Issue with generated sourcemaps via source-loader

Describe the bug We’ve hit an issue when upgrading our repo to the latest version of @storybook/vue. After going through the releases it appears the issue is linked to a change in source-loader which looks like it was introduced in v6.1.0-alpha.21.

I’ve pasted the error log below, but essentially it looks like the sourcemap being generated isn’t being converted to JSON properly – when logged via console, we see a SourceMapGenerator object, rather than just a JSON object – which is why we are seeing "version" is a required argument – as that argument doesn’t exist until the sourcemap is parsed properly into JSON.

To Reproduce

I’ve made a branch of our repo which you can checkout to reproduce the issue.

1. Checkkout ‘fozzie-components’ repo (package-updates branch)
2. Run yarn (or NPM) to install packages at the root of the repo.
3. Run yarn storybook:build at the root of the repo to build storybook.
4. See error.

Note that if you downgrade to alpha.20 in this file, the build successfully completes.

Expected behavior Storybook should build successfully.

Error log:

92% chunk asset optimization TerserPluginERR! => Failed to build the preview                                                                                                                                                               e @justeat/storybook: ERR! "version" is a required argument.                                                                                                                                                                                  e @justeat/storybook: (node:6368) UnhandledPromiseRejectionWarning: Error: "version" is a required argument.                                                                                                                                  n @justeat/storybook:     at Object.getArg (/_je/ui/components/fozzie-components/node_modules/source-map/lib/util.js:24:11)                                                                                                m @justeat/storybook:     at new BasicSourceMapConsumer (/_je/ui/components/fozzie-components/node_modules/source-map/lib/source-map-consumer.js:294:22)                                                                   d @justeat/storybook:     at new SourceMapConsumer (/_je/ui/components/fozzie-components/node_modules/source-map/lib/source-map-consumer.js:22:7)                                                                          = @justeat/storybook:     at SourceMapSource.node (/_je/ui/components/fozzie-components/node_modules/webpack-sources/lib/SourceMapSource.js:32:62)
@justeat/storybook:     at ReplaceSource.node (/_je/ui/components/fozzie-components/node_modules/webpack-sources/lib/ReplaceSource.js:82:27)
@justeat/storybook:     at CachedSource.node (/_je/ui/components/fozzie-components/node_modules/webpack-sources/lib/CachedSource.js:18:24)
@justeat/storybook:     at ReplaceSource.node (/_je/ui/components/fozzie-components/node_modules/webpack-sources/lib/ReplaceSource.js:82:27)
@justeat/storybook:     at /_je/ui/components/fozzie-components/node_modules/webpack-sources/lib/ConcatSource.js:59:50
@justeat/storybook:     at Array.map (<anonymous>)
@justeat/storybook:     at ConcatSource.node (/_je/ui/components/fozzie-components/node_modules/webpack-sources/lib/ConcatSource.js:58:63)
@justeat/storybook:     at ConcatSource.proto.sourceAndMap (/_je/ui/components/fozzie-components/node_modules/webpack-sources/lib/SourceAndMapMixin.js:29:18)
@justeat/storybook:     at CachedSource.sourceAndMap (/_je/ui/components/fozzie-components/node_modules/webpack-sources/lib/CachedSource.js:58:31)
@justeat/storybook:     at TerserPlugin.taskGenerator (/_je/ui/components/fozzie-components/node_modules/@storybook/core/node_modules/terser-webpack-plugin/dist/index.js:198:23)
@justeat/storybook:     at taskGenerator.next (<anonymous>)
@justeat/storybook:     at /_je/ui/components/fozzie-components/node_modules/@storybook/core/node_modules/terser-webpack-plugin/dist/index.js:455:49
@justeat/storybook:     at /_je/ui/components/fozzie-components/node_modules/@storybook/core/node_modules/p-limit/index.js:23:31
@justeat/storybook: (node:6368) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 2)

Code snippets If applicable, add code samples to help explain your problem.

System

Environment Info:

  System:
    OS: macOS Mojave 10.14.6
    CPU: (12) x64 Intel(R) Core(TM) i7-8750H CPU @ 2.20GHz
  Binaries:
    Node: 12.19.1 - /usr/local/bin/node
    Yarn: 1.19.1 - ~/.npm-packages/bin/yarn
    npm: 6.14.8 - ~/.npm-packages/bin/npm
  Browsers:
    Chrome: 87.0.4280.141
    Firefox: 84.0.1
    Safari: 14.0.2
  npmPackages:
    @storybook/storybook-deployer: 2.8.7 => 2.8.7

┆Issue is synchronized with this Asana task by Unito

[shilman]

@ankon any thoughts on this? i’m planning to revert the PR for now

[shilman]

ZOMG!! I just released https://github.com/storybookjs/storybook/releases/tag/v6.2.0-beta.14 containing PR #14199 that references this issue. Upgrade today to the @next NPM tag to try it out!

npx sb upgrade --prerelease

Closing this issue. Please re-open if you think there’s still more to do.