Fix warning on nix lazy-trees branch

[Artturin]

warning: Performing inefficient double copy of path 'X' to the store. This can typically be avoided by rewriting an attribute like src = ./.tosrc = builtins.path { path = ./.; name = "source"; }.

[astro]

Or, just src = self;?

How can I reproduce that warning?

[Artturin]

Or, just src = self;?

Good idea.

How can I reproduce that warning?

You have to use this nix branch https://github.com/NixOS/nix/pull/6530