[release/10.0] Fix Validation source generator deployment for non-Web SDKs (#63715)

* Proof-of-concept fix for getting validation SG to work in Blazor Wasm SDK projects

* Use special type symbol for missing type comparisons

---------

Co-authored-by: Ondřej Roztočil <roztocil@outlook.com>

Author: github-actions[bot]

src/Shared/RoslynUtils/WellKnownTypes.cs

@@ -19,6 +19,7 @@ public static WellKnownTypes GetOrCreate(Compilation compilation) =>
 
     private readonly INamedTypeSymbol?[] _lazyWellKnownTypes;
     private readonly Compilation _compilation;
+    private readonly INamedTypeSymbol _missingTypeSymbol;
 
     static WellKnownTypes()
     {
@@ -51,6 +52,7 @@ private WellKnownTypes(Compilation compilation)
     {
         _lazyWellKnownTypes = new INamedTypeSymbol?[WellKnownTypeData.WellKnownTypeNames.Length];
         _compilation = compilation;
+        _missingTypeSymbol = compilation.GetTypeByMetadataName(typeof(MissingType).FullName!)!;
     }
 
     public INamedTypeSymbol Get(SpecialType type)
@@ -74,11 +76,7 @@ public INamedTypeSymbol Get(WellKnownTypeData.WellKnownType type)
 
     private INamedTypeSymbol GetAndCache(int index)
     {
-        var result = GetTypeByMetadataNameInTargetAssembly(WellKnownTypeData.WellKnownTypeNames[index]);
-        if (result == null)
-        {
-            throw new InvalidOperationException($"Failed to resolve well-known type '{WellKnownTypeData.WellKnownTypeNames[index]}'.");
-        }
+        var result = GetTypeByMetadataNameInTargetAssembly(WellKnownTypeData.WellKnownTypeNames[index]) ?? _missingTypeSymbol;
         Interlocked.CompareExchange(ref _lazyWellKnownTypes[index], result, null);
 
         // GetTypeByMetadataName should always return the same instance for a name.
@@ -159,4 +157,6 @@ public static bool Implements(ITypeSymbol? type, ITypeSymbol interfaceType)
         }
         return false;
     }
+
+    internal class MissingType { }
 }

src/Validation/src/Microsoft.Extensions.Validation.csproj

@@ -11,6 +11,19 @@
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
+  <ItemGroup>
+    <ProjectReference Include="$(RepoRoot)src\Validation\gen\Microsoft.Extensions.Validation.ValidationsGenerator.csproj" Pack="false">
+      <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
+      <OutputItemType>Content</OutputItemType>
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </ProjectReference>
+  </ItemGroup>
+
+  <ItemGroup>
+    <!-- Package the generator in the analyzer directory of the nuget package -->
+    <None Include="$(OutputPath)\$(AssemblyName).ValidationsGenerator.dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
+  </ItemGroup>
+
   <ItemGroup>
     <Reference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
     <Reference Include="Microsoft.Extensions.Options" />