Bugfix: categorical axis tickson boundaries showgrid

draftlogs/6885_change.md

@@ -0,0 +1 @@
+- Fix bug where plots with axis `type='categorical'`, `tickson = "boundaries"` and `showgrid=true` wouldn't load, see [plotly.py # 3155](https://github.com/plotly/plotly.py/issues/3155). This feature was anonymously sponsored: thank you to our sponsor!

src/plots/cartesian/axes.js

@@ -2807,7 +2807,7 @@ function getBoundaryVals(ax, vals) {
     // boundaryVals are never used for labels;
     // no need to worry about the other tickTextObj keys
     var _push = function(d, bndIndex) {
-        var xb = d.xbnd[bndIndex];
+        var xb = d.xbnd ? d.xbnd[bndIndex] : d.x;
         if(xb !== null) {
             out.push(Lib.extendFlat({}, d, {x: xb}));
         }
@@ -3755,7 +3755,7 @@ axes.drawLabels = function(gd, ax, opts) {
                 // TODO should secondary labels also fall into this fix-overlap regime?
 
                 for(i = 0; i < lbbArray.length; i++) {
-                    var xbnd = vals[i].xbnd;
+                    var xbnd = (vals && vals[i].xbnd) ? vals[i].xbnd : [null, null];
                     var lbb = lbbArray[i];
                     if(
                         (xbnd[0] !== null && (lbb.left - ax.l2p(xbnd[0])) < gap) ||

test/image/mocks/zz-tickson_boundaries_showgrid_categorical.json

@@ -0,0 +1,20 @@
+{
+    "data": [
+        {
+            "type": "bar",
+            "y": [1, 2, 3, 4, 5],
+            "x": ["a", "b", "c", "d", "e"]
+        }
+    ],
+    "layout": {
+        "width": 600,
+        "height": 300,
+        "xaxis": {
+            "tickmode": "array",
+            "tickvals": [0,2,4], 
+            "ticktext": ["One", "Three", "Five"],
+            "tickson": "boundaries",
+            "showgrid": true
+        }
+    }
+}