Show addErrorContext traces by default

[roberth]

Is your feature request related to a problem? Please describe.

Module system stack traces are too long. The low information density makes users believe that they won't learn anything from reading through it, but essential information is in the stack trace, thanks to builtins.addErrorContext.

Describe the solution you'd like

addErrorContext traces are sufficiently valuable and terse that the should always be shown.

Optionally, add --no-trace, to disable that, but I don't think we even want that.

Describe alternatives you've considered

See the following and its alternatives

• Customizable summarized stack traces #7552

Additional context

Example

This would have been a 700 line stack trace with --show-trace (or --full-trace if you're confused by the other issue).

error: infinite recursion encountered

       … while evaluating definitions from `/home/user/h/nixpkgs/pkgs/top-level/all-packages.nix':

       … while evaluating the option `services.postgresql.enable':

       … while evaluating definitions from `/home/user/h/nixpkgs/pkgs/top-level/all-packages.nix':

       … while evaluating the option `services.rabbitmq.enable':

       … while evaluating definitions from `/home/user/h/nixpkgs/nixos/modules/services/amqp/rabbitmq.nix':

       … while evaluating the option `services.epmd.enable':

       … while evaluating definitions from `/home/user/h/nixpkgs/nixos/modules/services/networking/epmd.nix':

       … while evaluating the option `assertions':

See the full example in #7552

Priorities

Add 👍 to issues you find important.

[roberth]

We don't have "spammy addErrorContext" in NixOS, but we might want to restrict to a certain number of lines in case some other library does have it.

If spamming does happen in the future, we could add measures similar to what logging libraries use: log levels and/or labeling by module. This is completely hypothetical for now.

[edolstra]

Note from the team discussion: it might be nice to be able to associate priorities with messages.

[nixos-discourse]

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

https://discourse.nixos.org/t/2023-07-14-nix-team-meeting-minutes-71/30472/1