Document <nix/fetchurl.nix>

[PkmX]

The builder of a derivation accepts a few builtin builders as described here:

nix/src/libstore/build.cc

Line 3497 in 512753f

if (drv->builder == "builtin:fetchurl")

These should be documented somewhere and how they differ from some builtin functions. From my understanding builtins.fetchurl fetches during instantiation time but a derivation using builtins:fetchurl as builder downloads when actually realizing the derivation.

[edolstra]

No, they shouldn't be documented because they're internal. But <nix/fetchurl.nix> should be documented though.

[PkmX]

Sounds good for me, since that is supposed to be the user-facing API.

[domenkozar]

Duplicate of #1489 then

[PkmX]

It's not really a duplicate of #1489, which is about the builtins.fetchurl function. This is about the function from <nix/fetchurl.nix> which is a derivation that calls a builtin builder.

[stale]

I marked this as stale due to inactivity. → More info

[edolstra]

Still relevant.

[stale]

I marked this as stale due to inactivity. → More info

[jsoo1]

Can we make the builtin builders user-facing? We actually used <nix/fetchurl.nix> and corepkgs in production because they really help solving bootstrapping problems. corepkgs (and builtins:fetchurl and builtins:unpack-channel) were very helpful bootstrapping a nixpkgs from.

Especially in airgapped situations this can be extremely helpful since the fetchers do not (yet) try substitutes.

[edolstra]

👍 on documenting <nix/fetchurl.nix> / builtins:fetchurl, but builtins:unpack-channel is too nix-channel-specific to document. Ideally we would remove it in the future (nix profile doesn't use it anymore IIRC).

[jsoo1]

sweet! My only nit with that is that builtin:unpack-channel is close enough to a general unpacker that it is very close to a general-purpose builtin:unpack that is also very useful during bootstrap.