fix: replace deprecated axes grouper .join() with .sharex() for matplotlib>=3.6 (#635)

* Initial plan

* fix: Replace deprecated .join() with .sharex() for matplotlib>=3.6 compatibility

Co-authored-by: henryiii <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: henryiii <[email protected]>

Author: Copilot

src/mplhep/utils.py

@@ -472,14 +472,14 @@ def extend_ratio(ax, yhax):
                 fig.get_size_inches()[0],
                 fig.get_size_inches()[1] * extend_ratio(ax, yhax)[1],
             )
-            ax.get_shared_x_axes().join(ax, yhax)
+            yhax.sharex(ax)
         elif position in ["bottom"]:
             divider.set_vertical([*xsizes, axes_size.Fixed(height)])
             fig.set_size_inches(
                 fig.get_size_inches()[0],
                 fig.get_size_inches()[1] * extend_ratio(ax, yhax)[1],
             )
-            ax.get_shared_x_axes().join(ax, yhax)
+            yhax.sharex(ax)
 
     return yhax
 

tests/copilot/baseline/test_hist2dplot_cbarpos_bottom_visual.png

@@ -0,0 +1,106 @@
+"""
+Tests for hist2dplot cbarpos parameter with matplotlib >= 3.6.
+
+This test addresses the bug where using cbarpos="top" or cbarpos="bottom"
+causes an AttributeError due to matplotlib 3.6+ making groupers immutable.
+The fix uses ax.sharex() instead of the deprecated .join() method.
+"""
+
+from __future__ import annotations
+
+import os
+
+os.environ["RUNNING_PYTEST"] = "true"
+
+import matplotlib.pyplot as plt
+import numpy as np
+import pytest
+
+plt.switch_backend("Agg")
+
+import mplhep as mh
+
+
+@pytest.fixture
+def sample_2d_data():
+    """Create sample 2D histogram data."""
+    np.random.seed(42)
+    xedges = np.linspace(0, 10, 51)
+    yedges = np.linspace(0, 10, 51)
+    H = np.random.normal(size=(50, 50))
+    return H, xedges, yedges
+
+
+def test_hist2dplot_cbarpos_top(sample_2d_data):
+    """Test hist2dplot with cbarpos='top'."""
+    H, xedges, yedges = sample_2d_data
+    fig, ax = plt.subplots()
+    mh.hist2dplot(H, xedges, yedges, cbar=True, cbarpos="top", ax=ax)
+    plt.close(fig)
+
+
+def test_hist2dplot_cbarpos_bottom(sample_2d_data):
+    """Test hist2dplot with cbarpos='bottom'."""
+    H, xedges, yedges = sample_2d_data
+    fig, ax = plt.subplots()
+    mh.hist2dplot(H, xedges, yedges, cbar=True, cbarpos="bottom", ax=ax)
+    plt.close(fig)
+
+
+def test_hist2dplot_cbarpos_left(sample_2d_data):
+    """Test hist2dplot with cbarpos='left'."""
+    H, xedges, yedges = sample_2d_data
+    fig, ax = plt.subplots()
+    mh.hist2dplot(H, xedges, yedges, cbar=True, cbarpos="left", ax=ax)
+    plt.close(fig)
+
+
+def test_hist2dplot_cbarpos_right(sample_2d_data):
+    """Test hist2dplot with cbarpos='right'."""
+    H, xedges, yedges = sample_2d_data
+    fig, ax = plt.subplots()
+    mh.hist2dplot(H, xedges, yedges, cbar=True, cbarpos="right", ax=ax)
+    plt.close(fig)
+
+
+def test_hist2dplot_cbarpos_all_positions(sample_2d_data):
+    """Test hist2dplot with all cbarpos positions in one test."""
+    H, xedges, yedges = sample_2d_data
+    positions = ["top", "bottom", "left", "right"]
+
+    for pos in positions:
+        fig, ax = plt.subplots()
+        mh.hist2dplot(H, xedges, yedges, cbar=True, cbarpos=pos, ax=ax)
+        plt.close(fig)
+
+
+@pytest.mark.mpl_image_compare(style="default", remove_text=True, tolerance=10)
+def test_hist2dplot_cbarpos_top_visual():
+    """Visual comparison test for cbarpos='top'."""
+    np.random.seed(42)
+    xedges = np.linspace(0, 10, 21)
+    yedges = np.linspace(0, 10, 21)
+    x = np.random.normal(5, 2, 1000)
+    y = np.random.normal(5, 2, 1000)
+    H, _, _ = np.histogram2d(x, y, bins=(xedges, yedges))
+
+    fig, ax = plt.subplots(figsize=(8, 7))
+    mh.hist2dplot(H, xedges, yedges, cbar=True, cbarpos="top", ax=ax)
+
+    return fig
+
+
+@pytest.mark.mpl_image_compare(style="default", remove_text=True, tolerance=10)
+def test_hist2dplot_cbarpos_bottom_visual():
+    """Visual comparison test for cbarpos='bottom'."""
+    np.random.seed(42)
+    xedges = np.linspace(0, 10, 21)
+    yedges = np.linspace(0, 10, 21)
+    x = np.random.normal(5, 2, 1000)
+    y = np.random.normal(5, 2, 1000)
+    H, _, _ = np.histogram2d(x, y, bins=(xedges, yedges))
+
+    fig, ax = plt.subplots(figsize=(8, 7))
+    mh.hist2dplot(H, xedges, yedges, cbar=True, cbarpos="bottom", ax=ax)
+
+    return fig