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Compilers and cross-compilation#

To use a compiler in your project, it's best to use the ${{ compiler('lang') }} template function. The compiler function works by taking a language, determining the configured compiler for that language, and adding some information about the target platform to the selected compiler. To configure a compiler for a specific language, the variant_config.yaml file can be used.

For example, in a recipe that uses a C-compiler, you can use the following code:

requirements:
  build:
    - ${{ compiler('c') }}

To set the compiler that you want to use, create a variant config that looks like the following:

c_compiler:
  - gcc

# optionally you can specify a version
c_compiler_version:
  - 9.3.0

When the template function is evaluated, it will look something like: gcc_linux-64 9.3.0. You can define your own compilers. For example, for rust you can use ${{ compiler('rust') }} and rust_compiler_{version} in your variant config.

Cross compilation#

Cross compilation is supported by rattler-build and the compiler template function is part of what makes it possible. When you want to cross-compile from linux-64 to linux-aarch64 (intel to ARM), you can pass --target-platform linux-aarch64 to the rattler-build command. This will cause the compiler template function to select a compiler that is configured for linux-aarch64. The above example would resolve to gcc_linux-aarch64 9.3.0. Provided that the package is available for linux-64 (your build platform), the compilation should succeed.

The distinction between build and host section begins to make sense when thinking about cross compilation. The build enviromemnt is resolved to packages that need to run at compilation time. For example, cmake, gcc, autotools are all tools that need to be executed. Therefore, the build environment resolves to packages for the linux-64 architecture (in our example). On the other hand, the host packages resolve to linux-aarch64 - those are packages that we want to link against.

# packages that need to run at build time (cmake, gcc, autotools, etc.)
# in the platform that rattler-build is executed on (the build_platform)
build:
  - cmake
  - ${{ compiler('c') }}
# packages that we want to link against in the architecture we are cross-compiling to
# (the target_platform)
host:
  - libcurl
  - openssl