This tutorial by /u/andoriyu shows us how to get Rust along with Cargo set up on FreeBSD. Cargo allows Rust projects to declare various dependencies, ensuring a repeatable build.
rustcargo
Original: http://system.joekain.com/2015/07/04/rust-and-cargo-on-freebsd.html

This is a post of opportunity and not one of the regularly scheduled posts in my series on writing a debugger in C and Rust. In the course of working on the nix-rust crate I needed to get a Rust environment setup on FreeBSD and I thought I would document my experience here.

Rust on FreeBSD

Installing Rust itself on FreeBSD is easy. There is a binary package available so installation is as simple as:

# pkg install rust-1.1.0
Updating FreeBSD repository catalogue...
FreeBSD repository is up-to-date.
All repositories are up-to-date.
The following 1 package(s) will be affected (of 0 checked):

New packages to be INSTALLED:
	rust: 1.1.0

The process will require 172 MiB more space.
58 MiB to be downloaded.

Proceed with this action? [y/N]: y
Fetching rust-1.1.0.txz: 100%   58 MiB   3.0MB/s    00:20
Checking integrity... done (0 conflicting)
[1/1] Installing rust-1.1.0...
[1/1] Extracting rust-1.1.0: 100%

But, this rust doesn’t come with Cargo.

Cargo for FreeBSD

Building Cargo from source depends on Cargo. There is a bootstrapping process but it depends on the official Rust nightly builds which are only built for Linux, Mac OS X, and Windows. I’ve seen a number of posts on how to build Cargo for FreeBSD but they all seem very involved and potentially out of date.

This reddit post describes a pkg repo for nighly builds of Cargo for FreeBSD. These nighly builds are kindly provided by /u/andoriyu.

Installing the Repo

I had no idea how to install a pkg repo on FreeBSD so I did some Googling which was suprisingly unhelpful. However, the man page was quite useful. PKG.CONF(5) describes how to get things setup. Based on the man page I wrote

/etc/pkg/Cargo.conf:

Cargo: {
  url: "pkg+https://s3-us-west-1.amazonaws.com/freebsd-repos/edenbsd",
  mirror_type: "srv",
  signature_type: "pubkey",
  pubkey: "https://s3-us-west-1.amazonaws.com/freebsd-repos/eden-poudriere.pub"
  enabled: yes
}

After this I was able to install Cargo:

$ pkg install cargo
Updating Cargo repository catalogue...
Cargo repository is up-to-date.
Updating FreeBSD repository catalogue...
FreeBSD repository is up-to-date.
All repositories are up-to-date.
The following 7 package(s) will be affected (of 0 checked):

New packages to be INSTALLED:
	cargo: 0.4.0n_5 [Cargo]
	python27: 2.7.10 [Cargo]
	openssl: 1.0.2_3 [Cargo]
	python2: 2_3 [Cargo]
	libssh2: 1.4.3_5,2 [FreeBSD]
	curl: 7.43.0_2 [FreeBSD]
	c-ares-config: 1.10.0_1 [Cargo]

The process will require 109 MiB more space.
20 MiB to be downloaded.

Proceed with this action? [y/N]: y
Fetching cargo-0.4.0n_5.txz: 100%    5 MiB   1.8MB/s    00:03
Fetching python27-2.7.10.txz: 100%   10 MiB   2.1MB/s    00:05
...

It works!

And the resulting cargo build works:

$ cargo
Rust's package manager

Usage:
    cargo <command> [<args>...]
    cargo [options]

Options:
    -h, --help       Display this message
    -V, --version    Print version info and exit
    --list           List installed commands
    -v, --verbose    Use verbose output
    -q, --quiet             No output printed to stdout

Some common cargo commands are:
    build       Compile the current project
    clean       Remove the target directory
    doc         Build this project's and its dependencies' documentation
    new         Create a new cargo project
    run         Build and execute src/main.rs
    test        Run the tests
    bench       Run the benchmarks
    update      Update dependencies listed in Cargo.lock
    search      Search registry for crates

See 'cargo help <command>' for more information on a specific command.

Thanks /u/andoriyu!