fix: Prevent Tabulator page reset when clicking Last on a shrunk container (#8738)

Author: hoxbro

panel/models/tabulator.ts

@@ -827,10 +827,20 @@ export class DataTabulatorView extends HTMLBoxView {
     if (!this.model.pagination || (this.model.page_size !== null && !this._automatic_page_size) || this._initializing || !this.tabulator) {
       return
     }
-    this._automatic_page_size = true
-    const responsive = this.model.sizing_mode && (this.model.sizing_mode.includes("height") || this.model.sizing_mode.includes("both"))
     const holder = this.shadow_el.querySelector(".tabulator-tableholder")
     const table = this.shadow_el.querySelector(".tabulator-table")
+    if (
+      this.model.page_size != null &&
+      this.model.page >= this.model.max_page &&
+      table != null &&
+      table.children.length < this.model.page_size
+    ) {
+      // Partial page: holder has shrunk to fit it, so its height doesn't
+      // reflect full-page capacity. See https://github.com/holoviz/panel/issues/8737
+      return
+    }
+    this._automatic_page_size = true
+    const responsive = this.model.sizing_mode && (this.model.sizing_mode.includes("height") || this.model.sizing_mode.includes("both"))
     if (table != null && holder != null) {
       const table_height = holder.clientHeight
       let height = 0

panel/tests/ui/widgets/test_tabulator.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import datetime as dt
+import typing as t
 
 from contextlib import contextmanager
 
@@ -3990,6 +3991,29 @@ def test_tabulator_local_pagination_page_size_preserved_on_value_none(page, df_m
     expect(page.locator('.tabulator-row')).to_have_count(4)
 
 
+def test_tabulator_local_pagination_auto_page_size_last_button(page):
+    # https://github.com/holoviz/panel/issues/8737
+    df = pd.DataFrame({'value': range(6401)})
+    widget = Tabulator(df, max_height=500, show_index=True)
+
+    serve_component(page, widget)
+
+    expect(page.locator('.tabulator-table')).to_have_count(1)
+
+    wait_until(lambda: bool(widget.page_size), page)
+    initial_page_size = t.cast("int", widget.page_size)
+    counts = count_per_page(len(df), initial_page_size)
+    last_page = len(counts)
+
+    page.locator('text="Last"').click()
+    page.wait_for_timeout(1000)
+
+    assert widget.page_size == initial_page_size
+    assert widget.page == last_page
+    expect(page.locator('.tabulator-row')).to_have_count(counts[-1])
+    expect(page.locator('.tabulator-row').last).to_contain_text(str(df['value'].iloc[-1]))
+
+
 @pytest.mark.parametrize('pagination', ['local', 'remote', None])
 def test_selection_indices_on_paginated_and_filtered_data(page, df_strings, pagination):
     tbl = Tabulator(