Fix prompt line overflowing when resizing panes (#725)

* fix(wrap): do not wrap empty lines and properly place cursor when resizing

* fix(wrap): truncate last blank line wraps

* fix(wrap): truncate lines right after unwrapping them

* refactor(grid): remove unused method

* docs(changelog): document change

4 files changed, 24 insertions, 4 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1eec2618..17b4b9ae 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -37,6 +37,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 * Improve handling of empty valid `yaml` files (https://github.com/zellij-org/zellij/pull/716)
 * Add options subcommand to attach (https://github.com/zellij-org/zellij/pull/718)
 * Fix: do not pad empty pane frame title (https://github.com/zellij-org/zellij/pull/724)
+* Fix: Do not overflow empty lines when resizing panes (https://github.com/zellij-org/zellij/pull/725)
 
 
 ## [0.16.0] - 2021-08-31
diff --git a/zellij-server/src/panes/grid.rs b/zellij-server/src/panes/grid.rs
index 5e3479ee..2d2354c6 100644
--- a/zellij-server/src/panes/grid.rs
+++ b/zellij-server/src/panes/grid.rs
@@ -527,8 +527,8 @@ impl Grid {
         for (i, line) in self.viewport.iter().enumerate() {
             if line.is_canonical {
                 canonical_lines_traversed += 1;
+                y_coordinates = i;
                 if canonical_lines_traversed == canonical_line_index + 1 {
-                    y_coordinates = i;
                     break;
                 }
             }
@@ -628,6 +628,23 @@ impl Grid {
                     }
                 }
             }
+
+            // trim lines after the last empty space that has no following character, because
+            // terminals don't trim empty lines
+            for line in viewport_canonical_lines.iter_mut() {
+                let mut trim_at = None;
+                for (index, character) in line.columns.iter().enumerate() {
+                    if character.character != EMPTY_TERMINAL_CHARACTER.character {
+                        trim_at = None;
+                    } else if trim_at.is_none() {
+                        trim_at = Some(index);
+                    }
+                }
+                if let Some(trim_at) = trim_at {
+                    line.columns.truncate(trim_at);
+                }
+            }
+
             let mut new_viewport_rows = vec![];
             for mut canonical_line in viewport_canonical_lines {
                 let mut canonical_line_parts: Vec<Row> = vec![];
@@ -658,9 +675,11 @@ impl Grid {
                 }
                 new_viewport_rows.append(&mut canonical_line_parts);
             }
+
             self.viewport = new_viewport_rows;
 
             let mut new_cursor_y = self.canonical_line_y_coordinates(cursor_canonical_line_index);
+
             let new_cursor_x = (cursor_index_in_canonical_line / new_columns)
                 + (cursor_index_in_canonical_line % new_columns);
             let current_viewport_row_count = self.viewport.len();
diff --git a/zellij-server/src/panes/unit/snapshots/zellij_server__panes__grid__grid_tests__clear_scroll_region.snap b/zellij-server/src/panes/unit/snapshots/zellij_server__panes__grid__grid_tests__clear_scroll_region.snap
index b53826df..e5c302a0 100644
--- a/zellij-server/src/panes/unit/snapshots/zellij_server__panes__grid__grid_tests__clear_scroll_region.snap
+++ b/zellij-server/src/panes/unit/snapshots/zellij_server__panes__grid__grid_tests__clear_scroll_region.snap
@@ -3,7 +3,7 @@ source: zellij-server/src/panes/./unit/grid_tests.rs
 expression: "format!(\"{:?}\", grid)"
 
 ---
-00 (C): Welcome to fish, the friendly interactive shell                                                                     
+00 (C): Welcome to fish, the friendly interactive shell
 01 (C): ⋊> ~/c/mosaic on main ⨯ vim some-file                                                                       15:07:22
 02 (C): ⋊> ~/c/mosaic on main ⨯                                                                                     15:07:29
 
diff --git a/zellij-server/src/panes/unit/snapshots/zellij_server__panes__grid__grid_tests__emacs_longbuf.snap b/zellij-server/src/panes/unit/snapshots/zellij_server__panes__grid__grid_tests__emacs_longbuf.snap
index 5c08c323..71cc9bc8 100644
--- a/zellij-server/src/panes/unit/snapshots/zellij_server__panes__grid__grid_tests__emacs_longbuf.snap
+++ b/zellij-server/src/panes/unit/snapshots/zellij_server__panes__grid__grid_tests__emacs_longbuf.snap
@@ -3,8 +3,8 @@ source: zellij-server/src/panes/./unit/grid_tests.rs
 expression: "format!(\"{:?}\", grid)"
 
 ---
-00 (C): ➜  mosaic git:(mosaic#130) emacs                                                                                                                                                                                                                                                            
-01 (C): ➜  mosaic git:(mosaic#130) emacs -nw                                                                                                                                                                                                                                                        
+00 (C): ➜  mosaic git:(mosaic#130) emacs
+01 (C): ➜  mosaic git:(mosaic#130) emacs -nw
 02 (C): ➜  mosaic git:(mosaic#130) exit                                                                                                                                                                                                                                                             
 03 (C):