The error is happening because audiopus_sys falls back to building Opus from source, but the build environment doesn’t have cmake installed. That’s why you see:

failed to execute command: No such file or directory (os error 2)

is cmake not installed?

I believe to fix this, you need to update your nixpacks.toml so cmake is included in nixPkgs along with pkg-config, and keep opus in nixLibs
Example:

[phases.setup]

nixPkgs = [

"cmake",

"pkg-config"

]

nixLibs = [

"opus"

]

After redeploying with this config, the build should succeed!

Few things:

1. opus is not a valid Nix library or package

2. The crate should not even be attempting to build libopus; the intended behavior is that the presence of pkg-config and the libopus is sufficient for the crate discover it and statically link to it.

3. The proposed solution (including keeping libopus as a library) fails similarly to the original failure:
   ```
   process didn't exit successfully: /app/target/release/build/audiopus_sys-9601873073ea72a2/build-script-build (exit status: 101)

   --- stdout

   cargo:info=Static feature or environment variable found.

   cargo:rerun-if-env-changed=OPUS_NO_PKG_CONFIG

   cargo:rerun-if-env-changed=PKG_CONFIG_x86_64-unknown-linux-gnu

   cargo:rerun-if-env-changed=PKG_CONFIG_x86_64_unknown_linux_gnu

   cargo:rerun-if-env-changed=HOST_PKG_CONFIG

   cargo:rerun-if-env-changed=PKG_CONFIG

   cargo:rerun-if-env-changed=PKG_CONFIG_PATH_x86_64-unknown-linux-gnu

   cargo:rerun-if-env-changed=PKG_CONFIG_PATH_x86_64_unknown_linux_gnu

   cargo:rerun-if-env-changed=HOST_PKG_CONFIG_PATH

   cargo:rerun-if-env-changed=PKG_CONFIG_PATH

   cargo:rerun-if-env-changed=PKG_CONFIG_LIBDIR_x86_64-unknown-linux-gnu

   cargo:rerun-if-env-changed=PKG_CONFIG_LIBDIR_x86_64_unknown_linux_gnu

   cargo:rerun-if-env-changed=HOST_PKG_CONFIG_LIBDIR

   cargo:rerun-if-env-changed=PKG_CONFIG_LIBDIR

   cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR_x86_64-unknown-linux-gnu

   cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR_x86_64_unknown_linux_gnu

   cargo:rerun-if-env-changed=HOST_PKG_CONFIG_SYSROOT_DIR

   cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR

   cargo:infopkg_config could not find Opus.

   cargo:info=Opus source path used: "/root/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/audiopus_sys-0.2.2/opus".

   cargo:info=Building Opus via CMake.

   CMAKE_TOOLCHAIN_FILE_x86_64-unknown-linux-gnu = None

   CMAKE_TOOLCHAIN_FILE_x86_64_unknown_linux_gnu = None

   HOST_CMAKE_TOOLCHAIN_FILE = None

   CMAKE_TOOLCHAIN_FILE = None

   CMAKE_GENERATOR_x86_64-unknown-linux-gnu = None

   CMAKE_GENERATOR_x86_64_unknown_linux_gnu = None

   HOST_CMAKE_GENERATOR = None

   CMAKE_GENERATOR = None

   CMAKE_PREFIX_PATH_x86_64-unknown-linux-gnu = None

   CMAKE_PREFIX_PATH_x86_64_unknown_linux_gnu = None

   HOST_CMAKE_PREFIX_PATH = None

   CMAKE_PREFIX_PATH = None

   CMAKE_x86_64-unknown-linux-gnu = None

   CMAKE_x86_64_unknown_linux_gnu = None

   HOST_CMAKE = None

   CMAKE = None

   running: cd "/app/target/release/build/audiopus_sys-69cb3deaefc852a0/out/build" && CMAKE_PREFIX_PATH="" LC_ALL="C" "cmake" "/root/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/audiopus_sys-0.2.2/opus" "-DCMAKE_INSTALL_PREFIX=/app/target/release/build/audiopus_sys-69cb3deaefc852a0/out" "-DCMAKE_C_FLAGS= -ffunction-sections -fdata-sections -fPIC -m64" "-DCMAKE_C_COMPILER=/root/.nix-profile/bin/cc" "-DCMAKE_CXX_FLAGS= -ffunction-sections -fdata-sections -fPIC -m64" "-DCMAKE_CXX_COMPILER=/root/.nix-profile/bin/c++" "-DCMAKE_ASM_FLAGS= -ffunction-sections -fdata-sections -fPIC -m64" "-DCMAKE_ASM_COMPILER=/root/.nix-profile/bin/cc" "-DCMAKE_BUILD_TYPE=Release"

   --- stderr

   thread 'main' panicked at /root/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/cmake-0.1.54/src/lib.rs:1119:5:

   failed to execute command: No such file or directory (os error 2)

   is cmake not installed?

   build script failed, must exit now

   note: run with RUST_BACKTRACE=1 environment variable to display a backtrace

   warning: build failed, waiting for other jobs to finish...
   ```

Aaaah! I see. Thank you for that good explanation.

Maybe try updating your nixpacks.toml like so if you haven't tried this already:

[phases.setup]

nixPkgs = [

"cmake",

"pkg-config",

"libopus"

]

pkg-config should detect the system libopus and link against it.

Let me know how that goes!

This config still cannot find cmake:

[phase.setup]
nixPkgs = ["...", "pkg-config", "cmake", "libopus"]

The issue might be with the config section name. It should be [phases.setup] (plural), not [phase.setup]. Because of that, I don't think Nixpacks is actually installing any of your listed packages.

This works even if cmake is removed. Thank you for noticing that.

Awesome, I'm happy to hear that!
It's always the little things that cause havoc lol.

Happy deving!