fix: base logic and version doc

Author: sharonwoo

doc/source/whatsnew/v2.2.0.rst

@@ -848,6 +848,7 @@ Plotting
 ^^^^^^^^
 - Bug in :meth:`DataFrame.plot.box` with ``vert=False`` and a Matplotlib ``Axes`` created with ``sharey=True`` (:issue:`54941`)
 - Bug in :meth:`DataFrame.plot.scatter` discarding string columns (:issue:`56142`)
+- Bug in :meth:`DataFrame.plot` where bar and line plots are not aligned on the x-axis (:issue:`56611`)
 - Bug in :meth:`Series.plot` when reusing an ``ax`` object failing to raise when a ``how`` keyword is passed (:issue:`55953`)
 
 Groupby/resample/rolling

pandas/plotting/_matplotlib/core.py

@@ -1805,6 +1805,19 @@ def _kind(self) -> Literal["bar", "barh"]:
     def orientation(self) -> PlottingOrientation:
         return "vertical"
 
+    # GH56611 checks similar to LinePlot's _is_ts_plot and _use_dynamic_x
+    @final
+    def _is_usable_series(self) -> bool:
+        return self._is_series and not (
+            self.use_index and use_dynamic_x(self._get_ax(0), self.data)
+        )
+
+    def _set_tick_pos(self, data) -> np.ndarray:
+        if self._is_usable_series():
+            return np.array(self._get_xticks(), dtype=int)
+        else:
+            return np.arange(len(data))
+
     def __init__(
         self,
         data,
@@ -1823,7 +1836,6 @@ def __init__(
         self.bar_width = width
         self._align = align
         self._position = position
-        self.tick_pos = np.arange(len(data))
 
         if is_list_like(bottom):
             bottom = np.array(bottom)
@@ -1836,6 +1848,8 @@ def __init__(
 
         MPLPlot.__init__(self, data, **kwargs)
 
+        self.tick_pos = self._set_tick_pos(data)
+
     @cache_readonly
     def ax_pos(self) -> np.ndarray:
         return self.tick_pos - self.tickoffset