Guard against non-MPI installs

src/IO/HDF5/HDF5IOHandler.cpp

@@ -2938,16 +2938,21 @@ HDF5IOHandlerImpl::getFile(Writable *writable)
     return std::make_optional(std::move(res));
 }
 
+#define OPENPMD_HAVE_HDF5_INDEPENDENT_STORES openPMD_HAVE_MPI
+
 std::future<void> HDF5IOHandlerImpl::flush(internal::ParsedFlushParams &params)
 {
+#if OPENPMD_HAVE_HDF5_INDEPENDENT_STORES
     std::optional<H5FD_mpio_xfer_t> old_value;
+#endif
     if (params.backendConfig.json().contains("hdf5"))
     {
         auto hdf5_config = params.backendConfig["hdf5"];
 
         if (hdf5_config.json().contains("independent_stores"))
         {
             auto independent_stores_json = hdf5_config["independent_stores"];
+#if OPENPMD_HAVE_HDF5_INDEPENDENT_STORES
             if (!independent_stores_json.json().is_boolean())
             {
                 throw error::BackendConfigSchema(
@@ -2970,6 +2975,12 @@ std::future<void> HDF5IOHandlerImpl::flush(internal::ParsedFlushParams &params)
                 status >= 0,
                 "[HDF5] Internal error: Failed to set the local data "
                 "transfer mode before flushing.");
+#else
+            std::cerr << "[Warning] HDF5 backend option "
+                         "`hdf5.independent_stores` was specified, but "
+                         "HDF5 has no MPI support. Will ignore."
+                      << std::endl;
+#endif
         }
 
         if (auto shadow = hdf5_config.invertShadow(); shadow.size() > 0)
@@ -2993,6 +3004,7 @@ std::future<void> HDF5IOHandlerImpl::flush(internal::ParsedFlushParams &params)
     }
     auto res = AbstractIOHandlerImpl::flush();
 
+#if OPENPMD_HAVE_HDF5_INDEPENDENT_STORES
     if (old_value.has_value())
     {
         herr_t status = H5Pset_dxpl_mpio(m_datasetTransferProperty, *old_value);
@@ -3001,6 +3013,7 @@ std::future<void> HDF5IOHandlerImpl::flush(internal::ParsedFlushParams &params)
             "[HDF5] Internal error: Failed to reset the global data "
             "transfer mode after flushing.");
     }
+#endif
 
     return res;
 }

test/ParallelIOTest.cpp

@@ -1152,7 +1152,7 @@ TEST_CASE("hipace_like_write", "[parallel]")
 }
 #endif
 
-#if openPMD_HAVE_ADIOS2 && openPMD_HAS_ADIOS_2_9
+#if openPMD_HAVE_ADIOS2 && openPMD_HAS_ADIOS_2_9 && openPMD_HAVE_MPI
 TEST_CASE("independent_write_with_collective_flush", "[parallel]")
 {
     Series write(