fix bin size becomes 1 (very thin) when data changes with barmode: 'overlay' for histogram

draftlogs/7507_fix.md

@@ -0,0 +1 @@
+Fix `histogram` autobin size for single-point traces in `overlay` mode on data updates via `Plotly.react` [[#7507](https://github.com/plotly/plotly.js/pull/7507)]

src/traces/histogram/calc.js

@@ -308,10 +308,11 @@ function calcAllAutoBins(gd, trace, pa, mainData, _overlayEdgeCase) {
 
         // Edge case: single-valued histogram overlaying others
         // Use them all together to calculate the bin size for the single-valued one
-        // Don't re-calculate bin width if user manually specified it (checing in bingroup=='' or xbins is defined)
+        // Don't re-calculate bin width if user manually specified it
+        // Check if bingroup or bin size is defined
         if(isOverlay && !Registry.traceIs(trace, '2dMap') && newBinSpec._dataSpan === 0 &&
         pa.type !== 'category' && pa.type !== 'multicategory' &&
-        trace.bingroup === '' && (typeof trace.xbins === 'undefined')) {
+        trace.bingroup === '' && trace._input?.[binAttr]?.size === undefined) {
             // Several single-valued histograms! Stop infinite recursion,
             // just return an extra flag that tells handleSingleValueOverlays
             // to sort out this trace too

test/jasmine/tests/histogram_test.js

@@ -1335,6 +1335,43 @@ describe('Test histogram', function() {
             })
             .then(done, done.fail);
         });
+
+        it('should correctly recalculate autobin size for single-value overlays on Plotly.react', function(done) {
+            var initialData = [
+                {x: ['1457'], type: 'histogram'},
+                {x: ['820'], type: 'histogram'},
+                {x: ['720'], type: 'histogram'}
+            ];
+
+            var layout = {
+                barmode: 'overlay'
+            };
+
+            Plotly.newPlot(gd, initialData, layout)
+            .then(function() {
+                // minDiff = 820 - 720 = 100
+                console.log("gd._fullData=", gd._fullData);
+                expect(gd._fullData[0].xbins.size).toBe(100);
+                expect(gd._fullData[1].xbins.size).toBe(100);
+                expect(gd._fullData[2].xbins.size).toBe(100);
+
+                // Use a new trace data object
+                var newData = [
+                    {x: ['1400'], type: 'histogram'},
+                    {x: ['800'], type: 'histogram'},
+                    {x: ['600'], type: 'histogram'}
+                ];
+
+                return Plotly.react(gd, newData, layout);
+            })
+            .then(function() {
+                // minDiff = 800 - 600 = 200.
+                expect(gd._fullData[0].xbins.size).toBe(200);
+                expect(gd._fullData[1].xbins.size).toBe(200);
+                expect(gd._fullData[2].xbins.size).toBe(200);
+            })
+            .then(done, done.fail);
+        });
     });
 });