ensure that diffing a screen against itself always returns nothing

5 files changed, 13 insertions, 0 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a375680..e2c7a96 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,11 @@
 
 * `Screen::errors` to track the number of parsing errors seen so far
 
+### Fixed
+
+* No longer generate spurious diffs in some cases where the cursor is past the
+  end of a row
+
 ## [0.14.0] - 2021-12-06
 
 ### Changed
diff --git a/src/grid.rs b/src/grid.rs
index 9681638..a36491b 100644
--- a/src/grid.rs
+++ b/src/grid.rs
@@ -250,6 +250,7 @@ impl Grid {
     ) -> crate::attrs::Attrs {
         let mut prev_pos = prev.pos;
         let mut wrapping = false;
+        let mut prev_wrapping = false;
         for (i, (row, prev_row)) in
             self.visible_rows().zip(prev.visible_rows()).enumerate()
         {
@@ -261,12 +262,14 @@ impl Grid {
                 self.size.cols,
                 i,
                 wrapping,
+                prev_wrapping,
                 prev_pos,
                 prev_attrs,
             );
             prev_pos = new_pos;
             prev_attrs = new_attrs;
             wrapping = row.wrapped();
+            prev_wrapping = prev_row.wrapped();
         }
 
         self.write_cursor_position_formatted(
diff --git a/src/row.rs b/src/row.rs
index f1c3086..d60d48b 100644
--- a/src/row.rs
+++ b/src/row.rs
@@ -286,6 +286,7 @@ impl Row {
         width: u16,
         row: u16,
         wrapping: bool,
+        prev_wrapping: bool,
         mut prev_pos: crate::grid::Pos,
         mut prev_attrs: crate::attrs::Attrs,
     ) -> (crate::grid::Pos, crate::attrs::Attrs) {
@@ -294,6 +295,7 @@ impl Row {
         let first_cell = self.get(start).unwrap();
         let prev_first_cell = prev.get(start).unwrap();
         if wrapping
+            && !prev_wrapping
             && first_cell == prev_first_cell
             && prev_pos.row + 1 == row
             && prev_pos.col
diff --git a/src/screen.rs b/src/screen.rs
index cec1888..c885242 100644
--- a/src/screen.rs
+++ b/src/screen.rs
@@ -368,6 +368,7 @@ impl Screen {
                     width,
                     i,
                     false,
+                    false,
                     crate::grid::Pos { row: i, col: start },
                     crate::attrs::Attrs::default(),
                 );
diff --git a/tests/helpers/mod.rs b/tests/helpers/mod.rs
index a7eaadc..53e4f42 100644
--- a/tests/helpers/mod.rs
+++ b/tests/helpers/mod.rs
@@ -84,6 +84,8 @@ pub fn compare_screens(
         Bytes(&expected.contents_diff(vt100::Parser::default().screen()))
     );
 
+    is!(Bytes(&got.contents_diff(got)), Bytes(b""));
+
     for row in 0..rows {
         for col in 0..cols {
             let expected_cell = expected.cell(row, col);