@callback all_supported_targets(operation :: :compile | :fetch) :: [target()]

This callback should return a list of triplets ("arch-os-abi") for all supported targets of the given operation.

For the :compile operation, all_supported_targets should return a list of targets that the current host is capable of (cross-)compiling to.

For the :fetch operation, all_supported_targets should return the full list of targets.

For example, GitHub Actions provides Linux, macOS and Windows CI hosts, when operation is :compile, the precompiler might return ["x86_64-linux-gnu"] if it is running in the Linux CI environment, while returning ["x86_64-apple-darwin", "aarch64-apple-darwin"] on macOS, or ["amd64-windows", "x86-windows"] on Windows platform.

When operation is :fetch, the precompiler should return the full list. The full list for the above example should be:

[
  "x86_64-linux-gnu",
  "x86_64-apple-darwin",
  "aarch64-apple-darwin",
  "amd64-windows",
  "x86-windows"
]

This allows the precompiler to do the compilation work in multilple hosts and gather all the artefacts later with mix elixir_make.checksum --all.

@callback build_native(OptionParser.argv()) ::
  {Mix.Task.Compiler.status(), [Mix.Task.Compiler.Diagnostic.t()]}

This callback will be invoked when the user executes the mix compile (or mix compile.elixir_make) command.

The precompiler should then compile the NIF library "natively". Note that it is possible for the precompiler module to pick up other environment variables like TARGET_ARCH=aarch64 and adjust compile arguments correspondingly.

@callback current_target() :: {:ok, target()} | {:error, String.t()}

This callback should return the target triplet for current node.

@callback post_precompile() :: :ok

Optional post actions to run after all precompilation tasks are done.

It will only be called at the end of the mix elixir_make.precompile command. For example, actions can be archiving all precompiled artefacts and uploading the archive file to an object storage server.

@callback post_precompile_target(target()) :: :ok

Optional post actions to run after each precompilation target is archived.

It will be called when a target is precompiled and archived successfully. For example, actions can be deleting all target-specific files.

@callback precompile(OptionParser.argv(), target()) :: :ok | {:error, String.t()}

This callback should precompile the library to the given target(s).

Returns :ok if the requested target has successfully compiled.

@callback unavailable_target(String.t()) :: :compile | :ignore

Optional recover actions when the current target is unavailable.

There are two reasons that the current target might be unavailable: when the library only has precompiled binaries for some platforms, and it either

• needs to be compiled on other platforms.

  The callback should return :compile for this case.

• is intended to function as noop on other platforms.

  The callback should return :ignore for this case.

Defaults to :compile if this callback is not implemented.