Install ¶

1 Requirements ¶

A Fortran 2018 compiler (gfortran 13+ is what CI and pixi pin)
fpm for the library and tests
fypp to regenerate capnp_endian / capnp_message from .fypp sources
The Cap’n Proto capnp tool when compiling schemas or regenerating fixtures

Optional interop tier:

meson, ninja, a C/C++ toolchain, cmocka
libcapnp / libcapnp-rpc for the live C++ RPC peer test

2 fpm ¶

$ git clone https://github.com/HaoZeke/capnp-fortran.git
$ cd capnp-fortran
$ fpm build
$ fpm test

The package name in fpm.toml is capnp; the executable is capnpc-fortran.

3 pixi (recommended)¶

pixi.toml pins gfortran, fpm, fypp, and capnproto on linux-64:

$ pixi install
$ pixi run gen      # fypp → src/*.f90 (commit if templates change)
$ pixi run build
$ pixi run test

Environments:

Feature	Purpose
default	library + tests
interop	meson + cmocka + C++ for golden master / C++ peer
docs	Sphinx + emacs ox-rst export

4 Interop suite ¶

$ git clone --depth 1 https://github.com/HaoZeke/c-capnproto third_party/c-capnproto
$ pixi run -e interop meson setup build-interop .
$ pixi run -e interop meson compile -C build-interop
$ pixi run -e interop meson test -C build-interop -v

When libcapnp-rpc is available, meson also builds the Fortran RPC client against a C++ EzRpcServer (schema adder.capnp). Details: Interop.

5 Building documentation ¶

$ pixi run -e docs docs
# HTML under docs/build/

Live site: https://capnp-fortran.rgoswami.me (Cloudflare Pages via the Documentation workflow).

6 Using the library from another fpm project ¶

Add a dependency on this repository (or the fpm registry package capnp once published), then:

use capnp

Generated schema modules are ordinary Fortran sources you compile alongside your program after running capnpc-fortran.

Official Cap’n Proto C++ owns find_package(CapnProto) and CapnProto::capnp / CapnProto::capnp-rpc. This Fortran port uses a separate CMake project name and namespace so both can link in one tree:

	Cap’n Proto C++	capnp-fortran
`find_package`	`CapnProto`	`capnp_fortran`
link target	`CapnProto::capnp`	`capnp_fortran::capnp_fortran`
Fortran module	n/a	`use capnp`

Top-level CMakeLists.txt builds the same checked-in src/*.f90 set as the meson interop tier. Optional plugin: CAPNP_FORTRAN_BUILD_PLUGIN (default ON when this tree is the top-level project, OFF under FetchContent / add_subdirectory). Options use the CAPNP_FORTRAN_* prefix so they do not collide with Cap’n Proto’s CAPNP_* variables.

include(FetchContent)
FetchContent_Declare(
  capnp_fortran
  GIT_REPOSITORY https://github.com/HaoZeke/capnp-fortran.git
  GIT_TAG        v0.1.1
)
# Optional: set(CAPNP_FORTRAN_BUILD_PLUGIN ON CACHE BOOL "" FORCE)
FetchContent_MakeAvailable(capnp_fortran)
target_link_libraries(myapp PRIVATE capnp_fortran::capnp_fortran)

Standalone:

$ cmake -S . -B build-cmake -DCMAKE_BUILD_TYPE=Release
$ cmake --build build-cmake
# library: build-cmake/libcapnp_fortran.a  (or .so if CAPNP_FORTRAN_BUILD_SHARED=ON)
# plugin:  build-cmake/capnpc-fortran   when CAPNP_FORTRAN_BUILD_PLUGIN=ON

Installable package config (find_package(capnp_fortran)) is generated when CAPNP_FORTRAN_INSTALL is ON (default for top-level builds).