First pass at enabling CPM download by default.

rapids-cmake/export/cpm.cmake

@@ -31,6 +31,7 @@ given export set
                       <ExportSet>
                       CPM_ARGS <standard cpm args>
                       [GLOBAL_TARGETS <targets...>]
+                      [DEFAULT_DOWNLOAD_OPTION <option_name>]
                       )
 
 
@@ -53,6 +54,9 @@ generated information will include a :cmake:command:`CPMFindPackage` call for <P
   Which targets from this package should be made global. This information
   will be propagated to any associated export set.
 
+``DEFAULT_DOWNLOAD_OPTION``
+  If set, expose an option <option_name> in the config to use CPMAddPackage instead of CPMFindPackage. The option will default to true.
+
   .. note::
     It is an anti-pattern to use this command with `INSTALL` as most CMake
     based projects should be installed, and :cmake:command:`rapids_export_package(INSTALL` used
@@ -67,7 +71,7 @@ function(rapids_export_cpm type name export_set)
   string(TOLOWER ${type} type)
 
   set(options "")
-  set(one_value)
+  set(one_value DEFAULT_DOWNLOAD_OPTION)
   set(multi_value GLOBAL_TARGETS CPM_ARGS)
   cmake_parse_arguments(_RAPIDS "${options}" "${one_value}" "${multi_value}" ${ARGN})
 

rapids-cmake/export/template/cpm.cmake.in

@@ -23,9 +23,22 @@ if(possible_package_dir AND NOT DEFINED @name@_DIR)
   set(@name@_DIR "${possible_package_dir}")
 endif()
 
-CPMFindPackage(
-  "@_RAPIDS_CPM_ARGS@"
-  )
+if(NOT "@_RAPIDS_DEFAULT_DOWNLOAD_OPTION@" STREQUAL "")
+  option(@_RAPIDS_DEFAULT_DOWNLOAD_OPTION@ "Whether or not to download @name@" ON)
+  if(@_RAPIDS_DEFAULT_DOWNLOAD_OPTION@)
+    CPMAddPackage(
+      "@_RAPIDS_CPM_ARGS@"
+      )
+  else()
+    CPMFindPackage(
+      "@_RAPIDS_CPM_ARGS@"
+      )
+  endif()
+else()
+  CPMFindPackage(
+    "@_RAPIDS_CPM_ARGS@"
+    )
+endif()
 
 if(possible_package_dir)
   unset(possible_package_dir)