Feature/capps2/successreturnvalue (#1224)

Return success or failure from Group::save, load, loadExternalData.

During Group I/O calls (Group::save, load, loadExternalData), a utility class saves Conduit error handler routines, catches Conduit exceptions, logs them to the Group's DataStore.  The I/O call then returns whether any exceptions have been logged to the DataStore.  User code may directly query the DataStore for the presence of exception messages or the text of the messages themselves.  Code may clear the messages, so that subsequent successful I/O messages will return true.  Code may also append to the DataStore's exception messages.

---------

Co-authored-by: Rich Hornung <hornung1@llnl.gov>

src/axom/sidre/core/DataStore.cpp

@@ -86,6 +86,7 @@ DataStore::DataStore()
   , m_buffer_coll(new BufferCollection())
   , m_attribute_coll(new AttributeCollection())
   , m_need_to_finalize_slic(false)
+  , m_conduit_errors()
 {
   if(!axom::slic::isInitialized())
   {

src/axom/sidre/core/DataStore.hpp

@@ -88,6 +88,32 @@ class DataStore
    */
   const Group* getRoot() const { return m_RootGroup; };
 
+  //@{
+  /*!  @name Methods to query and clear Conduit I/O flags and exception messages.
+   *
+   * If an error occurs, the load(), save(), and loadExternalData() methods of
+   * any Group owned by this DataStore will return false (for I/O failure) and
+   * subsequent calls will continue to return false until the user clears the
+   * Conduit errors.
+   */
+
+  /// Return whether a Conduit error occurred.
+  bool getConduitErrorOccurred() const { return !m_conduit_errors.empty(); };
+
+  /// Return information on any Conduit errors.
+  std::string getConduitErrors() const { return m_conduit_errors; };
+
+  /// Clear any Conduit errors.
+  void clearConduitErrors() const { m_conduit_errors.clear(); };
+
+  /// Append a string to the accumulated Conduit errors.
+  void appendToConduitErrors(const std::string& mesg) const
+  {
+    m_conduit_errors = m_conduit_errors + "\n" + mesg;
+  };
+
+  //@}
+
 public:
   //@{
   //!  @name Methods to query, access, create, and destroy Buffers.
@@ -540,6 +566,9 @@ class DataStore
 
   /// Flag indicating whether SLIC logging environment was initialized in ctor.
   bool m_need_to_finalize_slic;
+
+  /// Details of the most recent Conduit error.  Length > 0 indicates an error occurred.
+  mutable std::string m_conduit_errors;
 };
 
 } /* end namespace sidre */