Fix bug in ADIOS2 that leaks dataset configs into other datasets

Author: franzpoeschel

src/IO/ADIOS/ADIOS2IOHandler.cpp

@@ -774,7 +774,7 @@ void ADIOS2IOHandlerImpl::createDataset(
         filePos->gd = GroupOrDataset::DATASET;
         auto const varName = nameOfVariable(writable);
 
-        json::TracingJSON config = [&]() {
+        json::TracingJSON config = [&]() -> json::ParsedConfig {
             if (!m_buffered_dataset_config.has_value())
             {
                 // we are only interested in these values from the global config
@@ -790,17 +790,20 @@ void ADIOS2IOHandlerImpl::createDataset(
                     *m_buffered_dataset_config,
                     nlohmann::json::parse(mask_for_global_conf));
             }
+            auto const &buffered_config = *m_buffered_dataset_config;
             auto parsed_config = json::parseOptions(
                 parameters.options, /* considerFiles = */ false);
             if (auto adios2_config_it = parsed_config.config.find("adios2");
                 adios2_config_it != parsed_config.config.end())
             {
-                adios2_config_it.value() = json::merge(
-                    *m_buffered_dataset_config, adios2_config_it.value());
+                auto copy = buffered_config;
+                json::merge(copy, adios2_config_it.value());
+                copy = nlohmann::json{{"adios2", std::move(copy)}};
+                parsed_config.config = std::move(copy);
             }
             else
             {
-                parsed_config.config["adios2"] = *m_buffered_dataset_config;
+                parsed_config.config["adios2"] = buffered_config;
             }
             return parsed_config;
         }();
@@ -896,7 +899,11 @@ void ADIOS2IOHandlerImpl::createDataset(
                     throw error::OperationUnsupportedInBackend(
                         "ADIOS2",
                         "Shape for local value array must be a 1D array "
-                        "equivalent to the MPI size.");
+                        "equivalent to the MPI size ('" +
+                            varName + "' has shape " +
+                            auxiliary::format_vec(parameters.extent) +
+                            ", but should have shape [" +
+                            std::to_string(required_size) + "]).");
                 }
                 return adios2::Dims{adios2::LocalValueDim};
             }