[Breaking Change]: Replace babel-istanbul-plugin and replace it by a webpack loader

[yannbf]

Closes #29
Closes #17
Closes #21
Closes #25

What Changed

The babel-istanbul-plugin was replaced by a custom webpack loader to enable support for all Webpack5 projects, independently, whether they are using Babel as a compiler or another solution, like SWC

Release Notes

• [BREAKING CHANGE]: Dropping Storybook < 7 support
• Replaced babel-istanbul-plugin with a custom Webpack loader to support coverage independently of the compiler used for Webpack5 projects. Before, the coverage addon only worked if Babel was used with Webpack5. Now, users might use other compilers like, for example, SWC.

📦 Published PR as canary version: 1.0.0-canary.27.12a4851.0

✨ Test out this PR locally via:

npm install @storybook/addon-coverage@1.0.0-canary.27.12a4851.0
# or 
yarn add @storybook/addon-coverage@1.0.0-canary.27.12a4851.0

[kasperpeulen]

Nice!

[sebaguozden]

@kasperpeulen @yannbf I tried this with an app created using pnpm create vite (React -> TypeScript + SWC) and I can't get coverage correctly (#28)

[taozhou-glean]

how should I expect to run the coverage on the webpack5 example folder ?

I am getting following errors:

Test Suites: 3 failed, 3 total
Tests:       8 failed, 8 total
Snapshots:   0 total
Time:        1.416 s
Ran all test suites.
Coverage file (2 bytes) written to .nyc_output/coverage.json
----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------|---------|----------|---------|---------|-------------------
All files |       0 |        0 |       0 |       0 |
----------|---------|----------|---------|---------|-------------------

while yarn test-storybook works just fine

 PASS   browser: chromium  stories/Page.stories.tsx
 PASS   browser: chromium  stories/Button.stories.tsx
 PASS   browser: chromium  stories/Header.stories.tsx

Test Suites: 3 passed, 3 total
Tests:       8 passed, 8 total
Snapshots:   0 total
Time:        1.318 s