Fix not generating polyfills when using InternalsVisibleTo with EmbeddedAttribute

PolySharp.slnx

@@ -9,6 +9,7 @@
     <Project Path="tests/PolySharp.MinimumCSharpVersion.Tests/PolySharp.MinimumCSharpVersion.Tests.csproj" />
     <Project Path="tests/PolySharp.PolySharpUseTypeAliasForUnmanagedCallersOnlyAttribute.Tests/PolySharp.PolySharpUseTypeAliasForUnmanagedCallersOnlyAttribute.Tests.csproj" />
     <Project Path="tests/PolySharp.Tests.UsePublicAccessibility/PolySharp.Tests.UsePublicAccessibility.csproj" />
+    <Project Path="tests/PolySharp.InternalsVisibleTo.Tests/PolySharp.InternalsVisibleTo.Tests.csproj" />
     <Project Path="tests/PolySharp.Tests/PolySharp.Tests.csproj" />
     <Project Path="tests/PolySharp.TypeForwards.Tests/PolySharp.TypeForwards.Tests.csproj" />
   </Folder>

src/PolySharp.SourceGenerators/Extensions/AnalyzerConfigOptionsProviderExtensions.cs

@@ -1,7 +1,3 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
 using System;
 using System.Collections.Immutable;
 using System.Diagnostics.CodeAnalysis;

src/PolySharp.SourceGenerators/Extensions/AssemblyExtensions.cs

@@ -1,7 +1,3 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
 using System.IO;
 using System.Reflection;
 

src/PolySharp.SourceGenerators/Extensions/CompilationExtensions.cs

@@ -1,7 +1,3 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
 
@@ -47,16 +43,37 @@ public static bool HasLanguageVersionAtLeastEqualTo(this Compilation compilation
     /// <returns>Whether a type with the specified metadata name can be accessed from the given compilation.</returns>
     public static bool HasAccessibleTypeWithMetadataName(this Compilation compilation, string fullyQualifiedMetadataName)
     {
+        // Helper to check for accessiblity and '[Embedded]' at the same time (Roslyn doesn't check the latter here)
+        static bool IsSymbolAccessibleAndNotEmbedded(Compilation compilation, INamedTypeSymbol symbol)
+        {
+            // First use the built-in Roslyn check (this doesn't check for '[Embedded]').
+            // If the symbol is already not embedded (e.g. it's internal), stop here.
+            if (!compilation.IsSymbolAccessibleWithin(symbol, compilation.Assembly))
+            {
+                return false;
+            }
+
+            // If the symbol is defined in this same assembly, then it's considered accessible
+            if (SymbolEqualityComparer.Default.Equals(compilation.Assembly, symbol.ContainingAssembly))
+            {
+                return true;
+            }
+
+            // If the type has '[Embedded]' on it, then it is not accessible, because Roslyn
+            // will just ignore it completely (even if its accessiblity is 'public' or similar).
+            return !symbol.HasEmbeddedAttribute();
+        }
+
         // If there is only a single matching symbol, check its accessibility
         if (compilation.GetTypeByMetadataName(fullyQualifiedMetadataName) is INamedTypeSymbol typeSymbol)
         {
-            return compilation.IsSymbolAccessibleWithin(typeSymbol, compilation.Assembly);
+            return IsSymbolAccessibleAndNotEmbedded(compilation, typeSymbol);
         }
 
         // Otherwise, check all available types
         foreach (INamedTypeSymbol currentTypeSymbol in compilation.GetTypesByMetadataName(fullyQualifiedMetadataName))
         {
-            if (compilation.IsSymbolAccessibleWithin(currentTypeSymbol, compilation.Assembly))
+            if (IsSymbolAccessibleAndNotEmbedded(compilation, currentTypeSymbol))
             {
                 return true;
             }

src/PolySharp.SourceGenerators/Extensions/ISymbolExtensions.cs

@@ -0,0 +1,42 @@
+using Microsoft.CodeAnalysis;
+
+namespace PolySharp.SourceGenerators.Extensions;
+
+/// <summary>
+/// Extensions for <see cref="ISymbol"/>.
+/// </summary>
+internal static class ISymbolExtensions
+{
+    /// <summary>
+    /// Checks whether a type has the <c>Microsoft.CodeAnalysis.EmbeddedAttribute</c> annotation.
+    /// </summary>
+    /// <param name="symbol">The <see cref="ISymbol"/> instance to check for the attribute.</param>
+    /// <returns>Whether or not <paramref name="symbol"/> has the embedded attribute.</returns>
+    public static bool HasEmbeddedAttribute(this ISymbol symbol)
+    {
+        foreach (AttributeData attribute in symbol.GetAttributes())
+        {
+            // The '[Embedded]' attribute is special, so we just match it by name.
+            // There could be any number of copies of it across different assemblies.
+            if (attribute.AttributeClass is
+                {
+                    ContainingNamespace:
+                    {
+                        ContainingNamespace:
+                        {
+                            ContainingNamespace.IsGlobalNamespace: true,
+                            Name: "Microsoft",
+                        },
+                        Name: "CodeAnalysis",
+
+                    },
+                    Name: "EmbeddedAttribute",
+                })
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
+}

tests/PolySharp.InternalsVisibleTo.Tests/PolySharp.InternalsVisibleTo.Tests.csproj

@@ -0,0 +1,29 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFrameworks>net472;net48;net481;netstandard2.0;netstandard2.1;net8.0;net9.0</TargetFrameworks>
+    <PolySharpIncludeRuntimeSupportedAttributes>true</PolySharpIncludeRuntimeSupportedAttributes>
+
+    <!-- Define a constant to change the namespace of the test files -->
+    <DefineConstants>$(DefineConstants);INTERNALS_VISIBLE_TO_TESTS</DefineConstants>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <CompilerVisibleProperty Include="PolySharpIncludeRuntimeSupportedAttributes" />
+  </ItemGroup>
+
+  <ItemGroup Condition="!$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'net8.0'))">
+    <PackageReference Include="System.Memory" Version="4.5.5" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\PolySharp.SourceGenerators\PolySharp.SourceGenerators.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" PrivateAssets="contentfiles;build" />
+    <ProjectReference Include="..\PolySharp.Tests\PolySharp.Tests.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Compile Include="..\PolySharp.Tests\LanguageFeatures.cs" Link="LanguageFeatures.cs" />
+    <Compile Include="..\PolySharp.Tests\RuntimeSupport.cs" Link="RuntimeSupport.cs" />
+  </ItemGroup>
+
+</Project>

tests/PolySharp.Tests/LanguageFeatures.cs

@@ -10,7 +10,11 @@
 
 #pragma warning disable CA2255
 
+#if INTERNALS_VISIBLE_TO_TESTS
+namespace PolySharp.InternalsVisbleTo.Tests;
+#else
 namespace PolySharp.Tests;
+#endif
 
 internal class TestClass
 {

tests/PolySharp.Tests/PolySharp.Tests.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFrameworks>net472;net48;net481;netstandard2.0;netstandard2.1;net8.0;net9.0</TargetFrameworks>
@@ -17,4 +17,12 @@
     <ProjectReference Include="..\..\src\PolySharp.SourceGenerators\PolySharp.SourceGenerators.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" PrivateAssets="contentfiles;build" />
   </ItemGroup>
 
+  <!--
+    Declare internal accessibility for the 'PolySharp.InternalsVisibleTo.Tests' project, which
+    is used to validate that '[Embedded]' is correctly filtered when detecting accessible types.
+  -->
+  <ItemGroup>
+    <InternalsVisibleTo Include="PolySharp.InternalsVisibleTo.Tests" />
+  </ItemGroup>
+
 </Project>

tests/PolySharp.Tests/RuntimeSupport.cs

@@ -9,7 +9,11 @@
 
 [assembly: DisableRuntimeMarshalling]
 
+#if INTERNALS_VISIBLE_TO_TESTS
+namespace PolySharp.InternalsVisbleTo.Tests;
+#else
 namespace PolySharp.Tests;
+#endif
 
 internal class RandomApis
 {