feat: Support nix package manager (AztecProtocol/barretenberg#234)

* feat: Support nix package manager & add github action to build nix artifacts

* Checking gnu flag for buildEnv override

* Need to be explicit about gcc11 for aarch64 linux

* Use runner.os name for artifacts

* Cleanup comments in nixfile

* Add concurrency group to workflow

* Update the cases when the workflow runs

circuits/cpp/barretenberg/.github/workflows/nix.yml

@@ -0,0 +1,49 @@
+name: Nix builds
+
+on:
+  push:
+    branches:
+      - phated/**
+  schedule:
+    - cron: "0 2 * * *" # run at 2 AM UTC
+  workflow_dispatch:
+
+# This will cancel previous runs when a branch or PR is updated
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.ref || github.run_id }}
+  cancel-in-progress: true
+
+jobs:
+  nix-build:
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+        target: [llvm12, wasm32, cross-aarch64]
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - uses: cachix/install-nix-action@v20
+        with:
+          nix_path: nixpkgs=channel:nixos-22.11
+          github_access_token: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build barretenberg as ${{ matrix.target }}
+        run: |
+          nix build -L .#${{ matrix.target }}
+
+      - name: Prepare artifact
+        run: |
+          mkdir artifacts
+          cp -a ./result/. artifacts
+          7z a -ttar -so -an ./artifacts/* | 7z a -si ./libbarretenberg.tar.gz
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v3
+        with:
+          name: libbarretenberg-${{ runner.os }}-${{ matrix.target }}.tar.gz
+          path: ./libbarretenberg.tar.gz

circuits/cpp/barretenberg/.gitignore

@@ -1 +1,2 @@
-.vscode
+.vscode
+result

circuits/cpp/barretenberg/barretenberg.nix

@@ -0,0 +1,41 @@
+{ overrideCC, stdenv, llvmPackages, cmake, ninja, lib, callPackage, binaryen, gcc11 }:
+let
+  targetPlatform = stdenv.targetPlatform;
+  buildEnv =
+    if (stdenv.targetPlatform.isGnu && stdenv.targetPlatform.isAarch64) then
+    # As per https://discourse.nixos.org/t/gcc11stdenv-and-clang/17734/7 since it seems that aarch64-linux uses
+    # gcc9 instead of gcc11 for the C++ stdlib, while all other targets we support provide the correct libstdc++
+      overrideCC llvmPackages.stdenv (llvmPackages.clang.override { gccForLibs = gcc11.cc; })
+    else
+      llvmPackages.stdenv;
+  optionals = lib.lists.optionals;
+  toolchain_file = ./cpp/cmake/toolchains/${targetPlatform.system}.cmake;
+in
+buildEnv.mkDerivation
+{
+  pname = "libbarretenberg";
+  version = "0.1.0";
+
+  src = ./cpp;
+
+  nativeBuildInputs = [ cmake ninja ]
+    ++ optionals targetPlatform.isWasm [ binaryen ];
+
+  buildInputs = [ ]
+    ++ optionals (targetPlatform.isDarwin || targetPlatform.isLinux) [
+    llvmPackages.openmp
+  ];
+
+  cmakeFlags = [
+    "-DTESTING=OFF"
+    "-DBENCHMARKS=OFF"
+    "-DCMAKE_TOOLCHAIN_FILE=${toolchain_file}"
+  ]
+  ++ optionals (targetPlatform.isDarwin || targetPlatform.isLinux)
+    [ "-DCMAKE_BUILD_TYPE=RelWithAssert" ];
+
+  NIX_CFLAGS_COMPILE =
+    optionals targetPlatform.isDarwin [ " -fno-aligned-allocation" ];
+
+  enableParallelBuilding = true;
+}

circuits/cpp/barretenberg/flake.nix

@@ -0,0 +1,99 @@
+{
+  description =
+    "Barretenberg: C++ cryptographic library, BN254 elliptic curve library, and PLONK SNARK prover";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-22.11";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    let
+      barretenbergOverlay = self: super: {
+        # It seems that llvmPackages_11 can't build WASI, so default to llvmPackages_12
+        barretenberg = super.callPackage ./barretenberg.nix {
+          llvmPackages = self.llvmPackages_12;
+        };
+      };
+    in
+    flake-utils.lib.eachDefaultSystem
+      (system:
+        let
+          pkgs = import nixpkgs {
+            inherit system;
+            overlays = [ barretenbergOverlay ];
+          };
+
+          optional = pkgs.lib.lists.optional;
+
+          crossTargets = builtins.listToAttrs
+            (
+              [ ] ++ optional (pkgs.hostPlatform.isx86_64 && pkgs.hostPlatform.isLinux) {
+                name = "cross-aarch64";
+                value = pkgs.pkgsCross.aarch64-multiplatform-musl.pkgsLLVM.barretenberg;
+              } ++ optional (pkgs.hostPlatform.isx86_64 && pkgs.hostPlatform.isDarwin) {
+                name = "cross-aarch64";
+                value = pkgs.pkgsCross.aarch64-darwin.barretenberg.override {
+                  # llvmPackages_12 seems to fail when we try to cross-compile but llvmPackages_11 works
+                  llvmPackages = pkgs.llvmPackages_11;
+                };
+              }
+            );
+
+          shellDefaults = {
+            nativeBuildInputs = [
+              pkgs.starship
+              pkgs.llvmPackages_12.llvm
+            ];
+
+            shellHook = ''
+              eval "$(starship init bash)"
+            '';
+          };
+        in
+        rec {
+          packages = {
+            llvm11 = pkgs.barretenberg.override {
+              llvmPackages = pkgs.llvmPackages_11;
+            };
+            llvm12 = pkgs.barretenberg;
+            llvm13 = pkgs.barretenberg.override {
+              llvmPackages = pkgs.llvmPackages_13;
+            };
+            llvm14 = pkgs.barretenberg.override {
+              llvmPackages = pkgs.llvmPackages_14;
+            };
+            wasm32 = pkgs.pkgsCross.wasi32.barretenberg;
+
+            # Defaulting to llvm12 so we can ensure consistent shells
+            default = packages.llvm12;
+          } // crossTargets;
+
+          # Provide legacyPackages with our overlay so we can run
+          # > `nix build .#pkgsCross.aarch64-multiplatform.barretenberg`
+          # Ref https://discourse.nixos.org/t/how-do-i-cross-compile-a-flake/12062/12
+          legacyPackages = import nixpkgs {
+            inherit system;
+            overlays = [ barretenbergOverlay ];
+            crossOverlays = [ barretenbergOverlay ];
+          };
+
+          devShells = {
+            default = pkgs.mkShell.override { stdenv = packages.default.stdenv; }
+              ({
+                inputsFrom =
+                  [ packages.default ];
+              } // shellDefaults);
+
+            wasm32 = pkgs.mkShell.override
+              {
+                stdenv = packages.wasm32.stdenv;
+              }
+              ({
+                inputsFrom = [ packages.wasm32 ];
+              } // shellDefaults);
+          };
+        }) // {
+      overlays.default = barretenbergOverlay;
+    };
+}