derivationOf primop

[roberth]

Is your feature request related to a problem? Please describe.

It behaves roughly as an inverse of outputOf and is equivalent to the planned ^.. syntax on the CLI.

This function improves RFC 92 and multi-derivation package support, by allowing the derivation path to be accessed for any output, whose derivations may be distinct, rather than only exposing a single drvPath.

pkg.drvPath is rarely needed. When we have a function for it, this attribute can be removed from the packages.

NixOS/nixpkgs#281536 adds such a function in Nixpkgs. Its implementation can serve as a polyfill for this builtin.

Describe the solution you'd like

A primop that takes the Nix language representation of a DerivingPath, a string with context, and returns the deriver field if it is present. Otherwise it should throw or return null.

Describe alternatives you've considered

Require the Nixpkgs library for this functionality.

Additional context

• ^.. installable syntax for retrieving "derivation of" #10121

Priorities

Add 👍 to issues you find important.

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/pre-rfc-implement-dependency-retrieval-primitive/43418/9