added an example procedural and catched to cases of invalid input

resources/Materials/TestSuite/libraries/custom/custom_inline_node.mtlx

@@ -22,6 +22,7 @@
     Input and output variables can just be used as if they where declared and initialized with the corresponding defaults before.
     Functions are not allowed to return, also no early returns allowed.
     All input and output names in the MDL implementation have a "mxp_" prefix in order to avoid collisions with reserved names.
+    When adding comments in the inline sourcecode, use `/* comment */` as `//` is not supported at this point.
   -->
   <implementation 
     name="IM_custom_inline_node"

resources/Materials/TestSuite/libraries/custom/custom_node.mtlx

@@ -18,8 +18,7 @@
 
   <!-- implementation -->
   <!-- specifies where to find the implementation of the custom node.
-    There is no need to add a signature because it will be generated from the definition.
-    All input and output names in the MDL implementation have a "mxp_" prefix in order to avoid collisions with reserved names.
+    Input and output names in the MDL implementation have a "mxp_" prefix in case they would collide with reserved names.
     Note, the defaults for output parameters (if present) must be matched in the MDL implementation
     in case the outputs remain unchanged in at least one code path.
   -->

resources/Materials/TestSuite/libraries/custom/example_procedural.mtlx

@@ -0,0 +1,83 @@
+<?xml version="1.0"?>
+<materialx version="1.39">
+
+  <!-- definition -->
+  <!-- specifies the interface of the node, including:
+    - the `node` that defines the name of the element during instantiation
+    - all input parameter types and names
+    - all output parameter types and names
+    - all inputs and outputs can have defaults
+    - the `name` that needs to br referenced when adding the implementation with the actual source code
+  -->
+  <nodedef name="ND_example_procedural" node="example_procedural" nodegroup="custom" doc="A simple example that creates a color.">
+    <input name="texcoord" type="vector2" />
+    <input name="thickness" type="float" value="1.0" />
+    <input name="power" type="float" value="1.0" />
+    <input name="time" type="float" value="0.0" />
+    <input name="iterations" type="integer" value="5" />
+    <input name="offset" type="float" value="1.85" />
+    <output name="out" type="color3" />
+  </nodedef>
+
+  <!-- implementation -->
+  <!-- specifies the body of the function.
+    There is no need to add a signature because it will be generated from the definition.
+    Input and output variables can just be used as if they where declared and initialized with the corresponding defaults before.
+    Functions are not allowed to return, also no early returns allowed.
+    All input and output names in the MDL implementation have a "mxp_" prefix in order to avoid collisions with reserved names.
+    When adding comments in the inline sourcecode, use `/* comment */` as `//` is not supported at this point.
+  -->
+  <implementation 
+    name="IM_example_procedural"
+    nodedef="ND_example_procedural"
+    target="genmdl"
+    sourcecode="
+      /* uv with origin in the center */
+      float2 uv = math::frac(mxp_texcoord) * 2.0 - 1.0;
+
+      /* accumulate rings of different size */
+      mxp_out = color(0.0);
+      for (int i = 0; i < mxp_iterations; ++i)
+      {
+          /* signed distance function for the color selection */
+          float d = math::length(uv);
+
+          /* cosine based coloring */
+          float phi = d + i * 0.33;
+          color tint_contrib = math::cos(math::TWO_PI * (float3(0.0, 0.1, 0.2) + phi)) * 0.5 + 0.5;
+
+          /* signed distance function for a ring + add some contrast */
+          d = math::abs(math::sin(d * 16 + mxp_time) * 0.0625);
+          d = math::pow(0.005 * mxp_thickness / math::max(d, 0.0001), mxp_power);
+
+          /* add contribution */
+          mxp_out += tint_contrib * d;
+          /* offset the coordinate for the next iteration */
+          uv = math::frac(uv * mxp_offset) - 0.5;
+      }
+    " />
+
+  <!-- instantiations -->
+  <!-- uses the node above in material graph -->
+  <texcoord name="texcoord1" type="vector2" />
+
+  <example_procedural name="example_procedural1" type="color3">
+    <input name="texcoord" type="vector2" nodename="texcoord1" />
+    <input name="power" type="float" value="1.25" />
+  </example_procedural>
+
+  <multiply name="emission_intensity" type="color3">
+    <input name="in1" type="color3" nodename="example_procedural1" />
+    <input name="in2" type="color3" value="0.3183 0.3183 0.3183" />
+  </multiply>
+  <uniform_edf name="emission" type="EDF">
+    <input name="color" type="color3" nodename="emission_intensity" />
+  </uniform_edf>
+  <surface name="surface1" type="surfaceshader">
+    <input name="edf" type="EDF" nodename="emission" />
+  </surface>
+  <surfacematerial name="example_procedural_test" type="material">
+    <input name="surfaceshader" type="surfaceshader" nodename="surface1" />
+  </surfacematerial>
+
+</materialx>

source/MaterialXGenMdl/MdlShaderGenerator.cpp

@@ -384,6 +384,10 @@ ShaderNodeImplPtr MdlShaderGenerator::getImplementation(const NodeDef& nodedef,
             {
                 impl = CustomCodeNodeMdl::create();
             }
+            else if (file.empty() && sourcecode.empty())
+            {
+                throw ExceptionShaderGenError("No valid MDL implementation found for '" + name + "'");
+            }
             else
             {
                 // Fall back to source code implementation.

source/MaterialXGenMdl/Nodes/CustomNodeMdl.cpp

@@ -65,6 +65,10 @@ void CustomCodeNodeMdl::initializeForInlineSourceCode(const InterfaceElement& el
     {
         throw ExceptionShaderGenError("No source code was specified for the implementation '" + impl.getName() + "'");
     }
+    if (_inlineSourceCode.find("//") != string::npos)
+    {
+        throw ExceptionShaderGenError("Source code contains unsupported comments '//', please use '/* comment */' instead in '" + impl.getName() + "'");
+    }
 
     NodeDefPtr nodeDef = impl.getNodeDef();
     _inlineFunctionName = nodeDef->getName();

source/MaterialXGenShader/Nodes/SourceCodeNode.cpp

@@ -51,23 +51,16 @@ void SourceCodeNode::initialize(const InterfaceElement& element, GenContext& con
     const Implementation& impl = static_cast<const Implementation&>(element);
 
     // Get source code from either an attribute or a file.
-    if (_functionSource.empty())
-    {
-        // only read the attribute if empty to allow inherited classes to override
-        _functionSource = impl.getAttribute("sourcecode");
-    }
+    _functionSource = impl.getAttribute("sourcecode");
     if (_functionSource.empty())
     {
         resolveSourceCode(element, context);
     }
 
     // Find the function name to use
     // If no function is given the source will be inlined.
-    if (_functionName.empty())
-    {
-        // only read the attribute if empty to allow inherited classes to override
-        _functionName = impl.getAttribute("function");
-    }
+    _functionName = impl.getAttribute("function");
+
     _inlined = _functionName.empty();
     if (!_inlined)
     {

source/MaterialXTest/MaterialXGenMdl/GenMdl.cpp

@@ -276,7 +276,7 @@ void MdlShaderGeneratorTester::compileSource(const std::vector<mx::FilePath>& so
 
         CHECK(returnValue == 0);
     }
-    if (false) //!renderExec.empty()) // render if renderer is availabe
+    if (!renderExec.empty()) // render if renderer is available
     {
         std::string renderCommand = renderExec;
 

source/MaterialXTest/MaterialXGenShader/GenShaderUtil.cpp

@@ -704,10 +704,6 @@ void ShaderGeneratorTester::validate(const mx::GenOptions& generateOptions, cons
     size_t documentIndex = 0;
     for (const auto& doc : _documents)
     {
-        std::string uri = doc->getSourceUri();
-        // if (uri.find("custom_inline_node_reserved_words") == std::string::npos)
-        //     continue;
-
         // Apply optional preprocessing.
         preprocessDocument(doc);
         _shaderGenerator->registerShaderMetadata(doc, context);