unified hover: fix for unspecified layout.paperbg_color

Author: antoinerg

src/components/fx/hover.js

@@ -991,7 +991,7 @@ function createHoverText(hoverData, opts, gd) {
             legend: {
                 title: {text: t0, font: fullLayout.hoverlabel.font},
                 font: fullLayout.hoverlabel.font,
-                bgcolor: fullLayout.hoverlabel.bgcolor,
+                bgcolor: fullLayout.hoverlabel.bgcolor || fullLayout.paper_bgcolor,
                 borderwidth: 1,
                 tracegroupgap: 7,
                 traceorder: fullLayout.legend ? fullLayout.legend.traceorder : undefined,

src/components/fx/hoverlabel_defaults.js

@@ -14,8 +14,9 @@ var isUnifiedHover = require('./helpers').isUnifiedHover;
 module.exports = function handleHoverLabelDefaults(contIn, contOut, coerce, opts) {
     opts = opts || {};
 
+    // In unified hover, inherit from legend if available
     if(contIn && isUnifiedHover(contIn.hovermode)) {
-        if(!opts.bgcolor) opts.bgcolor = contIn.legend ? contIn.legend.bgcolor : contIn.paper_bgcolor;
+        if(!opts.bgcolor && contIn.legend) opts.bgcolor = contIn.legend.bgcolor;
         // Merge in decreasing order of importance layout.font, layout.legend.font and hoverlabel.font
         opts.font = Lib.extendFlat({}, contIn.font, contIn.legend ? contIn.legend.font : {}, opts.font);
     }

test/jasmine/tests/hover_label_test.js

@@ -4338,9 +4338,15 @@ describe('hovermode: (x|y)unified', function() {
             'rgb(40, 40, 40)'
         ];
 
-        // Set paper_bgcolor
-        mockCopy.layout.paper_bgcolor = bgcolor[0];
         Plotly.newPlot(gd, mockCopy)
+            .then(function(gd) {
+                _hover(gd, { xval: 3 });
+
+                assertBgcolor('rgb(255, 255, 255)');
+
+                // Set paper_bgcolor
+                return Plotly.relayout(gd, 'paper_bgcolor', bgcolor[0]);
+            })
             .then(function(gd) {
                 _hover(gd, { xval: 3 });