From 36d6b3a9e617fed91d3e9d6ac45abbfd339805d7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Michal=20Strehovsk=C3=BD?=
 <MichalStrehovsky@users.noreply.github.com>
Date: Tue, 26 Jan 2021 19:34:40 +0100
Subject: [PATCH] Make XmlSerializer work with NativeAOT (#593)

Force the reflection-only code paths that don't Reflection.Emit.
---
 .../BuildIntegration/Microsoft.NETCore.Native.targets       | 3 +++
 .../ILCompiler.Compiler/Compiler/FeatureSwitchManager.cs    | 2 +-
 .../System.Private.Xml/src/ILLink/ILLink.Substitutions.xml  | 5 +++++
 .../System.Private.Xml/src/System.Private.Xml.csproj        | 3 +++
 .../src/System/Xml/Serialization/XmlSerializer.cs           | 6 ++++++
 5 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 src/libraries/System.Private.Xml/src/ILLink/ILLink.Substitutions.xml

diff --git a/src/coreclr/nativeaot/BuildIntegration/Microsoft.NETCore.Native.targets b/src/coreclr/nativeaot/BuildIntegration/Microsoft.NETCore.Native.targets
index 72eeba3f9d53..0556bce6d6e0 100644
--- a/src/coreclr/nativeaot/BuildIntegration/Microsoft.NETCore.Native.targets
+++ b/src/coreclr/nativeaot/BuildIntegration/Microsoft.NETCore.Native.targets
@@ -228,6 +228,9 @@ The .NET Foundation licenses this file to you under the MIT license.
       <IlcArg Include="@(_IlcRootedAssemblies->'--root:%(Identity)')" />
       <IlcArg Include="@(_IlcConditionallyRootedAssemblies->'--conditionalroot:%(Identity)')" />
 
+      <!-- The Emit-based XmlSerializer won't work -->
+      <IlcArg Include="--feature:System.Xml.Serialization.XmlSerializer.IsReflectionOnly=true" />
+
       <!-- Workaround for https://github.com/dotnet/corefx/issues/36723 -->
       <IlcArg Include="--removefeature:SerializationGuard" />
     </ItemGroup>
diff --git a/src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/FeatureSwitchManager.cs b/src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/FeatureSwitchManager.cs
index 46131d863ad6..57fc941b0761 100644
--- a/src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/FeatureSwitchManager.cs
+++ b/src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/FeatureSwitchManager.cs
@@ -876,7 +876,7 @@ protected override void ProcessField(FieldDesc field)
 
             private object TryCreateSubstitution(TypeDesc type, string value)
             {
-                switch (type.Category)
+                switch (type.UnderlyingType.Category)
                 {
                     case TypeFlags.Int32:
                         if (string.IsNullOrEmpty(value))
diff --git a/src/libraries/System.Private.Xml/src/ILLink/ILLink.Substitutions.xml b/src/libraries/System.Private.Xml/src/ILLink/ILLink.Substitutions.xml
new file mode 100644
index 000000000000..f349d51ec47e
--- /dev/null
+++ b/src/libraries/System.Private.Xml/src/ILLink/ILLink.Substitutions.xml
@@ -0,0 +1,5 @@
+<linker>
+  <type fullname="System.Xml.Serialization.XmlSerializer" featurevalue="true" feature="System.Xml.Serialization.XmlSerializer.IsReflectionOnly">
+    <method signature="System.Xml.Serialization.SerializationMode get_Mode()" body="stub" value="1" />
+  </type>
+</linker>
diff --git a/src/libraries/System.Private.Xml/src/System.Private.Xml.csproj b/src/libraries/System.Private.Xml/src/System.Private.Xml.csproj
index 526cc0ea8461..9ee379d4b1fe 100644
--- a/src/libraries/System.Private.Xml/src/System.Private.Xml.csproj
+++ b/src/libraries/System.Private.Xml/src/System.Private.Xml.csproj
@@ -5,6 +5,9 @@
     <TargetFrameworks>$(NetCoreAppCurrent)-windows;$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
+  <ItemGroup>
+    <ILLinkSubstitutionsXmls Include="ILLink\ILLink.Substitutions.xml" />
+  </ItemGroup>
   <ItemGroup>
     <Compile Include="$(CommonPath)System\Text\StringBuilderCache.cs" Link="Common\System\StringBuilderCache.cs" />
     <Compile Include="$(CommonPath)System\HexConverter.cs" Link="Common\System\HexConverter.cs" />
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs b/src/libraries/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs
index 8c9b1d98859e..b316e88b87e3 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs
@@ -199,6 +199,12 @@ public XmlSerializer(Type type, string? defaultNamespace)
                 _primitiveType = type;
                 return;
             }
+
+            if (Mode == SerializationMode.ReflectionOnly)
+            {
+                return;
+            }
+
             _tempAssembly = s_cache[defaultNamespace, type];
             if (_tempAssembly == null)
             {