Feature request: fixed_bottom_rows for DataTable

[Kohei-Wada]

Feature Request

Add a fixed_bottom_rows reactive attribute to DataTable, analogous to the existing fixed_rows (which pins rows to the top).

Motivation

fixed_rows is great for keeping header-like rows visible while scrolling, but there's no equivalent for pinning rows to the bottom of the table. This is a common need for summary/totals/workload rows that should always remain visible regardless of vertical scroll position.

Use case

I'm building a Gantt chart with a workload summary row at the bottom. Currently this row scrolls off-screen when there are many tasks. I'd like it to stay pinned at the bottom, just as date headers stay pinned at the top via fixed_rows.

Workarounds considered

• Splitting into two DataTables (main + footer): column widths can be matched, but horizontal scroll becomes independent between the two tables, so the timeline columns get out of sync.
• Syncing scroll_x between two tables via watch: introduces visual lag and feels hacky.
• Placing the summary row at the top with fixed_rows: semantically wrong for a totals/summary row.

None of these are satisfactory.

Proposed API

table = DataTable()
table.fixed_rows = 3         # existing: pin first 3 rows to top
table.fixed_bottom_rows = 1  # new: pin last 1 row to bottom

The fixed_bottom_rows attribute would:

• Keep the last N rows visible at the bottom of the scrollable area
• Apply the existing datatable--fixed component style (or a new datatable--fixed-bottom style)
• Work independently of fixed_rows

Implementation notes

The rendering logic in _get_fixed_offset and render_line would need to account for bottom-fixed rows:

• Calculate the height occupied by bottom-fixed rows
• Exclude them from the scrollable region
• Render them at the bottom of the visible area

This mirrors how fixed_rows works for the top, applied symmetrically to the bottom.

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