Undefined variable 'dotnet-sdk_9'

[michel-jump]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

This happens when I use nixpacks buid in a .NET 9 project.

nixpacks build ./

╔═════════════════════ Nixpacks v1.30.0 ═════════════════════╗
║ setup      │ dotnet-sdk_9                                  ║
║────────────────────────────────────────────────────────────║
║ install    │ dotnet restore                                ║
║────────────────────────────────────────────────────────────║
║ build      │ dotnet publish --no-restore -c Release -o out ║
║────────────────────────────────────────────────────────────║
║ start      │ ./out/Application                             ║
╚════════════════════════════════════════════════════════════╝

[+] Building 15.3s (8/13)                                                                                                                                                                              docker:desktop-linux
 => [internal] load build definition from Dockerfile                                                                                                                                                                   0.0s
 => => transferring dockerfile: 844B                                                                                                                                                                                   0.0s
 => [internal] load metadata for ghcr.io/railwayapp/nixpacks:ubuntu-1733184274                                                                                                                                         0.4s
 => [internal] load .dockerignore                                                                                                                                                                                      0.0s
 => => transferring context: 2B                                                                                                                                                                                        0.0s
 => [1/9] FROM ghcr.io/railwayapp/nixpacks:ubuntu-1733184274@sha256:91b1c0ad82b8a7ad531acdb8acf466f0cdbfd9738cf1b31286ca09f9dbb12e21                                                                                   0.0s
 => [internal] load build context                                                                                                                                                                                      0.3s
 => => transferring context: 2.56MB                                                                                                                                                                                    0.3s
 => CACHED [2/9] WORKDIR /app/                                                                                                                                                                                         0.0s
 => CACHED [3/9] COPY .nixpacks/nixpkgs-5148520bfab61f99fd25fb9ff7bfbb50dad3c9db.nix .nixpacks/nixpkgs-5148520bfab61f99fd25fb9ff7bfbb50dad3c9db.nix                                                                    0.0s
 => ERROR [4/9] RUN nix-env -if .nixpacks/nixpkgs-5148520bfab61f99fd25fb9ff7bfbb50dad3c9db.nix && nix-collect-garbage -d                                                                                              14.5s
------                                                                                                                                                                                                                      
 > [4/9] RUN nix-env -if .nixpacks/nixpkgs-5148520bfab61f99fd25fb9ff7bfbb50dad3c9db.nix && nix-collect-garbage -d:                                                                                                          
0.178 unpacking 'https://github.com/NixOS/nixpkgs/archive/5148520bfab61f99fd25fb9ff7bfbb50dad3c9db.tar.gz' into the Git cache...                                                                                            
13.83 installing '5148520bfab61f99fd25fb9ff7bfbb50dad3c9db-env'                                                                                                                                                             
13.90 error:                                                                                                                                                                                                                
13.90        … while calling the 'derivationStrict' builtin                                                                                                                                                                 
13.90          at <nix/derivation-internal.nix>:34:12:
13.90            33|
13.90            34|   strict = derivationStrict drvAttrs;
13.90              |            ^
13.90            35|
13.90 
13.90        … while evaluating derivation '5148520bfab61f99fd25fb9ff7bfbb50dad3c9db-env'
13.90          whose name attribute is located at /nix/store/lgcjj6s23v2203zyihsd0j26wh1saj0c-source/pkgs/stdenv/generic/make-derivation.nix:300:7
13.90 
13.90        … while evaluating attribute 'passAsFile' of derivation '5148520bfab61f99fd25fb9ff7bfbb50dad3c9db-env'
13.90          at /nix/store/lgcjj6s23v2203zyihsd0j26wh1saj0c-source/pkgs/build-support/trivial-builders/default.nix:88:7:
13.90            87|       inherit buildCommand name;
13.90            88|       passAsFile = [ "buildCommand" ]
13.90              |       ^
13.90            89|         ++ (derivationArgs.passAsFile or []);
13.90 
13.90        (stack trace truncated; use '--show-trace' to show the full, detailed trace)
13.90 
13.90        error: undefined variable 'dotnet-sdk_9'
13.90        at /app/.nixpacks/nixpkgs-5148520bfab61f99fd25fb9ff7bfbb50dad3c9db.nix:19:9:
13.90            18|         '')
13.90            19|         dotnet-sdk_9
13.90              |         ^
13.90            20|       ];
------
Dockerfile:8
--------------------
   6 |     
   7 |     COPY .nixpacks/nixpkgs-5148520bfab61f99fd25fb9ff7bfbb50dad3c9db.nix .nixpacks/nixpkgs-5148520bfab61f99fd25fb9ff7bfbb50dad3c9db.nix
   8 | >>> RUN nix-env -if .nixpacks/nixpkgs-5148520bfab61f99fd25fb9ff7bfbb50dad3c9db.nix && nix-collect-garbage -d
   9 |     
  10 |     
--------------------
ERROR: failed to solve: process "/bin/bash -ol pipefail -c nix-env -if .nixpacks/nixpkgs-5148520bfab61f99fd25fb9ff7bfbb50dad3c9db.nix && nix-collect-garbage -d" did not complete successfully: exit code: 1

View build details: docker-desktop://dashboard/build/desktop-linux/desktop-linux/m1n4wn2a8hvnswg3gn29yaz0d
Error: Docker build failed

To reproduce

• Setup an .NET 9 project.
• Run nixpacks build ./ in the right directory

Expected behavior

I expect nixpacks to build the application.

Environment

OS: macOS 15.2 (M3 Pro)
Nixpacks version: 1.30.0 (installed via Homebrew)

[DavidRod1865]

I would like to work on this issue.