Extract ShallowCopy

"this" is the node you're copying to so that the extension method is
only modifying "its" node

ModuleManager/Extensions/ConfigNodeExtensions.cs

@@ -0,0 +1,19 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace ModuleManager.Extensions
+{
+    public static class ConfigNodeExtensions
+    {
+        public static void ShallowCopyFrom(this ConfigNode toNode, ConfigNode fromeNode)
+        {
+            toNode.ClearData();
+            foreach (ConfigNode.Value value in fromeNode.values)
+                toNode.values.Add(value);
+            foreach (ConfigNode node in fromeNode.nodes)
+                toNode.nodes.Add(node);
+        }
+    }
+}

ModuleManager/MMPatchLoader.cs

@@ -802,7 +802,7 @@ private void CheckNeeds()
                         }
 
                         ConfigNode copy = new ConfigNode(type);
-                        ShallowCopy(currentMod.config, copy);
+                        copy.ShallowCopyFrom(currentMod.config);
                         currentMod = new UrlDir.UrlConfig(currentMod.parent, copy);
                         mod.parent.configs.Add(currentMod);
                     }
@@ -889,7 +889,7 @@ private void CheckNeeds(NodeStack stack, PatchContext context)
             }
 
             if (needsCopy)
-                ShallowCopy(copy, original);
+                original.ShallowCopyFrom(copy);
         }
 
         /// <summary>
@@ -2304,15 +2304,6 @@ private static void InsertValue(ConfigNode newNode, int index, string name, stri
             newNode.AddValue(name, value);
         }
 
-        private static void ShallowCopy(ConfigNode from, ConfigNode to)
-        {
-            to.ClearData();
-            foreach (ConfigNode.Value value in from.values)
-                to.values.Add(value);
-            foreach (ConfigNode node in from.nodes)
-                to.nodes.Add(node);
-        }
-
         private string PrettyConfig(UrlDir.UrlConfig config)
         {
             StringBuilder sb = new StringBuilder();

ModuleManager/ModuleManager.csproj

@@ -38,6 +38,7 @@
     <Compile Include="Collections\ImmutableStack.cs" />
     <Compile Include="Command.cs" />
     <Compile Include="CommandParser.cs" />
+    <Compile Include="Extensions\ConfigNodeExtensions.cs" />
     <Compile Include="Extensions\NodeStackExtensions.cs" />
     <Compile Include="IPatchProgress.cs" />
     <Compile Include="Logging\IBasicLogger.cs" />

ModuleManagerTests/Extensions/ConfigNodeExtensionsTest.cs

@@ -0,0 +1,87 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Xunit;
+using TestUtils;
+using ModuleManager.Extensions;
+
+namespace ModuleManagerTests.Extensions
+{
+    public class ConfigNodeExtensionsTest
+    {
+        public void TestShallowCopyFrom()
+        {
+            ConfigNode fromNode = new TestConfigNode("SOME_NODE")
+            {
+                { "abc", "def" },
+                { "ghi", "jkl" },
+                new TestConfigNode("INNER_NODE_1")
+                {
+                    { "mno", "pqr" },
+                    new TestConfigNode("INNER_INNER_NODE_1"),
+                },
+                new TestConfigNode("INNER_NODE_2")
+                {
+                    { "stu", "vwx" },
+                    new TestConfigNode("INNER_INNER_NODE_2"),
+                },
+            };
+
+            ConfigNode.Value value1 = fromNode.values[0];
+            ConfigNode.Value value2 = fromNode.values[1];
+
+            ConfigNode innerNode1 = fromNode.nodes[0];
+            ConfigNode innerNode2 = fromNode.nodes[1];
+
+            ConfigNode toNode = new TestConfigNode("SOME_OTHER_NODE")
+            {
+                { "value", "will be removed" },
+                new TestConfigNode("NODE_WILL_BE_REMOVED"),
+            };
+
+            toNode.ShallowCopyFrom(fromNode);
+
+            Assert.Equal("SOME_NODE", fromNode.name);
+            Assert.Equal("SOME_OTHER_NODE", toNode.name);
+
+            Assert.Equal(2, fromNode.values.Count);
+            Assert.Equal(2, toNode.values.Count);
+
+            Assert.Same(value1, fromNode.values[0]);
+            Assert.Same(value1, toNode.values[0]);
+            Assert.Equal("abc", value1.name);
+            Assert.Equal("def", value1.value);
+
+            Assert.Same(value2, fromNode.values[1]);
+            Assert.Same(value2, toNode.values[1]);
+            Assert.Equal("ghi", value2.name);
+            Assert.Equal("jkl", value2.value);
+
+            Assert.Equal(2, fromNode.nodes.Count);
+            Assert.Equal(2, toNode.nodes.Count);
+
+            Assert.Same(innerNode1, fromNode.nodes[0]);
+            Assert.Same(innerNode1, toNode.nodes[0]);
+            Assert.Equal("INNER_NODE_1", innerNode1.name);
+            Assert.Equal(1, innerNode1.values.Count);
+            Assert.Equal("mno", innerNode1.values[0].name);
+            Assert.Equal("pqr", innerNode1.values[0].value);
+            Assert.Equal(1, innerNode1.nodes.Count);
+            Assert.Equal("INNER_INNER_NODE_1", innerNode1.nodes[0].name);
+            Assert.Equal(0, innerNode1.nodes[0].values.Count);
+            Assert.Equal(0, innerNode1.nodes[0].nodes.Count);
+
+            Assert.Same(innerNode2, fromNode.nodes[1]);
+            Assert.Same(innerNode2, toNode.nodes[1]);
+            Assert.Equal("INNER_NODE_2", innerNode2.name);
+            Assert.Equal(1, innerNode2.values.Count);
+            Assert.Equal("stu", innerNode2.values[0].name);
+            Assert.Equal("vwx", innerNode2.values[0].value);
+            Assert.Equal(1, innerNode2.nodes.Count);
+            Assert.Equal("INNER_INNER_NODE_2", innerNode2.nodes[0].name);
+            Assert.Equal(0, innerNode2.nodes[0].values.Count);
+            Assert.Equal(0, innerNode2.nodes[0].nodes.Count);
+        }
+    }
+}

ModuleManagerTests/ModuleManagerTests.csproj

@@ -52,6 +52,7 @@
     <Compile Include="Collections\ImmutableStackTest.cs" />
     <Compile Include="CommandParserTest.cs" />
     <Compile Include="DummyTest.cs" />
+    <Compile Include="Extensions\ConfigNodeExtensionsTest.cs" />
     <Compile Include="Extensions\NodeStackExtensionsTest.cs" />
     <Compile Include="Logging\ModLoggerTest.cs" />
     <Compile Include="PatchProgressTest.cs" />