Basics
Formatting Rust code
To format all the Rust code within a directory $DIR
, run:
./mach lint -l rustfmt --fix $DIR
Using Cargo
Many Cargo commands can be run on individual crates. Change into the directory
containing the crate’s Cargo.toml
file, and then run the command with
MOZ_TOPOBJDIR
set appropriately. For example, to generate and view rustdocs
for the xpcom
crate, run these commands:
cd xpcom/rust/xpcom
MOZ_TOPOBJDIR=$OBJDIR cargo doc
cd -
firefox target/doc/xpcom/index.html
where $OBJDIR
is the path to the object directory.
Using static prefs
Static boolean/integer prefs can be easily accessed from Rust code. Add a
rust: true
field to the pref definition in
modules/libpref/init/StaticPrefList.yaml,
like this:
- name: my.lucky.pref
type: RelaxedAtomicBool
value: true
mirror: always
rust: true
The pref can then be accessed via the pref!
macro, like this:
let my_lucky_pref = static_prefs::pref!("my.lucky.pref");
Helper crates
The following in-tree helper crates provide idiomatic support for some common patterns.
nserror reflects
nsresult
codes into Rust.nsstring exposes bindings for XPCOM string types. You can use the same
ns{A,C}String
types as C++ for owned strings and pass them back and forth over the boundary. There is alsons{A,C}Str
for dependent or borrowed strings.thin-vec provides a Rust
Vec
-like type that is layout-compatible with Gecko’snsTArray
.xpcom provides multiple building blocks for a component’s implementation.
The
RefPtr
type is for managing reference-counted pointers.XPCOM component getters are generated by xpcom/components/gen_static_components.py, and can be called like this:
use xpcom::{interfaces::nsIPrefService, RefPtr}; let pref_service: RefPtr<nsIPrefService> = xpcom::components::Preferences::service()?;
There is also a
get_service
function that works likedo_GetService
in C++, as an alternative.A set of
derive
macros help with declaring interface implementations. The docs have details and examples.
moz_task wraps XPCOM’s threading functions in order to make it easy and safe to write threaded code. It has helpers for getting and creating threads, dispatching async runnables, and thread-safe handles.
storage is an interface to mozStorage, our wrapper for SQLite. It can wrap an existing storage connection, and prepare and execute statements. This crate wraps the synchronous connection API, and lets you execute statements asynchronously via
moz_task
.storage_variant is for working with variants. It also provides a
HashPropertyBag
type that’s useful for passing hash maps over XPCOM to JS.
Unfortunately, rustdocs are not yet generated and
hosted for crates within
mozilla-central. Therefore, the crate links shown above link to files
containing the relevant rustdocs source where possible. However, you can
generate docs locally using the cargo doc
command described above.