Add Windows build support with clang-cl and vcpkg

.gitattributes

@@ -0,0 +1,2 @@
+# Normalize all text files to LF in the repo and working copy.
+* text=auto eol=lf

.github/scripts/check_license_headers.py

@@ -16,6 +16,10 @@
 from pathlib import Path
 from typing import List, Optional, Tuple
 
+# Ensure emoji and other Unicode characters can be printed on Windows (cp1252)
+if hasattr(sys.stdout, "reconfigure"):
+    sys.stdout.reconfigure(encoding="utf-8")
+
 # Expected license headers for different file types
 CPP_LICENSE_PATTERNS = [
     # Full MIT license header - standard C-style comment with line breaks

.gitignore

@@ -17,11 +17,13 @@ dist/
 downloads/
 eggs/
 .eggs/
+install/
 lib/
 lib64/
 parts/
 sdist/
 var/
+vcpkg_installed/
 wheels/
 share/python-wheels/
 *.egg-info/

.pre-commit-config.yaml

@@ -24,8 +24,10 @@ repos:
     files: *linted_files
   - id: trailing-whitespace
     files: *linted_files
+    exclude: \.patch$
   - id: end-of-file-fixer
     files: *linted_files
+    exclude: \.patch$
   - id: debug-statements
     files: *linted_files
   - id: check-case-conflict

cpp/CMakeLists.txt

@@ -41,9 +41,22 @@ if(NOT CMAKE_BUILD_TYPE)
     set(CMAKE_BUILD_TYPE Release)
 endif()
 
-# Add compiler flags
-set(CMAKE_CXX_FLAGS_DEBUG_INIT "-g -O0 -Wall -Wextra")
-set(CMAKE_CXX_FLAGS_RELEASE_INIT "-O3 -DNDEBUG")
+# Set per-config compile flags.
+if(MSVC)  # clang-cl and cl
+    set(CMAKE_CXX_FLAGS_DEBUG          "/Zi /Od /W3 /RTC1")
+    set(CMAKE_CXX_FLAGS_RELEASE        "/O2 /W1 /DNDEBUG")
+    set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "/Zi /O2 /W1 /DNDEBUG")
+elseif(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang|AppleClang")
+    set(CMAKE_CXX_FLAGS_DEBUG          "-g -O0 -Wall -Wextra")
+    set(CMAKE_CXX_FLAGS_RELEASE        "-O3 -DNDEBUG")
+    set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-g -O3 -DNDEBUG")
+else()
+    message(WARNING "Unknown compiler ${CMAKE_CXX_COMPILER_ID}, using default CMAKE_CXX_FLAGS")
+endif()
+set(CMAKE_C_FLAGS_DEBUG          "${CMAKE_CXX_FLAGS_DEBUG}")
+set(CMAKE_C_FLAGS_RELEASE        "${CMAKE_CXX_FLAGS_RELEASE}")
+set(CMAKE_C_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_RELWITHDEBINFO}")
+
 
 # Options
 option(QDK_CHEMISTRY_ENABLE_COVERAGE    "Enable coverage build" OFF)
@@ -56,6 +69,12 @@ option(QDK_CHEMISTRY_ENABLE_MPI "Enable MPI Bindings for QDK Chemistry"  OFF)
 option(QDK_EMBED_RESOURCE_LOCATION "Point to embedded (permanent) resource location" ON)
 
 # Enable OpenMP by default, except on Apple platforms with AppleClang
+# On Windows with clang-cl, CMake resolves OpenMP to:
+#   OpenMP_CXX_FLAGS = -Xclang -fopenmp
+#   OpenMP_libomp_LIBRARY = .../VC/Tools/MSVC/.../lib/x64/libomp.lib
+# This uses LLVM's libomp runtime (not MSVC's vcomp*.dll). libomp.dll must
+# be present at runtime alongside the built binaries. It is found in:
+#   %VS_INSTALL_DIR%\VC\Tools\Llvm\x64\bin\libomp.dll
 cmake_dependent_option(QDK_ENABLE_OPENMP
     "Enable OpenMP support" ON
     "NOT (APPLE AND CMAKE_CXX_COMPILER_ID STREQUAL \"AppleClang\")" OFF)
@@ -92,6 +111,7 @@ if(NOT macis_FOUND)
     set(MACIS_ENABLE_MPI    OFF CACHE BOOL "MACIS enable MPI" FORCE)
     set(MACIS_ENABLE_PYTHON OFF CACHE BOOL "MACIS Enable Python" FORCE)
     set(MACIS_ENABLE_EXAMPLES OFF CACHE BOOL "MACIS Build Examples" FORCE)
+    set(MACIS_ENABLE_TESTS  ON CACHE BOOL "MACIS Build Tests")
     set(MACIS_ENABLE_OPENMP ${QDK_ENABLE_OPENMP} CACHE BOOL "MACIS Enable OpenMP" FORCE)
     if(DEFINED QDK_UARCH_USED)
       set(MACIS_UARCH  ${QDK_UARCH_USED} CACHE STRING "MACIS Microarchitecture" FORCE)
@@ -164,8 +184,12 @@ set_target_properties(chemistry PROPERTIES OUTPUT_NAME "qdk_chemistry")
 if(QDK_CHEMISTRY_ENABLE_COVERAGE)
     if(CMAKE_BUILD_TYPE STREQUAL "Debug" OR CMAKE_BUILD_TYPE STREQUAL "RelWithDebInfo")
         message(STATUS "Enabling coverage build")
-        target_compile_options(chemistry PRIVATE --coverage -fprofile-arcs -ftest-coverage)
-        target_link_libraries(chemistry PRIVATE --coverage)
+        if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang|AppleClang" AND NOT MSVC)
+            target_compile_options(chemistry PRIVATE --coverage -fprofile-arcs -ftest-coverage)
+            target_link_libraries(chemistry PRIVATE --coverage)
+        else()
+            message(WARNING "Coverage build is only supported with GCC or Clang compilers")
+        endif()
     else()
         message(FATAL_ERROR "Coverage build is only supported in CMAKE_BUILD_TYPE=Debug or RelWithDebInfo mode")
     endif()

cpp/cmake/qdk-uarch.cmake

@@ -1,20 +1,13 @@
+# --- Step 1: Resolve QDK_UARCH ---
 # Check environment variable first, then CMake variable
 if(NOT DEFINED QDK_UARCH AND DEFINED ENV{QDK_UARCH})
   set(QDK_UARCH $ENV{QDK_UARCH})
 endif()
 
 if(DEFINED QDK_UARCH)
   message(STATUS "Using user-defined uarch: ${QDK_UARCH}")
-  # If compiler ID is not GNU or Clang, we cannot use -march flag, so we will not set QDK_UARCH_FLAGS
-  if(NOT (CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang|AppleClang"))
-    message(WARNING "Compiler ${CMAKE_CXX_COMPILER_ID} does not support -march flag. QDK_UARCH_FLAGS will not be set.")
-    set(QDK_UARCH_USED "NONE" CACHE STRING "User-defined microarchitecture for optimization")
-  else()
-    set(QDK_UARCH_USED ${QDK_UARCH} CACHE STRING "User-defined microarchitecture for optimization")
-    set(QDK_UARCH_FLAGS "-march=${QDK_UARCH}" CACHE STRING "Compiler flags for user-defined microarchitecture")
-  endif()
 else()
-  # Set architecture-specific defaults based on the target platform
+  # Auto-detect based on the target platform
   if(CMAKE_SYSTEM_PROCESSOR MATCHES "x86_64|AMD64")
     set(QDK_UARCH "x86-64" CACHE STRING "Target microarchitecture")
     message(STATUS "Auto-detected x86_64 architecture, using: ${QDK_UARCH}")
@@ -25,24 +18,28 @@ else()
     message(WARNING "Unknown architecture ${CMAKE_SYSTEM_PROCESSOR}. QDK_UARCH not set. This may degrade performance")
     return()
   endif()
+endif()
 
-  # Set the used arch and flags
-  set(QDK_UARCH_USED ${QDK_UARCH} CACHE STRING "User-defined microarchitecture for optimization")
-  if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang|AppleClang")
-    set(QDK_UARCH_FLAGS "-march=${QDK_UARCH}" CACHE STRING "Compiler flags for user-defined microarchitecture")
-  else()
-    message(WARNING "Compiler syntax for ISA flags is unknown, defaulting to the system default generic ISA")
-  endif()
+# --- Step 2: Set QDK_UARCH_FLAGS based on compiler and uarch ---
+set(QDK_UARCH_USED ${QDK_UARCH} CACHE STRING "Target microarchitecture for optimization")
+if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang|AppleClang")
+  set(QDK_UARCH_FLAGS "-march=${QDK_UARCH}" CACHE STRING "Compiler flags for target microarchitecture")
+elseif(MSVC)
+  # Users should set QDK_UARCH to a valid MSVC /arch: argument (e.g. AVX2, AVX512)
+  set(QDK_UARCH_FLAGS "/arch:${QDK_UARCH}" CACHE STRING "Compiler flags for target microarchitecture")
+else()
+  message(WARNING "Compiler ${CMAKE_CXX_COMPILER_ID}: unknown flag syntax for ISA selection. QDK_UARCH_FLAGS will not be set.")
+  set(QDK_UARCH_USED "NONE" CACHE STRING "Target microarchitecture for optimization")
 endif()
 
-# Test that the produced flags are sane
+# --- Step 3: Validate the flags ---
 if(QDK_UARCH_FLAGS)
   message(STATUS "Testing QDK_UARCH_FLAGS: ${QDK_UARCH_FLAGS}")
   include(CheckCXXCompilerFlag)
   check_cxx_compiler_flag("${QDK_UARCH_FLAGS}" COMPILER_SUPPORTS_QDK_UARCH_FLAGS)
   if(NOT COMPILER_SUPPORTS_QDK_UARCH_FLAGS)
     message(WARNING "The compiler does not support the specified QDK_UARCH_FLAGS: ${QDK_UARCH_FLAGS}. Unsetting these flags.")
     unset(QDK_UARCH_FLAGS CACHE)
-    set(QDK_UARCH_USED "NONE" CACHE STRING "User-defined microarchitecture for optimization")
+    set(QDK_UARCH_USED "NONE" CACHE STRING "Target microarchitecture for optimization")
   endif()
 endif()

cpp/cmake/third_party.cmake

@@ -2,7 +2,10 @@
 include(DependencyManager)
 
 # Extract QDK_UARCH FLAGS
-set(DEPENDENCY_BUILD_FLAGS BUILD_ARGS "${QDK_UARCH_FLAGS} -fPIC")
+set(DEPENDENCY_BUILD_FLAGS BUILD_ARGS "${QDK_UARCH_FLAGS}")
+if(NOT MSVC)
+    set(DEPENDENCY_BUILD_FLAGS "${DEPENDENCY_BUILD_FLAGS} -fPIC")
+endif()
 
 # Save current warning settings
 get_property(_old_warn_deprecated CACHE CMAKE_WARN_DEPRECATED PROPERTY VALUE)
@@ -69,11 +72,17 @@ set(GAUXC_ENABLE_MAGMA   OFF CACHE BOOL "Enable gauxc MAGMA Support"   FORCE)
 set(GAUXC_ENABLE_CUTLASS ON  CACHE BOOL "Enable gauxc CUTLASS Support" FORCE)
 set(GAUXC_ENABLE_CUDA ${QDK_CHEMISTRY_ENABLE_GPU} CACHE BOOL "Enable gauxc CUDA Support" FORCE)
 set(GAUXC_ENABLE_MPI  ${QDK_CHEMISTRY_ENABLE_MPI} CACHE BOOL "Enable gauxc MPI Support"  FORCE)
-set(GAUXC_ENABLE_OPENMP ${QDK_ENABLE_OPENMP} CACHE BOOL "Enable gauxc OpenMP Support" FORCE)
+# Disable OpenMP in GauXC on Windows due to open issue: https://github.com/wavefunction91/GauXC/issues/196
+# Keep OpenMP for the rest of the project (MACIS, our own code). Re-enable once the upstream issue is fixed.
+if(MSVC)
+  set(GAUXC_ENABLE_OPENMP OFF CACHE BOOL "Enable gauxc OpenMP Support" FORCE)
+else()
+  set(GAUXC_ENABLE_OPENMP ${QDK_ENABLE_OPENMP} CACHE BOOL "Enable gauxc OpenMP Support" FORCE)
+endif()
 
 handle_dependency(gauxc
-  GIT_REPOSITORY https://github.com/wavefunction91/gauxc.git
-  GIT_TAG 62fea07c9306dbd83dd18b6957358827ac9b3da0
+  GIT_REPOSITORY https://github.com/lorisercole/gauxc.git
+  GIT_TAG 4e18eb1c4fc3b7bc1d2f91c59d8a4826b0997a4f
   BUILD_TARGET gauxc::gauxc
   INSTALL_TARGET gauxc::gauxc
   ${DEPENDENCY_BUILD_FLAGS}

cpp/include/qdk/chemistry/algorithms/dynamical_correlation_calculator.hpp

@@ -76,7 +76,7 @@ class DynamicalCorrelationCalculator
    *
    * @return The algorithm's name
    */
-  virtual std::string name() const = 0;
+  virtual std::string name() const override = 0;
 
   /**
    * @brief Access the algorithm's type name
@@ -99,7 +99,7 @@ class DynamicalCorrelationCalculator
    * wavefunction, and optionally a bra wavefunction
    */
   virtual DynamicalCorrelationResult _run_impl(
-      std::shared_ptr<data::Ansatz> ansatz) const = 0;
+      std::shared_ptr<data::Ansatz> ansatz) const override = 0;
 };
 
 /**

cpp/include/qdk/chemistry/algorithms/stability.hpp

@@ -114,7 +114,7 @@ class StabilityChecker
    * @return A pair containing stability status and detailed results
    */
   virtual std::pair<bool, std::shared_ptr<data::StabilityResult>> _run_impl(
-      std::shared_ptr<data::Wavefunction> wavefunction) const = 0;
+      std::shared_ptr<data::Wavefunction> wavefunction) const override = 0;
 };
 
 /**

cpp/include/qdk/chemistry/data/structure.hpp

@@ -117,12 +117,12 @@ class Structure : public DataClass,
   /**
    * @brief Copy assignment operator
    */
-  Structure& operator=(const Structure& other) = default;
+  Structure& operator=(const Structure&) = delete;
 
   /**
    * @brief Move assignment operator
    */
-  Structure& operator=(Structure&& other) noexcept = default;
+  Structure& operator=(Structure&&) = delete;
 
   /**
    * @brief Destructor

cpp/src/qdk/chemistry/algorithms/microsoft/localization/vvhv.cpp

@@ -64,10 +64,11 @@ class VVHVLocalization : public IterativeOrbitalLocalizationScheme {
       std::shared_ptr<IterativeOrbitalLocalizationScheme> inner_localizer)
       : IterativeOrbitalLocalizationScheme(settings),
         basis_set_(basis_set),
-        overlap_ori_(ao_overlap),
         minimal_basis_name_(minimal_basis_name),
-        basis_ori_fp_(utils::microsoft::convert_basis_set_from_qdk(*basis_set)),
-        inner_localizer_(inner_localizer) {
+        inner_localizer_(inner_localizer),
+        overlap_ori_(ao_overlap),
+        basis_ori_fp_(
+            utils::microsoft::convert_basis_set_from_qdk(*basis_set)) {
     QDK_LOG_TRACE_ENTERING();
 
     // Initialize all data structures and pre-compute integrals

cpp/src/qdk/chemistry/algorithms/microsoft/macis_base.hpp

@@ -292,7 +292,7 @@ class Macis : public qdk::chemistry::algorithms::MultiConfigurationCalculator {
    */
   virtual ~Macis() noexcept override = default;
 
-  virtual std::string name() const = 0;
+  virtual std::string name() const override = 0;
 
  protected:
   /**

cpp/src/qdk/chemistry/algorithms/microsoft/scf/include/qdk/chemistry/scf/eri/eri_multiplexer.h

@@ -64,9 +64,9 @@ class ERIMultiplexer : public ERI {
                  const SCFConfig& cfg, double omega);
 
   /**
-   * @brief Default constructor (private, used by factory methods)
+   * @brief Default constructor (deleted — base class ERI has no default ctor)
    */
-  ERIMultiplexer() noexcept = default;
+  ERIMultiplexer() noexcept = delete;
 
  public:
   /**

cpp/src/qdk/chemistry/algorithms/microsoft/scf/src/core/basis_set.cpp

@@ -132,8 +132,8 @@ BasisSet::BasisSet(std::shared_ptr<Molecule> mol,
                    int n_ecp_electrons, BasisMode mode, bool pure, bool sort)
     : mol(mol),
       mode(mode),
-      pure(pure),
       shells(input_shells),
+      pure(pure),
       ecp_shells(input_ecp_shells),
       element_ecp_electrons(element_ecp_electrons),
       n_ecp_electrons(n_ecp_electrons) {
@@ -188,7 +188,7 @@ BasisSet::BasisSet(std::shared_ptr<Molecule> mol,
 BasisSet::BasisSet(std::shared_ptr<Molecule> mol,
                    const std::vector<Shell>& input_shells, BasisMode mode,
                    bool pure, bool sort)
-    : mol(mol), mode(mode), pure(pure), shells(input_shells) {
+    : mol(mol), mode(mode), shells(input_shells), pure(pure) {
 #ifdef QDK_CHEMISTRY_ENABLE_MPI
   if (mpi::get_world_size() > 1) {
     MPI_Barrier(MPI_COMM_WORLD);
@@ -245,7 +245,7 @@ BasisSet::BasisSet(std::shared_ptr<Molecule> mol, const std::string& path,
               "basis" / (normalized_path + ".json");
     name = normalized_path;
   } else {
-    name = bs_path.stem();
+    name = bs_path.stem().string();
   }
   if (!std::filesystem::exists(bs_path)) {
     auto compressed_path = QDKChemistryConfig::get_resources_dir() /
@@ -425,7 +425,7 @@ Shell Shell::from_json(const nlohmann::ordered_json& rec,
                        const std::shared_ptr<Molecule> mol) {
   QDK_LOG_TRACE_ENTERING();
 
-  Shell sh;
+  Shell sh{};
   sh.atom_index = rec["atom"].template get<uint64_t>();
   sh.angular_momentum = rec["am"].template get<uint64_t>();
 

cpp/src/qdk/chemistry/algorithms/microsoft/scf/src/scf_algorithm/scf_algorithm.cpp

@@ -36,8 +36,8 @@ SCFAlgorithm::SCFAlgorithm(const SCFContext& ctx)
     : ctx_(ctx),
       step_count_(0),
       last_energy_(0.0),
-      density_rms_(std::numeric_limits<double>::infinity()),
-      delta_energy_(std::numeric_limits<double>::infinity()) {
+      delta_energy_(std::numeric_limits<double>::infinity()),
+      density_rms_(std::numeric_limits<double>::infinity()) {
   QDK_LOG_TRACE_ENTERING();
   auto num_atomic_orbitals = ctx.basis_set->num_atomic_orbitals;
   auto num_density_matrices =

cpp/src/qdk/chemistry/algorithms/microsoft/scf/src/util/int1e.cpp

@@ -91,7 +91,7 @@ class Libint2Engine : public OneBodyIntegralEngine {
    * @brief Get number of operator components
    * @return Number of matrices/operators this engine computes
    */
-  size_t nopers() const {
+  size_t nopers() const override {
     QDK_LOG_TRACE_ENTERING();
     return engine_.results().size();
   }
@@ -179,7 +179,7 @@ class ECPIntEngine : public OneBodyIntegralEngine {
    * @return Number of matrices this engine computes (1 for integrals, 3*natom
    * for gradients)
    */
-  size_t nopers() const {
+  size_t nopers() const override {
     QDK_LOG_TRACE_ENTERING();
     return buf_.size();
   }

cpp/src/qdk/chemistry/algorithms/microsoft/scf/tests/util_tests.cpp

@@ -472,11 +472,11 @@ TEST(ClassRegistryTest, PrimitiveKey) {
 TEST(AtomGuessTest, BasisSetMap) {
   // Test that the map correctly identifies equivalent basis sets
   auto mol = std::make_shared<Molecule>();
-  mol->atomic_nums = {1};
+  mol->atomic_nums = {3};
   mol->n_atoms = 1;
-  mol->atomic_charges = {1};
-  mol->total_nuclear_charge = 1;
-  mol->n_electrons = 1;
+  mol->atomic_charges = {3};
+  mol->total_nuclear_charge = 3;
+  mol->n_electrons = 3;
   mol->coords = {{0.0, 0.0, 0.0}};
 
   // Create two identical basis sets
@@ -485,10 +485,12 @@ TEST(AtomGuessTest, BasisSetMap) {
   auto basis2 =
       BasisSet::from_database_json(mol, "sto-3g", BasisMode::PSI4, true, false);
 
-  // Create same basis set in different shell order
+  // Create same basis set with reversed shell order via JSON round-trip.
+  // Lithium STO-3G has 3 shells, so reversing produces a different ordering
+  // that the BasisEqChecker should reject.
   auto basis_json = basis1->to_json();
-  // Reverse the shells
-  std::reverse(basis_json["shells"].begin(), basis_json["shells"].end());
+  std::reverse(basis_json["electron_shells"].begin(),
+               basis_json["electron_shells"].end());
   auto basis3 = BasisSet::from_serialized_json(mol, basis_json);
 
   // Create a different basis set (different basis name)
@@ -518,7 +520,7 @@ TEST(AtomGuessTest, BasisSetMap) {
   EXPECT_NE(it2, basis_map.end());
   EXPECT_TRUE(it2->second.isApprox(RowMajorMatrix::Identity(
       basis2->num_atomic_orbitals, basis2->num_atomic_orbitals)));
-  // Retrieve using basis3 (should not be found)
+  // Retrieve using basis3 (should not be found — shells are reversed)
   auto it3 = basis_map.find(*basis3);
   EXPECT_EQ(it3, basis_map.end());
   // Retrieve using basis4 (should not be found)

cpp/src/qdk/chemistry/data/basis_set.cpp

@@ -707,8 +707,8 @@ BasisSet::BasisSet(const BasisSet& other)
     : _name(other._name),
       _atomic_orbital_type(other._atomic_orbital_type),
       _shells_per_atom(other._shells_per_atom),
-      _ecp_name(other._ecp_name),
       _ecp_shells_per_atom(other._ecp_shells_per_atom),
+      _ecp_name(other._ecp_name),
       _ecp_electrons(other._ecp_electrons) {
   QDK_LOG_TRACE_ENTERING();
   if (other._structure) {