Only install thrust when using a non 'system' version (#9206)

Previously cudf presumed that no system version of Thrust matched the version cudf required, but with the merger
of rapidsai/rmm#854 this isn't true.

Authors:
  - Robert Maynard (https://github.com/robertmaynard)

Approvers:
  - Jake Hemstad (https://github.com/jrhemstad)
  - Mark Harris (https://github.com/harrism)

URL: #9206

cpp/cmake/thirdparty/get_thrust.cmake

@@ -24,6 +24,13 @@ function(find_and_configure_thrust VERSION)
         set(cpm_thrust_disconnect_update "")
     endif()
 
+    # We currently require cuDF to always build with a custom
+    # version of thrust. This is needed so that build times of
+    # of cudf are kept reasonable, without this CI builds
+    # of cudf will be killed as some source file can take
+    # over 45 minutes to build
+    #
+    set(CPM_DOWNLOAD_ALL TRUE)
     rapids_cpm_find(
         Thrust ${VERSION}
         BUILD_EXPORT_SET cudf-exports
@@ -40,26 +47,28 @@ function(find_and_configure_thrust VERSION)
         thrust_create_target(cudf::Thrust FROM_OPTIONS)
     endif()
 
-    include(GNUInstallDirs)
-    install(DIRECTORY "${Thrust_SOURCE_DIR}/thrust"
-        DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/libcudf/Thrust/"
-        FILES_MATCHING
-            PATTERN "*.h"
-            PATTERN "*.inl")
-    install(DIRECTORY "${Thrust_SOURCE_DIR}/dependencies/cub/cub"
-        DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/libcudf/Thrust/dependencies/"
-        FILES_MATCHING
-            PATTERN "*.cuh")
+    if(Thrust_SOURCE_DIR) # only install thrust when we have an in-source version
+        include(GNUInstallDirs)
+        install(DIRECTORY "${Thrust_SOURCE_DIR}/thrust"
+            DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/libcudf/Thrust/"
+            FILES_MATCHING
+                PATTERN "*.h"
+                PATTERN "*.inl")
+        install(DIRECTORY "${Thrust_SOURCE_DIR}/dependencies/cub/cub"
+            DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/libcudf/Thrust/dependencies/"
+            FILES_MATCHING
+                PATTERN "*.cuh")
 
-    install(DIRECTORY "${Thrust_SOURCE_DIR}/thrust/cmake"
-        DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/libcudf/Thrust/thrust/")
-    install(DIRECTORY "${Thrust_SOURCE_DIR}/dependencies/cub/cub/cmake"
-        DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/libcudf/Thrust/dependencies/cub/")
+        install(DIRECTORY "${Thrust_SOURCE_DIR}/thrust/cmake"
+            DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/libcudf/Thrust/thrust/")
+        install(DIRECTORY "${Thrust_SOURCE_DIR}/dependencies/cub/cub/cmake"
+            DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/libcudf/Thrust/dependencies/cub/")
 
 
-    # Store where CMake can find our custom Thrust install
-    include("${rapids-cmake-dir}/export/find_package_root.cmake")
-    rapids_export_find_package_root(INSTALL Thrust [=[${CMAKE_CURRENT_LIST_DIR}/../../../include/libcudf/Thrust/]=] cudf-exports)
+        # Store where CMake can find our custom Thrust install
+        include("${rapids-cmake-dir}/export/find_package_root.cmake")
+        rapids_export_find_package_root(INSTALL Thrust [=[${CMAKE_CURRENT_LIST_DIR}/../../../include/libcudf/Thrust/]=] cudf-exports)
+    endif()
 endfunction()
 
 set(CUDF_MIN_VERSION_Thrust 1.12.0)