fix(nextjs): Don't run webpack plugin on non-prod Vercel deployments

[lobsterkatie]

When someone adds our Vercel integration, it only adds sentry-cli-relevant environment variables to production deployments. This can cause non-production deployments to fail, because when the webpack loader tries to run, it doesn't find the information it needs. That said, there's a reason we only set the env variables for prod - we really shouldn't be creating releases or uploading sourcemaps for dev or preview deployments in any case.

This adds an environment check for vercel deployments (using the VERCEL_ENV env variable), and only enables the webpack plugin if the environment is production. To give users a way to override this, setting disableClientWebpackPlugin or disableServerWebpackPlugin to false now takes precedence over other checks, rather than being a no-op. Finally, given that the number of enablement checks is likely to grow, this pulls them into a separate function.

This supersedes getsentry/sentry#37649.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.4 KB (-0.02% 🔽)
@sentry/browser - ES5 CDN Bundle (minified)	60.06 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	17.98 KB (0%)
@sentry/browser - ES6 CDN Bundle (minified)	52.92 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	19.77 KB (0%)
@sentry/browser - Webpack (minified)	64.31 KB (0%)
@sentry/react - Webpack (gzipped + minified)	19.79 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	44.72 KB (0%)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	25.91 KB (-0.01% 🔽)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	24.28 KB (-0.01% 🔽)

[vladanpaunovic]

Thanks @lobsterkatie!

Can we make sure that there is some test for this scenario?

Also, once we close this, we should try to understand how this can be solved in non-vercel environments.

[vladanpaunovic]

Looking good now! Thanks @lobsterkatie!