Building cdylibs written in Rust for Debian

Premise

Complete C-compatible libraries written in Rust are, while not yet common, a thing. This tries give developers some guidance if they want to package such a library.

cdylib with cargo-c

Depend on cargo-c:native in d/rules (in addition to the existing build-dependencies). Change the entire d/rules to this:

#!/usr/bin/make -f

include /usr/share/dpkg/architecture.mk

ifneq (,$(filter parallel=%,$(DEB_BUILD_OPTIONS)))
	NUMJOBS = $(patsubst parallel=%,%,$(filter parallel=%,$(DEB_BUILD_OPTIONS)))
else
	NUMJOBS = 1
endif

CARGO_C_FLAGS = --release \
	--destdir=debian/tmp \
	--prefix=/usr \
	--libdir=/usr/lib/${DEB_HOST_MULTIARCH} \
	--offline \
	-v \
	-j $(NUMJOBS)

%:
	dh $@ --buildsystem cargo

execute_after_dh_auto_build:
	CARGO_HOME=debian/cargo_home \
		/usr/share/cargo/bin/cargo cbuild $(CARGO_C_FLAGS)

override_dh_auto_install:
	CARGO_HOME=debian/cargo_home \
		/usr/share/cargo/bin/cargo cinstall $(CARGO_C_FLAGS)
     dh_auto_install

execute_after_dh_install:
	find debian -name Cargo.lock -delete

Then you need to run sbuild a few times to "guess" the correct missing build dependecies for cargo-c. Unfortunately Cargo.toml isn't helpful here. Once a clean build succeeds you'll want to create a foo-cdylib.install file that installs the .so in the correct location.

Since cargo-c builds a foo.pc pkgconf file and foo.a static library file by default you might want to create a not-installed file preventing the install of either one (or both), depending on your needs.

If the package you're targeting is already a crate packaged with the Debian Rust team you need a custom d/rules and d/control, so touch them first in the crates' debian folder and then run ./update.sh crate again. Then you can copy the rules/control.debcargo.hint file to rules/control respectively and edit them accordingly.

Example: rav1e, gstreamer1.0-gtk4

cdylibs with other build systems

Package all crates the usual way within the Debian Rust team. Then prepare the packaging, following this ¹ as rough guideline. dh will automatically pick up the buildsystem which in turn will build the library for you. It should just work™ like with C. In case you run into any issues feel free to ask on the #debian-rust IRC channel on OFTC.

Example: librsvg