Core: Fix default sorting of docs-only stories

examples/official-storybook/intro.stories.mdx

@@ -0,0 +1,5 @@
+<Meta title="About/Intro" />
+
+# Official-storybook
+
+Welcome to `official-storybook`, a collection of test cases and demos for `@storybook/react` and all its addons.

examples/official-storybook/main.js

@@ -1,5 +1,6 @@
 module.exports = {
   stories: [
+    // FIXME: Breaks e2e tests './intro.stories.mdx',
     '../../lib/ui/src/**/*.stories.(js|tsx|mdx)',
     '../../lib/components/src/**/*.stories.(js|tsx|mdx)',
     './stories/**/*.stories.(js|tsx|mdx)',

lib/client-api/src/client_api.test.ts

@@ -514,21 +514,23 @@ describe('preview.client_api', () => {
         clientApi: { storiesOf, getStorybook },
         channel,
       } = getContext(undefined);
+      const module0 = new MockModule();
       const module1 = new MockModule();
       const module2 = new MockModule();
       channel.emit = jest.fn();
 
       expect(getStorybook()).toEqual([]);
 
+      storiesOf('kind0', module0).add('story0-docs-only', jest.fn(), { docsOnly: true });
       storiesOf('kind1', module1).add('story1', jest.fn());
       storiesOf('kind2', module2).add('story2', jest.fn());
 
       // storyStore debounces so we need to wait for the next tick
       await new Promise(r => setTimeout(r, 0));
 
-      let [event, storiesHash] = channel.emit.mock.calls[0];
+      let [event, args] = channel.emit.mock.calls[0];
       expect(event).toEqual(Events.SET_STORIES);
-      expect(Object.values(storiesHash.stories).map(v => v.kind)).toEqual(['kind1', 'kind2']);
+      expect(Object.values(args.stories).map(v => v.kind)).toEqual(['kind0', 'kind1', 'kind2']);
       expect(getStorybook().map(story => story.kind)).toEqual(['kind1', 'kind2']);
 
       channel.emit.mockClear();
@@ -540,10 +542,10 @@ describe('preview.client_api', () => {
 
       await new Promise(r => setTimeout(r, 0));
       // eslint-disable-next-line prefer-destructuring
-      [event, storiesHash] = channel.emit.mock.calls[0];
+      [event, args] = channel.emit.mock.calls[0];
 
       expect(event).toEqual(Events.SET_STORIES);
-      expect(Object.values(storiesHash.stories).map(v => v.kind)).toEqual(['kind1', 'kind2']);
+      expect(Object.values(args.stories).map(v => v.kind)).toEqual(['kind0', 'kind1', 'kind2']);
       expect(getStorybook().map(story => story.kind)).toEqual(['kind1', 'kind2']);
     });
   });

lib/client-api/src/story_store.ts

@@ -55,6 +55,8 @@ interface StoryOptions {
   includeDocsOnly?: boolean;
 }
 
+type KindOrder = Record<string, number>;
+
 const isStoryDocsOnly = (parameters?: Parameters) => {
   return parameters && parameters.docsOnly;
 };
@@ -81,6 +83,8 @@ export default class StoryStore extends EventEmitter {
 
   _selection: Selection;
 
+  _kindOrder: KindOrder;
+
   constructor(params: { channel: Channel }) {
     super();
 
@@ -90,6 +94,7 @@ export default class StoryStore extends EventEmitter {
     this._selection = {} as any;
     this._channel = params.channel;
     this._error = undefined;
+    this._kindOrder = {};
   }
 
   setChannel = (channel: Channel) => {
@@ -133,17 +138,11 @@ export default class StoryStore extends EventEmitter {
         stable.inplace(stories, sortFn);
       } else {
         // NOTE: when kinds are HMR'ed they get temporarily removed from the `_data` array
-        // and thus lose order. However in `_legacydata` they just get zeroed out, meaning
-        // that the order is preserved. Here we can use this to preserve the load
-        // order if there is no sort function, although it's a hack.
-        const kindOrder = Object.values(this._legacydata).reduce(
-          (acc: Record<string, number>, { kind }: any, idx: number) => {
-            acc[kind] = idx;
-            return acc;
-          },
-          {}
+        // and thus lose order. However `_kindOrder` preservers the original load order
+        stable.inplace(
+          stories,
+          (s1, s2) => this._kindOrder[s1[1].kind] - this._kindOrder[s2[1].kind]
         );
-        stable.inplace(stories, (s1, s2) => kindOrder[s1[1].kind] - kindOrder[s2[1].kind]);
       }
     }
     // removes function values from all stories so they are safe to transport over the channel
@@ -252,11 +251,18 @@ export default class StoryStore extends EventEmitter {
       parameters,
     };
 
-    // LEGACY DATA
+    // Don't store docs-only stories in legacy data because
+    // existing clients (at the time?!), e.g. storyshots/chromatic
+    // are not necessarily equipped to process them
     if (!isStoryDocsOnly(parameters)) {
       this.addLegacyStory({ kind, name, storyFn, parameters });
     }
 
+    // Store 1-based order of kind loading to preserve sorting on HMR
+    if (!this._kindOrder[kind]) {
+      this._kindOrder[kind] = 1 + Object.keys(this._kindOrder).length;
+    }
+
     // LET'S SEND IT TO THE MANAGER
     this.pushToManager();
   }