Fix CMake builds when Subfiling VFD isn't enabled (#3250)

* Fix CMake builds when Subfiling VFD isn't enabled

* Add Subfiling VFD entry to hdf5-config.cmake.in

2 files changed, 40 insertions, 33 deletions

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index f12b079..a0a67df 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -280,10 +280,10 @@ set (H5FD_HDRS
     ${HDF5_SRC_DIR}/H5FDwindows.h
 )
 
-# Append Subfiling VFD and Mercury sources to H5FD interface if Subfiling VFD is built
-if (HDF5_ENABLE_SUBFILING_VFD)
-  add_subdirectory (${H5FD_SUBFILING_DIR})
-endif()
+# Append Subfiling VFD and Mercury sources to H5FD
+# interface if Subfiling VFD is built. Append Subfiling
+# VFD public headers to H5FD_HDRS regardless.
+add_subdirectory (${H5FD_SUBFILING_DIR})
 
 IDE_GENERATED_PROPERTIES ("H5FD" "${H5FD_HDRS}" "${H5FD_SOURCES}" )
 
diff --git a/src/H5FDsubfiling/CMakeLists.txt b/src/H5FDsubfiling/CMakeLists.txt
index 89cd0c2..dd7f564 100644
--- a/src/H5FDsubfiling/CMakeLists.txt
+++ b/src/H5FDsubfiling/CMakeLists.txt
@@ -2,49 +2,56 @@ cmake_minimum_required (VERSION 3.18)
 project (HDF5_H5FD_SUBFILING C)
 
 # Sanity checking
-if (NOT H5FD_SOURCES)
-  message (FATAL_ERROR "internal configure error - H5FD_SOURCES not set")
-endif ()
 if (NOT H5FD_HDRS)
   message (FATAL_ERROR "internal configure error - H5FD_HDRS not set")
 endif ()
 if (NOT H5FD_SUBFILING_DIR)
   message (FATAL_ERROR "internal configure error - H5FD_SUBFILING_DIR not set")
 endif ()
-if (NOT H5FD_SUBFILING_MERCURY_DIR)
-  message (FATAL_ERROR "internal configure error - H5FD_SUBFILING_MERCURY_DIR not set")
-endif ()
 
-# Add mercury util sources to Subfiling VFD sources
-set (MERCURY_UTIL_SOURCES
-  ${H5FD_SUBFILING_MERCURY_DIR}/mercury_thread.c
-  ${H5FD_SUBFILING_MERCURY_DIR}/mercury_thread_condition.c
-  ${H5FD_SUBFILING_MERCURY_DIR}/mercury_thread_pool.c
-  ${H5FD_SUBFILING_MERCURY_DIR}/mercury_thread_mutex.c
-)
+if (HDF5_ENABLE_SUBFILING_VFD)
+  # Sanity checking
+  if (NOT H5FD_SOURCES)
+    message (FATAL_ERROR "internal configure error - H5FD_SOURCES not set")
+  endif ()
+  if (NOT H5FD_SUBFILING_MERCURY_DIR)
+    message (FATAL_ERROR "internal configure error - H5FD_SUBFILING_MERCURY_DIR not set")
+  endif ()
 
-set (HDF5_H5FD_SUBFILING_SOURCES
-  ${H5FD_SUBFILING_DIR}/H5FDioc.c
-  ${H5FD_SUBFILING_DIR}/H5FDioc_int.c
-  ${H5FD_SUBFILING_DIR}/H5FDioc_threads.c
-  ${H5FD_SUBFILING_DIR}/H5FDsubfiling.c
-  ${H5FD_SUBFILING_DIR}/H5FDsubfile_int.c
-  ${H5FD_SUBFILING_DIR}/H5subfiling_common.c
-  ${MERCURY_UTIL_SOURCES}
-)
+  # Add mercury util sources to Subfiling VFD sources
+  set (MERCURY_UTIL_SOURCES
+    ${H5FD_SUBFILING_MERCURY_DIR}/mercury_thread.c
+    ${H5FD_SUBFILING_MERCURY_DIR}/mercury_thread_condition.c
+    ${H5FD_SUBFILING_MERCURY_DIR}/mercury_thread_pool.c
+    ${H5FD_SUBFILING_MERCURY_DIR}/mercury_thread_mutex.c
+  )
+
+  set (HDF5_H5FD_SUBFILING_SOURCES
+    ${H5FD_SUBFILING_DIR}/H5FDioc.c
+    ${H5FD_SUBFILING_DIR}/H5FDioc_int.c
+    ${H5FD_SUBFILING_DIR}/H5FDioc_threads.c
+    ${H5FD_SUBFILING_DIR}/H5FDsubfiling.c
+    ${H5FD_SUBFILING_DIR}/H5FDsubfile_int.c
+    ${H5FD_SUBFILING_DIR}/H5subfiling_common.c
+    ${MERCURY_UTIL_SOURCES}
+  )
 
+  # Add Subfiling VFD sources to HDF5 library's H5FD sources
+  set (H5FD_SOURCES
+    ${H5FD_SOURCES}
+    ${HDF5_H5FD_SUBFILING_SOURCES}
+    PARENT_SCOPE
+  )
+endif ()
+
+# Add Subfiling VFD public headers to HDF5 library's
+# public H5FD headers, even if the Subfiling VFD isn't
+# enabled and built
 set (HDF5_H5FD_SUBFILING_HEADERS
   ${H5FD_SUBFILING_DIR}/H5FDsubfiling.h
   ${H5FD_SUBFILING_DIR}/H5FDioc.h
 )
 
-# Add Subfiling VFD sources to HDF5 library's H5FD sources
-set (H5FD_SOURCES
-  ${H5FD_SOURCES}
-  ${HDF5_H5FD_SUBFILING_SOURCES}
-  PARENT_SCOPE
-)
-
 # Add Subfiling VFD public headers to HDF5 library's public H5FD headers
 set (H5FD_HDRS
   ${H5FD_HDRS}