[Weaver] Fix System.Linq.Queryable not correctly referenced when not imported yet

CHANGELOG.md

@@ -6,6 +6,7 @@
 ### Fixed
 * Fixed a bug that would cause a `NullReferenceException` to be reported during compilation of a class containing a getter-only `RealmObject` property. (Issue [#2576](https://github.com/realm/realm-dotnet/issues/2576))
 * Fixed an issue that would result in `Unable to load DLL 'realm-wrappers'` when deploying a WPF .NET Framework application with ClickOnce. This was due to the incorrect BuildAction type being applied to the native libraries that Realm depends on. (Issue [#1877](https://github.com/realm/realm-dotnet/issues/1877))
+* Fixed a bug that would sometimes result in assemblies not found at runtime in a very specific edge scenario. More details about such a scenario can be found in its [PR](https://github.com/realm/realm-dotnet/pull/2639)'s description. (Issue [#1568](https://github.com/realm/realm-dotnet/issues/1568))
 
 ### Compatibility
 * Realm Studio: 11.0.0 or later.

Realm/Realm.Weaver/Extensions/ModuleDefinitionExtensions.cs

@@ -0,0 +1,41 @@
+////////////////////////////////////////////////////////////////////////////
+//
+// Copyright 2021 Realm Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+////////////////////////////////////////////////////////////////////////////
+
+using System.ComponentModel;
+using System.Linq;
+using Mono.Cecil;
+
+[EditorBrowsable(EditorBrowsableState.Never)]
+internal static class ModuleDefinitionExtensions
+{
+    public static ModuleDefinition ResolveReference(this ModuleDefinition module, string assembly)
+    {
+        var assemblyNameReference = module.FindReference(assembly);
+        if (assemblyNameReference != null)
+        {
+            return module.AssemblyResolver.Resolve(assemblyNameReference).MainModule;
+        }
+
+        return null;
+    }
+
+    public static AssemblyNameReference FindReference(this ModuleDefinition module, string assembly)
+    {
+        return module.AssemblyReferences.SingleOrDefault(a => a.Name == assembly);
+    }
+}

Realm/Realm.Weaver/ImportedReferences.cs

@@ -207,7 +207,7 @@ protected ImportedReferences(ModuleDefinition module, TypeSystem types)
             };
 
             // If the assembly has a reference to PropertyChanged.Fody, let's look up the DoNotNotifyAttribute for use later.
-            var PropertyChanged_Fody = Module.AssemblyReferences.SingleOrDefault(a => a.Name == "PropertyChanged");
+            var PropertyChanged_Fody = Module.FindReference("PropertyChanged");
             if (PropertyChanged_Fody != null)
             {
                 InitializePropertyChanged_Fody(PropertyChanged_Fody);
@@ -407,7 +407,19 @@ private void InitializePropertyChanged_Fody(AssemblyNameReference propertyChange
 
         protected AssemblyNameReference GetOrAddFrameworkReference(string assemblyName)
         {
-            var assembly = Module.AssemblyReferences.SingleOrDefault(a => a.Name == assemblyName);
+            var assembly = Module.FindReference(assemblyName);
+
+            // Since Remotion.Linq has all the needed dlls references, try to find the right version there first
+            if (assembly == null)
+            {
+                assembly = Module.ResolveReference("Realm")?.ResolveReference("Remotion.Linq")?.FindReference(assemblyName);
+                if (assembly != null)
+                {
+                    Module.AssemblyReferences.Add(assembly);
+                }
+            }
+
+            // if Remotion.Linq failed to be loaded then we fall back to search versions in System.CoreLib
             if (assembly == null)
             {
                 var corlib = (AssemblyNameReference)Module.TypeSystem.CoreLibrary;
@@ -573,7 +585,7 @@ public static ImportedReferences Create(ModuleDefinition module, string framewor
             references.InitializeFrameworkMethods();
 
             // Weaver may be run on an assembly which is not **yet** using Realm, if someone just adds nuget and builds.
-            var realmAssembly = module.AssemblyReferences.SingleOrDefault(r => r.Name == "Realm");
+            var realmAssembly = module.FindReference("Realm");
             if (realmAssembly != null)
             {
                 references.InitializeRealm(realmAssembly);