When using ticklabelindex, make sure tick labels use formatting compatible with minor ticks.

E.g. if major ticks are daily and minor ticks are hourly, tick labels on minor ticks should include hourly information.

Author: my-tien

src/plots/cartesian/axes.js

@@ -716,6 +716,13 @@ axes.prepMinorTicks = function(mockAx, ax, opts) {
         // ensure identical tick0
         mockAx.tick0 = ax.tick0;
     }
+    if (ax._useTicklabelIndex) {
+        // this could always be done but the additional information on the minor
+        // axis is just necessary when using ticklabelindex.
+        autoTickRound(mockAx);
+        delete mockAx.minor; // prevent self-reference
+        Lib.extendFlat(ax.minor, mockAx);
+    }
 };
 
 function isMultiple(bigger, smaller) {
@@ -1926,9 +1933,9 @@ function tickTextObj(ax, x, text) {
 }
 
 function formatDate(ax, out, hover, extraPrecision) {
-    var tr = ax._tickround;
-    var fmt = (hover && ax.hoverformat) || axes.getTickFormat(ax);
-
+    var periodAxis = ax._useTicklabelIndex ? ax.minor : ax;
+    var tr = periodAxis._tickround;
+    var fmt = (hover && ax.hoverformat) || axes.getTickFormat(periodAxis);
     // Only apply extra precision if no explicit format was provided.
     extraPrecision = !fmt && extraPrecision;