Fix type parsing issues in ILLink and ILC (#104060)

- Fixes #98955

   We will now produce a warning when a non-assembly-qualified type
   flows into a string location annotated with
   DynamicallyAccessedMembers, and we don't try to look up or mark the
   type (since we don't know which assemblies will be searched at
   runtime by the Type.GetType call).

- Fixes #103906

   The ILLink intrinsic handling for `Type.GetType` will now look in
   corelib for generic arguments, matching native AOT.

This replaces the existing warning IL2105. This uses a new warning
instead of repurposing IL2105, because we already documented IL2105
and older versions of ILLink will produce it. Best to avoid any
confusion about them.

Author: sbomer

docs/tools/illink/error-codes.md

@@ -1870,6 +1870,22 @@ void TestMethod()
   }
   ```
 
+#### `IL2122`: Type 'typeName' is not assembly qualified. Type name strings used for dynamically accessing a type should be assembly qualified.
+
+- The type name string passed to a location with `DynamicallyAccessedMembers` requirements was not assembly-qualified, so the trimmer cannot guarantee that the type is preserved. Consider using an assembly-qualified name instead.
+
+  ```C#
+  // warning IL2122: Type 'MyClass' is not assembly qualified. Type name strings used for dynamically accessing a type should be assembly qualified.
+  GetTypeWrapper("MyClass");
+
+  class MyClass { }
+
+  // May be defined in another assembly, so at runtime Type.GetType will look in that assembly for "MyClass".
+  void GetTypeWrapper([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] string typeName)
+  {
+      var type = Type.GetType(typeName);
+  }
+  ```
 
 ## Single-File Warning Codes
 

eng/testing/tests.mobile.targets

@@ -29,7 +29,7 @@
     <PublishTrimmed>true</PublishTrimmed>
     <!-- Suppress trimming warnings as these are tests -->
     <SuppressTrimAnalysisWarnings>true</SuppressTrimAnalysisWarnings>
-    <NoWarn>$(NoWarn);IL2103;IL2105;IL2025;IL2111</NoWarn>
+    <NoWarn>$(NoWarn);IL2103;IL2025;IL2111;IL2122</NoWarn>
 
     <!-- Reduce library test app size by trimming framework library features  -->
     <DebuggerSupport Condition="'$(DebuggerSupport)' == '' and '$(Configuration)' != 'Debug'">false</DebuggerSupport>

eng/testing/tests.singlefile.targets

@@ -29,7 +29,7 @@
     <IlcSdkPath>$(CoreCLRAotSdkDir)</IlcSdkPath>
     <IlcFrameworkPath>$(NetCoreAppCurrentTestHostSharedFrameworkPath)</IlcFrameworkPath>
     <IlcFrameworkNativePath>$(NetCoreAppCurrentTestHostSharedFrameworkPath)</IlcFrameworkNativePath>
-    <NoWarn>$(NoWarn);IL1005;IL2105;IL3000;IL3001;IL3002;IL3003;IL3050;IL3051;IL3052;IL3053</NoWarn>
+    <NoWarn>$(NoWarn);IL1005;IL2122;IL3000;IL3001;IL3002;IL3003;IL3050;IL3051;IL3052;IL3053</NoWarn>
     <TrimMode>partial</TrimMode>
     <SuppressTrimAnalysisWarnings>true</SuppressTrimAnalysisWarnings>
     <TrimmerSingleWarn>false</TrimmerSingleWarn>

src/coreclr/tools/Common/TypeSystem/Common/Utilities/CustomAttributeTypeNameParser.cs

@@ -36,13 +36,18 @@ public static TypeDesc GetTypeByCustomAttributeTypeName(this ModuleDesc module,
         }
 
         public static TypeDesc GetTypeByCustomAttributeTypeNameForDataFlow(string name, ModuleDesc callingModule,
-            TypeSystemContext context, List<ModuleDesc> referencedModules, out bool typeWasNotFoundInAssemblyNorBaseLibrary)
+            TypeSystemContext context, List<ModuleDesc> referencedModules, bool needsAssemblyName, out bool failedBecauseNotFullyQualified)
         {
-            typeWasNotFoundInAssemblyNorBaseLibrary = false;
-
+            failedBecauseNotFullyQualified = false;
             if (!TypeName.TryParse(name.AsSpan(), out TypeName parsed, s_typeNameParseOptions))
                 return null;
 
+            if (needsAssemblyName && !IsFullyQualified(parsed))
+            {
+                failedBecauseNotFullyQualified = true;
+                return null;
+            }
+
             TypeNameResolver resolver = new()
             {
                 _context = context,
@@ -52,8 +57,33 @@ public static TypeDesc GetTypeByCustomAttributeTypeNameForDataFlow(string name,
 
             TypeDesc type = resolver.Resolve(parsed);
 
-            typeWasNotFoundInAssemblyNorBaseLibrary = resolver._typeWasNotFoundInAssemblyNorBaseLibrary;
             return type;
+
+            static bool IsFullyQualified(TypeName typeName)
+            {
+                if (typeName.AssemblyName is null)
+                {
+                    return false;
+                }
+
+                if (typeName.IsArray || typeName.IsPointer || typeName.IsByRef)
+                {
+                    return IsFullyQualified(typeName.GetElementType());
+                }
+
+                if (typeName.IsConstructedGenericType)
+                {
+                    foreach (var typeArgument in typeName.GetGenericArguments())
+                    {
+                        if (!IsFullyQualified(typeArgument))
+                        {
+                            return false;
+                        }
+                    }
+                }
+
+                return true;
+            }
         }
 
         private struct TypeNameResolver
@@ -64,7 +94,6 @@ private struct TypeNameResolver
             internal Func<ModuleDesc, string, MetadataType> _canonResolver;
 
             internal List<ModuleDesc> _referencedModules;
-            internal bool _typeWasNotFoundInAssemblyNorBaseLibrary;
 
             internal TypeDesc Resolve(TypeName typeName)
             {
@@ -136,8 +165,6 @@ private TypeDesc GetSimpleType(TypeName typeName)
                             return type;
                         }
                     }
-
-                    _typeWasNotFoundInAssemblyNorBaseLibrary = true;
                 }
 
                 if (_throwIfNotFound)

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/Dataflow/ReflectionMarker.cs

@@ -89,12 +89,13 @@ internal bool TryResolveTypeNameAndMark(string typeName, in DiagnosticContext di
 
             List<ModuleDesc> referencedModules = new();
             TypeDesc foundType = CustomAttributeTypeNameParser.GetTypeByCustomAttributeTypeNameForDataFlow(typeName, callingModule, diagnosticContext.Origin.MemberDefinition!.Context,
-                referencedModules, out bool typeWasNotFoundInAssemblyNorBaseLibrary);
+                referencedModules, needsAssemblyName, out bool failedBecauseNotFullyQualified);
             if (foundType == null)
             {
-                if (needsAssemblyName && typeWasNotFoundInAssemblyNorBaseLibrary)
-                    diagnosticContext.AddDiagnostic(DiagnosticId.TypeWasNotFoundInAssemblyNorBaseLibrary, typeName);
-
+                if (failedBecauseNotFullyQualified)
+                {
+                    diagnosticContext.AddDiagnostic(DiagnosticId.TypeNameIsNotAssemblyQualified, typeName);
+                }
                 type = default;
                 return false;
             }

src/coreclr/tools/aot/ILCompiler.Trimming.Tests/TestCasesRunner/AssemblyChecker.cs

@@ -12,6 +12,7 @@
 using Mono.Cecil;
 using Mono.Cecil.Cil;
 using Mono.Linker.Tests.Cases.Expectations.Assertions;
+using Mono.Linker.Tests.Cases.Expectations.Helpers;
 using Mono.Linker.Tests.Extensions;
 using Xunit;
 using MetadataType = Internal.TypeSystem.MetadataType;

src/libraries/System.ObjectModel/tests/TrimmingTests/TypeDescriptionProviderAttributeCtorTest.cs

@@ -14,7 +14,7 @@ class Program
     /// </summary>
     static int Main(string[] args)
     {
-        TypeDescriptionProviderAttribute attr = new TypeDescriptionProviderAttribute("Program+MyTypeDescriptionProvider");
+        TypeDescriptionProviderAttribute attr = new TypeDescriptionProviderAttribute("Program+MyTypeDescriptionProvider, project");
         if (!RunTest(attr))
         {
             return -1;

src/libraries/System.Runtime/tests/System.Runtime.Tests/TrimmingTests/DebuggerTypeProxyAttributeTests.cs

@@ -53,7 +53,7 @@ public DebuggerProxy(MyClass instance)
         }
     }
 
-    [DebuggerTypeProxy("Program+MyClassWithProxyStringProxy")]
+    [DebuggerTypeProxy("Program+MyClassWithProxyStringProxy, project")]
     public class MyClassWithProxyString
     {
         public string Name { get; set; }

src/libraries/System.Runtime/tests/System.Runtime.Tests/TrimmingTests/DebuggerVisualizerAttributeTests.cs

@@ -113,8 +113,8 @@ public DebuggerVisualizerObjectSource(MyClass instance)
         }
     }
 
-    [DebuggerVisualizer("Program+MyClassWithVisualizerStringVisualizer")]
-    [DebuggerVisualizer("Program+MyClassWithVisualizerStringVisualizer2", "Program+MyClassWithVisualizerStringVisualizerObjectSource")]
+    [DebuggerVisualizer("Program+MyClassWithVisualizerStringVisualizer, project")]
+    [DebuggerVisualizer("Program+MyClassWithVisualizerStringVisualizer2, project", "Program+MyClassWithVisualizerStringVisualizerObjectSource, project")]
     public class MyClassWithVisualizerString
     {
         public string Name { get; set; }

src/mono/msbuild/apple/build/AppleBuild.LocalBuild.targets

@@ -37,7 +37,7 @@
   <PropertyGroup Condition="'$(EnableAggressiveTrimming)' == 'true'">
     <!-- Suppress trimming warnings as these are tests -->
     <SuppressTrimAnalysisWarnings>true</SuppressTrimAnalysisWarnings>
-    <NoWarn>$(NoWarn);IL2103;IL2105;IL2025;IL2111</NoWarn>
+    <NoWarn>$(NoWarn);IL2103;IL2025;IL2111;IL2122</NoWarn>
   </PropertyGroup>
 
   <!-- This .targets file is also imported by the runtime Trimming tests, and we want to be able to manually configure trimming in them so this