Add compiler.define option

[lforst]

Adds a compiler.define option to next.config.js to statically replace any variables during build-time for Turbopack. This is similar to Webpack's DefinePlugin.

Relates to: #71476

[ijjk]

Allow CI Workflow Run

• approve CI run for commit: dc71558

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer

[lforst]

I just had the dumb realization that the env option already exists. https://nextjs.org/docs/pages/api-reference/next-config-js/env

It doesn't do the exact same thing but very often it might just be enough 🤔 Feel free to make the call that this PR is unnecessary.

[lforst]

It might actually not be a bad idea because the experimental. fallbackNodePolyfills option exists which will more or less break process.env usage (at least right now).

Encountered through user report in: getsentry/sentry-javascript#14193

[timneutkens]

Was discussing this with @sokra and @feedthejim, can you move the option to compiler.define instead and then also apply it when using webpack, that way it's the same between webpack/turbopack. I'm convinced we need this option next to env as it's being used in custom webpack config currently as well, e.g. to replace MY_VARIABLE stuff.

[lforst]

@timneutkens Makes sense! I moved the option to compiler and also use it for webpack builds 👍

[timneutkens]

Awesome PR Luca!

[ijjk]

Tests Passed

[delbaoliveira]

Thank you for the docs! 🙏🏼

[timneutkens]

Seems the define.test.ts added is failing during test runs 👀

[lforst]

Seems the define.test.ts added is failing during test runs 👀

Just saw. I have to look into it but either I am missing something completely obvious or there is something fundamentally off with the mechanics beneath what I am touching in this PR.

[timneutkens]

Fixed the issue with the tests and opened a new bug report for Turbopack here: #72576. The issue was related to declare const.