Add fallbacks for manual manipulation of slider/frames

src/components/sliders/draw.js

@@ -72,10 +72,18 @@ module.exports = function draw(gd) {
         computeLabelSteps(sliderOpts);
 
         Plots.manageCommandObserver(gd, sliderOpts, sliderOpts.steps, function(data) {
-            if(sliderOpts.active === data.index) return;
-            if(sliderOpts._dragging) return;
-
-            setActive(gd, gSlider, sliderOpts, data.index, false, true);
+            // NB: Same as below. This is *not* always the same as sliderOpts since
+            // if a new set of steps comes in, the reference in this callback would
+            // be invalid. We need to refetch it from the slider group, which is
+            // the join data that creates this slider. So if this slider still exists,
+            // the group should be valid, *to the best of my knowledge.* If not,
+            // we'd have to look it up by d3 data join index/key.
+            var opts = gSlider.data()[0];
+
+            if(opts.active === data.index) return;
+            if(opts._dragging) return;
+
+            setActive(gd, gSlider, opts, data.index, false, true);
         });
 
         drawSlider(gd, d3.select(this), sliderOpts);
@@ -225,6 +233,15 @@ function findDimensions(gd, sliderOpts) {
 }
 
 function drawSlider(gd, sliderGroup, sliderOpts) {
+    // This is related to the other long notes in this file regarding what happens
+    // when slider steps disappear. This particular fix handles what happens when
+    // the *current* slider step is removed. The drawing functions will error out
+    // when they fail to find it, so the fix for now is that it will just draw the
+    // slider in the first position but will not execute the command.
+    if(sliderOpts.active >= sliderOpts.steps.length) {
+        sliderOpts.active = 0;
+    }
+
     // These are carefully ordered for proper z-ordering:
     sliderGroup
         .call(drawCurrentValue, sliderOpts)
@@ -251,9 +268,9 @@ function drawCurrentValue(sliderGroup, sliderOpts, valueOverride) {
 
     switch(sliderOpts.currentvalue.xanchor) {
         case 'right':
-        // This is anchored left and adjusted by the width of the longest label
-        // so that the prefix doesn't move. The goal of this is to emphasize
-        // what's actually changing and make the update less distracting.
+            // This is anchored left and adjusted by the width of the longest label
+            // so that the prefix doesn't move. The goal of this is to emphasize
+            // what's actually changing and make the update less distracting.
             x0 = sliderOpts.inputAreaLength - constants.currentValueInset - sliderOpts.currentValueMaxWidth;
             textAnchor = 'left';
             break;
@@ -402,11 +419,21 @@ function setActive(gd, sliderGroup, sliderOpts, index, doCallback, doTransition)
     }
 }
 
-function attachGripEvents(item, gd, sliderGroup, sliderOpts) {
+function attachGripEvents(item, gd, sliderGroup) {
     var node = sliderGroup.node();
     var $gd = d3.select(gd);
 
+    // NB: This is *not* the same as sliderOpts itself! These callbacks
+    // are in a closure so this array won't actually be correct if the
+    // steps have changed since this was initialized. The sliderGroup,
+    // however, has not changed since that *is* the slider, so it must
+    // be present to receive mouse events.
+    function getSliderOpts() {
+        return sliderGroup.data()[0];
+    }
+
     item.on('mousedown', function() {
+        var sliderOpts = getSliderOpts();
         gd.emit('plotly_sliderstart', {slider: sliderOpts});
 
         var grip = sliderGroup.select('.' + constants.gripRectClass);
@@ -420,11 +447,13 @@ function attachGripEvents(item, gd, sliderGroup, sliderOpts) {
         sliderOpts._dragging = true;
 
         $gd.on('mousemove', function() {
+            var sliderOpts = getSliderOpts();
             var normalizedPosition = positionToNormalizedValue(sliderOpts, d3.mouse(node)[0]);
             handleInput(gd, sliderGroup, sliderOpts, normalizedPosition, false);
         });
 
         $gd.on('mouseup', function() {
+            var sliderOpts = getSliderOpts();
             sliderOpts._dragging = false;
             grip.call(Color.fill, sliderOpts.bgcolor);
             $gd.on('mouseup', null);

src/plots/plots.js

@@ -1546,6 +1546,23 @@ plots.computeFrame = function(gd, frameName) {
     return result;
 };
 
+/*
+ * Recompute the lookup table that maps frame name -> frame object. addFrames/
+ * deleteFrames already manages this data one at a time, so the only time this
+ * is necessary is if you poke around manually in `gd._transitionData_frames`
+ * and create and haven't updated the lookup table.
+ */
+plots.recomputeFrameHash = function(gd) {
+    var hash = gd._transitionData._frameHash = {};
+    var frames = gd._transitionData._frames;
+    for(var i = 0; i < frames.length; i++) {
+        var frame = frames[i];
+        if(frame && frame.name) {
+            hash[frame.name] = frame;
+        }
+    }
+};
+
 /**
  * Extend an object, treating container arrays very differently by extracting
  * their contents and merging them separately.

test/jasmine/tests/sliders_test.js

@@ -191,6 +191,7 @@ describe('sliders initialization', function() {
 
         Plotly.plot(gd, [{x: [1, 2, 3]}], {
             sliders: [{
+                transition: {duration: 0},
                 steps: [
                     {method: 'restyle', args: [], label: 'first'},
                     {method: 'restyle', args: [], label: 'second'},
@@ -209,6 +210,59 @@ describe('sliders initialization', function() {
     });
 });
 
+describe('ugly internal manipulation of steps', function() {
+    'use strict';
+    var gd;
+
+    beforeEach(function(done) {
+        gd = createGraphDiv();
+
+        Plotly.plot(gd, [{x: [1, 2, 3]}], {
+            sliders: [{
+                transition: {duration: 0},
+                steps: [
+                    {method: 'restyle', args: [], label: 'first'},
+                    {method: 'restyle', args: [], label: 'second'},
+                ]
+            }]
+        }).then(done);
+    });
+
+    afterEach(function() {
+        Plotly.purge(gd);
+        destroyGraphDiv();
+    });
+
+    it('adds and removes slider steps gracefully', function(done) {
+        expect(gd._fullLayout.sliders[0].active).toEqual(0);
+
+        // Set the active index higher than it can go:
+        Plotly.relayout(gd, {'sliders[0].active': 2}).then(function() {
+            // Confirm nothing changed
+            expect(gd._fullLayout.sliders[0].active).toEqual(0);
+
+            // Add an option manually without calling API functions:
+            gd.layout.sliders[0].steps.push({method: 'restyle', args: [], label: 'first'});
+
+            // Now that it's been added, restyle and try again:
+            return Plotly.relayout(gd, {'sliders[0].active': 2});
+        }).then(function() {
+            // Confirm it's been changed:
+            expect(gd._fullLayout.sliders[0].active).toEqual(2);
+
+            // Remove the option:
+            gd.layout.sliders[0].steps.pop();
+
+            // And redraw the plot:
+            return Plotly.redraw(gd);
+        }).then(function() {
+            // The selected option no longer exists, so confirm it's
+            // been fixed during the process of updating/drawing it:
+            expect(gd._fullLayout.sliders[0].active).toEqual(0);
+        }).catch(fail).then(done);
+    });
+});
+
 describe('sliders interactions', function() {
     'use strict';