NextJS 15.2 build issues ("Multiple assets emit").

[yoohahn]

Describe the bug

Bumping next to 15.2.0 will result in the following error:

Conflict: Multiple assets emit different content to the same filename middleware-manifest.json

If I downgrade to 15.1.6 it works without any issues

Reproduction

https://github.com/yoohahn/vanilla-nextjs-bug

System Info

System:
    OS: Linux 5.15 Ubuntu 24.04.1 LTS 24.04.1 LTS (Noble Numbat)
    CPU: (12) x64 AMD Ryzen 5 3600 6-Core Processor
    Memory: 13.32 GB / 15.58 GB
    Container: Yes
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 23.6.0 - /run/user/1000/fnm_multishells/1621_1740677874806/bin/node
    Yarn: 4.6.0 - /run/user/1000/fnm_multishells/1621_1740677874806/bin/yarn
    npm: 10.9.2 - /run/user/1000/fnm_multishells/1621_1740677874806/bin/npm
    bun: 1.2.1 - ~/.bun/bin/bun
  npmPackages:
    @vanilla-extract/css: ^1.17.1 => 1.17.1 
    @vanilla-extract/css-utils: ^0.1.4 => 0.1.4 
    @vanilla-extract/dynamic: ^2.1.2 => 2.1.2 
    @vanilla-extract/next-plugin: ^2.4.10 => 2.4.10 
    @vanilla-extract/recipes: ^0.5.5 => 0.5.5

Used Package Manager

yarn

Logs

Reproduceable repo provided


git clean -fdx . ; yarn install ; yarn build

Failed to compile.

Conflict: Multiple assets emit different content to the same filename middleware-manifest.json


If we build again it will work. Same goes for `yarn dev` it will fail the first time with that error. If I restart the command it will then work.

If I clean the repo and start over the same issue occurs the first time, next time it will work.

Validations

• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• The provided reproduction is a minimal reproducible example of the bug.