Get CCCL revision outside of git repo (#1305)

* Get CCCL revision outside of git repo

* Handle shallow copies

benchmarks/cmake/CCCLBenchmarkRegistry.cmake

@@ -1,25 +1,32 @@
 find_package(CUDAToolkit REQUIRED)
 
-find_package(Git REQUIRED)
+set(cccl_revision "")
+find_package(Git)
 if(GIT_FOUND)
+  execute_process(
+      COMMAND ${GIT_EXECUTABLE} describe
+      WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
+      OUTPUT_VARIABLE cccl_revision
+      OUTPUT_STRIP_TRAILING_WHITESPACE)
+
+  if(cccl_revision STREQUAL "")
+    # Sometimes, there is no tag (shallow copy)
     execute_process(
-        COMMAND ${GIT_EXECUTABLE} describe
+        COMMAND ${GIT_EXECUTABLE} rev-parse --short HEAD
         WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
         OUTPUT_VARIABLE cccl_revision
         OUTPUT_STRIP_TRAILING_WHITESPACE)
+  endif()
+endif()
 
-    if(cccl_revision STREQUAL "")
-      # There's currently no tag
-      execute_process(
-          COMMAND ${GIT_EXECUTABLE} rev-parse --short HEAD
-          WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
-          OUTPUT_VARIABLE cccl_revision
-          OUTPUT_STRIP_TRAILING_WHITESPACE)
-    endif()
-    message(STATUS "Git revision: ${cccl_revision}")
-else()
-    message(WARNING "Git not found. Unable to determine Git revision.")
+# Sometimes this script is used outside of a Git repository. 
+# In this case, we read the revision from cccl/cccl_version instead.
+if ("${cccl_revision}" STREQUAL "")
+  file(READ "${CMAKE_SOURCE_DIR}/cccl_version" cccl_revision)
+  string(STRIP "${cccl_revision}" cccl_revision)
+  string(REPLACE "\n" "" cccl_revision "${cccl_revision}")
 endif()
+message(STATUS "Git revision: ${cccl_revision}")
 
 function(get_meta_path meta_path)
   set(meta_path "${CMAKE_BINARY_DIR}/cccl_meta_bench.csv" PARENT_SCOPE)