fix #8117 - don't reuse stale zmin/zmax for autocontour when coloring is 'none'

With `contours.coloring: 'none'` the colorscale attributes are not coerced,
so `zauto` is undefined on the full trace. After `Plotly.react`,
`relinkPrivateKeys` + `Colorscale.crossTraceDefaults` put the previous
`_zmin`/`_zmax` back onto `zmin`/`zmax`, and `setContours` used them because
`trace.zauto` was falsy. Treat an undefined `zauto` as auto, as
`Colorscale.calc` already does.

Author: capy-zhiao

src/traces/contour/set_contours.js

@@ -12,10 +12,14 @@ module.exports = function setContours(trace, vals) {
         // these values here are meant to remain "per-trace" for now
         var zmin = trace.zmin;
         var zmax = trace.zmax;
-        if(trace.zauto || zmin === undefined) {
+        // `zauto` is only coerced when the trace has a colorscale (i.e. not for
+        // `contours.coloring: 'none'`). Treat an undefined `zauto` as auto, like
+        // Colorscale.calc does, so that we never reuse the zmin/zmax relinked
+        // from a previous full trace after `Plotly.react` (see #8117).
+        if(trace.zauto !== false || zmin === undefined) {
             zmin = Lib.aggNums(Math.min, null, vals);
         }
-        if(trace.zauto || zmax === undefined) {
+        if(trace.zauto !== false || zmax === undefined) {
             zmax = Lib.aggNums(Math.max, null, vals);
         }
 

test/jasmine/tests/contour_test.js

@@ -622,6 +622,35 @@ describe('contour plotting and editing', function() {
         .then(done, done.fail);
     });
 
+    it('should recompute autocontour levels from the new z on react when coloring is *none*', function(done) {
+        // https://github.com/plotly/plotly.js/issues/8117
+        // with contours.coloring 'none' the colorscale attributes are not coerced,
+        // so setContours must not reuse the zmin/zmax relinked from the previous full trace
+        function _trace(z) {
+            return {type: 'contour', z: z, contours: {coloring: 'none'}};
+        }
+
+        function _assertLevels(msg, start, end, size) {
+            var contours = gd._fullData[0].contours;
+            expect(contours.start).toBe(start, msg + ' start');
+            expect(contours.end).toBe(end, msg + ' end');
+            expect(contours.size).toBe(size, msg + ' size');
+            expect(gd.querySelectorAll('.contourlevel path').length).toBeGreaterThan(0, msg + ' no contour lines drawn');
+        }
+
+        Plotly.newPlot(gd, [_trace([[1, 2, 3], [4, 5, 6], [7, 8, 9]])])
+        .then(function() {
+            _assertLevels('initial', 2, 8, 1);
+
+            // new trace object and new z array, with a completely different range
+            return Plotly.react(gd, [_trace([[4100, 4200, 4300], [4400, 4500, 4600], [4700, 4800, 4900]])]);
+        })
+        .then(function() {
+            _assertLevels('after react', 4200, 4800, 100);
+        })
+        .then(done, done.fail);
+    });
+
     it('keeps the correct ordering after hide and show', function(done) {
         function getIndices() {
             var out = [];