Flow: Throws error Cannot resolve module "react-redux" even tho it's installed

Question

Even tho module is installed and it exists, Flow cannot resolve it and throws error. See below: 1) Inside bash I ran flow and it throws error that module is not found

user@pc:~/code/project$ flow
Error ┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈ src/functionalities/Growth/index.js:3:25

Cannot resolve module react-redux.

     1│ // @flow
     2│ import React from "react"
     3│ import { connect } from "react-redux"
     4│
     5│ type Props = {
     6│   children: Function



Found 1 error

2) Below command checks whether directory exists and it does

user@pc:~/code/project$ ls node_modules | grep react-redux
react-redux

I tried to remove and reinstall both node_modules directory and yarn.lock file.

Versions should be matching:

flow version
Flow, a static type checker for JavaScript, version 0.77.0

.flowconfig:

[version]
0.77.0

This is very likely bug with Flow, I also submitted issue.

Answer 1

How to fix it

You have two options:

1. stub the dependency by hand
2. bring in flow-typed to find the dependency type file/stub it for you

I use option 2 but it is nice to know what is happening underneath

Option 1

In .flowconfig, add a directory under [libs],

...
[libs]
/type-def-libs
...

Now, create that directory at your project root and a file /type-def-libs/react-redux which contains,

declare module 'react-redux' {
  declare module.exports: any;
}

Option 2

• install flow-typed, if using yarn yarn add -D flow-typed
  • I prefer to install every locally to the project when possible
• run yarn flow-typed install
  • this will install any type definition files for modules that it finds AND it will stub any modules it doesn't find, which is similar to what we did in option 1

Why is this error happening

Flow is looking for the type definition for the module you are importing. So while the module does exist in /node_modules that module doesn't have a type definition file checked into its code.