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Move the error message to the bottom when showing traces#7494

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domenkozar wants to merge 1 commit intoNixOS:masterfrom
cachix:expose-error
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Move the error message to the bottom when showing traces#7494
domenkozar wants to merge 1 commit intoNixOS:masterfrom
cachix:expose-error

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@domenkozar
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@domenkozar domenkozar commented Dec 21, 2022

Given error.nix:

with (import <nixpkgs> {});

let 
  a = b: git.foo;
in a 3

Before:

❯ /nix/store/rz6a733dfhhycsf81mc6nf8jh3h729n8-nix-2.13.0pre20221221_b1223e1/bin/nix-instantiate error.nix -I ~/dev --show-trace
error:
       … while evaluating call site

       at /home/domen/dev/nix/error.nix:5:4:

            4|   a = b: git.foo;
            5| in a 3
             |    ^
            6|

       … while calling 'a'

       at /home/domen/dev/nix/error.nix:4:7:

            3| let
            4|   a = b: git.foo;
             |       ^
            5| in a 3

       error: attribute 'foo' missing

       at /home/domen/dev/nix/error.nix:4:10:

            3| let
            4|   a = b: git.foo;
             |          ^
            5| in a 3
       Did you mean doc?

After:

❯ ./outputs/out/bin/nix-instantiate error.nix -I ~/dev --show-trace
error:
       … while evaluating call site

       at /home/domen/dev/nix/error.nix:5:4:

            4|   a = b: git.foo;
            5| in a 3
             |    ^
            6|

       … while calling 'a'

       at /home/domen/dev/nix/error.nix:4:7:

            3| let
            4|   a = b: git.foo;
             |       ^
            5| in a 3

       at /home/domen/dev/nix/error.nix:4:10:

            3| let
            4|   a = b: git.foo;
             |          ^
            5| in a 3

       error: attribute 'foo' missing

       Did you mean doc?

@domenkozar domenkozar added the error-messages Confusing messages and better diagnostics label Dec 21, 2022
@domenkozar domenkozar mentioned this pull request Dec 21, 2022
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@Ericson2314
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Ericson2314 commented Dec 21, 2022

I'm on board with the general goal here, but I am not so sure about the inconsistency of going from a bunch of frames in "thing at" order to a final item in "at thing" order.

@roberth roberth added the language The Nix expression language; parser, interpreter, primops, evaluation, etc label Jul 2, 2023
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roberth commented Jul 2, 2023

Another problem is that it says error: at the beginning, leading at least some people to believe that the error description is on the next line. Looking for the first error is a good practice, so you really can't blame them.
Example: https://discourse.nixos.org/t/error-in-the-left-operand-of-the-update-operator/29901

If we keep error: at the start, we should at least start with something like "original error and most recent call appear last"

@domenkozar
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domenkozar commented Jul 2, 2023

I'd love if someone finishes this and ships it, it's a huge UX improvement.

Maybe @bburdette?

@bburdette
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bburdette commented Aug 10, 2023 •
edited
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What about this?

  • 'error:' at top replaced by 'an error occurred!'
  • ...thing-at pattern continues with '... error location:'
  • 'error location:' makes clear that the next block is where the actual error is.
  • error message (almost) at the end, so you can scroll to the bottom and reliably find it.
❯ ./outputs/out/bin/nix-instantiate error.nix -I ~/dev --show-trace
an error occurred!

       … while evaluating call site

       at /home/domen/dev/nix/error.nix:5:4:

            4|   a = b: git.foo;
            5| in a 3
             |    ^
            6|

       … while calling 'a'

       at /home/domen/dev/nix/error.nix:4:7:

            3| let
            4|   a = b: git.foo;
             |       ^
            5| in a 3

       … error location:

       at /home/domen/dev/nix/error.nix:4:10:

            3| let
            4|   a = b: git.foo;
             |          ^
            5| in a 3

       error: attribute 'foo' missing

       Did you mean doc?

Would need a bit of thinking through for the different verbosities - error, warn, debug, etc.

@domenkozar
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domenkozar commented Feb 6, 2026

Closing as not wanted

@domenkozar domenkozar closed this Feb 6, 2026
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@domenkozar @Ericson2314 @roberth @bburdette