[BUG] maxTicksLimit doesn't limit the number of ticks

[nagix]

Expected Behavior

maxTicksLimit should limit the number of ticks.

Current Behavior

maxTicksLimit doesn't limit the number of ticks. See https://jsfiddle.net/nagix/x68L9dw3/.

Possible Solution

Chart.js/src/scales/scale.linearbase.js

Line 27 in 2388eea

spacing = helpers.niceNum(niceRange / (generationOptions.maxTicks - 1), true);

sets the second argument to true, and rounding the first argument in

Chart.js/src/core/core.helpers.js

Lines 381 to 395 in 2388eea

	helpers.niceNum = function(range, round) {
	var exponent = Math.floor(helpers.log10(range));
	var fraction = range / Math.pow(10, exponent);
	var niceFraction;
	if (round) {
	if (fraction < 1.5) {
	niceFraction = 1;
	} else if (fraction < 3) {
	niceFraction = 2;
	} else if (fraction < 7) {
	niceFraction = 5;
	} else {
	niceFraction = 10;
	}

causes the problem.

However, when setting the second argument to false, multiple tests failed as the generated ticks were changed. It seems to me that a whole logic for ticks generation needs to be improved because results are not consistent even if the number of ticks is below maxTicksLimit.

In particular, I don't understand why niceRange is used as the base for calculation at the first place.

Chart.js/src/scales/scale.linearbase.js

Line 26 in 2388eea

niceRange = helpers.niceNum(dataRange.max - dataRange.min, false);

Context

The same logic is used for a radialLinear scale, and this causes overlaps between tick labels in #5914.

Environment

• Chart.js version: 2.4.0 and later
• Browser name and version: All