ENH: Apply TimeSeries_DateFormatter to bar plots with datetime indices (GH#1918)

Bar plots now use TimeSeries_DateFormatter for datetime and period indices,
matching the behavior of line plots. This provides consistent date formatting
across different plot types instead of converting indices to string labels.

Also update test_memory_leak to use 'D' (daily) frequency instead of
deprecated 'B' (business day) frequency to avoid FutureWarning.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: fangchenli

pandas/plotting/_matplotlib/core.py

@@ -2045,27 +2045,27 @@ def _post_plot_logic(self, ax: Axes, data) -> None:
         s_edge = self.ax_pos[0] - 0.25 + self.lim_offset
         e_edge = self.ax_pos[-1] + 0.25 + self.bar_width + self.lim_offset
 
-        # GH#1918: Use date formatter for time series indices
+        # GH#1918: Apply date formatter for time series indices
         if self._is_ts_plot():
-            ax.set_xlim((s_edge, e_edge))
-
-            if self.xticks is not None:
-                ax.set_xticks(np.array(self.xticks))
-            else:
-                ax.set_xticks(self.tick_pos)
-
-            if self._get_index_name() is not None and self.use_index:
-                ax.set_xlabel(self._get_index_name())
-
+            decorate_axes(ax, data.index.freq)
             freq = data.index.freq
-            decorate_axes(ax, freq)
 
             index = data.index
             if isinstance(index, ABCDatetimeIndex):
                 index = index.to_period(freq=freq)
 
-            if isinstance(index, (ABCPeriodIndex,)):
+            if isinstance(index, ABCPeriodIndex):
                 format_dateaxis(ax, freq, index)
+
+            ax.set_xlim((s_edge, e_edge))
+            if self.xticks is not None:
+                ax.set_xticks(np.array(self.xticks))
+            else:
+                ax.set_xticks(self.tick_pos)
+
+            index_name = self._get_index_name()
+            if index_name is not None and self.use_index:
+                ax.set_xlabel(index_name)
         else:
             if self.use_index:
                 str_index = [pprint_thing(key) for key in data.index]

pandas/tests/plotting/frame/test_frame.py

@@ -2155,13 +2155,13 @@ def test_memory_leak(self, kind):
             df = DataFrame(
                 np.random.default_rng(2).standard_normal((10, 4)),
                 columns=Index(list("ABCD"), dtype=object),
-                index=date_range("2000-01-01", periods=10, freq="B"),
+                index=date_range("2000-01-01", periods=10, freq="D"),
             ).abs()
         else:
             df = DataFrame(
                 np.random.default_rng(2).standard_normal((10, 4)),
                 columns=Index(list("ABCD"), dtype=object),
-                index=date_range("2000-01-01", periods=10, freq="B"),
+                index=date_range("2000-01-01", periods=10, freq="D"),
             )
 
         # Use a weakref so we can see if the object gets collected without