nix/show-config: allow getting the value of a specific setting #7595
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Instead of needing to run `nix show-config --json | jq -r '."warn-dirty".value'` to view the value of `warn-dirty`, you can now run `nix show-config warn-dirty`.
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| Category category() override { return catUtility; } | ||
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| void run() override | ||
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| if (name) { | ||
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| throw UsageError("'--json' is not supported when specifying a setting name"); |
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Shouldn't we allow that? Both for consistency and because some settings are themselves a structured value (substituters for example) so it's worth having them already parsed.
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Ah, I apparently didn't see the second half of the PR description 🤦♂️
Wouldn't it be enough to just print setting->second.toJSON() in here ?
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Sadly, SettingInfo doesn't have toJSON()... Which is why I left it unsupported 😅
Also, SettingInfo is stringly-typed, so I'm not sure if we can easily get (useful) structured values out of it?
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Though, if configRegistrations was somehow exposed, maybe we could go through that, since that appears to have toJSON with proper JSON types (that's how globalConfig.toJSON() is implemented from what I can see).
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Derp, it is exposed, just under globalConfig. Still, I did a bit of playing and it's real ugly, trying to get the proper toJSON stuff. Basically need to be able to do the following:
- Iterate through all of the
Configs inconfigRegistrations - Gain access to
Config::_settings(which isprivate) so we can look up the setting by key there - Gain access to
AbstractSetting::toJSON()(which isprotected)
If there was a general-purpose "C++ value to appropriate JSON value" function somewhere, we could just call that, but I don't know if that exists (all the json files appears to be under libexpr).
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I don't think we need JSON support here, because you can always get a specific flag by doing nix show-config --json | jq .<name>.value.
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I might follow an issue. Whether or not this an important feature (and I readily believe the jq way is good enough), it would be nice if our configuration infrastructure didn't get in the way of this.
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I'd be happy to see json supported, but my attempt was a bit of a pain, and I was in over my head.
…-config <setting>`
Instead of needing to run
nix show-config --json | jq -r '."warn-dirty".value'to view the value ofwarn-dirty, you can now runnix show-config warn-dirty.Fixes #7586.
I'm sure this isn't the most beautiful solution (and I couldn't figure out a good way to get JSON support for the single-option mode at this point in time), but it works!