UX: `nix-shell` doesn't clearly explain what went wrong

[Sporarum]

Describe the bug

When running nix-shell -p <name>, if <name> is not found, it will show a complicated-looking trace, as opposed to a clear error message.

For experienced users, this is not an issue, as they are used to reading parse traces, and filtering out this kind of noise.

For beginner users however, this is an issue:
This does not point them toward a solution, as none of the files shown in the trace are written by them.
And can even lead them to believe nix-shell itself broke.

As for wether this is a bug or an improvement request, the line is always blurry with UX.
In this case I believe exposing novice users to internal workings of a built-in construct to be bad enough to be considered a bug.
(Especially as it might be one of the very first commands they run)

Steps To Reproduce

1. Run nix-shell -p cowsya
2. Get:

error:
       … while calling the 'derivationStrict' builtin
         at <nix/derivation-internal.nix>:37:12:
           36|
           37|   strict = derivationStrict drvAttrs;
             |            ^
           38|

       … while evaluating derivation 'shell'
         whose name attribute is located at /nix/store/px86fbsnq65agwvrxnylrxnxp6bpcl76-source/pkgs/stdenv/generic/make-derivation.nix:480:13

       … while evaluating attribute 'buildInputs' of derivation 'shell'
         at /nix/store/px86fbsnq65agwvrxnylrxnxp6bpcl76-source/pkgs/stdenv/generic/make-derivation.nix:535:13:
          534|             depsHostHost = elemAt (elemAt dependencies 1) 0;
          535|             buildInputs = elemAt (elemAt dependencies 1) 1;
             |             ^
          536|             depsTargetTarget = elemAt (elemAt dependencies 2) 0;

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: undefined variable 'cowsya'
       at «string»:1:107:
            1| {...}@args: with import <nixpkgs> args; (pkgs.runCommandCC or pkgs.runCommand) "shell" { buildInputs = [ (cowsya) ]; } ""
             |                                                                                                           ^

Expected behavior

1. Run nix-shell -p cowsya
2. Get something like:

Package cowsya was not found

Or even

Package cowsya was not found
Did you mean "cowsay" ?

Metadata

nix-env (Nix) 2.28.5

Checklist

• checked latest Nix manual (source)
• checked open bug issues and pull requests for possible duplicates

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[nixos-discourse]

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

https://discourse.nixos.org/t/nix-shell-p-fails-with-undefined-variable/73565/3

[nixos-discourse]

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

https://discourse.nixos.org/t/nix-shell-p-fails-with-undefined-variable/73565/8

[rhendric]

My understanding is that new development on nix-shell is unlikely to be accepted (or I'd write the PR). Note that the future-oriented equivalent of this command doesn't have this issue:

$ nix shell --file '<nixpkgs>' cowsya   
error: attribute 'cowsya' in selection path 'cowsya' not found
       Did you mean one of costa, cowsay or cowsql?