Fix generateTicks when working with tiny numbers (chartjs#5948)

src/scales/scale.linearbase.js

@@ -4,6 +4,7 @@ var helpers = require('../helpers/index');
 var Scale = require('../core/core.scale');
 
 var noop = helpers.noop;
+var isNullOrUndef = helpers.isNullOrUndef;
 
 /**
  * Generate a set of linear ticks
@@ -17,24 +18,31 @@ function generateTicks(generationOptions, dataRange) {
 	// "nice number" algorithm. See https://stackoverflow.com/questions/8506881/nice-label-algorithm-for-charts-with-minimum-ticks
 	// for details.
 
+	var MIN_SPACING = 1e-14;
 	var stepSize = generationOptions.stepSize;
 	var unit = stepSize || 1;
 	var maxNumSpaces = generationOptions.maxTicks - 1;
 	var min = generationOptions.min;
 	var max = generationOptions.max;
 	var precision = generationOptions.precision;
-	var spacing, factor, niceMin, niceMax, numSpaces;
+	var rmin = dataRange.min;
+	var rmax = dataRange.max;
+	var spacing = helpers.niceNum((rmax - rmin) / maxNumSpaces / unit) * unit;
+	var factor, niceMin, niceMax, numSpaces;
+
+	// Beyond MIN_SPACING floating point numbers being to lose precision
+	// such that we can't do the math necessary to generate ticks
+	if (spacing < MIN_SPACING && isNullOrUndef(min) && isNullOrUndef(max)) {
+		return [rmin, rmax];
+	}
 
-	// spacing is set to a nice number of the dataRange divided by maxNumSpaces.
-	// stepSize is used as a minimum unit if it is specified.
-	spacing = helpers.niceNum((dataRange.max - dataRange.min) / maxNumSpaces / unit) * unit;
-	numSpaces = Math.ceil(dataRange.max / spacing) - Math.floor(dataRange.min / spacing);
+	numSpaces = Math.ceil(rmax / spacing) - Math.floor(rmin / spacing);
 	if (numSpaces > maxNumSpaces) {
 		// If the calculated num of spaces exceeds maxNumSpaces, recalculate it
 		spacing = helpers.niceNum(numSpaces * spacing / maxNumSpaces / unit) * unit;
 	}
 
-	if (stepSize || helpers.isNullOrUndef(precision)) {
+	if (stepSize || isNullOrUndef(precision)) {
 		// If a precision is not specified, calculate factor based on spacing
 		factor = Math.pow(10, helpers.decimalPlaces(spacing));
 	} else {
@@ -43,16 +51,16 @@ function generateTicks(generationOptions, dataRange) {
 		spacing = Math.ceil(spacing * factor) / factor;
 	}
 
-	niceMin = Math.floor(dataRange.min / spacing) * spacing;
-	niceMax = Math.ceil(dataRange.max / spacing) * spacing;
+	niceMin = Math.floor(rmin / spacing) * spacing;
+	niceMax = Math.ceil(rmax / spacing) * spacing;
 
 	// If min, max and stepSize is set and they make an evenly spaced scale use it.
 	if (stepSize) {
 		// If very close to our whole number, use it.
-		if (!helpers.isNullOrUndef(min) && helpers.almostWhole(min / spacing, spacing / 1000)) {
+		if (!isNullOrUndef(min) && helpers.almostWhole(min / spacing, spacing / 1000)) {
 			niceMin = min;
 		}
-		if (!helpers.isNullOrUndef(max) && helpers.almostWhole(max / spacing, spacing / 1000)) {
+		if (!isNullOrUndef(max) && helpers.almostWhole(max / spacing, spacing / 1000)) {
 			niceMax = max;
 		}
 	}
@@ -67,11 +75,11 @@ function generateTicks(generationOptions, dataRange) {
 
 	niceMin = Math.round(niceMin * factor) / factor;
 	niceMax = Math.round(niceMax * factor) / factor;
-	ticks.push(helpers.isNullOrUndef(min) ? niceMin : min);
+	ticks.push(isNullOrUndef(min) ? niceMin : min);
 	for (var j = 1; j < numSpaces; ++j) {
 		ticks.push(Math.round((niceMin + j * spacing) * factor) / factor);
 	}
-	ticks.push(helpers.isNullOrUndef(max) ? niceMax : max);
+	ticks.push(isNullOrUndef(max) ? niceMax : max);
 
 	return ticks;
 }

test/specs/scale.linear.tests.js

@@ -1170,4 +1170,29 @@ describe('Linear Scale', function() {
 		expect(data[0]._model.base + minBarLength).toEqual(data[0]._model.x);
 		expect(data[1]._model.base - minBarLength).toEqual(data[1]._model.x);
 	});
+
+	it('Should generate max and min that are not equal when data contains values that are very close to each other', function() {
+		var chart = window.acquireChart({
+			type: 'scatter',
+			data: {
+				datasets: [{
+					data: [
+						{x: 1, y: 1.8548483304974972},
+						{x: 2, y: 1.8548483304974974},
+					]
+				}],
+			},
+			options: {
+				scales: {
+					yAxes: [{
+						id: 'yScale0',
+						type: 'linear',
+					}]
+				}
+			}
+		});
+
+		expect(chart.scales.yScale0).not.toEqual(undefined); // must construct
+		expect(chart.scales.yScale0.max).toBeGreaterThan(chart.scales.yScale0.min);
+	});
 });