Generalize method for finding filename

Framework/DataHandling/inc/MantidDataHandling/Load.h

@@ -43,6 +43,9 @@ public:
   void setPropertyValue(const std::string &name,
                         const std::string &value) override;
 
+  /// Free function to find first file property
+  static std::string findFilenamePropertyName(const IAlgorithm *loader);
+
 protected:
   Parallel::ExecutionMode getParallelExecutionMode(
       const std::map<std::string, Parallel::StorageMode> &storageModes)

Framework/DataHandling/src/Load.cpp

@@ -214,26 +214,43 @@ API::IAlgorithm_sptr Load::getFileLoader(const std::string &filePath) {
   return winningLoader;
 }
 
-void Load::findFilenameProperty(const API::IAlgorithm_sptr &loader) {
+std::string Load::findFilenamePropertyName(const IAlgorithm *loader) {
+  std::string propertyName; // default is empty string
+
   // Use the first file property as the main Filename
   const auto &props = loader->getProperties();
   for (auto prop : props) {
-    auto *fp = dynamic_cast<API::MultipleFileProperty *>(prop);
-    auto *fp2 = dynamic_cast<API::FileProperty *>(prop);
-    if (fp) {
-      m_filenamePropName = fp->name();
+    auto *multiprop = dynamic_cast<API::MultipleFileProperty *>(prop);
+    auto *singleprop = dynamic_cast<API::FileProperty *>(prop);
+    if (multiprop) {
+      propertyName = multiprop->name();
       break;
     }
-    if (fp2) {
-      m_filenamePropName = fp2->name();
+    if (singleprop) {
+      propertyName = singleprop->name();
       break;
     }
   }
-  if (m_filenamePropName.empty()) {
+
+  // throw an exception if somehting nothing was found
+  if (propertyName.empty()) {
+    std::stringstream msg;
+    msg << "Cannot find FileProperty on \"" << loader->name() << "\" v"
+        << loader->version() << " algorithm.";
+    throw std::runtime_error(msg.str());
+  }
+
+  return propertyName;
+}
+
+void Load::findFilenameProperty(const API::IAlgorithm_sptr &loader) {
+  try {
+    m_filenamePropName = findFilenamePropertyName(loader.get());
+  } catch (std::runtime_error &) {
+    // unset member variables
     setPropertyValue("LoaderName", "");
     setProperty("LoaderVersion", -1);
-    throw std::runtime_error("Cannot find FileProperty on " + loader->name() +
-                             " algorithm.");
+    throw;
   }
 }
 

Framework/DataHandling/src/NexusFileLoader.cpp

@@ -5,13 +5,14 @@
 //     & Institut Laue - Langevin
 // SPDX - License - Identifier: GPL - 3.0 +
 #include "MantidDataHandling/NexusFileLoader.h"
+#include "MantidDataHandling/Load.h"
 
 namespace Mantid::DataHandling {
 void NexusFileLoader::exec() {
   // make sure the descriptor is initialized
   if (!m_fileInfo) {
-    const std::string filename =
-        this->getPropertyValue("Filename"); // TODO be more generic
+    const std::string filePropName = Load::findFilenamePropertyName(this);
+    const std::string filename = this->getPropertyValue(filePropName);
     m_fileInfo =
         std::make_shared<Mantid::Kernel::NexusHDF5Descriptor>(filename);
   }