Including Rust Code in Firefox¶
The build system has support for building and linking Rust crates.
Rust code is built using cargo
in the typical way, so it is
straightforward to take an existing Rust crate and integrate it
into Firefox.
Linking Rust Crates into libxul¶
Rust crates that you want to link into libxul should be listed in the
dependencies
section of toolkit/library/rust/shared/Cargo.toml.
After adding your crate, execute cargo update -p gkrust-shared
in
toolkit/library/rust
to update the Cargo.lock file. You’ll also
need to add an extern crate
reference to
toolkit/library/rust/shared/lib.rs.
This ensures that the Rust code will be linked properly into libxul as well
as the copy of libxul used for gtests.
Linking Rust Crates into something else¶
There currently is not any Rust code being linked into binaries other than
libxul. If you would like to do so, you’ll need to create a directory with
a Cargo.toml
file for your crate, and a moz.build
file that contains:
RustLibrary('crate_name')
Where crate_name matches the name from the [package]
section of your
Cargo.toml
. You can refer to the moz.build file and the Cargo.toml file that are used for libxul.
You can then add USE_LIBS += ['crate_name']
to the moz.build
file
that defines the binary as you would with any other library in the tree.
Important
You cannot link a Rust crate into an intermediate library that will wind
up being linked into libxul. The build system enforces that only a single
RustLibrary
may be linked into a binary. If you need to do this, you
will have to add a RustLibrary
to link to any standalone binaries that
link the intermediate library, and also add the Rust crate to the libxul
dependencies as in linking Rust Crates into libxul.
Where Should I put my Crate?¶
If your crate’s canonical home is mozilla-central, you can put it next to the other code in the module it belongs to.
If your crate is mirrored into mozilla-central from another repository, and
will not be actively developed in mozilla-central, you can simply list it
as a crates.io
-style dependency with a version number, and let it be
vendored into the third_party/rust
directory.
If your crate is mirrored into mozilla-central from another repository, but will be actively developed in both locations, you should send mail to the dev-builds mailing list to start a discussion on how to meet your needs.
Crate dependencies¶
All dependencies for in-tree Rust crates are vendored into the
third_party/rust
directory. Currently if you add a dependency on a new
crate you must run mach vendor rust
to vendor the dependencies into
that directory. In the future we hope to make it so that you only need to
vendor the dependencies in order to build your changes in a CI push.