Tools for running builds using Nix in a monorepo.

Goal: Using one coherent build tool, I can develop multiple projects with common dependencies.

# Background

I do a lot of Rust development. I also like to attach other programming languages so that I can, for instance, write a [go application that works in a web browser](https://git.luminescent-dreams.com/savanni/tools/src/branch/main/kifu/pwa). And, I tend to work in a [monorepo](https://git.luminescent-dreams.com/savanni/tools/), because that helps me keep all of my disparate interests somewhat in sync with one another.

Finally, I use Nix to manage my development tools.

However, what I cannot do is use Nix to actually build my projects. Most of my projects, admittedly, are Rust projects and so they are pretty easily built with a simple Cargo.toml. However, as soon as I want to do something complicated, such as a web application, I have to dig extensively to find documentation on how to actually lay out the application and get all of the tools in place. Plus, I have to use a different build tool and get all of the build tools to work together.

What I actually want to do is this.

```
> nix run .#kifu-gtk
```

And I want you to be able to just say this...

```
> nix run https://git.luminescent-dreams.com/savanni/tools/#.kifu-gtk
```

## Monorepos

For the purpose of this project, a monorepo as a single Git repository which contains potentially many libraries and applications, in separate packages (rust Crates, node Modules, etc), which interdepend and may be developed simultaneously with one another.

## Past experiences

I don't have many past experiences.

- I have the 1Password Monorepo, which is mostly held together with Makefiles which invoke platform-specific build tools. These were put together before I arrived at the company, and they are extensive. The developer build environment does not match the CI build environment.
- I have tried Bazel, but have not been able to build a purely Rust project even while following the tutorials.
- I have my [Tools Monorepo](https://git.luminescent-dreams.com/savanni/tools/) where I use a bunch of Makefiles to invoke platform-specific build commands. This doesn't work too badly, but I've hand-rolled every boilerplate Makefile, and should I want to add something like cross-compilation to Raspberry Pi, I am in for a world of pain.

I have evaluated all but one of the [[Rust build tools in Nix]], and found significant drawbacks in each. The biggest drawback, though, is that the tools are all for building an application. Binding two applications together is never a consideration with any of the build tools, and so something like the Kifu PWA application simply cannot be built with Nix as a build tool.
# Requirements

- select the toolchains and versions thereof for the project
- configure cross-compilation
- allow multiple languages
- co-exist with language ecosystems. For example, rust-analyzer needs cargo in order to understand Cargo.toml. However, it should be easier to fully build the project with Nix
- every module is compiled into a derivation that downstream modules can import. Each module derivation is cached separately so that Nix only rebuilds the changed module.
- Nix can generate a closure for an executable, even a cross-compiled one, to copy to the remote system

# Languages and Bindings

Languages:
- C
- Rust
- Typescript
- Javascript

Bindings:
- C -> Rust
- Rust -> Typescript
- Rust -> Javascript

Backends

|            | Linux x86 | Linux ARM | WASM | AVR | ESP32 |
| ---------- | --------- | --------- | ---- | --- | ----- |
| C          | yes       | yes       |      | yes |       |
| Rust       | yes       | yes       | yes  | yes | yes   |
| Typescript |           |           | yes  |     |       |
| Javascript |           |           | yes  |     |       |

- [[Mononix, C library]]
- [[Mononix, Rust library]]

# Build targets

- build
- run
- tests
- code coverage profiling
- linting
- performance testing

Each of these is a separate Nix command that builds or runs the desired result.

---
- [[Nix For Development]]
- [[Cross-compiling]]
- [[Scaling Rust Builds with Bazel]]
- [[Makefiles and Monorepos]]
- [Experiment in cross-compiling](https://github.com/jraygauthier/jrg-rust-cross-experiment/blob/master/simple-static-rustup-target-windows/shell.nix)
- [Building Nix flakes from Rust workspaces - Tweag](https://www.tweag.io/blog/2022-09-22-rust-nix/)