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

@@ -84,3 +84,17 @@ def test_multiple_traces_native_legend():
     assert plotly_fig.data[0].mode == "lines"
     assert plotly_fig.data[1].mode == "markers"
     assert plotly_fig.data[2].mode == "lines+markers"
+
+
+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