Platform Details

This action installs the Nim compiler so cibuildwheel can compile your extension. See the support matrix for what is tested.

Linux

Wheels are built inside manylinux Docker containers.

The action:

Appends *-musllinux* to CIBW_SKIP unless you already skipped musllinux (official Nim binaries are glibc).
Selects linux_x64 or linux_arm64 from the native runner architecture.
Prepends installation commands to CIBW_BEFORE_ALL_LINUX to install xz, curl, and gcc, download Nim, and verify its .sha256 file.
Runs any caller-provided CIBW_BEFORE_ALL_LINUX commands after Nim is available.

Linux aarch64 is tested on the native ubuntu-24.04-arm runner. Use a native runner matching the requested wheel architecture.

Container images

cibuildwheel chooses the manylinux image. You can override image names with the usual CIBW_MANYLINUX_* variables; the Nim archive continues to match the runner architecture.

Customizing Linux builds

The action preserves CIBW_BEFORE_ALL_LINUX and runs it after installing Nim:

env:
  CIBW_BEFORE_ALL_LINUX: "nimble install cligen -y"

macOS

The action downloads the official archive for the runner CPU:

nim-<version>-macosx_arm64.tar.xz on Apple Silicon
nim-<version>-macosx_x64.tar.xz on Intel

Checksums are verified with shasum -a 256 -c. Cross-compiling a macOS wheel for the other architecture is not in the tested matrix.

steps:
  - name: Build wheels (Apple Silicon runner)
    runs-on: macos-14
    # Native arm64 Nim

Windows

Installs the requested Nim version with Chocolatey
Uses the MinGW dependency installed by the Chocolatey Nim package
Adds C:\tools\Nim\nim-<version>\bin to PATH; Chocolatey supplies the compiler path

Default generated projects statically link MinGW runtimes via nuwa-build (windows-static-linking = true).

Environment variables

Use the standard cibuildwheel hooks for extra setup. On Linux, a supplied CIBW_BEFORE_ALL_LINUX hook is appended after Nim installation.

See cibuildwheel settings for CIBW_BUILD, CIBW_SKIP, and architecture flags.