(bus: Bus<BackgroundJob>) -> Result<()> {
                     let senders = bus.senders.clone();
                     async move {
                         let _ = senders.send_to_screen(
-                            ScreenInstruction::AddRedPaneFrameColorOverride(pane_id, Some(text)),
+                            ScreenInstruction::AddRedPaneFrameColorOverride(
+                                pane_ids.clone(),
+                                Some(text),
+                            ),
                         );
                         task::sleep(std::time::Duration::from_millis(FLASH_DURATION_MS)).await;
                         let _ = senders.send_to_screen(
-                            ScreenInstruction::ClearPaneFrameColorOverride(pane_id),
+                            ScreenInstruction::ClearPaneFrameColorOverride(pane_ids),
                         );
                     }
                 });
diff --git a/zellij-server/src/panes/plugin_pane.rs b/zellij-server/src/panes/plugin_pane.rs
index 3a0ec9c83..babb66b67 100644
--- a/zellij-server/src/panes/plugin_pane.rs
+++ b/zellij-server/src/panes/plugin_pane.rs
@@ -16,7 +16,7 @@ use zellij_utils::{
     channels::SenderWithContext,
     data::{Event, InputMode, Mouse, Palette, PaletteColor, Style},
     errors::prelude::*,
-    pane_size::{Dimension, PaneGeom},
+    pane_size::PaneGeom,
     shared::make_terminal_title,
     vte,
 };
@@ -341,28 +341,28 @@ impl Pane for PluginPane {
     }
     fn reduce_height(&mut self, percent: f64) {
         if let Some(p) = self.geom.rows.as_percent() {
-            self.geom.rows = Dimension::percent(p - percent);
+            self.geom.rows.set_percent(p - percent);
             self.resize_grids();
             self.set_should_render(true);
         }
     }
     fn increase_height(&mut self, percent: f64) {
         if let Some(p) = self.geom.rows.as_percent() {
-            self.geom.rows = Dimension::percent(p + percent);
+            self.geom.rows.set_percent(p + percent);
             self.resize_grids();
             self.set_should_render(true);
         }
     }
     fn reduce_width(&mut self, percent: f64) {
         if let Some(p) = self.geom.cols.as_percent() {
-            self.geom.cols = Dimension::percent(p - percent);
+            self.geom.cols.set_percent(p - percent);
             self.resize_grids();
             self.set_should_render(true);
         }
     }
     fn increase_width(&mut self, percent: f64) {
         if let Some(p) = self.geom.cols.as_percent() {
-            self.geom.cols = Dimension::percent(p + percent);
+            self.geom.cols.set_percent(p + percent);
             self.resize_grids();
             self.set_should_render(true);
         }
diff --git a/zellij-server/src/panes/terminal_pane.rs b/zellij-server/src/panes/terminal_pane.rs
index 4d5ed840c..d206245ad 100644
--- a/zellij-server/src/panes/terminal_pane.rs
+++ b/zellij-server/src/panes/terminal_pane.rs
@@ -18,8 +18,8 @@ use zellij_utils::pane_size::Offset;
 use zellij_utils::{
     data::{InputMode, Palette, PaletteColor, Style},
     errors::prelude::*,
+    pane_size::PaneGeom,
     pane_size::SizeInPixels,
-    pane_size::{Dimension, PaneGeom},
     position::Position,
     shared::make_terminal_title,
     vte,
@@ -446,25 +446,25 @@ impl Pane for TerminalPane {
     }
     fn reduce_height(&mut self, percent: f64) {
         if let Some(p) = self.geom.rows.as_percent() {
-            self.geom.rows = Dimension::percent(p - percent);
+            self.geom.rows.set_percent(p - percent);
             self.set_should_render(true);
         }
     }
     fn increase_height(&mut self, percent: f64) {
         if let Some(p) = self.geom.rows.as_percent() {
-            self.geom.rows = Dimension::percent(p + percent);
+            self.geom.rows.set_percent(p + percent);
             self.set_should_render(true);
         }
     }
     fn reduce_width(&mut self, percent: f64) {
         if let Some(p) = self.geom.cols.as_percent() {
-            self.geom.cols = Dimension::percent(p - percent);
+            self.geom.cols.set_percent(p - percent);
             self.set_should_render(true);
         }
     }
     fn increase_width(&mut self, percent: f64) {
         if let Some(p) = self.geom.cols.as_percent() {
-            self.geom.cols = Dimension::percent(p + percent);
+            self.geom.cols.set_percent(p + percent);
             self.set_should_render(true);
         }
     }
diff --git a/zellij-server/src/panes/tiled_panes/mod.rs b/zellij-server/src/panes/tiled_panes/mod.rs
index ee752ea15..726627f4b 100644
--- a/zellij-server/src/panes/tiled_panes/mod.rs
+++ b/zellij-server/src/panes/tiled_panes/mod.rs
@@ -577,9 +577,38 @@ impl TiledPanes {
                 *self.viewport.borrow(),
             );
 
-            pane_grid
+            match pane_grid
                 .change_pane_size(&active_pane_id, strategy, (RESIZE_PERCENT, RESIZE_PERCENT))
-                .with_context(err_context)?;
+                .with_context(err_context)
+            {
+                Ok(_) => {},
+                Err(err) => match err.downcast_ref::<ZellijError>() {
+                    Some(ZellijError::PaneSizeUnchanged) => {
+                        // try once more with double the resize percent, but let's keep it at that
+                        match pane_grid
+                            .change_pane_size(
+                                &active_pane_id,
+                                strategy,
+                                (RESIZE_PERCENT * 2.0, RESIZE_PERCENT * 2.0),
+                            )
+                            .with_context(err_context)
+                        {
+                            Ok(_) => {},
+                            Err(err) => match err.downcast_ref::<ZellijError>() {
+                                Some(ZellijError::PaneSizeUnchanged) => {
+                                    Err::<(), _>(err).non_fatal()
+                                },
+                                _ => {
+                                    return Err(err);
+                                },
+                            },
+                        }
+                    },
+                    _ => {
+                        return Err(err);
+                    },
+                },
+            }
 
             for pane in self.panes.values_mut() {
                 resize_pty!(pane, self.os_api, self.senders).unwrap();
diff --git a/zellij-server/src/panes/tiled_panes/pane_resizer.rs b/zellij-server/src/panes/tiled_panes/pane_resizer.rs
index 37eb6c4c6..c01e42e4b 100644
--- a/zellij-server/src/panes/tiled_panes/pane_resizer.rs
+++ b/zellij-server/src/panes/tiled_panes/pane_resizer.rs
@@ -53,7 +53,7 @@ impl<'a> PaneResizer<'a> {
         let spans = self
             .discretize_spans(grid, space)
             .map_err(|err| anyhow!("{}", err))?;
-        self.apply_spans(spans);
+        self.apply_spans(spans)?;
         Ok(())
     }
 
@@ -127,10 +127,13 @@ impl<'a> PaneResizer<'a> {
         Ok(grid.into_iter().flatten().collect())
     }
 
-    fn apply_spans(&mut self, spans: Vec<Span>) {
+    fn apply_spans(&mut self, spans: Vec<Span>) -> Result<()> {
+        let err_context = || format!("Failed to apply spans");
         let mut panes = self.panes.borrow_mut();
+        let mut geoms_changed = false;
         for span in spans {
             let pane = panes.get_mut(&span.pid).unwrap();
+            let current_geom = pane.position_and_size();
             let new_geom = match span.direction {
                 SplitDirection::Horizontal => PaneGeom {
                     x: span.pos,
@@ -143,12 +146,26 @@ impl<'a> PaneResizer<'a> {
                     ..pane.current_geom()
                 },
             };
+            if new_geom.rows.as_usize() != current_geom.rows.as_usize()
+                || new_geom.cols.as_usize() != current_geom.cols.as_usize()
+            {
+                geoms_changed = true;
+            }
             if pane.geom_override().is_some() {
                 pane.set_geom_override(new_geom);
             } else {
                 pane.set_geom(new_geom);
             }
         }
+        if geoms_changed {
+            Ok(())
+        } else {
+            // probably a rounding issue - this might be considered an error depending on who
+            // called us - if it's an explicit resize operation, it's clearly an error (the user
+            // wanted to resize and doesn't care about percentage rounding), if it's resizing the
+            // terminal window as a whole, it might not be
+            Err(ZellijError::PaneSizeUnchanged).with_context(err_context)
+        }
     }
 
     // FIXME: Functions like this should have unit tests!
diff --git a/zellij-server/src/panes/tiled_panes/tiled_pane_grid.rs b/zellij-server/src/panes/tiled_panes/tiled_pane_grid.rs
index fdb2f74ad..e34164f9e 100644
--- a/zellij-server/src/panes/tiled_panes/tiled_pane_grid.rs
+++ b/zellij-server/src/panes/tiled_panes/tiled_pane_grid.rs
@@ -88,6 +88,56 @@ impl<'a> TiledPaneGrid<'a> {
         }
         .is_fixed())
     }
+    fn neighbor_pane_ids(&self, pane_id: &PaneId, direction: Direction) -> Result<Vec<PaneId>> {
+        let err_context = || format!("Failed to get neighboring panes");
+        // Shorthand
+        use Direction as Dir;
+        let mut neighbor_terminals = self
+            .pane_ids_directly_next_to(pane_id, &direction)
+            .with_context(err_context)?;
+
+        let neighbor_terminal_borders: HashSet<_> = if direction.is_horizontal() {
+            neighbor_terminals
+                .iter()
+                .map(|t| self.panes.borrow().get(t).unwrap().y())
+                .collect()
+        } else {
+            neighbor_terminals
+                .iter()
+                .map(|t| self.panes.borrow().get(t).unwrap().x())
+                .collect()
+        };
+
+        // Only return those neighbors that are aligned and between pane borders
+        let (some_direction, other_direction) = match direction {
+            Dir::Left | Dir::Right => (Dir::Up, Dir::Down),
+            Dir::Down | Dir::Up => (Dir::Left, Dir::Right),
+        };
+        let (some_borders, _some_terminals) = self
+            .contiguous_panes_with_alignment(
+                pane_id,
+                &neighbor_terminal_borders,
+                &direction,
+                &some_direction,
+            )
+            .with_context(err_context)?;
+        let (other_borders, _other_terminals) = self
+            .contiguous_panes_with_alignment(
+                pane_id,
+                &neighbor_terminal_borders,
+                &direction,
+                &other_direction,
+            )
+            .with_context(err_context)?;
+        neighbor_terminals.retain(|t| {
+            if direction.is_horizontal() {
+                self.pane_is_between_horizontal_borders(t, some_borders, other_borders)
+            } else {
+                self.pane_is_between_vertical_borders(t, some_borders, other_borders)
+            }
+        });
+        Ok(neighbor_terminals)
+    }
 
     // Check if panes in the desired direction can be resized. Returns the maximum resize that's
     // possible (at most `change_by`).
@@ -100,12 +150,39 @@ impl<'a> TiledPaneGrid<'a> {
         let err_context = || format!("failed to determine if pane {pane_id:?} can {strategy}");
 
         if let Some(direction) = strategy.direction {
-            let mut pane_ids = self
-                .pane_ids_directly_next_to(pane_id, &direction)
+            if !self
+                .pane_is_flexible(direction.into(), pane_id)
+                .unwrap_or(false)
+            {
+                let pane_ids = match pane_id {
+                    PaneId::Terminal(id) => vec![(*id, true)],
+                    PaneId::Plugin(id) => vec![(*id, false)],
+                };
+                return Err(ZellijError::CantResizeFixedPanes { pane_ids })
+                    .with_context(err_context);
+            }
+            let pane_ids = self
+                .neighbor_pane_ids(pane_id, direction)
                 .with_context(err_context)?;
-            pane_ids.retain(|id| self.pane_is_flexible(direction.into(), id).unwrap_or(false));
 
+            let fixed_panes: Vec<PaneId> = pane_ids
+                .iter()
+                .filter(|p| !self.pane_is_flexible(direction.into(), p).unwrap_or(false))
+                .copied()
+                .collect();
+            if !fixed_panes.is_empty() {
+                let mut pane_ids = vec![];
+                for fixed_pane in fixed_panes {
+                    match fixed_pane {
+                        PaneId::Terminal(id) => pane_ids.push((id, true)),
+                        PaneId::Plugin(id) => pane_ids.push((id, false)),
+                    };
+                }
+                return Err(ZellijError::CantResizeFixedPanes { pane_ids })
+                    .with_context(err_context);
+            }
             if pane_ids.is_empty() {
+                // TODO: proper error
                 return Ok(false);
             }
 
@@ -160,37 +237,56 @@ impl<'a> TiledPaneGrid<'a> {
         change_by: (f64, f64),
     ) -> Result<bool> {
         let err_context = || format!("failed to {strategy} by {change_by:?} for pane {pane_id:?}");
-
         // Shorthand
         use Direction as Dir;
+        let mut fixed_panes_blocking_resize = vec![];
+
         // Default behavior is to only increase pane size, unless the direction being resized to is
         // a boundary. In this case, decrease size from the other side (invert strategy)!
-        let strategy = if strategy.resize_increase()  // Only invert when increasing
+        let can_invert_strategy_if_needed = strategy.resize_increase()  // Only invert when increasing
             && strategy.invert_on_boundaries          // Only invert if configured to do so
-            && strategy.direction.is_some()           // Only invert if there's a direction
-            && strategy
-                .direction
-                .and_then(|direction| {
-                    // Only invert if there are no neighbor IDs in the given direction
-                    let mut neighbors = self.pane_ids_directly_next_to(pane_id, &direction)
-                        .unwrap_or_default();
-                    neighbors.retain(|pane_id| self.pane_is_flexible(direction.into(), pane_id).unwrap_or(false));
-                    neighbors.is_empty().then_some(true)
+            && strategy.direction.is_some(); // Only invert if there's a direction
+
+        let can_change_pane_size_in_main_direction = self
+            .can_change_pane_size(pane_id, &strategy, change_by)
+            .unwrap_or_else(|err| {
+                if let Some(ZellijError::CantResizeFixedPanes { pane_ids }) =
+                    err.downcast_ref::<ZellijError>()
+                {
+                    fixed_panes_blocking_resize.append(&mut pane_ids.clone());
+                }
+                false
+            });
+        let can_change_pane_size_in_inverted_direction = if can_invert_strategy_if_needed {
+            let strategy = strategy.invert();
+            self.can_change_pane_size(pane_id, &strategy, change_by)
+                .unwrap_or_else(|err| {
+                    if let Some(ZellijError::CantResizeFixedPanes { pane_ids }) =
+                        err.downcast_ref::<ZellijError>()
+                    {
+                        fixed_panes_blocking_resize.append(&mut pane_ids.clone());
+                    }
+                    false
                 })
-                .unwrap_or(false)
-        {
-            strategy.invert()
         } else {
-            *strategy
+            false
         };
-
-        if !self
-            .can_change_pane_size(pane_id, &strategy, change_by)
-            .with_context(err_context)?
+        if strategy.direction.is_some()
+            && !can_change_pane_size_in_main_direction
+            && !can_change_pane_size_in_inverted_direction
         {
-            // Resize not possible, quit
-            return Ok(false);
+            // we can't resize in any direction, not playing the blame game, but I'm looking at
+            // you: fixed_panes_blocking_resize
+            return Err(ZellijError::CantResizeFixedPanes {
+                pane_ids: fixed_panes_blocking_resize,
+            })
+            .with_context(err_context);
         }
+        let strategy = if can_change_pane_size_in_main_direction {
+            *strategy
+        } else {
+            strategy.invert()
+        };
 
         if let Some(direction) = strategy.direction {
             let mut neighbor_terminals = self
@@ -407,7 +503,7 @@ impl<'a> TiledPaneGrid<'a> {
                     };
                     if self
                         .change_pane_size(pane_id, &new_strategy, change_by)
-                        .with_context(err_context)?
+                        .unwrap_or(false)
                     {
                         return Ok(true);
                     }
diff --git a/zellij-server/src/screen.rs b/zellij-server/src/screen.rs
index 9ed803bbd..a862cb405 100644
--- a/zellij-server/src/screen.rs
+++ b/zellij-server/src/screen.rs
@@ -224,8 +224,8 @@ pub enum ScreenInstruction {
     SearchToggleCaseSensitivity(ClientId),
     SearchToggleWholeWord(ClientId),
     SearchToggleWrap(ClientId),
-    AddRedPaneFrameColorOverride(PaneId, Option<String>), // Option<String> => optional error text
-    ClearPaneFrameColorOverride(PaneId),
+    AddRedPaneFrameColorOverride(Vec<PaneId>, Option<String>), // Option<String> => optional error text
+    ClearPaneFrameColorOverride(Vec<PaneId>),
 }
 
 impl From<&ScreenInstruction> for ScreenContext {
@@ -2120,22 +2120,26 @@ pub(crate) fn screen_thread_main(
                 screen.render()?;
                 screen.unblock_input()?;
             },
-            ScreenInstruction::AddRedPaneFrameColorOverride(pane_id, error_text) => {
+            ScreenInstruction::AddRedPaneFrameColorOverride(pane_ids, error_text) => {
                 let all_tabs = screen.get_tabs_mut();
-                for tab in all_tabs.values_mut() {
-                    if tab.has_pane_with_pid(&pane_id) {
-                        tab.add_red_pane_frame_color_override(pane_id, error_text);
-                        break;
+                for pane_id in pane_ids {
+                    for tab in all_tabs.values_mut() {
+                        if tab.has_pane_with_pid(&pane_id) {
+                            tab.add_red_pane_frame_color_override(pane_id, error_text.clone());
+                            break;
+                        }
                     }
                 }
                 screen.render()?;
             },
-            ScreenInstruction::ClearPaneFrameColorOverride(pane_id) => {
+            ScreenInstruction::ClearPaneFrameColorOverride(pane_ids) => {
                 let all_tabs = screen.get_tabs_mut();
-                for tab in all_tabs.values_mut() {
-                    if tab.has_pane_with_pid(&pane_id) {
-                        tab.clear_pane_frame_color_override(pane_id);
-                        break;
+                for pane_id in pane_ids {
+                    for tab in all_tabs.values_mut() {
+                        if tab.has_pane_with_pid(&pane_id) {
+                            tab.clear_pane_frame_color_override(pane_id);
+                            break;
+                        }
                     }
                 }
                 screen.render()?;
diff --git a/zellij-server/src/tab/mod.rs b/zellij-server/src/tab/mod.rs
index a841b39ae..c2b26ecf8 100644
--- a/zellij-server/src/tab/mod.rs
+++ b/zellij-server/src/tab/mod.rs
@@ -1048,7 +1048,7 @@ impl Tab {
             if let Some(active_pane_id) = self.tiled_panes.get_active_pane_id(client_id) {
                 self.senders
                     .send_to_background_jobs(BackgroundJob::DisplayPaneError(
-                        active_pane_id,
+                        vec![active_pane_id],
                         "TOO SMALL!".into(),
                     ))
                     .with_context(err_context)?;
@@ -1102,7 +1102,7 @@ impl Tab {
             if let Some(active_pane_id) = self.tiled_panes.get_active_pane_id(client_id) {
                 self.senders
                     .send_to_background_jobs(BackgroundJob::DisplayPaneError(
-                        active_pane_id,
+                        vec![active_pane_id],
                         "TOO SMALL!".into(),
                     ))
                     .with_context(err_context)?;
@@ -1630,6 +1630,7 @@ impl Tab {
         self.should_clear_display_before_rendering = true;
     }
     pub fn resize(&mut self, client_id: ClientId, strategy: ResizeStrategy) -> Result<()> {
+        let err_context = || format!("unable to resize pane");
         if self.floating_panes.panes_are_visible() {
             let successfully_resized = self
                 .floating_panes
@@ -1639,9 +1640,28 @@ impl Tab {
                 self.set_force_render(); // we force render here to make sure the panes under the floating pane render and don't leave "garbage" in case of a decrease
             }
         } else {
-            self.tiled_panes
-                .resize_active_pane(client_id, &strategy)
-                .unwrap();
+            match self.tiled_panes.resize_active_pane(client_id, &strategy) {
+                Ok(_) => {},
+                Err(err) => match err.downcast_ref::<ZellijError>() {
+                    Some(ZellijError::CantResizeFixedPanes { pane_ids }) => {
+                        let mut pane_ids_to_error = vec![];
+                        for (id, is_terminal) in pane_ids {
+                            if *is_terminal {
+                                pane_ids_to_error.push(PaneId::Terminal(*id));
+                            } else {
+                                pane_ids_to_error.push(PaneId::Plugin(*id));
+                            };
+                        }
+                        self.senders
+                            .send_to_background_jobs(BackgroundJob::DisplayPaneError(
+                                pane_ids_to_error,
+                                "FIXED!".into(),
+                            ))
+                            .with_context(err_context)?;
+                    },
+                    _ => Err::<(), _>(err).fatal(),
+                },
+            }
         }
         Ok(())
     }
diff --git a/zellij-server/src/tab/unit/tab_tests.rs b/zellij-server/src/tab/unit/tab_tests.rs
index 192c55e3e..86848045a 100644
--- a/zellij-server/src/tab/unit/tab_tests.rs
+++ b/zellij-server/src/tab/unit/tab_tests.rs
@@ -231,15 +231,8 @@ fn create_new_tab_with_layout(size: Size, layout: PaneLayout) -> Tab {
     for i in 0..layout.extract_run_instructions().len() {
         new_terminal_ids.push((i as u32, None));
     }
-    tab.apply_layout(
-        layout,
-        // vec![(1, None), (2, None)],
-        new_terminal_ids,
-        HashMap::new(),
-        index,
-        client_id,
-    )
-    .unwrap();
+    tab.apply_layout(layout, new_terminal_ids, HashMap::new(), index, client_id)
+        .unwrap();
     tab
 }
 
@@ -5933,6 +5926,144 @@ pub fn cannot_resize_down_when_pane_below_is_at_minimum_height() {
 }
 
 #[test]
+pub fn cannot_resize_down_when_pane_has_fixed_rows() {
+    // ┌───────────┐                  ┌───────────┐
+    // │███████████│                  │███████████│
+    // ├───────────┤ ==resize=down==> ├───────────┤
+    // │           │                  │           │
+    // └───────────┘                  └───────────┘
+    // █ == focused pane
+
+    let size = Size {
+        cols: 121,
+        rows: 20,
+    };
+
+    let mut initial_layout = PaneLayout::default();
+    initial_layout.children_split_direction = SplitDirection::Horizontal;
+    let mut fixed_child = PaneLayout::default();
+    fixed_child.split_size = Some(SplitSize::Fixed(10));
+    initial_layout.children = vec![fixed_child, PaneLayout::default()];
+    let mut tab = create_new_tab_with_layout(size, initial_layout);
+    tab_resize_down(&mut tab, 1);
+
+    assert_eq!(
+        tab.tiled_panes
+            .panes
+            .get(&PaneId::Terminal(0))
+            .unwrap()
+            .position_and_size()
+            .rows
+            .as_usize(),
+        10,
+        "pane 1 height stayed the same"
+    );
+    assert_eq!(
+        tab.tiled_panes
+            .panes
+            .get(&PaneId::Terminal(1))
+            .unwrap()
+            .position_and_size()
+            .rows
+            .as_usize(),
+        10,
+        "pane 2 height stayed the same"
+    );
+}
+
+#[test]