Show labeled spans in the legend

Author: robertoffmoura

plotly/matplotlylib/renderer.py

@@ -769,6 +769,9 @@ def _draw_axes_span(self, props):
         fillcolor = _export_color(style["facecolor"])
         edgecolor = _export_color(style["edgecolor"])
         linewidth = style["edgewidth"] if style["edgecolor"] != "none" else 0
+        label = props["mplobj"].get_label()
+        if not label or (isinstance(label, str) and label.startswith("_")):
+            label = None
         shape = go.layout.Shape(
             type="rect",
             x0=x0,
@@ -784,6 +787,8 @@ def _draw_axes_span(self, props):
                 dash=mpltools.convert_dash(style["dasharray"]),
             ),
             layer="below" if style.get("zorder", 1) < 2 else "above",
+            name=label,
+            showlegend=True if label is not None else None,
         )
         self.plotly_fig["layout"]["shapes"] += (shape,)
         self.msg += "    Heck yeah, I drew that reference span\n"

plotly/matplotlylib/tests/test_renderer.py

@@ -1525,3 +1525,19 @@ def test_axvspan_on_date_xaxis_converts_to_dates():
     assert vspan.x1.startswith("2023-01-06")
     assert hspan.xref == "x domain"
     assert np.allclose([hspan.x0, hspan.x1], [0, 1])
+
+
+def test_labeled_axvspan_shows_in_legend():
+    """A labeled span exports its label as the shape legend entry."""
+    fig, ax = plt.subplots()
+    ax.plot([0, 10], [0, 10], label="line")
+    ax.axvspan(2, 4, label="span")
+    ax.axhspan(6, 8)
+    ax.legend()
+
+    plotly_fig = tls.mpl_to_plotly(fig)
+
+    labeled, unlabeled = plotly_fig.layout.shapes
+    assert labeled.name == "span"
+    assert labeled.showlegend is True
+    assert unlabeled.showlegend is None