Cannot build in versions after next@14.1.0

[ravinggenius]

Link to the code that reproduces this issue

https://github.com/ravinggenius/minecraft-tools/tree/updates

To Reproduce

1. Clone project and checkout the updates branch
2. Configure environment: cp .env .env.local and fill in the missing values
3. Install exact dependencies: npm ci
4. Build project: npm run build runs as expected
5. Install any newer version of Next past 14.1.0: npm install next
6. Build project again and notice the absolute dump of minified JavaScript in the output

Current vs. Expected behavior

I expect to be able to install newer version of Next to keep my dependencies up-to-date. However every newer version of Next beyond 14.1.0 terminates the build process early and dumps a ton (2.1MB!) of minified JavaScript into the terminal. I've tried multiple versions of Next 14.1.x and 14.2.x with the same result.

I am also unable to run the dev server in any version past 14.1.0. Doing so produces copious erroneous output in the terminal when requesting a page.

Provide environment information

Operating System:
  Platform: linux (ChromeOS)
  Arch: x64
  Version: #1 SMP PREEMPT_DYNAMIC Sat, 17 Feb 2024 21:12:19 +0000
Binaries:
  Node: 18.18.2
  npm: 9.8.1
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  next: 14.1.0
  eslint-config-next: 14.2.2
  react: 18.2.0
  react-dom: 18.2.0
  typescript: 5.3.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Developer Experience

Which stage(s) are affected? (Select all that apply)

next dev (local), next build (local)

Additional context

I tested in the latest canary release (14.3.0-canary.44) also with the same result. You can find the full build output in this gist.

[ravinggenius]

I found a work-around, but I still don't understand the root cause. This function (https://github.com/ravinggenius/minecraft-tools/blob/a6ee5f4dba06f870bff9d861df216986cb36332e/src/i18n/server.ts#L41-L61) returns SupportedLocale (a string literal union) when run with Next 14.1.0. However in Next 14.1.1 and later, this function inexplicably returns Promise< SupportedLocale>. I'd really like to understand why it returns a promise, because nothing in the function appears to use promises. To be clear this function returns a promise in Next 14.1.1 and later, even without being maked async.

The work-around is simple: just call the function with await. To help remind me that it must be called with await, I also added async, though this has no effect on what it does.

[ravinggenius]

I found my issue. I was holding it wrong! I had "use server"; at the top of this file, even though the functions it defined where not server actions. Dang that was painful!