Fix flaky matplotlib-to-plotly conversion of touching bars (negative bargap)

plotly/matplotlylib/mpltools.py

@@ -269,7 +269,9 @@ def get_bar_gap(bar_starts, bar_ends, tol=1e-10):
         gap0 = gaps[0]
         uniform = all([abs(gap0 - gap) < tol for gap in gaps])
         if uniform:
-            return gap0
+            # plotly's bargap must be in [0, 1]; clamp to guard against
+            # floating point noise (e.g. -8.9e-16 for touching bars)
+            return min(max(gap0, 0.0), 1.0)
 
 
 def convert_rgba_array(color_list):

plotly/matplotlylib/tests/test_renderer.py

@@ -199,3 +199,30 @@ def test_filled_path_collection_date_xaxis():
     filled = [t for t in plotly_fig.data if t.fill == "toself"]
     assert len(filled) >= 1
     assert all(isinstance(x, str) for x in filled[0].x)
+
+
+def test_get_bar_gap_clamps_negative_float_noise():
+    """Touching bars can produce a tiny negative gap from floating point
+    noise (e.g. -8.88e-16 for a histogram); plotly rejects bargap outside
+    [0, 1], so the gap must be clamped."""
+    from plotly.matplotlylib.mpltools import get_bar_gap
+
+    # touching bars: gap is exactly 0
+    assert get_bar_gap([0.0, 1.0], [1.0, 2.0]) == 0.0
+    # overlapping-by-noise bars: gap is a tiny negative float, clamped to 0
+    assert get_bar_gap([0.0, 1.0], [1.0 + 1e-15, 2.0]) == 0.0
+    # positive gaps are unchanged
+    assert get_bar_gap([0.0, 2.0], [1.0, 3.0]) == 1.0
+
+
+def test_histogram_converts():
+    """Histograms must convert without error and keep bargap in plotly's
+    valid [0, 1] range; get_bar_gap can return a gap with floating point
+    noise for touching bars, which plotly rejects."""
+    fig, ax = plt.subplots()
+    ax.hist(np.random.randn(1000), 30)
+
+    plotly_fig = tls.mpl_to_plotly(fig)
+
+    assert len(plotly_fig.data) == 1
+    assert 0 <= plotly_fig.layout.bargap <= 1