Doesnt work with Yarn Berry (Workspaces)

[SagnikPradhan]

Describe the bug
Yarn requires a clear list of dependencies required, so it throws error when it tries to load any of the transformers

Logs

λ yarn rollup -c -w
rollup v2.6.1
bundles src/main.ts → public\build\bundle.js...
[!] (plugin svelte) Error: [svelte-preprocess] Error transforming 'typescript'.

Message:
svelte-preprocess tried to access typescript, but it isn't declared in its dependencies; this makes the require call ambiguous and unsound.

Required package: typescript (via "typescript")
Required by: svelte-preprocess@virtual:d293af44cc1e0d0fc09cc0c8c4a3d9e5fccdf4ddebae06b8fad52a312360d8122c830d53ecc46b13c13aaad8c6ae7dbd798566bd5cba581433425b2ff3f7540b#npm:3.7.1 (via /D:/Sagnik/Projects/d-zone/.yarn/unplugged/svelte-preprocess-virtual-129fc9d93a/node_modules/svelte-preprocess/dist/transformers/)

[STACK-TRACE-1]

Stack:
Error: svelte-preprocess tried to access typescript, but it isn't declared in its dependencies; this makes the require call ambiguous and unsound.

Required package: typescript (via "typescript")
Required by: svelte-preprocess@virtual:d293af44cc1e0d0fc09cc0c8c4a3d9e5fccdf4ddebae06b8fad52a312360d8122c830d53ecc46b13c13aaad8c6ae7dbd798566bd5cba581433425b2ff3f7540b#npm:3.7.1 (via /D:/Sagnik/Projects/d-zone/.yarn/unplugged/svelte-preprocess-virtual-129fc9d93a/node_modules/svelte-preprocess/dist/transformers/)

[STACK-TRACE-2]

To Reproduce

1. Create a directory and use yarn set version berry
2. Run yarn add lerna --dev and yarn lerna init
3. Change lerna.json to

{
  "packages": [
    "packages/webapp",
    "packages/server"
  ],
  "npmClient": "yarn",
  "useWorkspaces": true,
  "version": "0.2.0"
}

4. Create the same directory as https://github.com/sveltejs/template in packages/webapp and empty directory packages/server
5. Run cd packages/webapp
6. Run yarn install
7. Run yarn add svelte-preprocess and change Rollup Config
8. Run yarn add typescript --dev and yarn tsc --init
9. Change main.js to main.ts and add lang="ts" to script tags
10. Run yarn dev

Expected behavior
Run quietly and start the server

Stacktraces
If you have a stack trace to include, we recommend putting inside a <details> block for the sake of the thread's readability:

Stack trace

Require stack:
- D:\Sagnik\Projects\d-zone\.yarn\unplugged\svelte-preprocess-virtual-129fc9d93a\node_modules\svelte-preprocess\dist\transformers\typescript.js
- D:\Sagnik\Projects\d-zone\.yarn\unplugged\svelte-preprocess-virtual-129fc9d93a\node_modules\svelte-preprocess\dist\utils.js
- D:\Sagnik\Projects\d-zone\.yarn\unplugged\svelte-preprocess-virtual-129fc9d93a\node_modules\svelte-preprocess\dist\autoProcess.js
- D:\Sagnik\Projects\d-zone\.yarn\unplugged\svelte-preprocess-virtual-129fc9d93a\node_modules\svelte-preprocess\dist\index.js
- D:\Sagnik\Projects\d-zone\packages\webapp\rollup.config.js
- D:\Sagnik\Projects\d-zone\.yarn\cache\rollup-npm-2.6.1-6e29b31c16-2.zip\node_modules\rollup\dist\shared\loadConfigFile.js
- D:\Sagnik\Projects\d-zone\.yarn\cache\rollup-npm-2.6.1-6e29b31c16-2.zip\node_modules\rollup\dist\bin\rollup

Require stack:
- D:\Sagnik\Projects\d-zone\.yarn\unplugged\svelte-preprocess-virtual-129fc9d93a\node_modules\svelte-preprocess\dist\transformers\typescript.js
- D:\Sagnik\Projects\d-zone\.yarn\unplugged\svelte-preprocess-virtual-129fc9d93a\node_modules\svelte-preprocess\dist\utils.js
- D:\Sagnik\Projects\d-zone\.yarn\unplugged\svelte-preprocess-virtual-129fc9d93a\node_modules\svelte-preprocess\dist\autoProcess.js
- D:\Sagnik\Projects\d-zone\.yarn\unplugged\svelte-preprocess-virtual-129fc9d93a\node_modules\svelte-preprocess\dist\index.js
- D:\Sagnik\Projects\d-zone\packages\webapp\rollup.config.js
- D:\Sagnik\Projects\d-zone\.yarn\cache\rollup-npm-2.6.1-6e29b31c16-2.zip\node_modules\rollup\dist\shared\loadConfigFile.js
- D:\Sagnik\Projects\d-zone\.yarn\cache\rollup-npm-2.6.1-6e29b31c16-2.zip\node_modules\rollup\dist\bin\rollup
    at Object.makeError (D:\Sagnik\Projects\d-zone\.pnp.js:10171:34)
    at resolveToUnqualified (D:\Sagnik\Projects\d-zone\.pnp.js:17526:37)
    at resolveRequest (D:\Sagnik\Projects\d-zone\.pnp.js:17614:27)
    at Object.resolveRequest (D:\Sagnik\Projects\d-zone\.pnp.js:17682:26)
    at Function.module_1.Module._resolveFilename (D:\Sagnik\Projects\d-zone\.pnp.js:16879:34)
    at Function.module_1.Module._load (D:\Sagnik\Projects\d-zone\.pnp.js:16764:40)
    at Module.require (internal/modules/cjs/loader.js:1036:19)
    at require (internal/modules/cjs/helpers.js:72:18)
    at Object.<anonymous> (D:\Sagnik\Projects\d-zone\.yarn\unplugged\svelte-preprocess-virtual-129fc9d93a\node_modules\svelte-preprocess\dist\transformers\typescript.js:1:244)
    at Module._compile (internal/modules/cjs/loader.js:1147:30)

Information about your project:

• Your browser and the version: Doesn't Matter

• Your operating system: Windows 7 32bit

• svelte-preprocess version: 3.7.1

• Whether your project uses Webpack or Rollup: Rollup

Additional context
None

[SagnikPradhan]

IDK Why? But it works on a non workspace folder?

[SagnikPradhan]

Seems like the temporary solution is to use https://yarnpkg.com/configuration/yarnrc#packageExtensions

[kaisermann]

If people don't bother getting some warnings during a yarn/npm install, I can define the preprocessors as peerDependencies of the package. I'm not used to working with berry, but would that solve your issue?

[SagnikPradhan]

You can define the preprocessors as peerDependencies and use peerDependenciesMeta to declare them as optional.

Reference: peerDependenciesMeta in NPM and Yarn

[kaisermann]

@SagnikPradhan Ahhh, interesting! Didn't know that existed. Would you know the difference between an peerDependency with the peerDependenciesMeta "optional" set to true, and an optionalDependency? Found it.

[kaisermann]

@SagnikPradhan Just released 3.7.3 with explicit peerDeps. Can you check if it resolves your issue?

[SagnikPradhan]

Seems like your forgot to add less as optional, reference.

Other than the warning everything works great!

[kaisermann]

Heh, oops! Added it to 3.7.4