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`nix config show --json` outputs `experimental-features` as integer bitmap #738

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opened 2025-03-14 18:52:28 +00:00 by niklaskorz · 7 comments

niklaskorz commented

2025-03-14 18:52:28 +00:00

Describe the bug

Running nix config show --json renders the value field of experimental-features as an integer bitmap, likely because of 007211e7a2.

Thank to Vaskel for finding this (I don't think she's registered here).

Steps To Reproduce

Execute nix config show --json | jq '."experimental-features"'

{
  "aliases": [],
  "defaultValue": 0,
  "description": "Experimental features that are enabled.\n\nExample:\n\n```\nexperimental-features = nix-command flakes\n```\n\nThe following experimental features are available:\n\n{{#include @generated@/../../../lix/libutil/experimental-features-shortlist.md}}\n\nExperimental features are [further documented in the manual](@docroot@/contributing/experimental-features.md).\n",
  "documentDefault": true,
  "experimentalFeature": null,
  "value": 576
}

Expected behavior

Get the same output as in Lix 2.91, which is a list of strings with the names of the active experimental features:

{
  "aliases": [],
  "defaultValue": [],
  "description": "\nExperimental features that are enabled.\n\nExample:\n\n```\nexperimental-features = nix-command flakes\n```\n\nThe following experimental features are available:\n\n{{#include @generated@/command-ref/experimental-features-shortlist.md}}\n\nExperimental features are [further documented in the manual](@docroot@/contributing/experimental-features.md).\n\n",
  "documentDefault": true,
  "experimentalFeature": null,
  "value": [
    "flakes",
    "nix-command"
  ]
}

`nix --version` output

nix (Lix, like Nix) 2.93.0-devpre20250314_af15a44

Additional context

Running nix config show without --json still correctly serializes the experimental-features to their string representations:

experimental-features = flakes nix-command

## Describe the bug Running `nix config show --json` renders the `value` field of `experimental-features` as an integer bitmap, likely because of https://git.lix.systems/lix-project/lix/commit/007211e7a27a512cb343060e8b363c9f66ef67af. Thank to Vaskel for finding this (I don't think she's registered here). ## Steps To Reproduce Execute `nix config show --json | jq '."experimental-features"'` ```json { "aliases": [], "defaultValue": 0, "description": "Experimental features that are enabled.\n\nExample:\n\n```\nexperimental-features = nix-command flakes\n```\n\nThe following experimental features are available:\n\n{{#include @generated@/../../../lix/libutil/experimental-features-shortlist.md}}\n\nExperimental features are [further documented in the manual](@docroot@/contributing/experimental-features.md).\n", "documentDefault": true, "experimentalFeature": null, "value": 576 } ``` ## Expected behavior Get the same output as in Lix 2.91, which is a list of strings with the names of the active experimental features: ```json { "aliases": [], "defaultValue": [], "description": "\nExperimental features that are enabled.\n\nExample:\n\n```\nexperimental-features = nix-command flakes\n```\n\nThe following experimental features are available:\n\n{{#include @generated@/command-ref/experimental-features-shortlist.md}}\n\nExperimental features are [further documented in the manual](@docroot@/contributing/experimental-features.md).\n\n", "documentDefault": true, "experimentalFeature": null, "value": [ "flakes", "nix-command" ] } ``` ## `nix --version` output nix (Lix, like Nix) 2.93.0-devpre20250314_af15a44 ## Additional context Running `nix config show` without `--json` still correctly serializes the `experimental-features` to their string representations: ``` experimental-features = flakes nix-command ```

niklaskorz added the

bug

label

2025-03-14 18:52:28 +00:00

pennae commented

2025-03-14 19:46:46 +00:00

Owner

wait, what. nlohmann json automatically casts scoped enum to ints. that's some cursed nonsense right there

jade commented

2025-03-15 01:21:56 +00:00

Owner

is this a screw up involving experimental-features-json.hh that would otherwise set up the necessary specialization to not screw this up? i might have a CL deleting that file that's languishing for some reason; there's a ticket for it.

pennae commented

2025-03-15 08:35:54 +00:00

Owner

it doesn't look like it. that header implement json hooks for ExperimentalFeature, not ExperimentalFeatures, which is the bitmap type of ExperimentalFeature :/

it doesn't look like it. that header implement json hooks for `ExperimentalFeature`, not `ExperimentalFeatures`, which is the bitmap type of `ExperimentalFeature` :/

piegames was assigned by pennae

2025-03-16 17:37:36 +00:00

pennae added this to the 2.93 milestone

2025-03-19 00:27:46 +00:00

jade added the

release-blocker

label

2025-03-21 01:16:50 +00:00

pennae commented

2025-03-21 13:38:47 +00:00

Owner

looked at this for a bit and concluded that we need to abandon using straight nlohmann:json objects and define our own basic_json specialization instead; one that doesn't use the default adl_serializer but a variant that simply rejects enum types

looked at this for a bit and concluded that we need to abandon using straight `nlohmann:json` objects and define our own `basic_json` specialization instead; one that doesn't use the default adl_serializer but a variant that simply rejects enum types

pennae self-assigned this

2025-03-21 13:38:59 +00:00

piegames was unassigned by pennae

2025-03-21 13:39:00 +00:00

lix-bot commented

2025-03-23 14:37:07 +00:00

Member

This issue was mentioned on Gerrit on the following CLs:

commit message in cl/2882 ("libutil: disallow enum serialization by default")

This issue was mentioned on Gerrit on the following CLs: * commit message in [cl/2882](https://gerrit.lix.systems/c/lix/+/2882) ("libutil: disallow enum serialization by default")

pennae commented

2025-03-24 10:13:35 +00:00

Owner

this seems to have affected 2.92 as well

niklaskorz commented

2025-03-24 11:06:53 +00:00

Author

@pennae wrote in #738 (comment):

this seems to have affected 2.92 as well

Yes, 007211e7a2 was already shipped in 2.92

@pennae wrote in https://git.lix.systems/lix-project/lix/issues/738#issuecomment-9768: > this seems to have affected 2.92 as well Yes, 007211e7a27a512cb343060e8b363c9f66ef67af was already shipped in 2.92