Feature/nix support (#131)

# Description

This is a WIP PR to add nix support to the repo. The aim is to combat
the packaging requirements around cuda and tket.

It is not ready for merging yet. For effective use there are three
things remaining:
- Documentation
- Remote Caching with cachix. At current, cachix does not skip uploading
packages that are already available in the upstream
cuda-maintainers.cachix.org cache, so a push would be quite large and
fill up precious space. I have reached out to Domen and he has told me
that an update to help us on this will be out next week.
- Usage with non-nixos systems. I have successfully run this flake on an
ubuntu docker image with cuda drivers loaded, but it is awkward. We need
to make use of a third-party NixGL flake and wrap binaries in it, in
order to have the system's cuda drivers available for nix to use. I want
to improve this somewhat, otherwise it will be confusing for users.

When this is ready and merged, CI should build any changes and upload
them to cachix. I will pre-populate cachix with the heavy dependencies
to make this process quick and easy. When this is all in place, we can
think about use the nix flake for testing in CI using a gpu-enabled
machine without being concerned about the awkward dependency setup
process.

# Related issues

N/A

# Checklist

- [x] I have run the tests on a device with GPUs.
- [ ] I have performed a self-review of my code.
- [ ] I have commented hard-to-understand parts of my code.
- [ ] I have made corresponding changes to the public API documentation.
- [x] I have added tests that prove my fix is effective or that my
feature works.
- [ ] I have updated the changelog with any user-facing changes.

.github/workflows/build-with-nix.yml

@@ -0,0 +1,41 @@
+name: build with nix
+
+on:
+  pull_request:
+    branches:
+      - main
+  workflow_dispatch: {}
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+jobs:
+  build:
+    strategy:
+      matrix:
+        os: ['ubuntu-24.04']
+    runs-on: ${{matrix.os}}
+    steps:
+    - uses: actions/checkout@v4
+    - uses: cachix/install-nix-action@V27
+    - uses: cachix/cachix-action@v15
+      with:
+        name: tket
+        authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+    - name: Build pytket-cutensornet
+      run: nix build --accept-flake-config
+  #
+  # need GPU runners for this
+  #
+  #test:
+  #  needs: build
+  #  runs-on: nixos-gpu
+  #  steps:
+  #  - uses: actions/checkout@v4
+  #  - uses: cachix/install-nix-action@V27
+  #  - uses: cachix/cachix-action@v15
+  #    with:
+  #      name: tket
+  #      authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+  #  - name: Test pytket-cutensornet
+  #    run: nix run .#tests --accept-flake-config

.gitignore

@@ -9,4 +9,8 @@ dist
 obj
 docs/extensions
 .ipynb_checkpoints
-pytket/extensions/cutensornet/_metadata.py
+pytket/extensions/cutensornet/_metadata.py
+# nix artifacts
+result
+.direnv
+.envrc

flake.nix

@@ -0,0 +1,52 @@
+{
+  description = "Pytket Cutensornet Extension";
+  nixConfig.extra-substituters = "https://tket.cachix.org https://cache.nixos.org https://cuda-maintainers.cachix.org https://nix-community.cachix.org";
+  nixConfig.trusted-public-keys = ''
+    tket.cachix.org-1:ACdm5Zg19qPL0PpvUwTPPiIx8SEUy+D/uqa9vKJFwh0=
+    cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
+    cuda-maintainers.cachix.org-1:0dq3bujKpuEPMCX6U4WylrUDZ9JyUG0VpVZa7CNfq5E=
+    nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs=
+  '';
+  inputs.flake-utils.url = "github:numtide/flake-utils";
+  inputs.tket.url = "github:CQCL/tket";
+  inputs.nixpkgs.follows = "tket/nixpkgs";
+  outputs = { self, nixpkgs, flake-utils, tket }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs {
+          inherit system;
+          config = {
+            allowUnfree = true;
+            cudaSupport = true;
+          };
+          overlays = [
+            (self: super: {
+              inherit (tket.packages."${system}") tket pytket;
+            })
+            (self: super: {
+              cuda-bundle = pkgs.callPackage ./nix-support/cuda-bundle.nix {};
+            })
+            (self: super: {
+              cupy' = pkgs.python3Packages.callPackage ./nix-support/cupy.nix {};
+            })
+            (self: super: {
+              pycuquantum = pkgs.python3Packages.callPackage ./nix-support/pycuquantum.nix {};
+            })
+            (import ./nix-support/pytket-cutensornet.nix)
+          ];
+        };
+      in {
+        packages = {
+          default = pkgs.pytket-cutensornet;
+          cupy = pkgs.cupy';
+          pytket-cutensornet = pkgs.pytket-cutensornet;
+          tests = pkgs.run-pytket-cutensornet-tests;
+        };
+        devShells = {
+          default = pkgs.mkShell { buildInputs = [ pkgs.pytket-cutensornet ]; };
+        };
+        checks = {
+          # no GPU support in checks at the time of writing
+        };
+      });
+}

mypy.ini

@@ -26,3 +26,7 @@ ignore_errors = True
 [mypy-lark.*]
 ignore_missing_imports = True
 ignore_errors = True
+
+[mypy-sympy.*]
+ignore_missing_imports = True
+ignore_errors = True

nix-support/cuda-bundle.nix

@@ -0,0 +1,37 @@
+{
+  symlinkJoin,
+  cudaPackages,
+}:
+let
+  cutensor' = cudaPackages.callPackage ./cutensor.nix {};
+  cuquantum' = cudaPackages.callPackage ./cuquantum.nix {};
+  cusparselt' = cudaPackages.callPackage ./cusparselt.nix {};
+in
+symlinkJoin {
+  name = "cuda-bundle-${cudaPackages.cudaVersion}";
+  paths = with cudaPackages; [
+    cuda_cccl # <nv/target>
+    cuda_cccl.dev
+    cuda_cudart
+    cuda_nvcc.dev # <crt/host_defines.h>
+    cuda_nvcc
+    cuda_nvprof
+    cuda_nvrtc
+    cuda_nvtx
+    cuda_profiler_api
+    libcublas
+    libcufft
+    libcurand
+    libcusolver
+    libcusparse
+    cusparselt'
+    cusparselt'.dev
+    cutensor'
+    cutensor'.dev
+    cuquantum'
+  ];
+  postBuild = ''
+    ln -sfn lib $out/lib64
+  '';
+}
+