Infinitely recursive values stack-overflow with the `--json` output format #772

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opened 2025-03-26 18:34:13 +00:00 by jade · 2 comments

jade commented

2025-03-26 18:34:13 +00:00

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Describe the bug

$ nix eval --expr 'let self = { inherit self; foo = 2; }; in self'
{ foo = 2; self = «repeated»; }
$ nix eval --expr 'let self = { inherit self; foo = 2; }; in self' --json
zsh: segmentation fault  nix eval --expr 'let self = { inherit self; foo = 2; }; in self' --json

This isn't a real segfault, it's obviously just infinite recursion and stack overflow.

Steps To Reproduce

See above

Expected behavior

I am not sure what the strictly correct behaviour here is. Maybe we need a recursion limit and some way to signal infinite recursion. Maybe we need to emit NaNs.

The challenge with this is that we can't standardize that the printer will do the repeated thing exactly the same every time in a stable API.

`nix --version` output

nix (Lix, like Nix) 2.93.0-dev-pre20250324-4181796
System type: aarch64-darwin
Additional system types: x86_64-darwin
Features: gc, signed-caches
System configuration file: /etc/nix/nix.conf
User configuration files: /Users/jade/.config/nix/nix.conf:/etc/xdg/nix/nix.conf
Store directory: /nix/store
State directory: /nix/var/nix
Data directory: /nix/store/zrvf4zf2jl838kd987ngim3a18jpx6kj-lix-2.93.0-dev-pre20250324-4181796/share

Additional context

Add any other context about the problem here.

## Describe the bug ``` $ nix eval --expr 'let self = { inherit self; foo = 2; }; in self' { foo = 2; self = «repeated»; } $ nix eval --expr 'let self = { inherit self; foo = 2; }; in self' --json zsh: segmentation fault nix eval --expr 'let self = { inherit self; foo = 2; }; in self' --json ``` This isn't a real segfault, it's obviously just infinite recursion and stack overflow. ## Steps To Reproduce See above ## Expected behavior I am not sure what the strictly correct behaviour here is. Maybe we need a recursion limit and some way to signal infinite recursion. Maybe we need to emit NaNs. The challenge with this is that we can't standardize that the printer will do the `repeated` thing exactly the same every time in a stable API. ## `nix --version` output ``` nix (Lix, like Nix) 2.93.0-dev-pre20250324-4181796 System type: aarch64-darwin Additional system types: x86_64-darwin Features: gc, signed-caches System configuration file: /etc/nix/nix.conf User configuration files: /Users/jade/.config/nix/nix.conf:/etc/xdg/nix/nix.conf Store directory: /nix/store State directory: /nix/var/nix Data directory: /nix/store/zrvf4zf2jl838kd987ngim3a18jpx6kj-lix-2.93.0-dev-pre20250324-4181796/share ``` ## Additional context Add any other context about the problem here.

jade added the

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2025-03-26 18:34:13 +00:00

jade referenced this issue

2025-03-26 18:37:58 +00:00

Hard to get attrs of something having an outPath attribute with --json output format #773

pennae commented

2025-03-26 18:42:08 +00:00

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perhaps we should just disallow circular data in --json by default? we should have some way to allow circular data, perhaps by emitting not an immediately valid json object but an object with "<circular reference $id>" placeholders and a set of json pointer mappings that resolve these references (so as to not accidentally make the reference placeholder strings non-representable)

perhaps we should just disallow circular data in `--json` by default? we should have *some* way to allow circular data, perhaps by emitting not an immediately valid json object but an object with `"<circular reference $id>"` placeholders and a set of json pointer mappings that resolve these references (so as to not accidentally make the reference placeholder strings non-representable)

jade commented

2025-03-26 21:39:41 +00:00

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Owner

I think that's a really smart idea! I'm not blocked on this either way because I just use --apply to remove the problematic attrs.