refs #7541. Use candidate list.

Construct a list of candidate workspace properties, then filter those to find a preferred one.

Code/Mantid/MantidQt/API/src/AlgorithmPropertiesWidget.cpp

@@ -10,6 +10,8 @@
 #include "MantidAPI/FrameworkManager.h"
 #include "MantidAPI/Algorithm.h"
 #include "MantidAPI/AlgorithmProxy.h"
+#include <list>
+#include <algorithm>
 
 using namespace Mantid::Kernel;
 using Mantid::API::IWorkspaceProperty;
@@ -302,6 +304,12 @@ namespace API
     this->hideOrDisableProperties();
   }
 
+  bool isCalledInputWorkspace(PropertyWidget * const candidate)
+  {
+    Mantid::Kernel::Property const * const  property  = candidate->getProperty();
+    const std::string& propertyName = property->name();
+    return propertyName == "InputWorkspace";
+  }
 
   //-------------------------------------------------------------------------------------------------
   /** A slot to handle the replace workspace button click
@@ -312,6 +320,8 @@ namespace API
   {
     if (m_propWidgets.contains(propName))
     {
+      typedef std::list<PropertyWidget*> CollectionOfPropertyWidget;
+      CollectionOfPropertyWidget candidateReplacementSources;
       PropertyWidget * propWidget = m_propWidgets[propName];
       if (propWidget)
       {
@@ -328,19 +338,31 @@ namespace API
             if (prop->direction() == Direction::Input)
             {
               // Input workspace property. Get the text typed in.
-              const std::string propName = otherWidget->getProperty()->name();
-              const std::string WSNAME = otherWidget->getValue().toStdString();
               wsName = otherWidget->getValue();
               if (!wsName.isEmpty())
               {
-                propWidget->setValue(wsName);
-                break;
+                // Add the candidate to the list of candidates.
+                candidateReplacementSources.push_back(otherWidget);
               }
             }
           }
         }
 
-
+        // Choose from candidates, only do this if there are candidates to select from.
+        if(candidateReplacementSources.size() > 0)
+        {
+          CollectionOfPropertyWidget::iterator selectedIt = std::find_if(candidateReplacementSources.begin(), candidateReplacementSources.end(), isCalledInputWorkspace);
+          if(selectedIt != candidateReplacementSources.end())
+          {
+            // Use the InputWorkspace property called "InputWorkspace" as the source for the OutputWorkspace.
+            propWidget->setValue((*selectedIt)->getValue());
+          }
+          else
+          {
+            // Take the first candidate if there are none called "InputWorkspace" as the source for the OutputWorkspace.
+            propWidget->setValue(candidateReplacementSources.front()->getValue());
+          }
+        }
       }
     }