USD ShaderAlgo : Emit warning for unsupported parameter types

In conjunction with the previous commit, this means that we now gracefully print a warning message for any parameter types we can't write to USD. Prior to this we were throwing a not very helpful exception and not writing anything at all. This came up in production with a GLSL shader with an ImagePlug input in Gaffer, where we pack an entire image into a CompoundData value.

Author: johnhaddon

Changes

@@ -11,6 +11,7 @@ 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.
 - 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/ShaderAlgo.cpp

@@ -322,10 +322,16 @@ void writeShaderParameterValues( const IECoreScene::Shader *shader, pxr::UsdShad
 		pxr::UsdShadeInput input = usdShader.GetInput( usdParameterName );
 		if( !input )
 		{
-			input = usdShader.CreateInput(
-				toUSDParameterName( p.first ),
-				IECoreUSD::DataAlgo::valueTypeName( p.second.get() )
-			);
+			pxr::SdfValueTypeName typeName = IECoreUSD::DataAlgo::valueTypeName( p.second.get() );
+			if( !typeName )
+			{
+				IECore::msg( IECore::Msg::Warning, "ShaderAlgo",
+					boost::format( "Shader parameter `%1%.%2%` has unsupported type `%3%`" )
+						% shader->getName() % p.first % p.second->typeName()
+				);
+				continue;
+			}
+			input = usdShader.CreateInput( toUSDParameterName( p.first ), typeName );
 		}
 		if( auto *s = IECore::runTimeCast<IECore::StringData>( p.second.get() ) )
 		{

contrib/IECoreUSD/test/IECoreUSD/USDSceneTest.py

@@ -3181,6 +3181,42 @@ def testShadersAcrossDifferentScopes( self ):
 			) ]
 		)
 
+	def testUnsupportedShaderParameterTypes( self ) :
+
+		sourceNetwork = IECoreScene.ShaderNetwork(
+			shaders = {
+				"test" : IECoreScene.Shader(
+					"test",
+					parameters = {
+						"unsupported1" : IECore.CompoundData(),
+						"unsupported2" : IECore.PathMatcherData(),
+						"supported" : "abc"
+					}
+				)
+			},
+			output = "test"
+		)
+
+		fileName = os.path.join( self.temporaryDirectory(), "test.usda" )
+		root = IECoreScene.SceneInterface.create( fileName, IECore.IndexedIO.OpenMode.Write )
+
+		with IECore.CapturingMessageHandler() as mh :
+			root.createChild( "test" ).writeAttribute( "surface", sourceNetwork, 0 )
+
+		self.assertEqual(
+			{ m.message for m in mh.messages },
+			{
+				"Shader parameter `test.unsupported1` has unsupported type `CompoundData`",
+				"Shader parameter `test.unsupported2` has unsupported type `PathMatcherData`",
+			}
+		)
+
+		del root
+
+		root = IECoreScene.SceneInterface.create( fileName, IECore.IndexedIO.OpenMode.Read )
+		network = root.child( "test" ).readAttribute( "surface", 0 )
+		self.assertEqual( network.outputShader().parameters, IECore.CompoundData( { "supported" : "abc" } ) )
+
 	def testHoudiniVaryingLengthArrayPrimVar( self ) :
 
 		root = IECoreScene.SceneInterface.create(