Do not fail if spdlog already is instantiated but the build folder is…

… missing.

Signed-off-by: fruffy <fruffy@nyu.edu>

backends/tofino/cmake/spdlog.cmake

@@ -1,21 +1,33 @@
 message(STATUS "Fetching spdlog")
 
-include(FetchContent)
-
 # Preserve previous FETCHCONTENT_QUIET setting
 set(FETCHCONTENT_QUIET_PREV ${FETCHCONTENT_QUIET})
 set(FETCHCONTENT_QUIET OFF)
 
+set(SPDLOG_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/third_party/spdlog)
+
+# Check if the source directory exists.
+if(EXISTS ${SPDLOG_SOURCE_DIR}/CMakeLists.txt)
+    # If it exists but wasn't built before, manually add it.
+    set(FETCHCONTENT_SOURCE_DIR_SPDLOG ${SPDLOG_SOURCE_DIR})
+    # Avoid fetching again.
+    set(FETCHCONTENT_UPDATES_DISCONNECTED_SPDLOG ON)
+endif()
+
 FetchContent_Declare(
   spdlog
   GIT_REPOSITORY https://github.com/gabime/spdlog.git
   GIT_TAG v1.8.3
-  SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/third_party/spdlog
+  SOURCE_DIR ${SPDLOG_SOURCE_DIR}
   USES_TERMINAL_DOWNLOAD TRUE
   GIT_PROGRESS TRUE
 )
 
-FetchContent_MakeAvailable(spdlog)
+FetchContent_GetProperties(spdlog)
+if(NOT spdlog_POPULATED)
+  FetchContent_Populate(spdlog)
+  add_subdirectory(${SPDLOG_SOURCE_DIR} ${CMAKE_BINARY_DIR}/spdlog)
+endif()
 
 # Restore FETCHCONTENT_QUIET setting
 set(FETCHCONTENT_QUIET ${FETCHCONTENT_QUIET_PREV})