Changed how Thrust would be used in the build.

Instead of setting up a single traccc::Thrust target that would
take care of everything related to Thrust, the code rather
sets up traccc::Thrust in a way that allows very little access
in traccc::core to Thrust.

Instead, traccc::cuda and traccc::sycl (and also traccc_test_cuda)
privately link against Thrust in specific ways. So that the
appropriate "device headers" would get included everywhere.

CMakeLists.txt

@@ -176,12 +176,8 @@ if( TRACCC_SETUP_THRUST )
       add_subdirectory( extern/cccl )
    endif()
 endif()
-# Set up an IMPORTED library on top of the Thrust library/libraries. One that
-# the TRACCC/Detray code could depend on publicly.
-set( TRACCC_THRUST_OPTIONS "" CACHE STRING
-   "Extra options for configuring how Thrust should be used" )
-mark_as_advanced( TRACCC_THRUST_OPTIONS )
-thrust_create_target( traccc::Thrust ${TRACCC_THRUST_OPTIONS} )
+add_library( traccc::Thrust INTERFACE IMPORTED )
+target_link_libraries( traccc::Thrust INTERFACE Thrust::Thrust )
 
 # Set up rocThrust.
 option( TRACCC_SETUP_ROCTHRUST

cmake/traccc-config.cmake.in

@@ -56,8 +56,8 @@ endif()
 
 # Set up the traccc::Thrust target.
 if ( NOT TARGET traccc::Thrust )
-   set( TRACCC_THRUST_OPTIONS @TRACCC_THRUST_OPTIONS@ )
-   thrust_create_target( traccc::Thrust ${TRACCC_THRUST_OPTIONS} )
+   add_library( traccc::Thrust INTERFACE IMPORTED )
+   target_link_libraries( traccc::Thrust INTERFACE Thrust::Thrust )
 endif()
 
 # Include the file listing all the imported targets and options.

device/common/include/traccc/finding/device/find_tracks.hpp

@@ -1,6 +1,6 @@
 /** TRACCC library, part of the ACTS project (R&D line)
  *
- * (c) 2023 CERN for the benefit of the ACTS project
+ * (c) 2023-2024 CERN for the benefit of the ACTS project
  *
  * Mozilla Public License Version 2.0
  */
@@ -19,9 +19,6 @@
 #include "traccc/finding/finding_config.hpp"
 #include "traccc/fitting/kalman_filter/gain_matrix_updater.hpp"
 
-// Thrust include(s)
-#include <thrust/binary_search.h>
-
 namespace traccc::device {
 template <typename detector_t>
 struct find_tracks_payload {

device/common/include/traccc/finding/device/impl/find_tracks.ipp

@@ -1,6 +1,6 @@
 /** TRACCC library, part of the ACTS project (R&D line)
  *
- * (c) 2023 CERN for the benefit of the ACTS project
+ * (c) 2023-2024 CERN for the benefit of the ACTS project
  *
  * Mozilla Public License Version 2.0
  */
@@ -21,6 +21,7 @@
 
 // Thrust include(s)
 #include <thrust/binary_search.h>
+#include <thrust/execution_policy.h>
 
 namespace traccc::device {
 

device/cuda/CMakeLists.txt

@@ -106,7 +106,14 @@ target_compile_options( traccc_cuda
   PRIVATE $<$<COMPILE_LANGUAGE:CUDA>:--expt-relaxed-constexpr> )
 target_link_libraries( traccc_cuda
   PUBLIC traccc::core detray::core vecmem::core covfie::core
-  PRIVATE CUDA::cudart traccc::Thrust traccc::device_common vecmem::cuda )
+  PRIVATE CUDA::cudart traccc::device_common vecmem::cuda )
+
+# Set up Thrust specifically for the traccc::cuda library.
+thrust_create_target( traccc::cuda_thrust
+  HOST CPP
+  DEVICE CUDA )
+target_link_libraries( traccc_cuda
+  PRIVATE traccc::cuda_thrust )
 
 # For CUDA 11 turn on separable compilation. This is necessary for using
 # Thrust 2.1.0.

device/sycl/CMakeLists.txt

@@ -57,3 +57,10 @@ traccc_add_library( traccc_sycl sycl TYPE SHARED
 target_link_libraries( traccc_sycl
   PUBLIC traccc::core detray::core vecmem::core covfie::core
   PRIVATE traccc::device_common vecmem::sycl oneDPL )
+
+# Set up Thrust specifically for the traccc::sycl library.
+thrust_create_target( traccc::sycl_thrust
+  HOST CPP
+  DEVICE CPP )
+target_link_libraries( traccc_sycl
+  PRIVATE traccc::sycl_thrust )

tests/cuda/CMakeLists.txt

@@ -23,6 +23,11 @@ target_link_libraries(
     GTest::gtest
 )
 
+# Set up Thrust specifically for the CUDA unit tests.
+thrust_create_target( traccc_test_cuda_thrust
+  HOST CPP
+  DEVICE CUDA )
+
 traccc_add_test(
     cuda
 
@@ -48,7 +53,7 @@ traccc_add_test(
 
     LINK_LIBRARIES
     CUDA::cudart
-    traccc::Thrust
+    traccc_test_cuda_thrust
     GTest::gtest
     vecmem::cuda
     detray::core