Avoid duplicating nixpkgs in the nix store #67
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I noticed that this line was making my nix evaluations significantly slower. It turns out that simply evaluating `"${pkgs.path}"` causes nixpkgs to be copied into the nix store twice.
e.g. notice the two different paths here:
```
nix-repl> pkgs.path
/nix/store/p69bcs7ma6ijj8v9xsrg3nq3nn8ryn95-source
nix-repl> "${pkgs.path}"
"/nix/store/aj917y3jd6srg7jfmhgwglbfx36l5h9b-p69bcs7ma6ijj8v9xsrg3nq3nn8ryn95-source"
```
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I noticed that this line was making my nix evaluations significantly slower. It turns out that simply evaluating
"${pkgs.path}"causes nixpkgs to be copied into the nix store an extra time.e.g. notice the two different paths here:
I'm not sure if this is a problem when running under flakes, but I am consuming this in a repo that is too big to enable flakes with.EDIT: I believe that flakes do suffer the extra copy, but its much less noticeable due to flake evaluation caching.