DataTable - allow the cursor to enter fixed columns

CHANGELOG.md

@@ -66,6 +66,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - `DOMNode.tree` now displays simple DOM structure only https://github.com/Textualize/textual/pull/1778
 - `App.install_screen` now returns None rather than AwaitMount https://github.com/Textualize/textual/pull/1778
 - `DOMNode.children` is now a simple sequence, the NodesList is exposed as `DOMNode._nodes` https://github.com/Textualize/textual/pull/1778
+- `DataTable` cursor can now enter fixed columns https://github.com/Textualize/textual/pull/1799
 
 ### Fixed
 

src/textual/widgets/_data_table.py

@@ -877,7 +877,7 @@ def _clamp_cursor_coordinate(self, coordinate: Coordinate) -> Coordinate:
         """Clamp a coordinate such that it falls within the boundaries of the table."""
         row, column = coordinate
         row = clamp(row, 0, self.row_count - 1)
-        column = clamp(column, self.fixed_columns, len(self.columns) - 1)
+        column = clamp(column, 0, len(self.columns) - 1)
         return Coordinate(row, column)
 
     def watch_cursor_type(self, old: str, new: str) -> None:
@@ -1590,11 +1590,7 @@ def _get_fixed_offset(self) -> Spacing:
         that is occupied by fixed rows and columns respectively. Fixed rows and columns
         are rows and columns that do not participate in scrolling."""
         top = self.header_height if self.show_header else 0
-        top += sum(
-            self.rows[self._row_locations.get_key(row_index)].height
-            for row_index in range(self.fixed_rows)
-            if row_index in self.rows
-        )
+        top += sum(row.height for row in self.ordered_rows[: self.fixed_rows])
         left = sum(
             column.render_width for column in self.ordered_columns[: self.fixed_columns]
         )