Fix swizzle edge cases in version upgrade (#1957)

This PR fixes 2 edge cases when upgrading materials from version 1.38 to 1.39 involving swizzle nodes:
- swizzle xyz -> xyz, rgb -> rgb wasn't handled properly, because convert nodedefs were missing for such cases
- swizzle xy -> xxx is incorrectly changed to convert node

source/MaterialXCore/Version.cpp

@@ -992,16 +992,19 @@ void Document::upgradeVersion()
             { "color3", 3 }, { "color4", 4 },
             { "vector2", 2 }, { "vector3", 3 }, { "vector4", 4 }
         };
-        const StringSet CHANNEL_CONVERT_PATTERNS =
-        {
-            "rgb", "rgba", "xyz", "xyzw", "rrr", "xxx"
-        };
-        const vector<std::pair<StringSet, string>> CHANNEL_ATTRIBUTE_PATTERNS =
-        {
+        const std::array<std::pair<string, size_t>, 10> CHANNEL_CONVERT_PATTERNS =
+        { {
+            { "rgb", 3 }, { "rgb", 4 }, { "rgba", 4 },
+            { "xyz", 3 }, { "xyz", 4 }, { "xyzw", 4 },
+            { "rr", 1 }, { "rrr", 1 },
+            { "xx", 1 }, { "xxx", 1 }
+        } };
+        const std::array<std::pair<StringSet, string>, 3> CHANNEL_ATTRIBUTE_PATTERNS =
+        { {
             { { "xx", "xxx", "xxxx" }, "float" },
             { { "xyz", "x", "y", "z" }, "vector3" },
             { { "rgba", "a" }, "color4" }
-        };
+        } };
 
         // Convert channels attributes to legacy swizzle nodes, which are then converted
         // to modern nodes in a second pass.
@@ -1169,8 +1172,10 @@ void Document::upgradeVersion()
                     CHANNEL_COUNT_MAP.count(node->getType()))
                 {
                     string channelString = channelsInput ? channelsInput->getValueString() : EMPTY_STRING;
-                    size_t sourceChannelCount = CHANNEL_COUNT_MAP.at(inInput->getType());
-                    size_t destChannelCount = CHANNEL_COUNT_MAP.at(node->getType());
+                    string sourceType = inInput->getType();
+                    string destType = node->getType();
+                    size_t sourceChannelCount = CHANNEL_COUNT_MAP.at(sourceType);
+                    size_t destChannelCount = CHANNEL_COUNT_MAP.at(destType);
 
                     // Resolve the invalid case of having both a connection and a value
                     // by removing the value attribute.
@@ -1228,7 +1233,8 @@ void Document::upgradeVersion()
                             node->setInputValue("index", (int) CHANNEL_INDEX_MAP.at(channelString[0]));
                         }
                     }
-                    else if (CHANNEL_CONVERT_PATTERNS.count(channelString))
+                    else if (sourceType != destType && std::find(CHANNEL_CONVERT_PATTERNS.begin(), CHANNEL_CONVERT_PATTERNS.end(),
+                             std::make_pair(channelString, sourceChannelCount)) != CHANNEL_CONVERT_PATTERNS.end())
                     {
                         // Replace swizzle with convert.
                         node->setCategory("convert");