Re: [PATCH V4 8/8] libgpiod: Integrate building of rust bindings with make

[Kent Gibson <warthog618@gmail.com>]

On Fri, Jul 08, 2022 at 05:05:01PM +0530, Viresh Kumar wrote:
> Lets make build rust bindings as well.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
>  README                    |  8 +++++---
>  TODO                      |  8 --------
>  bindings/Makefile.am      |  6 ++++++
>  bindings/rust/Makefile.am | 18 ++++++++++++++++++
>  configure.ac              | 16 ++++++++++++++++
>  5 files changed, 45 insertions(+), 11 deletions(-)
>  create mode 100644 bindings/rust/Makefile.am
> 
> diff --git a/README b/README
> index 814a0f161fd2..68b5d69f9b66 100644
> --- a/README
> +++ b/README
> @@ -119,9 +119,9 @@ TOOLS
>  BINDINGS
>  --------
>  
> -High-level, object-oriented bindings for C++ and python3 are provided. They
> -can be enabled by passing --enable-bindings-cxx and --enable-bindings-python
> -arguments respectively to configure.
> +High-level, object-oriented bindings for C++, python3 and Rust are provided.
> +They can be enabled by passing --enable-bindings-cxx, --enable-bindings-python
> +and --enable-bindings-rust arguments respectively to configure.
>  
>  C++ bindings require C++11 support and autoconf-archive collection if building
>  from git.
> @@ -132,6 +132,8 @@ the PYTHON_CPPFLAGS and PYTHON_LIBS variables in order to point the build
>  system to the correct locations. During native builds, the configure script
>  can auto-detect the location of the development files.
>  
> +Rust bindings require cargo support.
> +
>  TESTING
>  -------
>  
> diff --git a/TODO b/TODO
> index 8bb4d8f3ad56..cf4fd7b4a962 100644
> --- a/TODO
> +++ b/TODO
> @@ -28,14 +28,6 @@ and is partially functional.
>  
>  ----------
>  
> -* implement rust bindings
> -
> -With Rust gaining popularity as a low-level system's language and the
> -possibility of it making its way into the linux kernel, it's probably time to
> -provide Rust bindings to libgpiod as part of the project.
> -
> -----------
> -
>  * implement a simple daemon for controlling GPIOs in C together with a client
>    program
>  
> diff --git a/bindings/Makefile.am b/bindings/Makefile.am
> index 8f8c762f254f..004ae23dbc58 100644
> --- a/bindings/Makefile.am
> +++ b/bindings/Makefile.am
> @@ -14,3 +14,9 @@ if WITH_BINDINGS_PYTHON
>  SUBDIRS += python
>  
>  endif
> +
> +if WITH_BINDINGS_RUST
> +
> +SUBDIRS += rust
> +
> +endif
> diff --git a/bindings/rust/Makefile.am b/bindings/rust/Makefile.am
> new file mode 100644
> index 000000000000..79a52bc691ae
> --- /dev/null
> +++ b/bindings/rust/Makefile.am
> @@ -0,0 +1,18 @@
> +# SPDX-License-Identifier: GPL-2.0-or-later
> +# SPDX-FileCopyrightText: 2022 Viresh Kumar <viresh.kumar@linaro.org>
> +
> +command = cargo build --release --lib
> +
> +if WITH_TESTS
> +command += --tests
> +endif
> +
> +if WITH_EXAMPLES
> +command += --examples
> +endif
> +
> +all:
> +	$(command)
> +
> +clean:
> +	cargo clean
> diff --git a/configure.ac b/configure.ac
> index ab03673589e9..8458f734a606 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -211,6 +211,21 @@ then
>  		[AC_SUBST(PYTHON_LIBS, [`$PYTHON-config --libs`])])
>  fi
>  
> +AC_ARG_ENABLE([bindings-rust],
> +	[AS_HELP_STRING([--enable-bindings-rust],[enable rust bindings [default=no]])],
> +	[if test "x$enableval" = xyes; then with_bindings_rust=true; fi],
> +	[with_bindings_rust=false])
> +AM_CONDITIONAL([WITH_BINDINGS_RUST], [test "x$with_bindings_rust" = xtrue])
> +
> +if test "x$with_bindings_rust" = xtrue
> +then
> +	AC_CHECK_PROG([has_cargo], [cargo], [true], [false])
> +	if test "x$has_cargo" = xfalse
> +	then
> +		AC_MSG_ERROR([cargo not found - needed for rust bindings])
> +	fi
> +fi
> +
>  AC_CHECK_PROG([has_doxygen], [doxygen], [true], [false])
>  AM_CONDITIONAL([HAS_DOXYGEN], [test "x$has_doxygen" = xtrue])
>  if test "x$has_doxygen" = xfalse
> @@ -245,6 +260,7 @@ AC_CONFIG_FILES([Makefile
>  		 bindings/python/Makefile
>  		 bindings/python/examples/Makefile
>  		 bindings/python/tests/Makefile
> +		 bindings/rust/Makefile
>  		 man/Makefile])
>  
>  AC_OUTPUT
> -- 
> 2.31.1.272.g89b43f80a514
> 

Wouldn't build for me on a Debian bullseye VM.
Apparently bindgen requires clang to find the system headers [1][2], and
there is no dep check or warning about that.

Also not sure why the build wanted bindgen, as by default it uses the
pre-generated bindings?

Anyway, for reference this was the build error without clang installed:

...
   Compiling thiserror v1.0.31
   Compiling libgpiod-sys v0.1.0 (/home/dev/libgpiod/bindings/rust/libgpiod-sys)
error: failed to run custom build command for `libgpiod-sys v0.1.0 (/home/dev/libgpiod/bindings/rust/libgpiod-sys)`

Caused by:
  process didn't exit successfully: `/home/dev/libgpiod/bindings/rust/target/release/build/libgpiod-sys-0fb8ce8170c88d8f/build-script-build` (exit status: 101)
  --- stdout
  cargo:rerun-if-changed=wrapper.h
  cargo:rerun-if-changed=../../../lib/chip.c
  cargo:rerun-if-changed=../../../lib/chip-info.c
  cargo:rerun-if-changed=../../../lib/edge-event.c
  cargo:rerun-if-changed=../../../lib/info-event.c
  cargo:rerun-if-changed=../../../lib/internal.c
  cargo:rerun-if-changed=../../../lib/line-config.c
  cargo:rerun-if-changed=../../../lib/line-info.c
  cargo:rerun-if-changed=../../../lib/line-request.c
  cargo:rerun-if-changed=../../../lib/misc.c
  cargo:rerun-if-changed=../../../lib/request-config.c
  cargo:rerun-if-changed=../../../tests/gpiosim/gpiosim.c
  cargo:rerun-if-changed=gpiosim_wrapper.h
  cargo:rustc-link-lib=kmod
  cargo:rustc-link-lib=mount

  --- stderr
  /usr/include/string.h:33:10: fatal error: 'stddef.h' file not found
  /usr/include/string.h:33:10: fatal error: 'stddef.h' file not found, err: true
  thread 'main' panicked at 'Unable to generate bindings: ()', libgpiod-sys/build.rs:42:10

Cheers,
Kent.

[1] https://rust-lang.github.io/rust-bindgen/requirements.html
[2] https://github.com/rust-lang/rust-bindgen/issues/242