This PRfixes#7506

Description

When usingPlotly.react to update the data of a histogram withbarmode: 'overlay', if the traces contain single data points (one point per trace), the calculatedbin.size could incorrectly set to1. This results in the histogram bars becoming visually very thin after a data update.

This issue is particularly noticeable for react-plotly users, where data mutations are frequent.

Changes

This new logic ensures that auto-binning is correctly triggered when usingPlotly.react (for data mutations).

Before/After

See the fixed look in#7506 (comment).

Note onPlotly.react andlayout object

This PR directly fixes the incorrect histogram auto-binning size calculation for single-point traces inoverlay mode on data updates. However, it's worth noting that this issue is often triggered by a deeper behavior withinPlotly.react concerning layout object reuse. See the Note in#7506.

I found that if the samelayout object is reused inPlotly.react calls while the data's axis type (xaxis.type inlayout) changes (e.g., fromlinear tocategory), the layout object can become "stuck" (stale) with the last-used axis type. For instance, after switching from numeric to string data, the axis type becomescategory. When switching back to numeric data, the axis type incorrectly remainscategory, leading to rendering issues.

The long-term solution might involve changes to howPlotly.react handles the layout object. For now, the good practice for users might be:if your data update might change the axis type (i.e., change the layout), you should also provide a new layout object (or a deep copy) toPlotly.react to ensure correct rendering.

The test case added in this PR (histogram_test.js) intentionally uses data of the same type (linear, auto-detected by Plotly) to specifically test theauto-binning fix when data changes, without being affected by the separate layout reuse behavior.