obazl_ctypes

Table of Contents

• Usage
• Rule: ctypes_module
• How it works
• Comparison: Dune’s ctypes stanza

Bazel rules for the ocaml-ctypes library.

Usage

Since obazl_ctypes is designed for use with rules_ocaml and opam, this example shows a complete minimal configuration:

MODULE.bazel

bazel_dep(name = "rules_ocaml", version = "3.0.0")
bazel_dep(name = "tools_opam",  version = "1.0.0")
opam = use_extension("@tools_opam//extensions:opam.bzl", "opam")
opam.deps(
    pkgs          = { "pkg": "x.y.z", ...other opam deps...  },
    toolchain     = "global" # | "local" | "xdg"
    ocaml_version = "5.3.0"
)
use_repo(opam, "opam.ocamlsdk")
use_repo(opam, "opam.pkg", ...other opam deps...)
register_toolchains(
    "@opam.ocamlsdk//toolchain/selectors/local:all",
    "@opam.ocamlsdk//toolchain/profiles:all",
)

bazel_dep(name = "obazl_ctypes", version = "0.23.0")
use_repo(opam, "opam.ctypes", "opam.ctypes-foreign")

Your build code:

BUILD.bazel

load("@obazl_ctypes//build/rules:ctypes.bzl", "ctypes_module")
ctypes_module(
    name     = "zstd",
    functors = {"type_description.ml": "Types",
                "function_description.ml": "Functions"},
    cclibs   = ["@zstd"],                                 (1)
    cchdrs   = ["zstd.h"]
)

1. In this example, @zstd is the label of an external Bazel module, registered in MODULE.bazel, that will build libzstd.a when this target is built.

Here Types and Functions are Ctypes-dependent functors, defined in type_description.ml and function_description.ml respetively:

type_description.ml

module Types (F : Ctypes.TYPE) = struct
       open F
       ...
end

function_description.ml

module Functions (F : Cstubs.FOREIGN) = struct
  open F
       ...
end

Note	You can choose your own names in place of Types, type_description.ml, etc.

Rule: ctypes_module

Note	ctypes_module is actually a macro, but it behaves like a rule so we call it one.

Attribute	Type	Default	Mandatory?	Notes
name	string	none	yes	Target name. Sets <api_stem>.
functors	string_map, keys: file names; vals: functor names	none	yes	specifies structure of source code
cclibs	label_list	none	yes	CC lib being wrapped
cchdrs	string_list	none	no	CC lib headers
api_name	string	<api_stem>_api	no	Name of API module (not archive) to be generated. No relation to dune/opam/findlib pkg naming;
wrapper	string	none	no	names module embedded in API module, wrapping the Types and Functions modules;
types_module	string	<api_stem>_Types	no	name of Types module
functions_module	string	<api_stem>_Functions	no	name of Functions module

How it works

To list the files generated by the build:

bazel query 'kind("generated file", //stubs:*)'

The essential files:

• Zstd_CtypesTYPE - specialization of mtype Ctypes.TYPE

• Zstd_CtypesFOREIGN - specialization of mtype Ctypes.FOREIGN

• libzstd_c_adapter_lib.a - dep of Zstd_CtypesFOREIGN

Conveniences:

• Zstd_api - simple wrapper, aliases Types and Functions functor applications

• Zstd_Types (dune: Types_generated) - wrapper, includes Type_description.Types(Zstd_CtypesTYPE). Not really needed.

Comparison: Dune’s ctypes stanza