terminal: handle case grow allocates but cursor is multiple pages back

src/terminal/Screen.zig

@@ -757,45 +757,8 @@ pub fn cursorScrollAbove(self: *Screen) !void {
     assert(self.cursor.y < self.pages.rows - 1);
 
     const old_pin = self.cursor.page_pin.*;
-    if (try self.pages.grow()) |new_page_node| {
+    if (try self.pages.grow()) |_| {
-        // We allocated a new page and went to it. In this case, our new
+        try self.cursorScrollAboveRotate();
-        // empty line is at the top of this page.
-
-        // Prev is never null because pagelist asserts that we always have
-        // memory for at least two pages. This is an assertion.
-        assert(new_page_node.prev.? == old_pin.page);
-        const prev_page = &old_pin.page.data;
-        const new_page = &new_page_node.data;
-
-        const prev_rows = prev_page.rows.ptr(prev_page.memory.ptr);
-        const new_rows = new_page.rows.ptr(new_page.memory.ptr);
-        const prev_last_row = &prev_rows[prev_page.size.rows - 1];
-
-        // First, copy the last row of the previous page to the top
-        // of our current page.
-        try new_page.cloneRowFrom(
-            prev_page,
-            &new_rows[0],
-            prev_last_row,
-        );
-
-        // Update our cursor metadata now. We call methods below that assert
-        // integrity in debug modes so we want to put ourselves in a
-        // consistent state first.
-        self.cursor.page_pin.* = self.cursor.page_pin.down(1).?;
-        self.cursorChangePin(self.cursor.page_pin.*);
-        const page_rac = self.cursor.page_pin.rowAndCell();
-        self.cursor.page_row = page_rac.row;
-        self.cursor.page_cell = page_rac.cell;
-
-        // Third, clear the last row of the previous page.
-        self.clearCells(
-            prev_page,
-            prev_last_row,
-            prev_page.getCells(prev_last_row),
-        );
-        var dirty = prev_page.dirtyBitSet();
-        dirty.set(prev_page.size.rows - 1);
     } else {
         // In this case, it means grow() didn't allocate a new page.
 
@@ -847,7 +810,22 @@ pub fn cursorScrollAbove(self: *Screen) !void {
             //    1 |5E00000000| | 4
             //      +----------+ :
             //     +-------------+
+            try self.cursorScrollAboveRotate();
+        }
+    }
 
+    if (self.cursor.style_id != style.default_id) {
+        // The newly created line needs to be styled according to
+        // the bg color if it is set.
+        if (self.cursor.style.bgCell()) |blank_cell| {
+            const cell_current: [*]pagepkg.Cell = @ptrCast(self.cursor.page_cell);
+            const cells = cell_current - self.cursor.x;
+            @memset(cells[0..self.pages.cols], blank_cell);
+        }
+    }
+}
+
+fn cursorScrollAboveRotate(self: *Screen) !void {
     self.cursor.page_pin.* = self.cursor.page_pin.down(1).?;
 
     // Go through each of the pages following our pin, shift all rows
@@ -899,18 +877,6 @@ pub fn cursorScrollAbove(self: *Screen) !void {
     const page_rac = self.cursor.page_pin.rowAndCell();
     self.cursor.page_row = page_rac.row;
     self.cursor.page_cell = page_rac.cell;
-        }
-    }
-
-    if (self.cursor.style_id != style.default_id) {
-        // The newly created line needs to be styled according to
-        // the bg color if it is set.
-        if (self.cursor.style.bgCell()) |blank_cell| {
-            const cell_current: [*]pagepkg.Cell = @ptrCast(self.cursor.page_cell);
-            const cells = cell_current - self.cursor.x;
-            @memset(cells[0..self.pages.cols], blank_cell);
-        }
-    }
 }
 
 /// Move the cursor down if we're not at the bottom of the screen. Otherwise
@@ -4196,7 +4162,7 @@ test "Screen: scroll above creates new page" {
     // Only y=1 is dirty because they are the ones that CHANGED contents
     try testing.expect(!s.pages.isDirty(.{ .active = .{ .x = 0, .y = 0 } }));
     try testing.expect(s.pages.isDirty(.{ .active = .{ .x = 0, .y = 1 } }));
-    try testing.expect(!s.pages.isDirty(.{ .active = .{ .x = 0, .y = 2 } }));
+    try testing.expect(s.pages.isDirty(.{ .active = .{ .x = 0, .y = 2 } }));
 }
 
 test "Screen: scroll above no scrollback bottom of page" {