Allow specifying a recursionLimit for toPretty

[infinisil]

Motivation for this change

For being able to print infinitely-recursing values in #98155

Also, toPretty now adds relevant error context when recursing

See also #97133 which did other toPretty improvements

Ping @Profpatsch

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[infinisil]

The error trace shows like this:

$ nix-instantiate --eval -E 'with import ./lib; generators.toPretty {} { x.y = [ (throw "nope") ]; }' --show-trace
error: while evaluating 'go' at /home/infinisil/src/nixpkgs/lib/generators.nix:211:17, called from (string):1:20:
while evaluating anonymous function at /home/infinisil/src/nixpkgs/lib/attrsets.nix:234:10, called from undefined position:
while evaluating anonymous function at /home/infinisil/src/nixpkgs/lib/generators.nix:262:22, called from /home/infinisil/src/nixpkgs/lib/attrsets.nix:234:16:
while lib.generators.toPretty descended into the `x' attribute
while evaluating 'go' at /home/infinisil/src/nixpkgs/lib/generators.nix:211:17, called from /home/infinisil/src/nixpkgs/lib/generators.nix:264:57:
while evaluating anonymous function at /home/infinisil/src/nixpkgs/lib/attrsets.nix:234:10, called from undefined position:
while evaluating anonymous function at /home/infinisil/src/nixpkgs/lib/generators.nix:262:22, called from /home/infinisil/src/nixpkgs/lib/attrsets.nix:234:16:
while lib.generators.toPretty descended into the `y' attribute
while evaluating 'go' at /home/infinisil/src/nixpkgs/lib/generators.nix:211:17, called from /home/infinisil/src/nixpkgs/lib/generators.nix:264:57:
while evaluating anonymous function at /home/infinisil/src/nixpkgs/lib/lists.nix:106:29, called from undefined position:
while evaluating anonymous function at /home/infinisil/src/nixpkgs/lib/generators.nix:240:61, called from /home/infinisil/src/nixpkgs/lib/lists.nix:106:32:
while lib.generators.toPretty descended into list index `0'
while evaluating 'go' at /home/infinisil/src/nixpkgs/lib/generators.nix:211:17, called from /home/infinisil/src/nixpkgs/lib/generators.nix:242:14:
nope

[Profpatsch]

I’m getting a bit worried that toPretty is becoming really complicated, and kind of a bit of a kitchen sink. What can we do to make it simpler again?

[Profpatsch]

Like, the __pretty argument was explicitly designed to avoid this kind of scenario, and now we are moving in a direction I’m very uncomfortable with. For my taste the function is already twice as long as it should be, even before this change.

[infinisil]

Closing this for now as I have other changes relating to this

[infinisil]

Now #98761 adds the recursionLimit argument