flow types fail compilation in monorepo with CRA next.66cc7a90

[bebbi]

Is this a bug report?

yes.

It's a project with flow annotations. Lines like these appear to trigger the issue:

import type { Props, ComponentState } from './MyComponent.type'

The error is:

Failed to compile.

./src/components/MyComponent.js
Module build failed: TypeError: Cannot read property 'type' of undefined
    at Array.forEach (<anonymous>)
    at Array.forEach (<anonymous>)

Moving the code outside the monorepo and yarn; yarn start: works.
Keep it inside and remove all flow annotations: works.

Did you try recovering your dependencies?

Yes.
In fact, adding a package.json declaration of

"nohoist": [
  "**/react-scripts", "**/react-scripts/**"
]

works around the issue.

Which terms did you search for in User Guide?

flow, monorepo, workspaces

Environment

Environment:
  OS:  macOS High Sierra 10.13.4
  Node:  8.9.1
  Yarn:  1.6.0
  npm:  6.0.1
  Watchman:  4.9.0
  Xcode:  Xcode 9.3.1 Build version 9E501
  Android Studio:  Not Found

Packages: (wanted => installed)

(paste the output of the command here)

Steps to Reproduce

1. Create a CRA project from scratch
2. Add flow annotations as above
3. yarn; yarn start
4. See it working
5. Move the code into an existing monorepo with yarn workspaces enabled
6. yarn; yarn start
7. See it failing

Expected Behavior

Should just work.

Actual Behavior

Compilation failure per above error.

[bugzpodder]

I cannot repro this. Can you provide a clean repo?
I also tried import { type Props } from "..." and it worked fine.

[stale]

This issue has been automatically marked as stale because it has not had any recent activity. It will be closed in 5 days if no further activity occurs.

[apolkingg8]

Dear bot, it's still a issue.

[bugzpodder]

Can you provide a repro?

[eduardomoroni]

I'm facing the same issue with my current mono repo:
https://github.com/eduardomoroni/trading-card-manager
Folders structure

|_core
|_web (uses core)
|_mobile (uses core)

If you want to use this repo to reproduce:

• clone the project
• checkout mtg-community/trading-card-manager@f27ad9d
• under web folder run make install
• npm start or yarn start

I followed https://flow.org/en/docs/tools/create-react-app/.

Explaining better this case:
I'd like to share the module core between two apps. The module core is using flow annotations and type keywords. I'm installing this module via npm install ../core which make the apps create a symlink under its node_module folder. This module needs to be parsed by babel during run-time, the same way babel does with the files under src folder. What I think it's happening is that we're trying to run this module without transforming it.
I'm inclined to say that this problem is related to Babel and not CRA. The mobile project is using babel 6 and it's working fine
https://babeljs.io/docs/en/config-files#6x-vs-7x-babelrc-loading

[bugzpodder]

This should be import { type StateType } from '../types';
flowconfig

[libs]
../core/flow-typed
./flow-typed

[options]
module.name_mapper='^core\/(.*\)$' -> '<PROJECT_ROOT>/../core/src\1'

[eduardomoroni]

Thanks @bugzpodder for you answer. I've tried you tip, no luck though.

When I tried to run flow, it got stuck.

When I try to run the App

Now it show Unexpected token, expected "," there's no comma on this line.

I also tried some variations of your suggestion, I thought that could be a typo on module.name_mapper='^core\/(.*\)$' -> '<PROJECT_ROOT>/../core/src\1', Based on the option docs.

Don't you think that this could be caused by how babel deals with Monorepos?

The changes you suggested was pushed on branch babel-error.

[bugzpodder]

Hey, sorry about that. I didn't pay attention to the details of the problem you described. So the issue isn't with flow typed, but it is because create-react-app is not stripping out flow-types from your symlinked node_modules/ when building your app.

So this is done on purpose as part of create-react-app configuration. The recommended way is to first run babel on your core module to strip out the flow types and then import it from web.
I have a working version here: https://github.com/bugzpodder/yarn-workspace-cra but it is using babel 7 and yarn workspaces.

So tooling (yarn workspaces/make) aside, here is what needs to happen:

1. run babel on your core, generating dist/ from src/
2. set package.json in your core to point to dist/
3. link core to your node-modules
4. set your flow-config to resolve import 'core/...' to 'core/src/...'

You maybe able to use a forked version of create-react-app, or otherwise modify the webpack config of react-scripts to achieve 1 - 3.

[eduardomoroni]

Thanks, @bugzpodder this worked great.
For what you said this behavior is part of the expected behavior of the library. So I think we can close this issue @bebbi.
Just out of curiosity, the reason why CRA doesn't allow transpile node_modules is to avoid unnecessary babel work?

[bugzpodder]

The reason is that create-react-app won't process libraries from using non-standard features such as flow and other js features and proposals that are not currently finalized, in order to avoid defragmentation of the js landscape.
What you are doing however is just sharing source code between different apps, so its a different use case that create-react-app isn't supporting right now but will in the future.

[stale]

This issue has been automatically marked as stale because it has not had any recent activity. It will be closed in 5 days if no further activity occurs.

[stale]

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