Get rid of impure mode

[domenkozar]

NixOS/nix#5663

[Atry]

It is possible to set DEVENV_ROOT to support pure mode
See #706, #566 and #583

[Atry]

Why do we need plain Nix expressions as flake inputs? Why not just generate a flake that contains current environment variables, including PWD, then just pass --override-input to use the generated flake.

[domenkozar]

For devenv we can do that, but not for the flakes integration.

[Atry]

How about using --redirect:

nix develop --redirect .#devenv-root .

[Atry]

I think the current impure devenv.root is a dangerous design when packing images via nix2container, because the image content could depend on devenv.root and reference to non-existing directory at runtime.

[Atry]

Ideally, there should be a perWorkingDirectory submodule under devenv, where we can access root. Environment variables that contain abstract paths should be configured under devent.perWorkingDirectory.env, instead of devent.env

[domenkozar]

In #745 we now generate PWD instead of using --impure when using devenv cli.

[Atry]

How about also avoid --impure when using flake? See #745 (comment)

[khaled]

Looking forward to the Python rewrite, as --impure seems to prevent evaluation caching from occurring. This makes devenv annoyingly slow when e.g. entering directories with a use flake --impure in .envrc.

[khaled]

Looking forward to the Python rewrite, as --impure seems to prevent evaluation caching from occurring. This makes devenv annoyingly slow when e.g. entering directories with a use flake --impure in .envrc.

Unless one uses nix-direnv, which caches the nix shell environment. The point about evaluation caching stands though.

[Atry]

Why is this issue closed? --impure is still needed according to https://devenv.sh/guides/using-with-flakes/#getting-started

[Atry]

See #1018

[domenkozar]

This issue was about devenv itself, for flakes it needs to be fixed in Nix itself. Let's see if #1018 will work :)