[cDAC] Pack DataGenerator as analyzer asset in Abstractions nupkg (#128903)

> [!NOTE]
> This PR description was AI-generated with GitHub Copilot CLI.

## Summary

Packs the cDAC source generator
(`Microsoft.Diagnostics.DataContractReader.DataGenerator`) as an
analyzer asset inside the
`Microsoft.Diagnostics.DataContractReader.Abstractions` transport NuGet
package, so downstream consumers pick the generator up automatically via
`PackageReference` — no in-repo `ProjectReference` to the generator
csproj required.

## Changes

- **Moved**
`src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.DataGenerator/`
→ `src/native/managed/cdac/gen/`. The repo-wide `Directory.Build.props`
auto-detects projects under `gen/` and sets `IsGeneratorProject=true`,
which imports `eng/generatorProjects.targets` (providing the
`GetAnalyzerPackFiles` target that `PackAsAnalyzer="true"` relies on).
- **Wired** the generator into `Abstractions.csproj` via
`<ProjectReference ... ReferenceOutputAssembly="false"
PackAsAnalyzer="true" />`. The compiled generator dll ships under
`analyzers/dotnet/cs/` in the transport nupkg.
- **Cleanup** in the generator csproj: dropped `IsSourceProject=false`
and `EnforceExtendedAnalyzerRules=true` overrides that are now redundant
under the `gen/` convention.
- **Updated** `Contracts.csproj` and `DataGeneratorTests.csproj`
`ProjectReference` paths to the new location.

## Generator bug fixes (uncovered by external `PackageReference`
consumption)

1. `LayoutPair` / `TypeNameResolver` emission gate used
`GetTypeByMetadataName(...) is null`, which suppressed emission whenever
the type was *present in metadata* even if **not accessible** to the
current compilation (internal type in a referenced assembly without
`InternalsVisibleTo`). Replaced with an `IsSymbolAccessibleWithin` check
so external consumers get their own internal copy generated.
2. The singular `GetTypeByMetadataName` returns null on cross-assembly
duplicates (more than one referenced assembly exposes the same internal
helper). Switched to plural `GetTypesByMetadataName` + `Any(accessible)`
so the gate behaves correctly in that case.

These bugs do not affect the in-repo `Contracts` build (it has
`InternalsVisibleTo` to itself and sees a single copy), only external
`PackageReference` consumers.

## Validation

- In-repo cDAC build and `DataGeneratorTests` continue to use the
generator via `ProjectReference OutputItemType="Analyzer"` (unchanged
behavior).
- Abstractions nupkg now contains
`analyzers/dotnet/cs/Microsoft.Diagnostics.DataContractReader.DataGenerator.dll`.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: max-charlamb

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Microsoft.Diagnostics.DataContractReader.Abstractions.csproj

@@ -11,4 +11,19 @@
     <InvariantGlobalization>true</InvariantGlobalization>
     <JsonSerializerIsReflectionEnabledByDefault>false</JsonSerializerIsReflectionEnabledByDefault>
   </PropertyGroup>
+
+  <ItemGroup>
+    <!--
+      Pack the cDAC source generator into this transport package as an
+      analyzer asset. Anyone who PackageReferences the Abstractions package
+      (in particular downstream cDAC consumers writing their own [CdacType]
+      partial classes).
+
+      ReferenceOutputAssembly=false because we don't link the generator at
+      runtime; only its compiled output flows in the nupkg.
+    -->
+    <ProjectReference Include="..\gen\Microsoft.Diagnostics.DataContractReader.DataGenerator.csproj"
+                      ReferenceOutputAssembly="false"
+                      PackAsAnalyzer="true" />
+  </ItemGroup>
 </Project>

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Microsoft.Diagnostics.DataContractReader.Contracts.csproj

@@ -20,7 +20,7 @@
     <ProjectReference Include="..\Microsoft.Diagnostics.DataContractReader.Abstractions\Microsoft.Diagnostics.DataContractReader.Abstractions.csproj" GlobalPropertiesToRemove="RuntimeIdentifier" />
 
     <!-- Wire the cdac source generator as a Roslyn analyzer. -->
-    <ProjectReference Include="..\Microsoft.Diagnostics.DataContractReader.DataGenerator\Microsoft.Diagnostics.DataContractReader.DataGenerator.csproj"
+    <ProjectReference Include="..\gen\Microsoft.Diagnostics.DataContractReader.DataGenerator.csproj"
                       OutputItemType="Analyzer"
                       ReferenceOutputAssembly="false" />
   </ItemGroup>

src/native/managed/cdac/cdac.slnx

@@ -9,7 +9,7 @@
     <Project Path="Microsoft.Diagnostics.DataContractReader.Contracts/Microsoft.Diagnostics.DataContractReader.Contracts.csproj" />
     <Project Path="Microsoft.Diagnostics.DataContractReader/Microsoft.Diagnostics.DataContractReader.csproj" />
     <Project Path="Microsoft.Diagnostics.DataContractReader.Legacy/Microsoft.Diagnostics.DataContractReader.Legacy.csproj" />
-    <Project Path="Microsoft.Diagnostics.DataContractReader.DataGenerator/Microsoft.Diagnostics.DataContractReader.DataGenerator.csproj" />
+    <Project Path="gen/Microsoft.Diagnostics.DataContractReader.DataGenerator.csproj" />
     <Project Path="mscordaccore_universal/mscordaccore_universal.csproj" />
   </Folder>
   <Folder Name="/tests/">

…actReader.DataGenerator/CdacGenerator.cs …native/managed/cdac/gen/CdacGenerator.cssrc/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.DataGenerator/CdacGenerator.cs renamed to src/native/managed/cdac/gen/CdacGenerator.cs src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.DataGenerator/CdacGenerator.cs renamed to src/native/managed/cdac/gen/CdacGenerator.cs

@@ -36,8 +36,8 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
         // one helper is present but the other is not.
         IncrementalValueProvider<(bool EmitLayoutSet, bool EmitTypeNameResolver)> shouldEmitHelpers = context.CompilationProvider
             .Select(static (compilation, _) => (
-                EmitLayoutSet: compilation.GetTypeByMetadataName(LayoutSetSource.FullyQualifiedName) is null,
-                EmitTypeNameResolver: compilation.GetTypeByMetadataName(TypeNameResolverSource.FullyQualifiedName) is null));
+                EmitLayoutSet: !IsTypeAccessible(compilation, LayoutSetSource.FullyQualifiedName),
+                EmitTypeNameResolver: !IsTypeAccessible(compilation, TypeNameResolverSource.FullyQualifiedName)));
 
         context.RegisterSourceOutput(shouldEmitHelpers, static (ctx, flags) =>
         {
@@ -67,4 +67,22 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
         context.RegisterSourceOutput(models, static (spc, model) =>
             spc.AddSource(Emitter.HintNameFor(model), SourceText.From(Emitter.Emit(model), Encoding.UTF8)));
     }
+
+    /// <summary>
+    /// Returns true if the consuming compilation can already see a usable
+    /// <paramref name="metadataName"/> (declared here, or in a referenced assembly
+    /// and accessible).
+    /// </summary>
+    private static bool IsTypeAccessible(Compilation compilation, string metadataName)
+    {
+        foreach (INamedTypeSymbol type in compilation.GetTypesByMetadataName(metadataName))
+        {
+            if (compilation.IsSymbolAccessibleWithin(type, compilation.Assembly))
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
 }

…aContractReader.DataGenerator/Emitter.cs src/native/managed/cdac/gen/Emitter.cssrc/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.DataGenerator/Emitter.cs renamed to src/native/managed/cdac/gen/Emitter.cs src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.DataGenerator/Emitter.cs renamed to src/native/managed/cdac/gen/Emitter.cs

@@ -1,19 +1,22 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
+  <!--
+    cDAC source generator. Lives under gen/ so the auto-detect rule in
+    Directory.Build.props sets IsGeneratorProject=true, which imports
+    eng/generatorProjects.targets (defines GetAnalyzerPackFiles, used by
+    PackAsAnalyzer="true" in consuming packages).
+  -->
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
     <RootNamespace>Microsoft.Diagnostics.DataContractReader.DataGenerator</RootNamespace>
     <Nullable>enable</Nullable>
     <IsRoslynComponent>true</IsRoslynComponent>
-    <!-- Generator ships inline with the consuming assembly; not a standalone package. -->
+    <!-- Generator does not ship on its own; flows inside the Abstractions
+         transport package as an analyzer asset and is linked directly by
+         Contracts via ProjectReference OutputItemType="Analyzer". -->
     <IsShipping>false</IsShipping>
     <IsPackable>false</IsPackable>
-    <!-- Opt out of the repo-wide source-project flag so the DownlevelLibraryImportGenerator
-         isn't applied to this netstandard2.0 generator project (it would emit duplicate
-         polyfills for InteropServices types it doesn't actually need). -->
-    <IsSourceProject>false</IsSourceProject>
     <AnalyzerLanguage>cs</AnalyzerLanguage>
-    <EnforceExtendedAnalyzerRules>true</EnforceExtendedAnalyzerRules>
   </PropertyGroup>
 
   <ItemGroup>