Idea for pure flakes

[yajo]

I'm being affected by DeterminateSystems/flakehub-push#170.

Of course that's not devenv's fault. However, it made me wonder: why do we need a static value? This is how it's defined:

devenv/src/modules/top-level.nix

Lines 164 to 168 in 8f8c96b

	root = lib.mkOption {
	type = types.str;
	internal = true;
	default = builtins.getEnv "PWD";
	};

We can learn from other projects.

devshell uses environmental values from nix shell or direnv if available, and otherwise allows to provide a fallback script that can apply any custom logic that sets their PRJ_ROOT variable.

dream2nix allows setting path.projectRootFile, so that the script traverses the file tree up to finding this file, to find what is considered the project root.

That should let devenv flakes be evaluated purely, while still having a working dev shell with direnv, nix-shell or nix develop.

[sandydoo]

The long-term solution to this is #1548.

devshell uses environmental values from nix shell or direnv if available, and otherwise allows to provide a fallback script that can apply any custom logic that sets their PRJ_ROOT variable.

This only works for scripts that are executed after enterShell. There is a lot of value in knowing the project root path during the shell build, i.e. inside of Nix.

dream2nix allows setting path.projectRootFile, so that the script traverses the file tree up to finding this file, to find what is considered the project root.

devenv is currently implemented on top of Nix flakes. Flakes are always copied to the store before evaluation, so any path traversal would return the immutable store path. In fact, this root path is exposed as an API within flakes, but it's not useful to us for hooking up local state. What we want instead is the original path to your project.

[yajo]

There is a lot of value in knowing the project root path during the shell build, i.e. inside of Nix.

Could you give some examples? It'd help understand better.