Refactor libcuvs_c header and source locations (rapidsai#1357)

In support of building a stable C interface for libcuvs I have moved all `C` code into a separate directory for both the headers and sources. This will make it easier to install just 'C' language headers, make it easier to apply code rules for C headers, and in the future add more CI checks for our C API.

Authors:
  - Robert Maynard (https://github.com/robertmaynard)
  - MithunR (https://github.com/mythrocks)
  - Ben Frederickson (https://github.com/benfred)

Approvers:
  - Kyle Edwards (https://github.com/KyleFromNVIDIA)
  - Ben Frederickson (https://github.com/benfred)

URL: rapidsai#1357

Author: robertmaynard

c/CMakeLists.txt

@@ -0,0 +1,173 @@
+# =============================================================================
+# Copyright (c) 2025, NVIDIA CORPORATION.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+# in compliance with the License. You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software distributed under the License
+# is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+# or implied. See the License for the specific language governing permissions and limitations under
+# the License.
+# =============================================================================
+
+cmake_minimum_required(VERSION 3.30.4 FATAL_ERROR)
+include(../cmake/rapids_config.cmake)
+include(rapids-cmake)
+include(rapids-cpm)
+include(rapids-export)
+include(rapids-find)
+
+project(
+  CUVS_C
+  VERSION "${RAPIDS_VERSION}"
+  LANGUAGES CXX C
+)
+set(CMAKE_INSTALL_MESSAGE LAZY)
+
+# ##################################################################################################
+# * User Options  ------------------------------------------------------------
+
+option(BUILD_SHARED_LIBS "Build cuvs_c shared libraries" ON)
+option(BUILD_TESTS "Build cuvs unit-tests" ON)
+
+option(BUILD_CAGRA_HNSWLIB "Build CAGRA+hnswlib interface" ON)
+option(BUILD_MG_ALGOS "Build with multi-GPU support" ON)
+
+option(CUVSC_STATIC_CUVS_LIBRARY "Link against statical version of libcuvs" OFF)
+
+# Check if cuVS is already available. If so, it is the user's responsibility to ensure that the
+# CMake package is also available at build time of the Python cuvs package.
+if(NOT TARGET cuvs::cuvs)
+  find_package(cuvs "${RAPIDS_VERSION}" REQUIRED)
+else()
+  set(BUILDING_FROM_CUVS ON)
+endif()
+
+# ##################################################################################################
+# * build type ---------------------------------------------------------------
+
+# Set a default build type if none was specified
+rapids_cmake_build_type(Release)
+
+# this is needed for clang-tidy runs
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+
+if(NOT DEFINED CUVS_CXX_FLAGS)
+  include(../cpp/cmake/modules/ConfigureCUDA.cmake)
+endif()
+
+# ##################################################################################################
+# * Requirements -------------------------------------------------------------
+
+# add third party dependencies using CPM
+rapids_cpm_init()
+
+# add third party dependencies using CPM
+include(../cpp/cmake/thirdparty/get_dlpack.cmake)
+
+if(BUILD_CAGRA_HNSWLIB)
+  include(../cpp/cmake/thirdparty/get_hnswlib.cmake)
+endif()
+
+# ##################################################################################################
+# * cuvs_c -------------------------------------------------------------------------------
+add_library(
+  cuvs_c SHARED
+  src/core/c_api.cpp
+  src/cluster/kmeans.cpp
+  src/neighbors/brute_force.cpp
+  src/neighbors/ivf_flat.cpp
+  src/neighbors/ivf_pq.cpp
+  src/neighbors/cagra.cpp
+  $<$<BOOL:${BUILD_CAGRA_HNSWLIB}>:src/neighbors/hnsw.cpp>
+  $<$<BOOL:${BUILD_MG_ALGOS}>:src/neighbors/mg_ivf_pq.cpp>
+  $<$<BOOL:${BUILD_MG_ALGOS}>:src/neighbors/mg_ivf_flat.cpp>
+  $<$<BOOL:${BUILD_MG_ALGOS}>:src/neighbors/mg_cagra.cpp>
+  src/neighbors/nn_descent.cpp
+  src/neighbors/vamana.cpp
+  src/neighbors/refine.cpp
+  src/neighbors/tiered_index.cpp
+  src/neighbors/all_neighbors.cpp
+  src/preprocessing/quantize/binary.cpp
+  src/preprocessing/quantize/scalar.cpp
+  src/distance/pairwise_distance.cpp
+)
+add_library(cuvs::c_api ALIAS cuvs_c)
+set_target_properties(
+  cuvs_c
+  PROPERTIES BUILD_RPATH "\$ORIGIN"
+             INSTALL_RPATH "\$ORIGIN"
+             CXX_STANDARD 17
+             CXX_STANDARD_REQUIRED ON
+             POSITION_INDEPENDENT_CODE ON
+             INTERFACE_POSITION_INDEPENDENT_CODE ON
+             EXPORT_NAME c_api
+)
+
+target_compile_definitions(cuvs_c PUBLIC $<$<BOOL:${BUILD_CAGRA_HNSWLIB}>:CUVS_BUILD_CAGRA_HNSWLIB>)
+
+target_compile_options(cuvs_c PRIVATE "$<$<COMPILE_LANGUAGE:CXX>:${CUVS_CXX_FLAGS}>")
+
+target_include_directories(
+  cuvs_c
+  PUBLIC "$<BUILD_INTERFACE:${DLPACK_INCLUDE_DIR}>"
+         "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>"
+  INTERFACE "$<INSTALL_INTERFACE:include>"
+)
+
+target_link_libraries(
+  cuvs_c
+  PUBLIC $<IF:$<BOOL:${CUVSC_STATIC_CUVS_LIBRARY}>,cuvs::cuvs_static,cuvs::cuvs>
+  PRIVATE raft::raft $<TARGET_NAME_IF_EXISTS:hnswlib::hnswlib>
+)
+
+# ##################################################################################################
+# * install targets-----------------------------------------------------------
+if(PROJECT_IS_TOP_LEVEL)
+  rapids_cmake_install_lib_dir(lib_dir)
+  include(GNUInstallDirs)
+  include(CPack)
+
+  # Add CUDAToolkit as an export dependency
+  rapids_export_package(INSTALL CUDAToolkit cuvs-c-exports)
+  rapids_export_package(BUILD CUDAToolkit cuvs-c-exports)
+
+  install(
+    TARGETS cuvs_c
+    DESTINATION ${lib_dir}
+    COMPONENT cuvs_c
+    EXPORT cuvs-c-exports
+  )
+
+  rapids_export(
+    INSTALL cuvs_c
+    VERSION "${RAPIDS_VERSION}"
+    EXPORT_SET cuvs-c-exports
+    GLOBAL_TARGETS cuvs_c
+    NAMESPACE cuvs::
+  )
+  rapids_export(
+    BUILD cuvs_c
+    VERSION "${RAPIDS_VERSION}"
+    EXPORT_SET cuvs-c-exports
+    GLOBAL_TARGETS cuvs_c
+    NAMESPACE cuvs::
+  )
+  install(
+    DIRECTORY include/cuvs
+    COMPONENT cuvs_c
+    DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
+  )
+endif()
+
+# ##################################################################################################
+# * build tests ----------------------------------------------------
+if(BUILD_TESTS)
+  enable_language(CUDA)
+  find_package(CUDAToolkit REQUIRED)
+
+  enable_testing()
+  add_subdirectory(tests)
+endif()

cpp/include/cuvs/cluster/kmeans.h renamed to c/include/cuvs/cluster/kmeans.h

@@ -34,17 +34,17 @@ typedef enum {
   /**
    * Sample the centroids using the kmeans++ strategy
    */
-  KMeansPlusPlus,
+  KMeansPlusPlus = 0,
 
   /**
    * Sample the centroids uniformly at random
    */
-  Random,
+  Random = 1,
 
   /**
    * User provides the array of initial centroids
    */
-  Array
+  Array = 2
 } cuvsKMeansInitMethod;
 
 /**

cpp/include/cuvs/core/c_api.h renamed to c/include/cuvs/core/c_api.h

@@ -33,7 +33,7 @@ extern "C" {
  * @brief An enum denoting error statuses for function calls
  *
  */
-typedef enum { CUVS_ERROR, CUVS_SUCCESS } cuvsError_t;
+typedef enum { CUVS_ERROR = 0, CUVS_SUCCESS = 1 } cuvsError_t;
 
 /** @brief Returns a string describing the last seen error on this thread, or
  *         NULL if the last function succeeded.

cpp/include/cuvs/distance/distance.h renamed to c/include/cuvs/distance/distance.h

@@ -39,13 +39,13 @@ extern "C" {
  */
 enum cuvsCagraGraphBuildAlgo {
   /* Select build algorithm automatically */
-  AUTO_SELECT,
+  AUTO_SELECT = 0,
   /* Use IVF-PQ to build all-neighbors knn graph */
-  IVF_PQ,
+  IVF_PQ = 1,
   /* Experimental, use NN-Descent to build all-neighbors knn graph */
-  NN_DESCENT,
+  NN_DESCENT = 2,
   /* Experimental, use iterative cagra search and optimize to build the knn graph */
-  ITERATIVE_CAGRA_SEARCH
+  ITERATIVE_CAGRA_SEARCH = 3
 };
 
 /** Parameters for VPQ compression. */
@@ -210,18 +210,18 @@ cuvsError_t cuvsCagraExtendParamsDestroy(cuvsCagraExtendParams_t params);
  */
 enum cuvsCagraSearchAlgo {
   /** For large batch sizes. */
-  SINGLE_CTA,
+  SINGLE_CTA = 0,
   /** For small batch sizes. */
-  MULTI_CTA,
-  MULTI_KERNEL,
-  AUTO
+  MULTI_CTA    = 1,
+  MULTI_KERNEL = 2,
+  AUTO         = 3
 };
 
 /**
  * @brief Enum to denote Hash Mode used while searching CAGRA index
  *
  */
-enum cuvsCagraHashMode { HASH, SMALL, AUTO_HASH };
+enum cuvsCagraHashMode { HASH = 0, SMALL = 1, AUTO_HASH = 2 };
 
 /**
  * @brief Supplemental parameters to search CAGRA index

cpp/include/cuvs/distance/pairwise_distance.h renamed to c/include/cuvs/distance/pairwise_distance.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2024, NVIDIA CORPORATION.
+ * Copyright (c) 2024-2025, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -34,11 +34,11 @@ extern "C" {
  */
 enum cuvsFilterType {
   /* No filter */
-  NO_FILTER,
+  NO_FILTER = 0,
   /* Filter an index with a bitset */
-  BITSET,
+  BITSET = 1,
   /* Filter an index with a bitmap */
-  BITMAP
+  BITMAP = 2
 };
 
 /**

cpp/include/cuvs/neighbors/all_neighbors.h renamed to c/include/cuvs/neighbors/all_neighbors.h

@@ -40,11 +40,11 @@ extern "C" {
  */
 enum cuvsHnswHierarchy {
   /* Flat hierarchy, search is base-layer only */
-  NONE,
+  NONE = 0,
   /* Full hierarchy is built using the CPU */
-  CPU,
+  CPU = 1,
   /* Full hierarchy is built using the GPU */
-  GPU
+  GPU = 2
 };
 
 struct cuvsHnswIndexParams {