USD AttributeAlgo : Don't treat arnold:* light primvars as attributes

Since 0590bbf, they have been converted to light parameters instead.

Changes

@@ -11,7 +11,9 @@ Fixes
 
 - ShaderNetworkAlgo : Fixed crash caused by cyclic connections in `removeUnusedShaders()`.
 - ShaderStateComponent : Fixed GL rendering failures caused by unsupported values for texture parameters.
-- USDScene : Fixed exceptions caused by attempt to write shader parameters with unsupported value types.
+- USDScene :
+  - Fixed exceptions caused by attempt to write shader parameters with unsupported value types.
+  - Fixed duplicate loading of `arnold:*` primvars on lights as attributes. These are now only loaded as parameters on the light shader.
 - IECoreUSD::DataAlgo : Fixed exceptions thrown by `toUSD()` and `valueTypeName()` when passed datatypes not supported by `dispatch()`. An empty VtValue or SdfValueTypeName is now returned instead.
 
 Build

contrib/IECoreUSD/src/IECoreUSD/AttributeAlgo.cpp

@@ -40,6 +40,8 @@
 IECORE_PUSH_DEFAULT_VISIBILITY
 #include "pxr/usd/usdGeom/primvar.h"
 #include "pxr/usd/usdGeom/primvarsAPI.h"
+
+#include "pxr/usd/usdLux/lightAPI.h"
 IECORE_POP_DEFAULT_VISIBILITY
 
 using namespace IECoreUSD;
@@ -92,6 +94,17 @@ bool IECoreUSD::AttributeAlgo::isCortexAttribute( const pxr::UsdGeomPrimvar &pri
 		}
 	}
 
+	// Check for `arnold:*` primvars on lights. These will be loaded as
+	// parameters in `ShaderAlgo::readLight()`.
+
+	if(
+		boost::starts_with( primVar.GetPrimvarName().GetString(), "arnold:" ) &&
+		pxr::UsdLuxLightAPI( primVar.GetAttr().GetPrim() )
+	)
+	{
+		return false;
+	}
+
 	// Everything else should be loaded as a Cortex attribute.
 
 	return true;

contrib/IECoreUSD/test/IECoreUSD/USDSceneTest.py

@@ -4165,6 +4165,7 @@ def testArnoldSpecificLightInputs( self ) :
 
 		root = IECoreScene.SceneInterface.create( fileName, IECore.IndexedIO.OpenMode.Read )
 		self.assertEqual( root.child( "light" ).readAttribute( "light", 0 ), lightShader )
+		self.assertEqual( root.child( "light" ).attributeNames(), [ "light" ] )
 
 	def testTreatLightAsPointOrLine( self ) :