term: fixup cursor position during rewrap

refs: https://github.com/wez/wezterm/issues/2162

term/src/screen.rs

@@ -105,7 +105,7 @@ impl Screen {
         let mut rewrapped = VecDeque::new();
         let mut logical_line: Option<Line> = None;
         let mut logical_cursor_x: Option<usize> = None;
-        let mut adjusted_cursor = (cursor_y, cursor_y);
+        let mut adjusted_cursor = (cursor_x, cursor_y);
 
         for (phys_idx, mut line) in self.lines.drain(..).enumerate() {
             line.update_last_change_seqno(seqno);
@@ -140,6 +140,25 @@ impl Screen {
                 let num_lines = x / physical_cols;
                 let last_x = x - (num_lines * physical_cols);
                 adjusted_cursor = (last_x, rewrapped.len() + num_lines);
+
+                // Special case: if the cursor lands in column zero, we'll
+                // lose track of its logical association with the wrapped
+                // line and it won't resize with the line correctly.
+                // Put it back on the prior line. The cursor is now
+                // technically outside of the viewport width.
+                if adjusted_cursor.0 == 0 && adjusted_cursor.1 > 0 {
+                    if physical_cols < self.physical_cols {
+                        // getting smaller: preserve its original position
+                        // on the prior line
+                        adjusted_cursor.0 = cursor_x;
+                    } else {
+                        // getting larger; we were most likely in column 1
+                        // or somewhere close. Jump to the end of the
+                        // prior line.
+                        adjusted_cursor.0 = physical_cols;
+                    }
+                    adjusted_cursor.1 -= 1;
+                }
             }
 
             if line.len() <= physical_cols {

term/src/terminalstate/mod.rs

@@ -914,7 +914,11 @@ impl TerminalState {
                     if self.dec_origin_mode {
                         self.left_and_right_margins.end
                     } else {
-                        self.screen().physical_cols
+                        // We allow 1 extra for the cursor x position
+                        // to account for some resize/rewrap scenarios
+                        // where we don't want to forget that the
+                        // cursor belongs to a wrapped line
+                        self.screen().physical_cols + 1
                     } as i64
                         - 1,
                 )

term/src/test/csi.rs

@@ -298,7 +298,7 @@ fn test_cup() {
     term.cup(-1, -1);
     term.assert_cursor_pos(0, 0, None, None);
     term.cup(500, 500);
-    term.assert_cursor_pos(3, 2, None, None);
+    term.assert_cursor_pos(4, 2, None, None);
 }
 
 #[test]
@@ -313,7 +313,7 @@ fn test_hvp() {
     term.hvp(-1, -1);
     term.assert_cursor_pos(0, 0, None, None);
     term.hvp(500, 500);
-    term.assert_cursor_pos(3, 2, None, None);
+    term.assert_cursor_pos(4, 2, None, None);
 }
 
 #[test]
@@ -354,7 +354,7 @@ fn test_cha() {
     term.assert_cursor_pos(0, 1, None, Some(seqno));
 
     term.print("\x1b[100G");
-    term.assert_cursor_pos(3, 1, None, None);
+    term.assert_cursor_pos(4, 1, None, None);
 }
 
 #[test]

term/src/test/mod.rs

@@ -756,6 +756,162 @@ fn test_dec_double_width() {
     assert!(lines[3].is_single_width());
 }
 
+/// This test skips over an edge case with cursor positioning,
+/// while sizing down, but tries to trip over the same edge
+/// case while sizing back up again
+#[test]
+fn test_resize_2162_by_2_then_up_1() {
+    let num_lines = 4;
+    let num_cols = 20;
+
+    let mut term = TestTerm::new(num_lines, num_cols, 0);
+    term.print("some long long text");
+    assert_visible_contents(
+        &term,
+        file!(),
+        line!(),
+        &["some long long text", "", "", ""],
+    );
+    term.assert_cursor_pos(19, 0, None, Some(0));
+    term.resize(TerminalSize {
+        rows: num_lines,
+        cols: num_cols - 2,
+        pixel_width: 0,
+        pixel_height: 0,
+        dpi: 0,
+    });
+    assert_visible_contents(
+        &term,
+        file!(),
+        line!(),
+        &["some long long tex", "t", "", ""],
+    );
+    eprintln!("check cursor pos 2");
+    term.assert_cursor_pos(1, 1, None, Some(5));
+    term.resize(TerminalSize {
+        rows: num_lines - 1,
+        cols: num_cols,
+        pixel_width: 0,
+        pixel_height: 0,
+        dpi: 0,
+    });
+    assert_visible_contents(&term, file!(), line!(), &["some long long text", "", ""]);
+    eprintln!("check cursor pos 3");
+    term.assert_cursor_pos(19, 0, None, Some(5));
+    term.resize(TerminalSize {
+        rows: num_lines,
+        cols: num_cols,
+        pixel_width: 0,
+        pixel_height: 0,
+        dpi: 0,
+    });
+    assert_visible_contents(
+        &term,
+        file!(),
+        line!(),
+        &["some long long text", "", "", ""],
+    );
+    eprintln!("check cursor pos 3");
+    term.assert_cursor_pos(19, 0, None, Some(5));
+}
+
+/// This test skips over an edge case with cursor positioning,
+/// so it passes even ahead of a fix for issue 2162.
+#[test]
+fn test_resize_2162_by_2() {
+    let num_lines = 4;
+    let num_cols = 20;
+
+    let mut term = TestTerm::new(num_lines, num_cols, 0);
+    term.print("some long long text");
+    assert_visible_contents(
+        &term,
+        file!(),
+        line!(),
+        &["some long long text", "", "", ""],
+    );
+    term.assert_cursor_pos(19, 0, None, Some(0));
+    term.resize(TerminalSize {
+        rows: num_lines,
+        cols: num_cols - 2,
+        pixel_width: 0,
+        pixel_height: 0,
+        dpi: 0,
+    });
+    assert_visible_contents(
+        &term,
+        file!(),
+        line!(),
+        &["some long long tex", "t", "", ""],
+    );
+    eprintln!("check cursor pos 2");
+    term.assert_cursor_pos(1, 1, None, Some(5));
+    term.resize(TerminalSize {
+        rows: num_lines,
+        cols: num_cols,
+        pixel_width: 0,
+        pixel_height: 0,
+        dpi: 0,
+    });
+    assert_visible_contents(
+        &term,
+        file!(),
+        line!(),
+        &["some long long text", "", "", ""],
+    );
+    eprintln!("check cursor pos 3");
+    term.assert_cursor_pos(19, 0, None, Some(5));
+}
+
+/// This case tickles an edge case where the cursor ends
+/// up drifting away from where the line wraps and ends up
+/// in the wrong place
+#[test]
+fn test_resize_2162() {
+    let num_lines = 4;
+    let num_cols = 20;
+
+    let mut term = TestTerm::new(num_lines, num_cols, 0);
+    term.print("some long long text");
+    assert_visible_contents(
+        &term,
+        file!(),
+        line!(),
+        &["some long long text", "", "", ""],
+    );
+    term.assert_cursor_pos(19, 0, None, Some(0));
+    term.resize(TerminalSize {
+        rows: num_lines,
+        cols: num_cols - 1,
+        pixel_width: 0,
+        pixel_height: 0,
+        dpi: 0,
+    });
+    assert_visible_contents(
+        &term,
+        file!(),
+        line!(),
+        &["some long long text", "", "", ""],
+    );
+    eprintln!("check cursor pos 2");
+    term.assert_cursor_pos(19, 0, None, Some(5));
+    term.resize(TerminalSize {
+        rows: num_lines,
+        cols: num_cols,
+        pixel_width: 0,
+        pixel_height: 0,
+        dpi: 0,
+    });
+    assert_visible_contents(
+        &term,
+        file!(),
+        line!(),
+        &["some long long text", "", "", ""],
+    );
+    eprintln!("check cursor pos 3");
+    term.assert_cursor_pos(19, 0, None, Some(5));
+}
+
 /// Test the behavior of wrapped lines when we resize the terminal
 /// wider and then narrower.
 #[test]