CLI: Do not use modern TS assets in legacy TS projects

code/frameworks/sveltekit/README.md

@@ -23,20 +23,20 @@ Check out our [Frameworks API](https://storybook.js.org/blog/framework-api/) ann
 All Svelte language features are supported out of the box, as Storybook uses the Svelte compiler underneath.
 However SvelteKit has some [Kit-specific modules](https://kit.svelte.dev/docs/modules) that currently aren't supported. It's on our roadmap to support most of them soon:
 
-| **Module**                                                                         | **Status**                                                                                        | **Note**                                                                                                                                                                                                                           |
-| ---------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
-| [`$app/environment`](https://kit.svelte.dev/docs/modules#$app-environment)         | ✅ Supported                                                                                      | `version` is always empty in Storybook.                                                                                                                                                                                           |
-| [`$app/forms`](https://kit.svelte.dev/docs/modules#$app-forms)                     | ⏳ Planned for 7.1                                                                                | Will use mocks. Tracked in [#20999](https://github.com/storybookjs/storybook/issues/20999) |
-| [`$app/navigation`](https://kit.svelte.dev/docs/modules#$app-navigation)           | ⏳ Planned for 7.1                                                                                | Will use mocks. Tracked in [#20999](https://github.com/storybookjs/storybook/issues/20999) |
-| [`$app/paths`](https://kit.svelte.dev/docs/modules#$app-paths)                     | ✅ Supported                                                                                      | Requires SvelteKit 1.4.0 or newer                                                                                                                                                                                                 |
-| [`$app/stores`](https://kit.svelte.dev/docs/modules#$app-stores)                   | ✅ Supported                                                                                      | Mocks planned for 7.1, so you can set different store values per story.                                                                                                                                                           |
-| [`$env/dynamic/private`](https://kit.svelte.dev/docs/modules#$env-dynamic-private) | ⛔ Not supported                                                                                  | They are meant to only be available server-side, and Storybook renders all components on the client.                                                                                                                               |
-| [`$env/dynamic/public`](https://kit.svelte.dev/docs/modules#$env-dynamic-public)   | 🚧 Partially supported                                                                            | Only supported in development mode. Storybook is built as a static app with no server-side API so cannot dynamically serve content.                                                                                            |
-| [`$env/static/private`](https://kit.svelte.dev/docs/modules#$env-static-private)   | ⛔ Not supported                                                                                  | They are meant to only be available server-side, and Storybook renders all components on the client.                                                                                                                               |
-| [`$env/static/public`](https://kit.svelte.dev/docs/modules#$env-static-public)     | ✅ Supported                                                                                      |                                                                                                                                                                                                                                   |
-| [`$lib`](https://kit.svelte.dev/docs/modules#$lib)                                 | ✅ Supported                                                                                      |                                                                                                                                                                                                                                   |
-| [`$service-worker`](https://kit.svelte.dev/docs/modules#$service-worker)           | ⛔ Not supported                                                                                  | They are only meant to be used in service workers                                                                                                                                                                                 |
-| [`@sveltejs/kit/*`](https://kit.svelte.dev/docs/modules#sveltejs-kit)              | ✅ Supported                                                                                      |                                                                                                                                                                                                                                   |
+| **Module**                                                                         | **Status**             | **Note**                                                                                                                            |
+| ---------------------------------------------------------------------------------- | ---------------------- | ----------------------------------------------------------------------------------------------------------------------------------- |
+| [`$app/environment`](https://kit.svelte.dev/docs/modules#$app-environment)         | ✅ Supported           | `version` is always empty in Storybook.                                                                                             |
+| [`$app/forms`](https://kit.svelte.dev/docs/modules#$app-forms)                     | ⏳ Planned for 7.1     | Will use mocks. Tracked in [#20999](https://github.com/storybookjs/storybook/issues/20999)                                          |
+| [`$app/navigation`](https://kit.svelte.dev/docs/modules#$app-navigation)           | ⏳ Planned for 7.1     | Will use mocks. Tracked in [#20999](https://github.com/storybookjs/storybook/issues/20999)                                          |
+| [`$app/paths`](https://kit.svelte.dev/docs/modules#$app-paths)                     | ✅ Supported           | Requires SvelteKit 1.4.0 or newer                                                                                                   |
+| [`$app/stores`](https://kit.svelte.dev/docs/modules#$app-stores)                   | ✅ Supported           | Mocks planned for 7.1, so you can set different store values per story.                                                             |
+| [`$env/dynamic/private`](https://kit.svelte.dev/docs/modules#$env-dynamic-private) | ⛔ Not supported       | They are meant to only be available server-side, and Storybook renders all components on the client.                                |
+| [`$env/dynamic/public`](https://kit.svelte.dev/docs/modules#$env-dynamic-public)   | 🚧 Partially supported | Only supported in development mode. Storybook is built as a static app with no server-side API so cannot dynamically serve content. |
+| [`$env/static/private`](https://kit.svelte.dev/docs/modules#$env-static-private)   | ⛔ Not supported       | They are meant to only be available server-side, and Storybook renders all components on the client.                                |
+| [`$env/static/public`](https://kit.svelte.dev/docs/modules#$env-static-public)     | ✅ Supported           |                                                                                                                                     |
+| [`$lib`](https://kit.svelte.dev/docs/modules#$lib)                                 | ✅ Supported           |                                                                                                                                     |
+| [`$service-worker`](https://kit.svelte.dev/docs/modules#$service-worker)           | ⛔ Not supported       | They are only meant to be used in service workers                                                                                   |
+| [`@sveltejs/kit/*`](https://kit.svelte.dev/docs/modules#sveltejs-kit)              | ✅ Supported           |                                                                                                                                     |
 
 This is just the beginning. We're close to adding basic support for many of the SvelteKit features. Longer term we're planning on making it an even better experience to [build](https://storybook.js.org/docs/7.0/react/writing-stories/introduction), [test](https://storybook.js.org/docs/7.0/react/writing-tests/introduction) and [document](https://storybook.js.org/docs/7.0/react/writing-docs/introduction) all the SvelteKit goodies like [pages](https://kit.svelte.dev/docs/routing), [forms](https://kit.svelte.dev/docs/form-actions) and [layouts](https://kit.svelte.dev/docs/routing#layout) in Storybook, while still integrating with all the addons and workflows you know and love.
 

code/lib/cli/src/detect.test.ts

@@ -1,5 +1,5 @@
 import * as fs from 'fs';
-
+import { logger } from '@storybook/node-logger';
 import { getBowerJson } from './helpers';
 import { detect, detectFrameworkPreset, detectLanguage, isStorybookInstalled } from './detect';
 import { ProjectType, SUPPORTED_RENDERERS, SupportedLanguage } from './project_types';
@@ -21,6 +21,8 @@ jest.mock('path', () => ({
   join: jest.fn((_, p) => p),
 }));
 
+jest.mock('@storybook/node-logger');
+
 const MOCK_FRAMEWORK_FILES: {
   name: string;
   files: Record<'package.json', PackageJsonWithMaybeDeps> | Record<string, string>;
@@ -298,27 +300,40 @@ describe('Detect', () => {
     expect(detect(undefined)).toBe(ProjectType.UNDETECTED);
   });
 
-  it(`should return language legacy typescript if the dependency is present`, () => {
+  it(`should return language javascript if the TS dependency is present but less than minimum supported`, () => {
+    (logger.warn as jest.MockedFunction<typeof logger.warn>).mockClear();
     expect(detectLanguage({ dependencies: { typescript: '1.0.0' } })).toBe(
-      SupportedLanguage.TYPESCRIPT_LEGACY
+      SupportedLanguage.JAVASCRIPT
+    );
+    expect(logger.warn).toHaveBeenCalledWith(
+      'Detected TypeScript < 3.8, populating with JavaScript examples'
+    );
+  });
+
+  it(`should return language typescript-3-8 if the TS dependency is >=3.8 and <4.9`, () => {
+    expect(detectLanguage({ dependencies: { typescript: '3.8.0' } })).toBe(
+      SupportedLanguage.TYPESCRIPT_3_8
+    );
+    expect(detectLanguage({ dependencies: { typescript: '4.8.0' } })).toBe(
+      SupportedLanguage.TYPESCRIPT_3_8
     );
   });
 
-  it(`should return language typescript if the dependency is >TS4.9`, () => {
+  it(`should return language typescript-4-9 if the dependency is >TS4.9`, () => {
     expect(detectLanguage({ dependencies: { typescript: '4.9.1' } })).toBe(
-      SupportedLanguage.TYPESCRIPT
+      SupportedLanguage.TYPESCRIPT_4_9
     );
   });
 
   it(`should return language typescript if the dependency is =TS4.9`, () => {
     expect(detectLanguage({ dependencies: { typescript: '4.9.0' } })).toBe(
-      SupportedLanguage.TYPESCRIPT
+      SupportedLanguage.TYPESCRIPT_4_9
     );
   });
 
   it(`should return language typescript if the dependency is =TS4.9beta`, () => {
     expect(detectLanguage({ dependencies: { typescript: '^4.9.0-beta' } })).toBe(
-      SupportedLanguage.TYPESCRIPT
+      SupportedLanguage.TYPESCRIPT_4_9
     );
   });
 

code/lib/cli/src/detect.ts

@@ -1,6 +1,7 @@
 import fs from 'fs';
 import findUp from 'find-up';
 import semver from 'semver';
+import { logger } from '@storybook/node-logger';
 
 import type { TemplateConfiguration, TemplateMatcher } from './project_types';
 import {
@@ -177,9 +178,19 @@ export function detectLanguage(packageJson?: PackageJson) {
         semver.gte(semver.coerce(version), '0.6.8')
       ))
   ) {
-    language = SupportedLanguage.TYPESCRIPT;
-  } else if (hasDependency(packageJson, 'typescript')) {
-    language = SupportedLanguage.TYPESCRIPT_LEGACY;
+    language = SupportedLanguage.TYPESCRIPT_4_9;
+  } else if (
+    hasDependency(packageJson, 'typescript', (version) =>
+      semver.gte(semver.coerce(version), '3.8.0')
+    )
+  ) {
+    language = SupportedLanguage.TYPESCRIPT_3_8;
+  } else if (
+    hasDependency(packageJson, 'typescript', (version) =>
+      semver.lt(semver.coerce(version), '3.8.0')
+    )
+  ) {
+    logger.warn('Detected TypeScript < 3.8, populating with JavaScript examples');
   }
 
   return language;

code/lib/cli/src/generators/configure.test.ts

@@ -42,7 +42,7 @@ describe('configureMain', () => {
 
   test('should generate main.ts', async () => {
     await configureMain({
-      language: SupportedLanguage.TYPESCRIPT,
+      language: SupportedLanguage.TYPESCRIPT_4_9,
       addons: [],
       storybookConfigFolder: '.storybook',
       framework: {
@@ -141,7 +141,7 @@ describe('configurePreview', () => {
 
   test('should generate preview.ts', async () => {
     await configurePreview({
-      language: SupportedLanguage.TYPESCRIPT,
+      language: SupportedLanguage.TYPESCRIPT_4_9,
       storybookConfigFolder: '.storybook',
     });
 
@@ -168,15 +168,15 @@ describe('configurePreview', () => {
   test('should not do anything if the framework template already included a preview', async () => {
     (fse.pathExists as unknown as jest.Mock).mockReturnValueOnce(true);
     await configurePreview({
-      language: SupportedLanguage.TYPESCRIPT,
+      language: SupportedLanguage.TYPESCRIPT_4_9,
       storybookConfigFolder: '.storybook',
     });
     expect(fse.writeFile).not.toHaveBeenCalled();
   });
 
   test('should add prefix if frameworkParts are passed', async () => {
     await configurePreview({
-      language: SupportedLanguage.TYPESCRIPT,
+      language: SupportedLanguage.TYPESCRIPT_4_9,
       storybookConfigFolder: '.storybook',
       frameworkPreviewParts: {
         prefix: dedent`

code/lib/cli/src/generators/configure.ts

@@ -62,7 +62,7 @@ export async function configureMain({
   };
 
   const isTypescript =
-    language === SupportedLanguage.TYPESCRIPT || language === SupportedLanguage.TYPESCRIPT_LEGACY;
+    language === SupportedLanguage.TYPESCRIPT_4_9 || language === SupportedLanguage.TYPESCRIPT_3_8;
 
   let mainConfigTemplate = dedent`<<import>>const config<<type>> = <<mainContents>>;
     export default config;`;
@@ -96,8 +96,8 @@ export async function configureMain({
 export async function configurePreview(options: ConfigurePreviewOptions) {
   const { prefix = '' } = options.frameworkPreviewParts || {};
   const isTypescript =
-    options.language === SupportedLanguage.TYPESCRIPT ||
-    options.language === SupportedLanguage.TYPESCRIPT_LEGACY;
+    options.language === SupportedLanguage.TYPESCRIPT_4_9 ||
+    options.language === SupportedLanguage.TYPESCRIPT_3_8;
 
   const previewPath = `./${options.storybookConfigFolder}/preview.${isTypescript ? 'ts' : 'js'}`;
 

code/lib/cli/src/helpers.test.ts

@@ -60,12 +60,15 @@ describe('Helpers', () => {
   });
 
   it.each`
-    language        | exists          | expected
-    ${'javascript'} | ${['js', 'ts']} | ${'/js'}
-    ${'typescript'} | ${['js', 'ts']} | ${'/ts'}
-    ${'typescript'} | ${['js']}       | ${'/js'}
-    ${'javascript'} | ${[]}           | ${''}
-    ${'typescript'} | ${[]}           | ${''}
+    language            | exists                        | expected
+    ${'javascript'}     | ${['js', 'ts-4-9']}           | ${'/js'}
+    ${'typescript-4-9'} | ${['js', 'ts-4-9']}           | ${'/ts-4-9'}
+    ${'typescript-4-9'} | ${['js', 'ts-3-8']}           | ${'/ts-3-8'}
+    ${'typescript-3-8'} | ${['js', 'ts-3-8', 'ts-4-9']} | ${'/ts-3-8'}
+    ${'typescript-3-8'} | ${['js', 'ts-4-9']}           | ${'/js'}
+    ${'typescript-4-9'} | ${['js']}                     | ${'/js'}
+    ${'javascript'}     | ${[]}                         | ${''}
+    ${'typescript-4-9'} | ${[]}                         | ${''}
   `(
     `should copy $expected when folder $exists exists for language $language`,
     async ({ language, exists, expected }) => {

code/lib/cli/src/helpers.ts

@@ -193,33 +193,30 @@ export async function copyComponents(
 ) {
   const languageFolderMapping: Record<SupportedLanguage, string> = {
     [SupportedLanguage.JAVASCRIPT]: 'js',
-    [SupportedLanguage.TYPESCRIPT]: 'ts',
-    [SupportedLanguage.TYPESCRIPT_LEGACY]: 'ts-legacy',
+    [SupportedLanguage.TYPESCRIPT_3_8]: 'ts-3-8',
+    [SupportedLanguage.TYPESCRIPT_4_9]: 'ts-4-9',
   };
   const componentsPath = async () => {
     const baseDir = getRendererDir(renderer);
     const assetsDir = join(baseDir, 'template/cli');
 
     const assetsLanguage = join(assetsDir, languageFolderMapping[language]);
     const assetsJS = join(assetsDir, languageFolderMapping[SupportedLanguage.JAVASCRIPT]);
-    const assetsTSLegacy = join(
-      assetsDir,
-      languageFolderMapping[SupportedLanguage.TYPESCRIPT_LEGACY]
-    );
-    const assetsTS = join(assetsDir, languageFolderMapping[SupportedLanguage.TYPESCRIPT]);
+    const assetsTS38 = join(assetsDir, languageFolderMapping[SupportedLanguage.TYPESCRIPT_3_8]);
 
+    // Ideally use the assets that match the language & version.
     if (await fse.pathExists(assetsLanguage)) {
       return assetsLanguage;
     }
-    if (language === SupportedLanguage.TYPESCRIPT && (await fse.pathExists(assetsTSLegacy))) {
-      return assetsTSLegacy;
-    }
-    if (language === SupportedLanguage.TYPESCRIPT_LEGACY && (await fse.pathExists(assetsTS))) {
-      return assetsTS;
+    // Use fallback typescript 3.8 assets if new ones aren't available
+    if (language === SupportedLanguage.TYPESCRIPT_4_9 && (await fse.pathExists(assetsTS38))) {
+      return assetsTS38;
     }
+    // Fallback further to JS
     if (await fse.pathExists(assetsJS)) {
       return assetsJS;
     }
+    // As a last resort, look for the root of the asset directory
     if (await fse.pathExists(assetsDir)) {
       return assetsDir;
     }

code/lib/cli/src/project_types.ts

@@ -113,8 +113,8 @@ export type Builder = CoreBuilder | (string & {});
 
 export enum SupportedLanguage {
   JAVASCRIPT = 'javascript',
-  TYPESCRIPT_LEGACY = 'typescript-legacy',
-  TYPESCRIPT = 'typescript',
+  TYPESCRIPT_3_8 = 'typescript-3-8',
+  TYPESCRIPT_4_9 = 'typescript-4-9',
 }
 
 export type TemplateMatcher = {