Bad error message for nix build of a string

[lf-]

Describe the bug

Invoking nix build against a string containing a store path causes sadness: it does not build anything and returns an error seemingly nothing to do with the actual problem.

Steps To Reproduce

Put this in a file:

let
  Caddyfile-formatted = builtins.derivation { system = "x86_64-linux"; name = "test"; builder = "/bin/sh"; args = ["-c" "> $out" ]; };
in
"${Caddyfile-formatted}/Caddyfile"

nix build -f ./bug.nix

error:
       … while evaluating the attribute ''

         at «none»:0: (source not available)

       error: string '/nix/store/nfb1lb8dd7wxn0g9cccq2a9zf8dk219a-test/Caddyfile' has context with the output 'out' from derivation '/nix/store/qvryn0lpyyizpqn55i9fdklb5l3d97b6-test.drv', but the string is not the right placeholder for this derivation 
output. It should be '/nix/store/nfb1lb8dd7wxn0g9cccq2a9zf8dk219a-test'

Expected behavior

I expected the error message to be less bad, for example, what nix-build bug.nix does:

error: expression does not evaluate to a derivation (or a set or list of those)

although I will note that that error is also terrible, but for different reasons: it doesn't do the thing you want. The case I had here is that I needed to nix eval some string, and then build the derivation from it. I took the store path in the string and gave it to nix build, but it couldn't identify the derivation file necessary to build it.

nix-env --version output

nix-env (Nix) 2.18.1

Additional context

This occurred in practice while trying to get something out of a NixOS config under environment.etc.something.source.

Priorities

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[roberth]

nix eval some string, and then build the derivation from it.

I've previously proposed to add this as a feature

• Realise a string with context #7654

The error should then also be improved to point out that this feature exists.
I think the new behavior should only be enabled when explicitly requested; otherwise things get very ambiguous when the wrong behavior is activated by mistake.

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/how-to-handle-error-string-has-context-with-the-output-out-from-derivation-nix-store-cherami-0-0-0-drv-but-the-string-is-not-the-right-placeholder-for-this-derivation-output-it-should-be-nix-store-cherami-0-0-0/43298/3

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/how-to-handle-error-string-has-context-with-the-output-out-from-derivation-nix-store-cherami-0-0-0-drv-but-the-string-is-not-the-right-placeholder-for-this-derivation-output-it-should-be-nix-store-cherami-0-0-0/43298/4