nix copy can't copy an InstallableStorePath from a binary cache

[thufschmitt]

Describe the bug

Trying to run nix copy

1. from a binary cache, and
2. when the paths to copy are given as a nix expression rather than directly passing a store path

fails with operation 'addTempRoot' is not supported, even if the output path of the given expression is present in the binary cache.

Steps To Reproduce

nix copy --from https://cache.nixos.org nixpkgs#hello

Otoh, nix copy --from https://cache.nixos.org $(nix eval --raw nixpkgs#hello.outPath) works fine

Expected behavior

If the output path of nixpkgs#hello is already on the remote cache, I'd expect the command to succeed.

Alternatively, it should at least fail with a clearer error message

nix-env --version output

nix-env (Nix) 3.0pre20201020_e0ca98c

[stale]

I marked this as stale due to inactivity. → More info