`Cannot use e "__Schema" from another module or realm.` and `Duplicate "graphql" modules` using ApolloClient

Question

I have a React application with ApolloClient with Apollo-Link-Schema. The application works fine locally but in our staging environment (using GOCD), we get the following error:

Uncaught Error: Cannot use e "__Schema" from another module or realm.

Ensure that there is only one instance of "graphql" in the node_modules
directory. If different versions of "graphql" are the dependencies of other
relied on modules, use "resolutions" to ensure only one version is installed.

https://yarnpkg.com/en/docs/selective-version-resolutions

Duplicate "graphql" modules cannot be used at the same time since different
versions may have different capabilities and behavior. The data from one
version used in the function from another could produce confusing and
spurious results.
    at t.a (instanceOf.mjs:21)
    at C (definition.mjs:37)
    at _ (definition.mjs:22)
    at X (definition.mjs:284)
    at J (definition.mjs:287)
    at new Y (definition.mjs:252)
    at Y (definition.mjs:254)
    at Object.<anonymous> (introspection.mjs:459)
    at u (NominationsApprovals.module.js:80)
    at Object.<anonymous> (validate.mjs:1)

Dependencies are installed with yarn, I've added the resolutions field to the package.json.

    "resolutions": {
        "graphql": "^14.5.8"
    },

I've checked the yarn.lock and can only find one reference for the graphql package. npm ls graphql does not display any duplicates.

I thought maybe its a build issue with webpack - I have a different build script for staging, but running that locally I am still able to get the react application to run with that bundle.

Can anyone suggest anything else to help me fix this?

Answer 1

I managed to find the cause of the issue, if this helps anyone else. The issue is not to do with duplicate instances of the package at all, this is a false positive triggered by us using webpack's DefinePlugin to set the process.env.NODE_ENV to staging for our staging build.

However, in webpack the mode (see https://webpack.js.org/configuration/mode/), which sets the process.env.NODE_ENV, only accepts none, development and production as valid values. This was triggering an env check in the graphql package to fail and trigger this error message.

In our case, we need to differentiate between staging and production as our API endpoint differs based on this, but the solution we implemented is to not rely on the process.env.NODE_ENV, but to assign a custom variable on build (e.g. process.env.API_URL)

Answer 2

I would try to replicate the error locally and debug it:

try this:

rm -rf node_modules yarn.lock
# also remove any lock files if you have package-lock.json too
yarn install
# build the project locally and see if you got the error

I got this problem one time where I was working with Gatsby and 2 different themes where using different versions of GraphQL. Also be more explicit with the version (without caret) and check if the error persist.

do you have a repo youc an share? that would also help us to help you :)