Allow access to Loader's graph without creating a n2 db

[hinshun]

Would you be amendable to this change?

I'm interesting in depending on n2's ninja parser & loader to access a build.ninja's build graph but I don't want a n2 db created.

[evmar]

Hm... I'd like to better understand what you're doing. I don't want to support an n2 crate on crates.io, so if you're using this code I think you'll need to vendor it. And if you're doing that, maybe you could carry the modification in your copy? But also this seems harmless so maybe you have a better idea?

PS the person holding 'n2' on crates.io said they'd give me the name a while back but when I followed up they never responded...

[hinshun]

I'm doing an experiment where I wanted to parse build.ninja files and generate Nix dynamic derivations (i.e. incremental compilation in Nix, which previously wasn't possible), following the footsteps of https://github.com/obsidiansystems/sandstone. Since Nix itself is built with meson, this will let Nix be self-hosting.

Essentially, I'll need to generate a Nix derivation per ninja build action.

When I found out that the original author of ninja build was writing it again in Rust, I wanted to leverage it as it'll likely be the most well maintained Rust ninja parser. Happy to maintain my own fork.

[evmar]

What I’m trying to understand is how you can write code that uses n2 code without forking it in the first place, I think I am misunderstanding something! :)