[opam-devel] opam and "So you want to write a package manager"

[Thomas Gazagnaire]

> Looking upwards to a `.opam` directory and use it as opam root would be 
> straightforward to implement (well, I'd just have to copy-paste some code from 
> ocp-indent). But I don't think it is a good idea:
> 1. it duplicates lots of stuff, including synchronising repositories, caches, 
> and compiling OCaml
> 2. does it replace ~/.opam or add to it ?
> 3. how about `opam config env` ? Should you ensure to run it after you cd to 
> your project ? Sounds dangerous, but it might be handled by the build system.
> 4. and what about tools such as merlin ? You surely won't install them within 
> every project...

I think the idea of a local .opam is to fully replace the global one, so all the state is associated to the project directory. I think having a global .opam directory to be used as a cache should be an "implementation detail", as a cache where you can store and symlink stuff if needed. You can do similar tricks with Git and share a global block store, but the user only think about distinct "repositories".

> Another big question is that we otherwise need build systems to be opam-aware. 
> Without interfering when they are run from within opam, of course. Guess I'll 
> get back to working on opam-as-build-system ;)

Having a way to optimally configure opam and a build system to work together is certainly a good idea of evolution...

Thomas