Reorganize clearExpandedTraceDefaultColors code

Author: rreusser

src/plots/plots.js

@@ -659,12 +659,15 @@ plots.linkSubplots = function(newFullData, newFullLayout, oldFullData, oldFullLa
     }
 };
 
-// This function clears defaults between the first and second pass of
-// supplyDefaults. It exists because otherwise null attributes are
-// supplyDefault'd and inherited as *colors* instead of an actual null
-// attribute which needs to be supplydefaulted by the individual
-// expanded traces.
-plots.clearTraceDefaultColors = function(trace) {
+// This function clears any attributes with useExpandedTraceDefaultColor
+// set to true in the plot schema. This is needed because groupby (which
+// is the only transform for which this currently applies) supplies parent
+// trace defaults, then expanded trace defaults. The result is that `null`
+// colors are default-supplied and inherited as a color instead of a null.
+// The result is that expanded trace default colors have no effect, with
+// the final result that groups are indistinguishable. This function clears
+// those colors so that individual groupby groups get unique colors.
+plots.clearExpandedTraceDefaultColors = function(trace) {
     var colorAttrs, path, i;
 
     // This uses weird closure state in order to satisfy the linter rule

src/transforms/groupby.js

@@ -173,7 +173,7 @@ function transformOne(trace, state) {
 
         newTrace.name = groupName;
 
-        Plots.clearTraceDefaultColors(newTrace);
+        Plots.clearExpandedTraceDefaultColors(newTrace);
 
         // there's no need to coerce styleLookup[groupName] here
         // as another round of supplyDefaults is done on the transformed traces

test/jasmine/tests/transform_expanded_trace_test.js

@@ -692,6 +692,34 @@ describe('groupby', function() {
         it('passes with no groups', test(mockData0));
         it('passes with empty groups', test(mockData1));
         it('passes with falsey groups', test(mockData2));
+    });
+
+    describe('expanded trace coloring', function() {
+        it('assigns unique colors to each group', function() {
+            var uniqueColors = {};
+            var dataOut = [];
+            var dataIn = [{
+                y: [1, 2, 3],
+                transforms: [
+                    {type: 'filter', operation: '<', value: 4},
+                    {type: 'groupby', groups: ['a', 'b', 'c']}
+                ]
+            }, {
+                y: [4, 5, 6],
+                transforms: [
+                    {type: 'filter', operation: '<', value: 4},
+                    {type: 'groupby', groups: ['a', 'b', 'b']}
+                ]
+            }];
 
+            Plots.supplyDataDefaults(dataIn, dataOut, {}, {});
+
+            for(var i = 0; i < dataOut.length; i++) {
+                uniqueColors[dataOut[i].marker.color] = true;
+            }
+
+            // Confirm that five total colors exist:
+            expect(Object.keys(uniqueColors).length).toEqual(5);
+        });
     });
 });