Make automatic recognition of access mode more intelligent

Previous commits uncovered an old bug

Author: franzpoeschel

include/openPMD/IO/ADIOS/ADIOS2IOHandler.hpp

@@ -194,8 +194,7 @@ class ADIOS2IOHandlerImpl
      * @brief The ADIOS2 access type to chose for Engines opened
      * within this instance.
      */
-    adios2::Mode adios2AccessMode( );
-
+    adios2::Mode adios2AccessMode( std::string const & fullPath );
 
 private:
     adios2::ADIOS m_ADIOS;

src/IO/ADIOS/ADIOS2IOHandler.cpp

@@ -903,19 +903,31 @@ ADIOS2IOHandlerImpl::availableChunks(
     switchType( datatype, rbi, parameters, ba.m_IO, engine, varName );
 }
 
-adios2::Mode ADIOS2IOHandlerImpl::adios2AccessMode( )
+adios2::Mode
+ADIOS2IOHandlerImpl::adios2AccessMode( std::string const & fullPath )
 {
-    switch ( m_handler->m_backendAccess )
+    switch( m_handler->m_backendAccess )
     {
     case Access::CREATE:
         return adios2::Mode::Write;
     case Access::READ_ONLY:
         return adios2::Mode::Read;
     case Access::READ_WRITE:
-        std::cerr << "ADIOS2 does currently not yet implement ReadWrite "
-                     "(Append) mode. "
-                  << "Replacing with Read mode." << std::endl;
-        return adios2::Mode::Read;
+        if( auxiliary::directory_exists( fullPath ) ||
+            auxiliary::file_exists( fullPath ) )
+        {
+            std::cerr << "ADIOS2 does currently not yet implement ReadWrite "
+                         "(Append) mode. "
+                      << "Replacing with Read mode." << std::endl;
+            return adios2::Mode::Read;
+        }
+        else
+        {
+            std::cerr << "ADIOS2 does currently not yet implement ReadWrite "
+                         "(Append) mode. "
+                      << "Replacing with Write mode." << std::endl;
+            return adios2::Mode::Write;
+        }
     default:
         return adios2::Mode::Undefined;
     }
@@ -2047,13 +2059,12 @@ namespace detail
     }
 
     BufferedActions::BufferedActions(
-        ADIOS2IOHandlerImpl & impl,
-        InvalidatableFile file )
+        ADIOS2IOHandlerImpl & impl, InvalidatableFile file )
         : m_file( impl.fullPath( std::move( file ) ) )
         , m_IOName( std::to_string( impl.nameCounter++ ) )
         , m_ADIOS( impl.m_ADIOS )
         , m_IO( impl.m_ADIOS.DeclareIO( m_IOName ) )
-        , m_mode( impl.adios2AccessMode() )
+        , m_mode( impl.adios2AccessMode( m_file ) )
         , m_writeDataset( &impl )
         , m_readDataset( &impl )
         , m_attributeReader()