migrate build system from setuptools to scikit-build-core

Replace the manual setup.py (which compiled ~49 C files with per-platform
BLAS logic and Windows workarounds) with a top-level CMakeLists.txt that
delegates to the submodule's existing CMake build. This eliminates the
dense_matrix_stub.c, the #ifdef _MSC_VER guards in bindings.c, and enables
dense matmul support on Windows via vcpkg OpenBLAS.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Transurgeon

.github/workflows/build-and-publish.yml

@@ -65,6 +65,8 @@ jobs:
           CIBW_ARCHS_MACOS: "x86_64 universal2"
           CIBW_ARCHS_LINUX: "auto aarch64"
           CIBW_BEFORE_BUILD_LINUX: "yum install -y openblas-devel || apt-get install -y libopenblas-dev"
+          CIBW_BEFORE_BUILD_WINDOWS: "vcpkg install openblas:x64-windows"
+          CIBW_ENVIRONMENT_WINDOWS: "CMAKE_TOOLCHAIN_FILE=C:/vcpkg/scripts/buildsystems/vcpkg.cmake"
       - name: Check wheels
         shell: bash
         run: |

CMakeLists.txt

@@ -0,0 +1,29 @@
+cmake_minimum_required(VERSION 3.15)
+project(SparseDiffPy LANGUAGES C)
+
+add_subdirectory(SparseDiffEngine)
+
+find_package(Python3 REQUIRED COMPONENTS Interpreter Development.Module NumPy)
+
+# Linux: CMake find_package(BLAS) doesn't set include dirs;
+# openblas puts cblas.h in /usr/include/openblas/
+if(UNIX AND NOT APPLE)
+    find_path(OPENBLAS_INCLUDE_DIR cblas.h PATHS /usr/include/openblas /usr/include)
+    if(OPENBLAS_INCLUDE_DIR)
+        target_include_directories(dnlp_diff PRIVATE ${OPENBLAS_INCLUDE_DIR})
+    endif()
+endif()
+
+python3_add_library(_sparsediffengine MODULE
+    sparsediffpy/_bindings/bindings.c
+)
+
+target_include_directories(_sparsediffengine PRIVATE
+    ${CMAKE_CURRENT_SOURCE_DIR}/SparseDiffEngine/include
+    ${CMAKE_CURRENT_SOURCE_DIR}/SparseDiffEngine/src
+    ${CMAKE_CURRENT_SOURCE_DIR}/sparsediffpy/_bindings
+)
+
+target_link_libraries(_sparsediffengine PRIVATE dnlp_diff Python3::NumPy)
+
+install(TARGETS _sparsediffengine DESTINATION sparsediffpy)

pyproject.toml

@@ -1,6 +1,6 @@
 [build-system]
-requires = ["numpy >= 2.0.0", "setuptools >= 68.1.0", "wheel"]
-build-backend = "setuptools.build_meta"
+requires = ["scikit-build-core >= 0.10", "numpy >= 2.0.0"]
+build-backend = "scikit_build_core.build"
 
 [project]
 name = "sparsediffpy"
@@ -14,8 +14,6 @@ license = "Apache-2.0"
 file = "README.md"
 content-type = "text/markdown"
 
-[tool.setuptools]
-include-package-data = false
-
-[tool.setuptools.packages.find]
-include = ["sparsediffpy*"]
+[tool.scikit-build]
+cmake.minimum-version = "3.15"
+wheel.packages = ["sparsediffpy"]

setup.py

@@ -11,9 +11,7 @@
 #include "atoms/const_vector_mult.h"
 #include "atoms/constant.h"
 #include "atoms/cos.h"
-#ifndef _MSC_VER
 #include "atoms/dense_matmul.h"
-#endif
 #include "atoms/diag_vec.h"
 #include "atoms/entr.h"
 #include "atoms/exp.h"
@@ -114,16 +112,12 @@ static PyMethodDef DNLPMethods[] = {
     {"make_xexp", py_make_xexp, METH_VARARGS, "Create xexp node"},
     {"make_sparse_left_matmul", py_make_sparse_left_matmul, METH_VARARGS,
      "Create sparse left matmul node (A @ f(x))"},
-#ifndef _MSC_VER
     {"make_dense_left_matmul", py_make_dense_left_matmul, METH_VARARGS,
      "Create dense left matmul node (A @ f(x)) where A is dense"},
-#endif
     {"make_sparse_right_matmul", py_make_sparse_right_matmul, METH_VARARGS,
      "Create sparse right matmul node (f(x) @ A)"},
-#ifndef _MSC_VER
     {"make_dense_right_matmul", py_make_dense_right_matmul, METH_VARARGS,
      "Create dense right matmul node (f(x) @ A) where A is dense"},
-#endif
     {"make_quad_form", py_make_quad_form, METH_VARARGS,
      "Create quadratic form node (x' * Q * x)"},
     {"make_quad_over_lin", py_make_quad_over_lin, METH_VARARGS,