packaging: remove unused dependency on onetbb

[uninsane]

#14509 configured meson to not use any onetbb features. nixpkgs exposes an option to blake3 to remove onetbb from the runtime closure as well, so enable that.

Motivation

Context

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[xokdvium]

Isn't onetbb used to make hash calculation multithreaded?

[xokdvium]

We are not using any of the features ourselves, but iirc blake3 relies on it for parallel hash computation. Would be nice to clarify this.

[xokdvium]

Would like to better understand
the implications of this.

[Mic92]

cc @silvanshade

[philiptaron]

We are not using any of the features ourselves, but iirc blake3 relies on it for parallel hash computation. Would be nice to clarify this.

You are correct, however there is no meson option to turn this on.

nix/src/libutil/hash.cc

Line 324 in 907a576

#ifdef BLAKE3_USE_TBB

So unless there's something out-of-tree, it's effectively dead code at the moment.

[xokdvium]

So unless there's something out-of-tree, it's effectively dead code at the moment.

That define comes from blake3. There's no option needed to turn it on

[xokdvium]

Specifically from the pkg-config: https://github.com/BLAKE3-team/BLAKE3/blob/308b95dfa15d5a0aa8cb3c5534ffd90d76122c46/c/CMakeLists.txt#L250C35-L250C49

cat result-dev/lib/pkgconfig/libblake3.pc
prefix="/nix/store/nvzryxzj8yqbsws3a9inmpqs9xrl8v58-libblake3-1.8.2"
exec_prefix="${prefix}"
libdir="/nix/store/nvzryxzj8yqbsws3a9inmpqs9xrl8v58-libblake3-1.8.2/lib"
includedir="/nix/store/nb6955lvlxl0a5hs99jchgjcnzadjh4g-libblake3-1.8.2-dev/include"

Name: libblake3
Description: BLAKE3 C implementation
Version: 1.8.2

Requires: tbb >= 2022.3.0
Libs: -L"${libdir}" -lblake3 -lstdc++
Cflags: -I"${includedir}" -DBLAKE3_DLL -DBLAKE3_USE_TBB

[philiptaron]

Ah, I understand. So the proposed PR disabled that by changing the pkg-config file that libblake3 shipped.

[Ericson2314]

OneTTB is an optional dependency of Blake3. I don't care if our experimental blake3 hashing is fast or not. Nixpkgs is free to hard-disable OneTBB in blake3. Nix I think should still support Blake3 built either way in case other non-Nix packaging of blake3 enables this, but we don't need to test that, we can just keep the small bit of CPP around as a minimal effort attempt.

[Ericson2314]

https://github.com/NixOS/nix/pull/14509/files this change is about the C++ standard library, and should be viewed as completely orthogonal knob --- all combinations of blake3 with/without TBB, and libstdc++ with/without TBB should work. This just exists to undo an (IMO poor form) header hack impl in libstc++ to auto-enable this feature.

[Ericson2314]

I don't think we need to do this PR because I think Nix should just use whatever blake3 Nixpkgs wants to give us. I want to purely follow Nixpkg's lead here.