ShufflePlug : Fix fail to create dests with fallback identity shuffle

Changes.md

@@ -17,6 +17,7 @@ Fixes
 - UVInspector : Fixed `Unable to find ScriptNode for UVView` warnings.
 - Scene Editors : Fixed update when ScenePlugs are added to or removed from the node being viewed.
 - PrimitiveInspector : Fixed failure to update when the location being viewed ceases to exist, or is recreated.
+- Shuffle : Fixed very specific bug where ensuring a channel exists by shuffling "channelName" to "channelName" with `missingSourceMode` set to black would fail to create the channel if it didn't already exist.
 
 API
 ---

include/Gaffer/ShufflePlug.inl

@@ -117,6 +117,8 @@ T ShufflesPlug::shuffleInternal( const T &sourceContainer, const T *extraSources
 			const std::string &srcName = srcPattern;
 			const typename T::mapped_type *srcValue = nullptr;
 			typename T::const_iterator sIt = sourceContainer.find( srcName );
+			bool usingExtraSource = false;
+
 			if( sIt != sourceContainer.end() )
 			{
 				srcValue = &sIt->second;
@@ -131,6 +133,7 @@ T ShufflesPlug::shuffleInternal( const T &sourceContainer, const T *extraSources
 				if( sIt != extraSources->end() )
 				{
 					srcValue = &sIt->second;
+					usingExtraSource = true;
 				}
 			}
 
@@ -142,7 +145,7 @@ T ShufflesPlug::shuffleInternal( const T &sourceContainer, const T *extraSources
 				if( ! dstPattern.empty() )
 				{
 					const std::string dstName = scope.context()->substitute( dstPattern );
-					if( srcName != dstName )
+					if( srcName != dstName || usingExtraSource )
 					{
 						if( dstReplace || ( destinationContainer.find( dstName ) == destinationContainer.end() ) )
 						{

python/GafferTest/ShufflePlugTest.py

@@ -526,5 +526,10 @@ def testExtraSources( self ) :
 		self.assertEqual( plug.shuffleWithExtraSources( source, extraSources ), IECore.CompoundData( { "bar" : 20 } ) )
 		self.assertEqual( plug.shuffleWithExtraSources( source, extraSources, ignoreMissingSource = False ), IECore.CompoundData( { "bar" : 20 } ) )
 
+		# When using an extra source of `*`, we should be able to create a new value with a fallback by shuffling
+		# from "toto" to "toto"
+		plug[0]["destination"].setValue( "toto" )
+		self.assertEqual( plug.shuffleWithExtraSources( source, extraSources ), IECore.CompoundData( { "toto" : 20 } ) )
+
 if __name__ == "__main__":
 	unittest.main()