Improve perf in generator cache cases

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/SourceGenerators/RazorSourceGenerator.Helpers.cs

@@ -74,7 +74,6 @@ private static StaticCompilationTagHelperFeature GetStaticTagHelperFeature(Compi
             // the tagHelperFeature will have its Engine property set as part of adding it to the engine, which is used later when doing the actual discovery
             var discoveryProjectEngine = RazorProjectEngine.Create(RazorConfiguration.Default, new VirtualRazorProjectFileSystem(), b =>
             {
-                b.Features.Add(new DefaultMetadataReferenceFeature { References = compilation.References.ToImmutableArray() });
                 b.Features.Add(tagHelperFeature);
                 b.Features.Add(new DefaultTagHelperDescriptorProvider());
 

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/SourceGenerators/RazorSourceGenerator.cs

@@ -145,7 +145,20 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
                     var ((compilationA, razorSourceGeneratorOptionsA), hasRazorFilesA) = a;
                     var ((compilationB, razorSourceGeneratorOptionsB), hasRazorFilesB) = b;
 
-                    if (!compilationA.References.SequenceEqual(compilationB.References))
+                    // when using the generator cache in the compiler its possible to encounter metadata references that are different instances
+                    // but ultimately represent the same underlying assembly. We compare the module version ids to determine if the references are the same
+                    if (!compilationA.References.SequenceEqual(compilationB.References, new LambdaComparer<MetadataReference>((old, @new) => 
+                    {
+                        if (old is null || @new is null)
+                        {
+                            return false;
+                        }
+
+                        return compilationA.GetAssemblyOrModuleSymbol(old) is IAssemblySymbol oldAssembly
+                            && compilationB.GetAssemblyOrModuleSymbol(@new) is IAssemblySymbol newAssembly
+                            && oldAssembly.Modules.Select(m => m.GetMetadata()?.GetModuleVersionId() ?? Guid.Empty)
+                                                  .SequenceEqual(newAssembly.Modules.Select(m => m.GetMetadata()?.GetModuleVersionId() ?? Guid.Empty));
+                    })))
                     {
                         return false;
                     }

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/SourceGenerators/SourceGeneratorProjectItem.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.IO;
+using System.Linq;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.CodeAnalysis;
 
@@ -47,7 +48,19 @@ public override Stream Read()
             => throw new NotSupportedException("This API should not be invoked. We should instead be relying on " +
                 "the RazorSourceDocument associated with this item instead.");
 
-        public bool Equals(SourceGeneratorProjectItem? other) => other is not null && AdditionalText == other.AdditionalText;
+        public bool Equals(SourceGeneratorProjectItem? other)
+        {
+            if (ReferenceEquals(AdditionalText, other?.AdditionalText))
+            {
+                return true;
+            }
+
+            // in the compiler server when the generator driver cache is enabled the
+            // additional files are always different instances even if their content is the same
+            var thisHash = AdditionalText.GetText()?.GetChecksum() ?? [];
+            var otherHash = other?.AdditionalText.GetText()?.GetChecksum() ?? [];
+            return Enumerable.SequenceEqual(thisHash, otherHash);
+        }
 
         public override int GetHashCode() => AdditionalText.GetHashCode();