Begin supporting nix flakes build system

.github/workflows/nix-github-actions.yml

@@ -0,0 +1,15 @@
+name: "build nix flake"
+on:
+  pull_request:
+  push:
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+      with:
+       submodules: true
+    - uses: cachix/install-nix-action@v26
+      with:
+       install_url: https://releases.nixos.org/nix/nix-2.18.1/install
+    - run: nix build .?submodules=1

.github/workflows/update-flake-lock.yml

@@ -0,0 +1,21 @@
+name: update-flake-lock
+on:
+  workflow_dispatch: # allows manual triggering
+  schedule:
+    - cron: '0 0 * * 0' # runs weekly on Sunday at 00:00
+
+jobs:
+  lockfile:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@main
+      - name: Update flake.lock
+        uses: DeterminateSystems/update-flake-lock@main
+        with:
+          pr-title: "Update flake.lock" # Title of PR to be created
+          pr-labels: |                  # Labels to be set on the PR
+            dependencies
+            automated

.gitignore

@@ -45,3 +45,4 @@ __pycache__
 /tests/unit/bintest/
 /tests/unit/objtest/
 /tests/ystests
+/result

flake.nix

@@ -0,0 +1,48 @@
+{
+  description = "A nix flake for the Yosys synthesis suite";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs {
+          inherit system;
+        };
+        # TODO: don't override src when ./abc is empty
+        # which happens when the command used is `nix build` and not `nix build ?submodules=1`
+        abc-verifier = pkgs.abc-verifier.overrideAttrs(x: y: {src = ./abc;});
+        yosys = pkgs.clangStdenv.mkDerivation {
+          name = "yosys";
+          src = ./. ;
+          buildInputs = with pkgs; [ clang bison flex libffi tcl readline python3 llvmPackages.libcxxClang zlib git pkg-configUpstream ];
+          checkInputs = with pkgs; [ gtest ];
+          propagatedBuildInputs = [ abc-verifier ];
+          preConfigure = "make config-clang";
+          checkTarget = "test";
+          installPhase = ''
+            make install PREFIX=$out ABCEXTERNAL=yosys-abc
+            ln -s ${abc-verifier}/bin/abc $out/bin/yosys-abc
+          '';
+					buildPhase = ''
+            make -j$(nproc) ABCEXTERNAL=yosys-abc
+          '';
+          meta = with pkgs.lib; {
+            description = "Yosys Open SYnthesis Suite";
+            homepage = "https://yosyshq.net/yosys/";
+            license = licenses.isc;
+            maintainers = with maintainers; [ ];
+          };
+        };
+      in {
+        packages.default = yosys;
+        defaultPackage = yosys;
+        devShell = pkgs.mkShell {
+          buildInputs = with pkgs; [ clang bison flex libffi tcl readline python3 llvmPackages.libcxxClang zlib git gtest abc-verifier ];
+        };
+      }
+    );
+}