Use own flag for the warning

Previously implementation did not work: ornladios/ADIOS2#4466

Author: franzpoeschel

include/openPMD/IO/ADIOS/ADIOS2Auxiliary.hpp

@@ -97,6 +97,8 @@ namespace adios_defaults
     constexpr const_str str_usesteps = "usesteps";
     constexpr const_str str_flushtarget = "preferred_flush_target";
     constexpr const_str str_usesstepsAttribute = "__openPMD_internal/useSteps";
+    constexpr const_str str_useModifiableAttributes =
+        "__openPMD_internal/useModifiableAttributes";
     constexpr const_str str_adios2Schema =
         "__openPMD_internal/openPMD2_adios2_schema";
     constexpr const_str str_isBoolean = "__is_boolean__";

src/IO/ADIOS/ADIOS2File.cpp

@@ -21,6 +21,7 @@
 
 #include "openPMD/IO/ADIOS/ADIOS2File.hpp"
 #include "openPMD/Error.hpp"
+#include "openPMD/IO/ADIOS/ADIOS2Auxiliary.hpp"
 #include "openPMD/IO/ADIOS/ADIOS2IOHandler.hpp"
 #include "openPMD/IO/AbstractIOHandler.hpp"
 #include "openPMD/IterationEncoding.hpp"
@@ -500,6 +501,12 @@ void ADIOS2File::configure_IO()
                 ? ADIOS2IOHandlerImpl::ModifiableAttributes::Yes
                 : ADIOS2IOHandlerImpl::ModifiableAttributes::No;
         }
+        m_IO.DefineAttribute<bool_representation>(
+            adios_defaults::str_useModifiableAttributes,
+            m_impl->m_modifiableAttributes ==
+                    ADIOS2IOHandlerImpl::ModifiableAttributes::No
+                ? 0
+                : 1);
 #else
         if (!m_impl->m_useGroupTable.has_value())
         {

src/IO/ADIOS/ADIOS2IOHandler.cpp

@@ -1541,37 +1541,30 @@ namespace
         }
         static constexpr char const *errorMsg = "DistributeToAllRanks";
     };
+#endif
 
-    void warn_ignored_modifiable_attributes(
-        adios2::IO &IO, std::string const &exempt_this_from_warnings)
+    void warn_ignored_modifiable_attributes(adios2::IO &IO)
     {
-        auto all_attributes = IO.AvailableAttributes();
-        std::deque<std::string> modifiable_attributes;
-        for (auto const &[identifier, params] : all_attributes)
-        {
-            if (params.at("Modifiable") == "1")
-            {
-                modifiable_attributes.emplace_back(identifier);
-            }
-        }
-        if (modifiable_attributes.size() > 1 ||
-            (modifiable_attributes.size() == 1 &&
-             *modifiable_attributes.begin() != exempt_this_from_warnings))
-        {
-            std::cerr << &R"(
-Warning: Random-access for variable-encoding in ADIOS2 is currently
+        auto modifiable_flag = IO.InquireAttribute<detail::bool_representation>(
+            adios_defaults::str_useModifiableAttributes);
+        auto print_warning = [](std::string const &note) {
+            std::cerr << "Warning: " << note << R"(
+Random-access for variable-encoding in ADIOS2 is currently
 experimental. Support for modifiable attributes is currently not implemented
 yet, meaning that attributes such as /data/time will show useless values.
 Use Access::READ_LINEAR to retrieve those values if needed.
 The following modifiable attributes have been found:
-)"[1];
-            for (auto const &identifier : modifiable_attributes)
-            {
-                std::cerr << '\t' << identifier << '\n';
-            }
+)";
+        };
+        if (!modifiable_flag)
+        {
+            print_warning("File might be using modifiable attributes.");
+        }
+        else if (modifiable_flag.Data().at(0) != 0)
+        {
+            print_warning("File uses modifiable attributes.");
         }
     }
-#endif
 } // namespace
 
 void ADIOS2IOHandlerImpl::readAttributeAllsteps(
@@ -1589,7 +1582,7 @@ void ADIOS2IOHandlerImpl::readAttributeAllsteps(
         IO.SetParameter("StreamReader", "ON"); // this be for BP4
         auto engine = IO.Open(fullPath(*file), adios2::Mode::Read);
         auto status = engine.BeginStep();
-        warn_ignored_modifiable_attributes(IO, name);
+        warn_ignored_modifiable_attributes(IO);
         auto type = detail::attributeInfo(IO, name, /* verbose = */ true);
         switchType<ReadAttributeAllsteps>(
             type, IO, engine, name, status, *param.resource);