v12.0.0 -- Mono repo setups and extending tsconfigs break the build

[akadop]

What version of Next.js are you using?

12

What version of Node.js are you using?

14.17.5

What browser are you using?

Chrome

What operating system are you using?

mac, windows

How are you deploying your application?

Vercel

Describe the Bug

Next v12 has a function that, on dev or build, will look at the tsconfig and make suggestions.

If you have a mono repo setup and the nearest tsconfig is not at the root of the repo, extending a tsconfig without the incremental config option will break the build.

Check this repro repo out:
https://github.com/akadop/next-v12-monorepo-bug

Expected Behavior

The next commands (dev, build, start) all work correctly as they have been with prior versions

To Reproduce

Check this repro repo out:
https://github.com/akadop/next-v12-monorepo-bug

To see this, just try running yarn dev without making any changes. You should see this error:

TypeError: Cannot set property 'incremental' of undefined
    at ~\v12-next-bug\node_modules\next\dist\lib\typescript\writeConfigurationDefaults.js:150:57)
    at async Object.verifyTypeScriptSetup (~\v12-next-bug\node_modules\next\dist\lib\verifyTypeScriptSetup.js:81:9)
    at async DevServer.prepare (~\v12-next-bug\node_modules\next\dist\server\dev\next-dev-server.js:262:9)
    ```

If you go into the next.config and point the tsconfigPath at the nearest tsconfig, you get the same error.

If you instead point it to the tsconfig at the root of the repo, the build has no issues

[ijjk]

Hi, this has been updated in the latest version of Next.js v12.0.2-canary.1 please update and give it a try!

[balazsorban44]

This issue has been automatically locked due to no recent activity. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.