Fix issue with duplicate keys and last item.

We are using `renderState.handledMorphs` as a way to know if a given
key is duplicated or not (if it is duplicated we use a binning strategy
to prevent errors), but we were accidentally setting `handleMorphs[key]`
to `null` when the given morph was the last item in the list.

There is a slight disparity with how we use `handledMorphs` in
`yieldItem` and the way it is used in `renderAndCleanup`.  In
`renderAndCleanup` we check via `if (key in handledMorphs) {}`, but in
`yieldItem` we check `if (handledMorphs[key]) {}`. This difference
combined with the other issue, meant that we were setting
`handledMorphs[key] = null` which failed the duplicate check for
subsequent renders.

The fix is to update `handledMorphs` prior to changing `currentMorph`'s
value.

Author: rwjblue

packages/htmlbars-compiler/tests/diffing-test.js

@@ -80,3 +80,18 @@ test("Morph order is preserved when rerendering with duplicate keys", function()
   equalTokens(result.fragment, `<ul><li>B1</li><li>A2</li></ul>`);
   deepEqual(getNames(), ['B1', 'A1']);
 });
+
+test("duplicate keys are allowed when duplicate is last morph", function() {
+  var template = compile(`<ul>{{#each items as |item|}}<li>{{item.name}}</li>{{/each}}</ul>`);
+
+  let a1 = { key: "a", name: "A1" };
+  let a2 = { key: "a", name: "A2" };
+
+  var result = template.render({ items: [ ] }, env);
+
+  result.rerender(env, { items: [ a1 ] });
+  equalTokens(result.fragment, `<ul><li>A1</li></ul>`);
+
+  result.rerender(env, { items: [a1, a2] });
+  equalTokens(result.fragment, `<ul><li>A1</li><li>A2</li></ul>`);
+});

packages/htmlbars-runtime/lib/hooks.js

@@ -247,8 +247,8 @@ function yieldItem(template, env, parentScope, morph, renderState, visitor) {
 
     if (currentMorph && currentMorph.key === key) {
       yieldTemplate(template, env, parentScope, currentMorph, renderState, visitor)(blockArguments, self);
-      currentMorph = currentMorph.nextMorph;
       handledMorphs[key] = currentMorph;
+      currentMorph = currentMorph.nextMorph;
     } else if (morphMap[key] !== undefined) {
       let foundMorph = morphMap[key];