set enabled:false when filter target array is empty

- see #2908 for more info,
- this fixes many potential problems downstream

Author: etpinard

src/transforms/filter.js

@@ -138,10 +138,16 @@ exports.supplyDefaults = function(transformIn) {
     var enabled = coerce('enabled');
 
     if(enabled) {
+        var target = coerce('target');
+
+        if(Lib.isArrayOrTypedArray(target) && target.length === 0) {
+            transformOut.enabled = false;
+            return transformOut;
+        }
+
         coerce('preservegaps');
         coerce('operation');
         coerce('value');
-        coerce('target');
 
         var handleCalendarDefaults = Registry.getComponentMethod('calendars', 'handleDefaults');
         handleCalendarDefaults(transformIn, transformOut, 'valuecalendar', null);

test/jasmine/tests/transform_filter_test.js

@@ -86,6 +86,33 @@ describe('filter transforms defaults:', function() {
         expect(traceOut.transforms[2].target).toEqual('x');
         expect(traceOut.transforms[3].target).toEqual('marker.color');
     });
+
+    it('supplyTraceDefaults should set *enabled:false* and return early when *target* is an empty array', function() {
+        // see https://github.com/plotly/plotly.js/issues/2908
+        // this solves multiple problems downstream
+
+        traceIn = {
+            x: [1, 2, 3],
+            transforms: [{
+                type: 'filter',
+                target: []
+            }]
+        };
+        traceOut = Plots.supplyTraceDefaults(traceIn, {type: 'scatter'}, 0, fullLayout);
+        expect(traceOut.transforms[0].target).toEqual([]);
+        expect(traceOut.transforms[0].enabled).toBe(false, 'set to false!');
+
+        traceIn = {
+            x: new Float32Array([1, 2, 3]),
+            transforms: [{
+                type: 'filter',
+                target: new Float32Array()
+            }]
+        };
+        traceOut = Plots.supplyTraceDefaults(traceIn, {type: 'scatter'}, 0, fullLayout);
+        expect(traceOut.transforms[0].target).toEqual(new Float32Array());
+        expect(traceOut.transforms[0].enabled).toBe(false, 'set to false!');
+    });
 });
 
 describe('filter transforms calc:', function() {