# Building the Roc compiler from source

Installation should be a smooth process, let us now if anything does not work perfectly on [Roc Zulip](https://roc.zulipchat.com) or by creating an issue.

## Using Nix

On Macos and Linux, we highly recommend Using [nix](https://nixos.org/download.html) to quickly install all dependencies necessary to build roc.

:warning: If you tried to run `cargo` in the repo folder before installing nix, make sure to execute `cargo clean` first. To prevent you from executing `cargo` outside of nix, tools like [direnv](https://github.com/nix-community/nix-direnv) and [lorri](https://github.com/nix-community/lorri) can put you in a nix shell automatically when you `cd` into the directory.

### On Linux x86_64/aarch64 or MacOS aarch64/arm64/x86_64

#### Install

If you are running ArchLinux or a derivative like Manjaro, you'll need to run `sudo sysctl -w kernel.unprivileged_userns_clone=1` before installing nix.

Install nix (not necessary on NixOS):
- If you are using WSL (Windows subsystem for Linux):
```
sh <(curl -L https://nixos.org/nix/install) --no-daemon
```
- For everything else:
```
sh <(curl -L https://nixos.org/nix/install) --daemon
```

Open a new terminal and install nixFlakes in your environment:
```
nix-env -iA nixpkgs.nixFlakes
```

Edit either `~/.config/nix/nix.conf` or `/etc/nix/nix.conf` and add:
```
experimental-features = nix-command flakes
```

If Nix was installed in multi-user mode, make sure to restart the nix-daemon.
If you don't know how to do this, restarting your computer will also do the job.

#### Usage

Now with nix set up, you just need to run one command from the roc project root directory:
```
nix develop
```
You should be in a shell with everything needed to build already installed.
Use `cargo run help` to see all subcommands.
To use the `repl` subcommand, execute `cargo run repl`.
Use `cargo build` to build the whole project.

Read the instructions [here](devtools/README.md) to make nix work well with your development tools (vscode, vim, rust-analyzer...)

#### Extra tips

If you want to load all dependencies automatically whenever you `cd` into `roc`, check out [direnv](https://direnv.net/).
Then you will no longer need to execute `nix develop` first.

### Editor

The editor is a :construction:WIP:construction: and not ready yet to replace your favorite editor, although if you want to try it out on nix, read on.
`cargo run edit` should work on NixOS and MacOS. If you use Linux x86_64, follow the instructions below.

If you're not already in a nix shell, execute `nix develop` at the the root of the repo folder and then execute:
```
nixVulkanIntel cargo run edit
```

## Troubleshooting

Create an issue if you run into problems not listed here.
That will help us improve this document for everyone who reads it in the future!

## Manual Install

To build the compiler, you need these installed:

* [Zig](https://ziglang.org/), see below for version
* `libxkbcommon` - macOS seems to have it already; on Ubuntu or Debian you can get it with `apt-get install libxkbcommon-dev`
* On Debian/Ubuntu `sudo apt-get install pkg-config`
* LLVM, see below for version
* [rust](https://rustup.rs/)
* Also run `cargo install bindgen` after installing rust. You may need to open a new terminal.

To run the test suite (via `cargo test`), you additionally need to install:

* [`valgrind`](https://www.valgrind.org/) (needs special treatment to [install on macOS](https://stackoverflow.com/a/61359781)
Alternatively, you can use `cargo test --no-fail-fast` or `cargo test -p specific_tests` to skip over the valgrind failures & tests.

For debugging LLVM IR, we use [DebugIR](https://github.com/vaivaswatha/debugir). This dependency is only required to build with the `--debug` flag, and for normal development you should be fine without it.

### libxcb libraries

You may see an error like this during builds:

```
/usr/bin/ld: cannot find -lxcb-render
/usr/bin/ld: cannot find -lxcb-shape
/usr/bin/ld: cannot find -lxcb-xfixes
```

If so, you can fix it like so:

```
sudo apt-get install libxcb-render0-dev libxcb-shape0-dev libxcb-xfixes0-dev
```

### Zig
**version: 0.9.1**

For any OS, you can use [`zigup`](https://github.com/marler8997/zigup) to manage zig installations.

If you prefer a package manager, you can try the following:
- For MacOS, you can install with `brew install zig`
- For, Ubuntu, you can use Snap, you can install with `snap install zig --classic --beta`
- For other systems, checkout this [page](https://github.com/ziglang/zig/wiki/Install-Zig-from-a-Package-Manager)

If you want to install it manually, you can also download Zig directly [here](https://ziglang.org/download/). Just make sure you download the right version, the bleeding edge master build is the first download link on this page.

### LLVM
**version: 13.0.x**

For macOS, you can install LLVM 13 using `brew install llvm@13` and then adding
`$(brew --prefix llvm@13)/bin` to your `PATH`. You can confirm this worked by
running `llc --version` - it should mention "LLVM version 13.0.0" at the top.
You may also need to manually specify a prefix env var like so:
```
export LLVM_SYS_130_PREFIX=/usr/local/opt/llvm@13
```

For Ubuntu and Debian:
```
sudo apt -y install lsb-release software-properties-common gnupg
wget https://apt.llvm.org/llvm.sh
chmod +x llvm.sh
./llvm.sh 13
```

If you use this script, you'll need to add `clang` to your `PATH`.
By default, the script installs it as `clang-13`. You can address this with symlinks like so:

```
sudo ln -s /usr/bin/clang-13 /usr/bin/clang
```

There are also alternative installation options at http://releases.llvm.org/download.html

[Troubleshooting](#troubleshooting)

### Building

Use `cargo build` to build the whole project.
Use `cargo run help` to see all subcommands.
To use the `repl` subcommand, execute `cargo run repl`.

### LLVM installation on Linux

For a current list of all dependency versions and their names in apt, see the Earthfile.

On some Linux systems we've seen the error "failed to run custom build command for x11".
On Ubuntu, running `sudo apt install pkg-config cmake libx11-dev` fixed this.

If you encounter `cannot find -lz` run `sudo apt install zlib1g-dev`.

If you encounter:
```
error: No suitable version of LLVM was found system-wide or pointed
       to by LLVM_SYS_130_PREFIX.
```
Add `export LLVM_SYS_130_PREFIX=/usr/lib/llvm-13` to your `~/.bashrc` or equivalent file for your shell.

### LLVM installation on macOS

If installing LLVM fails, it might help to run `sudo xcode-select -r` before installing again.

It might also be useful to add these exports to your shell:

```
export LDFLAGS="-L/usr/local/opt/llvm/lib -Wl,-rpath,/usr/local/opt/llvm/lib"
export CPPFLAGS="-I/usr/local/opt/llvm/include"
```

### LLVM installation on Windows

**Warning** While `cargo build` works on windows, linking roc programs does not yet, see issue #2608. This also means the repl, the editor and many tests will not work on windows.
Installing LLVM's prebuilt binaries doesn't seem to be enough for the `llvm-sys` crate that Roc depends on, so I had to follow the steps below:

1. I downloaded and installed [Build Tools for Visual Studio 2019](https://visualstudio.microsoft.com/thank-you-downloading-visual-studio/?sku=BuildTools&rel=16) (a full Visual Studio install should work too; the Build Tools are just the CLI tools, which is all I wanted)
1. Download the custom LLVM 7z archive [here](https://github.com/PLC-lang/llvm-package-windows/releases/tag/v13.0.0).
1. [Download 7-zip](https://www.7-zip.org/) to be able to extract this archive.
1. Extract the 7z file to where you want to permanently keep the folder.
1. In powershell, set the `LLVM_SYS_130_PREFIX` environment variable (check [here](https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_environment_variables?view=powershell-7.2#saving-environment-variables-with-the-system-control-panel) to make this a permanent environment variable):
```
<# ! Replace YOUR_USERNAME ! #>
$env:LLVM_SYS_130_PREFIX = 'C:\Users\YOUR_USERNAME\Downloads\LLVM-13.0.0-win64'
```
1. add the LLVM bin to the path to prevent issue #3952:
```
<# ! Replace YOUR_USERNAME ! #>
[Environment]::SetEnvironmentVariable(
   "Path",
   [Environment]::GetEnvironmentVariable("Path", "User") + ";C:\Users\YOUR_USERNAME\Downloads\LLVM-13.0.0-win64\bin",
   "User"
)
```

Once all that was done, `cargo build` ran successfully for Roc!

### Build speed on WSL/WSL2

If your Roc project folder is in the Windows filesystem but you're compiling from Linux, rebuilds may be as much as 20x slower than they should be!
Disk access during linking seems to be the bottleneck. It's recommended to move your folder to the Linux filesystem.

## Use LLD for the linker

Using [`lld` for Rust's linker](https://github.com/rust-lang/rust/issues/39915#issuecomment-538049306)
makes build times a lot faster, and I highly recommend it.

Create `~/.cargo/config.toml` if it does not exist and add this to it:

```
[build]
# Link with lld, per https://github.com/rust-lang/rust/issues/39915#issuecomment-538049306
# Use target-cpu=native, per https://deterministic.space/high-performance-rust.html
rustflags = ["-C", "link-arg=-fuse-ld=lld", "-C", "target-cpu=native"]
```

Then install `lld` version 13 (e.g. with `$ sudo apt-get install lld-13`)
and add make sure there's a `ld.lld` executable on your `PATH` which
is symlinked to `lld-13`.

That's it! Enjoy the faster builds.