fixes Waterfall hovermode closest bug 3776

Author: archmoj

src/traces/bar/hover.js

@@ -34,6 +34,7 @@ function hoverOnBars(pointData, xval, yval, hovermode) {
     var trace = cd[0].trace;
     var t = cd[0].t;
     var isClosest = (hovermode === 'closest');
+    var isWaterfall = (trace.type === 'waterfall');
     var maxHoverDistance = pointData.maxHoverDistance;
     var maxSpikeDistance = pointData.maxSpikeDistance;
 
@@ -82,10 +83,17 @@ function hoverOnBars(pointData, xval, yval, hovermode) {
     }
 
     function sizeFn(di) {
+        var v = sizeVal;
+        var b = di.b;
+        var s = di[sizeLetter];
+
+        if(isWaterfall) {
+            s += Math.abs(di.rawS || 0);
+        }
+
         // add a gradient so hovering near the end of a
         // bar makes it a little closer match
-        return Fx.inbox(di.b - sizeVal, di[sizeLetter] - sizeVal,
-            maxHoverDistance + (di[sizeLetter] - sizeVal) / (di[sizeLetter] - di.b) - 1);
+        return Fx.inbox(b - v, s - v, maxHoverDistance + (s - v) / (s - b) - 1);
     }
 
     if(trace.orientation === 'h') {