Out of range access on empty swizzle

[seang-ilm]

Another edge case on the upgrade path.

If you add this test case to MaterialXTest/MaterialXCore/Document.cpp and run with MATERIALX_DYNAMIC_ANALYSIS=ON.

TEST_CASE("Document upgrade swizzle empty value", "[document]")
{
    mx::DocumentPtr doc = mx::createDocument();
    mx::XmlReadOptions readOptions;
    readOptions.upgradeVersion = false;
    mx::readFromXmlString(doc,
        "<?xml version=\"1.0\"?>"
        "<materialx version=\"1.38\">"
        "  <nodegraph name=\"NG1\">"
        "    <swizzle name=\"swz1\" type=\"color3\" nodedef=\"ND_swizzle\">"
        "      <input name=\"in\" type=\"color3\" value=\"\"/>"
        "      <input name=\"channels\" type=\"string\" value=\"\"/>"
        "    </swizzle>"
        "  </nodegraph>"
        "</materialx>",
        mx::FileSearchPath(), &readOptions);
    REQUIRE_NOTHROW(doc->upgradeVersion());
}

/usr/include/c++/11/bits/stl_vector.h:1046:34: runtime error: reference binding to null pointer of type 'struct value_type'

It's specifically on the upgrade path for 1.38-1.39, that converts old swizzle nodes to constant nodes.

The in input has an empty value value="". This means inInput->hasValue(); returns true and we go down path

convertToConstantNode = true; // because inInput exists and has a value attribute
...
if (convertToConstantNode)
{
    ...
    string valueString = inInput ? inInput->getValueString() : "0"; // <-- ""
    StringVec origValueTokens = splitString(valueString, ARRAY_VALID_SEPARATORS); // <-- empty vector {}
    ...
    newValueTokens.push_back(origValueTokens[0]); // <-- out of range access here

MaterialX/source/MaterialXCore/Version.cpp

Lines 1264 to 1288 in 8b4b222

	string valueString = inInput ? inInput->getValueString() : "0";
	StringVec origValueTokens = splitString(valueString, ARRAY_VALID_SEPARATORS);
	StringVec newValueTokens;
	for (size_t i = 0; i < destChannelCount; i++)
	{
	if (i < channelString.size())
	{
	if (CHANNEL_INDEX_MAP.count(channelString[i]))
	{
	size_t index = CHANNEL_INDEX_MAP.at(channelString[i]);
	if (index < origValueTokens.size())
	{
	newValueTokens.push_back(origValueTokens[index]);
	continue;
	}
	}
	else if (CHANNEL_CONSTANT_MAP.count(channelString[i]))
	{
	newValueTokens.push_back(std::to_string(CHANNEL_CONSTANT_MAP.at(channelString[i])));
	continue;
	}
	}
	// Invalid channel name, or missing channel name:
	newValueTokens.push_back(origValueTokens[0]);
	}

[kshivam4781]

Opened a PR for this: #3069