Support building nextpnr with nix flakes

.github/workflows/nix.yml

@@ -0,0 +1,13 @@
+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@v25
+    - run: nix build '.?submodules=1'

.gitignore

@@ -43,3 +43,4 @@ install_manifest.txt
 *.phys
 *.dcp
 *.bit
+result

flake.nix

@@ -0,0 +1,85 @@
+{
+  description = "A flake for the nextpnr FPGA place and route tool";
+
+  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;
+          overlays = [];
+        };
+        # Define custom overrides or additional packages
+        myPythonPackages = pkgs.python3Packages.override {
+          overrides = self: super: {
+            apycula = super.apycula.override {
+              # Place any necessary overrides here
+            };
+          };
+        };
+        enableGui = false;
+      in
+        {
+          packages = {
+            nextpnr = pkgs.stdenv.mkDerivation {
+              pname = "nextpnr";
+              version = "0.6";
+              src = ./.;
+
+              nativeBuildInputs = [ pkgs.cmake ]
+                                  ++ (pkgs.lib.optional enableGui pkgs.qt6.wrapQtAppsHook);
+              buildInputs = [
+                (pkgs.boost.override { python = pkgs.python3; enablePython = true; })
+                pkgs.python3
+                pkgs.eigen
+                myPythonPackages.apycula
+                pkgs.icestorm
+                pkgs.trellis
+                pkgs.tcl
+                pkgs.zlib
+                pkgs.capnproto
+                pkgs.lzma
+                pkgs.tk
+                pkgs.wget
+              ] ++ (pkgs.lib.optional enableGui pkgs.qt6.qtbase)
+              ++ (pkgs.lib.optional pkgs.stdenv.cc.isClang pkgs.llvmPackages.openmp);
+
+              cmakeFlags = [
+                "-DARCH=all"
+                "-DBUILD_TESTS=ON"
+                "-DICESTORM_INSTALL_PREFIX=${pkgs.icestorm}"
+                "-DTRELLIS_INSTALL_PREFIX=${pkgs.trellis}"
+                "-DTRELLIS_LIBDIR=${pkgs.trellis}/lib/trellis"
+                "-DGOWIN_BBA_EXECUTABLE=${myPythonPackages.apycula}/bin/gowin_bba"
+                "-DUSE_OPENMP=ON"
+                # warning: high RAM usage
+                "-DSERIALIZE_CHIPDBS=OFF"
+              ] ++ (pkgs.lib.optional enableGui "-DBUILD_GUI=ON");
+
+              meta = with pkgs.lib; {
+                description = "Place and route tool for FPGAs";
+                homepage = "https://github.com/yosyshq/nextpnr";
+                license = licenses.isc;
+                platforms = platforms.all;
+                maintainers = with maintainers; [ ];
+              };
+            };
+          };
+
+          packages.default = self.packages.${system}.nextpnr;
+
+          devShell = pkgs.mkShell {
+            inputsFrom = [ self.packages.${system}.default ];
+
+            shellHook = ''
+             export TRELLIS_INSTALL_PREFIX=${pkgs.trellis}
+             export ICESTORM_INSTALL_PREFIX=${pkgs.icestorm}
+             export QT_QPA_PLATFORM_PLUGIN_PATH="${pkgs.libsForQt5.qt5.qtbase.bin}/lib/qt-${pkgs.libsForQt5.qt5.qtbase.version}/plugins";
+            '';
+          };
+        });
+}