feat: Allowing extra base types to be used for SyncLists and other SyncObjects (#1729)

* Tests for most uses of sync list

renaming classes for existing test files

* improving error message for Paramless constructor

* More tests for SyncLists

* updating error message

* ignore abstract classes

we dont need to process abstract classes because classes that
inherit from them will be processed instead

* check and error for syncList item being genric

* allowing extra base types for synclist

* checking for nested types in abstract classes

* test for nested types inside structs

Assets/Mirror/Editor/Weaver/Processors/GenericArgumentResolver.cs

@@ -0,0 +1,110 @@
+using System.Collections.Generic;
+using Mono.CecilX;
+
+namespace Mirror.Weaver
+{
+    public class GenericArgumentResolver
+    {
+        readonly Stack<TypeReference> stack = new Stack<TypeReference>();
+        readonly int maxGenericArgument;
+
+        public GenericArgumentResolver(int maxGenericArgument)
+        {
+            this.maxGenericArgument = maxGenericArgument;
+        }
+
+        public bool GetGenericFromBaseClass(TypeDefinition td, int genericArgument, TypeReference baseType, out TypeReference itemType)
+        {
+            itemType = null;
+            if (GetGenericBaseType(td, baseType, out GenericInstanceType parent))
+            {
+                TypeReference arg = parent.GenericArguments[genericArgument];
+                if (arg.IsGenericParameter)
+                {
+                    itemType = FindParameterInStack(genericArgument);
+                }
+                else
+                {
+                    itemType = Weaver.CurrentAssembly.MainModule.ImportReference(arg);
+                }
+            }
+
+            return itemType != null;
+        }
+
+        TypeReference FindParameterInStack(int genericArgument)
+        {
+            while (stack.Count > 0)
+            {
+                TypeReference next = stack.Pop();
+
+                if (!(next is GenericInstanceType genericType))
+                {
+                    // if type is not GenericInstanceType something has gone wrong
+                    return null;
+                }
+
+                if (genericType.GenericArguments.Count < genericArgument)
+                {
+                    // if less than `genericArgument` then we didnt find generic argument
+                    return null;
+                }
+
+                if (genericType.GenericArguments.Count > maxGenericArgument)
+                {
+                    // if greater than `genericArgument` it is hard to know which generic arg we want
+                    // See SyncListGenericInheritanceWithMultipleGeneric test
+                    Weaver.Error($"Too many generic argument for {next}");
+                    return null;
+                }
+
+                TypeReference genericArg = genericType.GenericArguments[genericArgument];
+                if (!genericArg.IsGenericParameter)
+                {
+                    // if not generic, sucessfully found type
+                    return Weaver.CurrentAssembly.MainModule.ImportReference(genericArg);
+                }
+            }
+
+            // nothing left in stack, something went wrong
+            return null;
+        }
+
+        bool GetGenericBaseType(TypeDefinition td, TypeReference baseType, out GenericInstanceType found)
+        {
+            stack.Clear();
+            TypeReference parent = td.BaseType;
+            found = null;
+
+            while (parent != null)
+            {
+                string parentName = parent.FullName;
+
+                // strip generic parameters
+                int index = parentName.IndexOf('<');
+                if (index != -1)
+                {
+                    parentName = parentName.Substring(0, index);
+                }
+
+                if (parentName == baseType.FullName)
+                {
+                    found = parent as GenericInstanceType;
+                    break;
+                }
+                try
+                {
+                    stack.Push(parent);
+                    parent = parent.Resolve().BaseType;
+                }
+                catch (AssemblyResolutionException)
+                {
+                    // this can happen for plugins.
+                    break;
+                }
+            }
+
+            return found != null;
+        }
+    }
+}

Assets/Mirror/Editor/Weaver/Processors/GenericArgumentResolver.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: fd67b3f7c2d66074a9bc7a23787e2ffb
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Assets/Mirror/Editor/Weaver/Processors/SyncDictionaryProcessor.cs

@@ -11,8 +11,26 @@ static class SyncDictionaryProcessor
         /// <param name="td">The synclist class</param>
         public static void Process(TypeDefinition td)
         {
-            SyncObjectProcessor.GenerateSerialization(td, 0, "SerializeKey", "DeserializeKey");
-            SyncObjectProcessor.GenerateSerialization(td, 1, "SerializeItem", "DeserializeItem");
+            GenericArgumentResolver resolver = new GenericArgumentResolver(2);
+
+            if (resolver.GetGenericFromBaseClass(td, 0, Weaver.SyncDictionaryType, out TypeReference keyType))
+            {
+                SyncObjectProcessor.GenerateSerialization(td, keyType, "SerializeKey", "DeserializeKey");
+            }
+            else
+            {
+                Weaver.Error($"Could not find generic arguments for {Weaver.SyncDictionaryType} using {td}");
+                return;
+            }
+
+            if (resolver.GetGenericFromBaseClass(td, 1, Weaver.SyncDictionaryType, out TypeReference itemType))
+            {
+                SyncObjectProcessor.GenerateSerialization(td, itemType, "SerializeItem", "DeserializeItem");
+            }
+            else
+            {
+                Weaver.Error($"Could not find generic arguments for {Weaver.SyncDictionaryType} using {td}");
+            }
         }
     }
 }

Assets/Mirror/Editor/Weaver/Processors/SyncListProcessor.cs

@@ -9,9 +9,18 @@ static class SyncListProcessor
         /// Generates serialization methods for synclists
         /// </summary>
         /// <param name="td">The synclist class</param>
-        public static void Process(TypeDefinition td)
+        public static void Process(TypeDefinition td, TypeReference baseType)
         {
-            SyncObjectProcessor.GenerateSerialization(td, 0, "SerializeItem", "DeserializeItem");
+            GenericArgumentResolver resolver = new GenericArgumentResolver(1);
+
+            if (resolver.GetGenericFromBaseClass(td, 0, baseType, out TypeReference itemType))
+            {
+                SyncObjectProcessor.GenerateSerialization(td, itemType, "SerializeItem", "DeserializeItem");
+            }
+            else
+            {
+                Weaver.Error($"Could not find generic arguments for {baseType} using {td}");
+            }
         }
     }
 }

Assets/Mirror/Editor/Weaver/Processors/SyncObjectInitializer.cs

@@ -41,7 +41,7 @@ static void GenerateSyncObjectInstanceInitializer(ILProcessor ctorWorker, FieldD
             MethodDefinition ctor = fieldType.Methods.FirstOrDefault(x => x.Name == ".ctor" && !x.HasParameters);
             if (ctor == null)
             {
-                Weaver.Error($"{fd} does not have a default constructor");
+                Weaver.Error($"{fd} Can not intialize field because no default constructor was found. Manually intialize the field (call the constructor) or add constructor without Parameter");
                 return;
             }
             MethodReference objectConstructor = Weaver.CurrentAssembly.MainModule.ImportReference(ctor);

Assets/Mirror/Editor/Weaver/Processors/SyncObjectProcessor.cs

@@ -10,19 +10,11 @@ public static class SyncObjectProcessor
         /// </summary>
         /// <param name="td">The type of the class that needs serialization methods</param>
         /// <param name="genericArgument">Which generic argument to serialize,  0 is the first one</param>
+        /// <param name="baseType">the type that has generic arguments</param>
         /// <param name="serializeMethod">The name of the serialize method</param>
         /// <param name="deserializeMethod">The name of the deserialize method</param>
-        public static void GenerateSerialization(TypeDefinition td, int genericArgument, string serializeMethod, string deserializeMethod)
+        public static void GenerateSerialization(TypeDefinition td, TypeReference itemType, string serializeMethod, string deserializeMethod)
         {
-            // find item type
-            GenericInstanceType gt = (GenericInstanceType)td.BaseType;
-            if (gt.GenericArguments.Count <= genericArgument)
-            {
-                Weaver.Error($"{td} should have {genericArgument} generic arguments");
-                return;
-            }
-            TypeReference itemType = Weaver.CurrentAssembly.MainModule.ImportReference(gt.GenericArguments[genericArgument]);
-
             Weaver.DLog(td, "SyncObjectProcessor Start item:" + itemType.FullName);
 
             MethodReference writeItemFunc = GenerateSerialization(serializeMethod, td, itemType);
@@ -47,6 +39,15 @@ static MethodReference GenerateSerialization(string methodName, TypeDefinition t
             if (existing != null)
                 return existing;
 
+
+            // this check needs to happen inside GenerateSerialization because
+            // we need to check if user has made custom function above
+            if (itemType.IsGenericInstance)
+            {
+                Weaver.Error($"{td} Can not create Serialize or Deserialize for generic element. Override virtual methods with custom Serialize and Deserialize to use {itemType} in SyncList");
+                return null;
+            }
+
             MethodDefinition serializeFunc = new MethodDefinition(methodName, MethodAttributes.Public |
                     MethodAttributes.Virtual |
                     MethodAttributes.Public |
@@ -57,12 +58,6 @@ static MethodReference GenerateSerialization(string methodName, TypeDefinition t
             serializeFunc.Parameters.Add(new ParameterDefinition("item", ParameterAttributes.None, itemType));
             ILProcessor serWorker = serializeFunc.Body.GetILProcessor();
 
-            if (itemType.IsGenericInstance)
-            {
-                Weaver.Error($"{td} cannot have generic elements {itemType}");
-                return null;
-            }
-
             MethodReference writeFunc = Writers.GetWriteFunc(itemType);
             if (writeFunc != null)
             {
@@ -88,6 +83,14 @@ static MethodReference GenerateDeserialization(string methodName, TypeDefinition
             if (existing != null)
                 return existing;
 
+            // this check needs to happen inside GenerateDeserialization because
+            // we need to check if user has made custom function above
+            if (itemType.IsGenericInstance)
+            {
+                Weaver.Error($"{td} Can not create Serialize or Deserialize for generic element. Override virtual methods with custom Serialize and Deserialize to use {itemType} in SyncList");
+                return null;
+            }
+
             MethodDefinition deserializeFunction = new MethodDefinition(methodName, MethodAttributes.Public |
                     MethodAttributes.Virtual |
                     MethodAttributes.Public |

Assets/Mirror/Editor/Weaver/Weaver.cs

@@ -406,31 +406,37 @@ static bool WeaveMessage(TypeDefinition td)
 
         static bool WeaveSyncObject(TypeDefinition td)
         {
-            if (!td.IsClass)
-                return false;
-
+            bool modified = false;
+            
             // ignore generic classes
             // we can not process generic classes
             // we give error if a generic syncObject is used in NetworkBehaviour
             if (td.HasGenericParameters)
                 return false;
 
-            bool modified = false;
+            // ignore abstract classes
+            // we dont need to process abstract classes because classes that
+            // inherit from them will be processed instead
 
-            if (td.IsDerivedFrom(SyncListType))
+            // We cant early return with non classes or Abstract classes
+            // because we still need to check for embeded types
+            if (td.IsClass || !td.IsAbstract)
             {
-                SyncListProcessor.Process(td);
-                modified = true;
-            }
-            else if (td.IsDerivedFrom(SyncSetType))
-            {
-                SyncListProcessor.Process(td);
-                modified = true;
-            }
-            else if (td.IsDerivedFrom(SyncDictionaryType))
-            {
-                SyncDictionaryProcessor.Process(td);
-                modified = true;
+                if (td.IsDerivedFrom(SyncListType))
+                {
+                    SyncListProcessor.Process(td, SyncListType);
+                    modified = true;
+                }
+                else if (td.IsDerivedFrom(SyncSetType))
+                {
+                    SyncListProcessor.Process(td, SyncSetType);
+                    modified = true;
+                }
+                else if (td.IsDerivedFrom(SyncDictionaryType))
+                {
+                    SyncDictionaryProcessor.Process(td);
+                    modified = true;
+                }
             }
 
             // check for embedded types

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests.cs

@@ -5,7 +5,43 @@ namespace Mirror.Weaver.Tests
     public class WeaverSyncListTests : WeaverTestsBuildFromTestName
     {
         [Test]
-        public void SyncListValid()
+        public void SyncList()
+        {
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.False);
+            Assert.That(weaverErrors, Is.Empty);
+        }
+
+        [Test]
+        public void SyncListByteValid()
+        {
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.False);
+            Assert.That(weaverErrors, Is.Empty);
+        }
+
+        [Test]
+        public void SyncListGenericAbstractInheritance()
+        {
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.False);
+            Assert.That(weaverErrors, Is.Empty);
+        }
+
+        [Test]
+        public void SyncListGenericInheritance()
+        {
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.False);
+            Assert.That(weaverErrors, Is.Empty);
+        }
+
+        [Test]
+        public void SyncListGenericInheritanceWithMultipleGeneric()
+        {
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.True);
+            Assert.That(weaverErrors, Has.Some.Match(@"Mirror\.Weaver error: Could not find generic arguments for Mirror\.SyncList`1 using MirrorTest\.SomeListInt"));
+            Assert.That(weaverErrors, Has.Some.Match(@"Mirror\.Weaver error: Too many generic argument for MirrorTest\.SomeList`2<System.String,System.Int32>"));
+        }
+
+        [Test]
+        public void SyncListInheritance()
         {
             Assert.That(CompilationFinishedHook.WeaveFailed, Is.False);
             Assert.That(weaverErrors, Is.Empty);
@@ -15,11 +51,116 @@ public void SyncListValid()
         public void SyncListMissingParamlessCtor()
         {
             Assert.That(CompilationFinishedHook.WeaveFailed, Is.True);
-            Assert.That(weaverErrors, Contains.Item("Mirror.Weaver error: MirrorTest.MirrorTestPlayer/SyncListString2 MirrorTest.MirrorTestPlayer::Foo does not have a default constructor"));
+            string weaverError = @"Mirror\.Weaver error:";
+            string fieldType = @"MirrorTest\.SyncListString2 MirrorTest\.SyncListMissingParamlessCtor::Foo";
+            string errorMessage = @"Can not intialize field because no default constructor was found\. Manually intialize the field \(call the constructor\) or add constructor without Parameter";
+            Assert.That(weaverErrors, Has.Some.Match($"{weaverError} {fieldType} {errorMessage}"));
+        }
+        
+        [Test]
+        public void SyncListMissingParamlessCtorManuallyInitialized()
+        {
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.False);
+            Assert.That(weaverErrors, Is.Empty);
         }
 
         [Test]
-        public void SyncListByteValid()
+        public void SyncListNestedStruct()
+        {
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.False);
+            Assert.That(weaverErrors, Is.Empty);
+        }
+
+        [Test]
+        public void SyncListNestedInAbstractClass()
+        {
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.False);
+            Assert.That(weaverErrors, Is.Empty);
+        }
+
+        [Test]
+        public void SyncListNestedInAbstractClassWithInvalid()
+        {
+            // we need this negative test to make sure that SyncList is being processed 
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.True);
+            Assert.That(weaverErrors, Has.Some.Match(@"Mirror\.Weaver error: UnityEngine\.Object MirrorTest\.SomeAbstractClass/MyNestedStruct::target has unsupported type\. Use a type supported by Mirror instead"));
+        }
+
+        [Test]
+        public void SyncListNestedInStruct()
+        {
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.False);
+            Assert.That(weaverErrors, Is.Empty);
+        }
+
+        [Test]
+        public void SyncListNestedInStructWithInvalid()
+        {
+            // we need this negative test to make sure that SyncList is being processed 
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.True);
+            Assert.That(weaverErrors, Has.Some.Match(@"Mirror\.Weaver error: UnityEngine\.Object MirrorTest\.SomeData::target has unsupported type\. Use a type supported by Mirror instead"));
+        }
+
+        [Test]
+        public void SyncListStruct()
+        {
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.False);
+            Assert.That(weaverErrors, Is.Empty);
+        }
+
+        [Test]
+        public void SyncListStructWithCustomDeserializeOnly()
+        {
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.False);
+            Assert.That(weaverErrors, Is.Empty);
+        }
+
+        [Test]
+        public void SyncListStructWithCustomMethods()
+        {
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.False);
+            Assert.That(weaverErrors, Is.Empty);
+        }
+
+        [Test]
+        public void SyncListStructWithCustomSerializeOnly()
+        {
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.False);
+            Assert.That(weaverErrors, Is.Empty);
+        }
+
+        [Test]
+        public void SyncListErrorForGenericStruct()
+        {
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.True);
+            string weaverError = @"Mirror\.Weaver error:";
+            string type = @"MirrorTest\.MyGenericStructList";
+            string errorMessage = @"Can not create Serialize or Deserialize for generic element\. Override virtual methods with custom Serialize and Deserialize to use MirrorTest.MyGenericStruct`1<System.Single> in SyncList";
+            Assert.That(weaverErrors, Has.Some.Match($"{weaverError} {type} {errorMessage}"));
+        }
+
+        [Test]
+        public void SyncListErrorForGenericStructWithCustomDeserializeOnly()
+        {
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.True);
+            string weaverError = @"Mirror\.Weaver error:";
+            string type = @"MirrorTest\.MyGenericStructList";
+            string errorMessage = @"Can not create Serialize or Deserialize for generic element\. Override virtual methods with custom Serialize and Deserialize to use MirrorTest.MyGenericStruct`1<System.Single> in SyncList";
+            Assert.That(weaverErrors, Has.Some.Match($"{weaverError} {type} {errorMessage}"));
+        }
+
+        [Test]
+        public void SyncListErrorForGenericStructWithCustomSerializeOnly()
+        {
+            Assert.That(CompilationFinishedHook.WeaveFailed, Is.True);
+            string weaverError = @"Mirror\.Weaver error:";
+            string type = @"MirrorTest\.MyGenericStructList";
+            string errorMessage = @"Can not create Serialize or Deserialize for generic element\. Override virtual methods with custom Serialize and Deserialize to use MirrorTest.MyGenericStruct`1<System.Single> in SyncList";
+            Assert.That(weaverErrors, Has.Some.Match($"{weaverError} {type} {errorMessage}"));
+        }
+
+        [Test]
+        public void SyncListGenericStructWithCustomMethods()
         {
             Assert.That(CompilationFinishedHook.WeaveFailed, Is.False);
             Assert.That(weaverErrors, Is.Empty);

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncList.cs

@@ -3,7 +3,7 @@
 
 namespace MirrorTest
 {
-    class MirrorTestPlayer : NetworkBehaviour
+    class SyncListValid : NetworkBehaviour
     {
         public SyncListInt Foo;
     }

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListByteValid.cs

@@ -3,7 +3,7 @@
 
 namespace MirrorTest
 {
-    class MirrorTestPlayer : NetworkBehaviour
+    class SyncListByteValid : NetworkBehaviour
     {
         class MyByteClass : SyncList<byte> {};
 

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListErrorForGenericStruct.cs

@@ -0,0 +1,16 @@
+using Mirror;
+
+namespace MirrorTest
+{
+    class SyncListErrorForGenericStruct : NetworkBehaviour
+    {
+        MyGenericStructList harpseals;
+    }
+
+    struct MyGenericStruct<T>
+    {
+        T genericpotato;
+    }
+
+    class MyGenericStructList : SyncList<MyGenericStruct<float>> { };
+}

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListErrorForGenericStructWithCustomDeserializeOnly.cs

@@ -0,0 +1,22 @@
+using Mirror;
+
+namespace MirrorTest
+{
+    class SyncListErrorForGenericStructWithCustomDeserializeOnly : NetworkBehaviour
+    {
+        MyGenericStructList harpseals;
+    }
+
+    struct MyGenericStruct<T>
+    {
+        public T genericpotato;
+    }
+
+    class MyGenericStructList : SyncList<MyGenericStruct<float>>
+    {
+        protected override MyGenericStruct<float> DeserializeItem(NetworkReader reader)
+        {
+            return new MyGenericStruct<float>() { genericpotato = reader.ReadSingle() };
+        }
+    };
+}

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListErrorForGenericStructWithCustomSerializeOnly.cs

@@ -0,0 +1,22 @@
+using Mirror;
+
+namespace MirrorTest
+{
+    class SyncListErrorForGenericStructWithCustomSerializeOnly : NetworkBehaviour
+    {
+        MyGenericStructList harpseals;
+    }
+
+    struct MyGenericStruct<T>
+    {
+        public T genericpotato;
+    }
+
+    class MyGenericStructList : SyncList<MyGenericStruct<float>>
+    {
+        protected override void SerializeItem(NetworkWriter writer, MyGenericStruct<float> item)
+        {
+            writer.WriteSingle(item.genericpotato);
+        }
+    };
+}

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListGenericAbstractInheritance.cs

@@ -0,0 +1,13 @@
+using Mirror;
+
+namespace MirrorTest
+{
+    class SyncListGenericAbstractInheritance : NetworkBehaviour
+    {
+        readonly SomeListInt superSyncListString = new SomeListInt();
+    }
+
+    public abstract class SomeList<T> : SyncList<T> { }
+
+    public class SomeListInt : SomeList<int> { }
+}

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListGenericInheritance.cs

@@ -0,0 +1,13 @@
+using Mirror;
+
+namespace MirrorTest
+{
+    class SyncListGenericInheritance : NetworkBehaviour
+    {
+        readonly SomeListInt someList = new SomeListInt();
+    }
+
+    public class SomeList<T> : SyncList<T> { }
+
+    public class SomeListInt : SomeList<int> { }
+}

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListGenericInheritanceWithMultipleGeneric.cs

@@ -0,0 +1,19 @@
+using Mirror;
+
+namespace MirrorTest
+{
+    /*
+    This test will fail
+    It is hard to know which generic argument we want from `SomeList<string, int>`
+    So instead give a useful error for this edge case
+    */
+
+    class SyncListGenericInheritanceWithMultipleGeneric : NetworkBehaviour
+    {
+        readonly SomeListInt someList = new SomeListInt();
+    }
+
+    public class SomeList<G, T> : SyncList<T> { }
+
+    public class SomeListInt : SomeList<string, int> { }
+}

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListGenericStructWithCustomMethods.cs

@@ -0,0 +1,27 @@
+using Mirror;
+
+namespace MirrorTest
+{
+    class SyncListGenericStructWithCustomMethods : NetworkBehaviour
+    {
+        MyGenericStructList harpseals;
+    }
+
+    struct MyGenericStruct<T>
+    {
+        public T genericpotato;
+    }
+
+    class MyGenericStructList : SyncList<MyGenericStruct<float>>
+    {
+        protected override void SerializeItem(NetworkWriter writer, MyGenericStruct<float> item)
+        {
+            writer.WriteSingle(item.genericpotato);
+        }
+
+        protected override MyGenericStruct<float> DeserializeItem(NetworkReader reader)
+        {
+            return new MyGenericStruct<float>() { genericpotato = reader.ReadSingle() };
+        }
+    };
+}

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListInheritance.cs

@@ -0,0 +1,15 @@
+using UnityEngine;
+using Mirror;
+
+namespace MirrorTest
+{
+    class SyncListInheritance : NetworkBehaviour
+    {
+        readonly SuperSyncListString superSyncListString = new SuperSyncListString();
+    }
+    
+    public class SuperSyncListString : SyncListString
+    {
+
+    }
+}

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListMissingParamlessCtor.cs

@@ -3,15 +3,15 @@
 
 namespace MirrorTest
 {
-    class MirrorTestPlayer : NetworkBehaviour
+    class SyncListMissingParamlessCtor : NetworkBehaviour
     {
-        public class SyncListString2 : SyncList<string>
-        {
-            public SyncListString2(int phooey) {}
-            protected override void SerializeItem(NetworkWriter w, string item) {}
-            protected override string DeserializeItem(NetworkReader r) => "";
-        }
-
         public SyncListString2 Foo;
     }
+
+    public class SyncListString2 : SyncList<string>
+    {
+        public SyncListString2(int phooey) {}
+        protected override void SerializeItem(NetworkWriter w, string item) {}
+        protected override string DeserializeItem(NetworkReader r) => "";
+    }
 }

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListMissingParamlessCtorManuallyInitialized.cs

@@ -0,0 +1,17 @@
+using UnityEngine;
+using Mirror;
+
+namespace MirrorTest
+{
+    class SyncListMissingParamlessCtorManuallyInitialized : NetworkBehaviour
+    {
+        public SyncListString2 Foo = new SyncListString2(20);
+    }
+
+    public class SyncListString2 : SyncList<string>
+    {
+        public SyncListString2(int phooey) {}
+        protected override void SerializeItem(NetworkWriter w, string item) {}
+        protected override string DeserializeItem(NetworkReader r) => "";
+    }
+}

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListNestedInAbstractClass.cs

@@ -0,0 +1,21 @@
+using UnityEngine;
+using Mirror;
+
+namespace MirrorTest
+{
+    class SyncListNestedStruct : NetworkBehaviour
+    {
+        SomeAbstractClass.MyNestedStructList Foo;
+    }
+
+    public abstract class SomeAbstractClass
+    {
+        public struct MyNestedStruct
+        {
+            public int potato;
+            public float floatingpotato;
+            public double givemetwopotatoes;
+        }
+        public class MyNestedStructList : SyncList<MyNestedStruct> { }
+    }
+}

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListNestedInAbstractClassWithInvalid.cs

@@ -0,0 +1,20 @@
+using UnityEngine;
+using Mirror;
+
+namespace MirrorTest
+{
+    class SyncListNestedStructWithInvalid : NetworkBehaviour
+    {
+        SomeAbstractClass.MyNestedStructList Foo;
+    }
+
+    public abstract class SomeAbstractClass
+    {
+        public struct MyNestedStruct
+        {
+            public int potato;
+            public Object target;
+        }
+        public class MyNestedStructList : SyncList<MyNestedStruct> { }
+    }
+}

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListNestedInStruct.cs

@@ -0,0 +1,17 @@
+using UnityEngine;
+using Mirror;
+
+namespace MirrorTest
+{
+    class SyncListNestedStruct : NetworkBehaviour
+    {
+        SomeData.SyncList Foo;
+    }
+
+    public struct SomeData 
+    {
+        public int usefulNumber;
+
+        public class SyncList : Mirror.SyncList<SomeData> { }
+    }
+}

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListNestedInStructWithInvalid.cs

@@ -0,0 +1,18 @@
+using UnityEngine;
+using Mirror;
+
+namespace MirrorTest
+{
+    class SyncListNestedInStructWithInvalid : NetworkBehaviour
+    {
+        SomeData.SyncList Foo;
+    }
+
+    public struct SomeData 
+    {
+        public int usefulNumber;
+        public Object target;
+
+        public class SyncList : Mirror.SyncList<SomeData> { }
+    }
+}

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListNestedStruct.cs

@@ -3,15 +3,16 @@
 
 namespace MirrorTest
 {
-    class MirrorTestPlayer : NetworkBehaviour
+    class SyncListNestedStruct : NetworkBehaviour
     {
-        struct MyStruct
+        MyNestedStructList Foo;
+        
+        struct MyNestedStruct
         {
             int potato;
             float floatingpotato;
             double givemetwopotatoes;
         }
-        class MyStructClass : SyncList<MyStruct> {};
-        MyStructClass Foo;
+        class MyNestedStructList : SyncList<MyNestedStruct> { }
     }
 }

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListStruct.cs

@@ -0,0 +1,17 @@
+using UnityEngine;
+using Mirror;
+
+namespace MirrorTest
+{
+    class SyncListStruct : NetworkBehaviour
+    {
+        MyStructList Foo;
+    }
+    struct MyStruct
+    {
+        int potato;
+        float floatingpotato;
+        double givemetwopotatoes;
+    }
+    class MyStructList : SyncList<MyStruct> { }
+}

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListStructWithCustomDeserializeOnly.cs

@@ -0,0 +1,23 @@
+using UnityEngine;
+using Mirror;
+
+namespace MirrorTest
+{
+    class SyncListStructWithCustomDeserializeOnly : NetworkBehaviour
+    {
+        MyStructList Foo;
+    }
+    struct MyStruct
+    {
+        int potato;
+        float floatingpotato;
+        double givemetwopotatoes;
+    }
+    class MyStructList : SyncList<MyStruct> 
+    {
+        protected override MyStruct DeserializeItem(NetworkReader reader)
+        {
+            return new MyStruct() { /* read some stuff here */ };
+        }
+    }
+}

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListStructWithCustomMethods.cs

@@ -0,0 +1,28 @@
+using UnityEngine;
+using Mirror;
+
+namespace MirrorTest
+{
+    class SyncListStructWithCustomMethods : NetworkBehaviour
+    {
+        MyStructList Foo;
+    }
+    struct MyStruct
+    {
+        int potato;
+        float floatingpotato;
+        double givemetwopotatoes;
+    }
+    class MyStructList : SyncList<MyStruct> 
+    { 
+        protected override void SerializeItem(NetworkWriter writer, MyStruct item)
+        {
+            // write some stuff here
+        }
+
+        protected override MyStruct DeserializeItem(NetworkReader reader)
+        {
+            return new MyStruct() { /* read some stuff here */ };
+        }
+    }
+}

Assets/Mirror/Tests/Editor/Weaver/WeaverSyncListTests~/SyncListStructWithCustomSerializeOnly.cs

@@ -0,0 +1,23 @@
+using UnityEngine;
+using Mirror;
+
+namespace MirrorTest
+{
+    class SyncListStructWithCustomSerializeOnly : NetworkBehaviour
+    {
+        MyStructList Foo;
+    }
+    struct MyStruct
+    {
+        int potato;
+        float floatingpotato;
+        double givemetwopotatoes;
+    }
+    class MyStructList : SyncList<MyStruct> 
+    { 
+         protected override void SerializeItem(NetworkWriter writer, MyStruct item)
+        {
+            // write some stuff here
+        }
+    }
+}