roc/BUILDING_FROM_SOURCE.md

Building the Roc compiler from source

Installing LLVM

To build the compiler, you need a particular version of LLVM installed on your system.

To see which version of LLVM you need, take a look at Cargo.toml, in particular the branch section of the inkwell dependency. It should have something like llvmX-Y where X and Y are the major and minor revisions of LLVM you need.

For Ubuntu, I used the Automatic installation script at apt.llvm.org - but there are plenty of alternative options at http://releases.llvm.org/download.html

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

Use LLD for the linker

Using lld for Rust's linker makes build times a lot faster, and I highly recommend it.

Create ~/.config/cargo 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 9 (e.g. with $ sudo apt-get install lld-9) and add make sure there's a ld.lld executable on your PATH which is symlinked to lld-9.

That's it! Enjoy the faster builds.