Replacing nlohmann::json with a much faster alternative

[wyattgill9]

Is your feature request related to a problem?

If you consider performance a problem then yes!, else no.

Within nixpkgs, theres ~900k lines of JSON across 740+ files, from nix develop to the store, JSON is used throughout the entire system, making JSON generation and parsing performance critical.

Proposed solution

nlohmann::json is a staple in the C++ JSON world. But Nix has grown far larger than the everyday pet projects that it was designed to support. Many newer, much more performant JSON parsers and generators have been developed in order to combat this problem, many of which are used every day in the private sector. C++ JSON benchmark: https://github.com/miloyip/nativejson-benchmark

Alternative solutions

Instead of a full scale rewrite, wrap one of these high performance JSON implementations with an API that more closely resembles that of nlohmann::json.

Additional context

Checklist

• checked latest Nix manual (source)
• checked open feature issues and pull requests for possible duplicates

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[xokdvium]

The main question is: since eval reproducibility is paramount we must ensure that a possible replacement (simdjson comes to mind and I'm pretty sure there was an issue about that at some point) behaves identically in all observable aspects. That would be a non-trivial effort with mandatory fuzzing surely.

[wyattgill9]

https://github.com/stephenberry/glaze
Is a C++23 solution, that claims to be faster than simdjson & rapidjson, with a simpler API, any of the following is worth looking into