ResultProvider: Consume DkmClrModuleInstance.GetMetaDataImportHolder (#…

…76395)

Previous to this change, the ResultProvider would use `DkmClrModuleInstance.GetMetaDataImport`, but did NOT use Marshal.ReleaseComObject on the result. This could result in locked files if the RCW took a long time to be finalized.

This PR switches to use a new `GetMetaDataImportHolder` API that adds an IDisposable wrapper struct to take care of this cleanup.

This PR requires VS 17.13 Build 35612.30 or newer.

eng/Directory.Packages.props

@@ -122,8 +122,8 @@
       VS Debugger
     -->
     <PackageVersion Include="Microsoft.VisualStudio.Debugger.Contracts" Version="17.13.0-beta.24561.1" />
-    <PackageVersion Include="Microsoft.VisualStudio.Debugger.Engine-implementation" Version="17.13.1110101-preview" />
-    <PackageVersion Include="Microsoft.VisualStudio.Debugger.Metadata-implementation" Version="17.13.1110101-preview" />
+    <PackageVersion Include="Microsoft.VisualStudio.Debugger.Engine-implementation" Version="17.13.1121201-preview" />
+    <PackageVersion Include="Microsoft.VisualStudio.Debugger.Metadata-implementation" Version="17.13.1121201-preview" />
 
     <!--
       VS .NET Runtime

src/ExpressionEvaluator/Core/Source/ResultProvider/Formatter.cs

@@ -182,18 +182,18 @@ string IDkmClrFullNameProvider2.GetClrNameForLocalVariable(DkmInspectionContext
 
         string IDkmClrFullNameProvider2.GetClrNameForField(DkmInspectionContext inspectionContext, DkmClrModuleInstance moduleInstance, int fieldToken)
         {
-            var import = (IMetadataImport)moduleInstance.GetMetaDataImport();
+            using var importHolder = moduleInstance.GetMetaDataImportHolder();
 
             // Just get some of information about properties. Get rest later only if needed.
-            int hr = import.GetFieldProps(fieldToken, out _, null, 0, out var nameLength, out _, out _, out _, out _, out _, out _);
+            int hr = importHolder.Value.GetFieldProps(fieldToken, out _, null, 0, out var nameLength, out _, out _, out _, out _, out _, out _);
             const int S_OK = 0;
             if (hr != S_OK)
             {
                 throw new ArgumentException("Invalid field token.", nameof(fieldToken));
             }
 
             var sb = new StringBuilder(nameLength);
-            hr = import.GetFieldProps(fieldToken, out _, sb, sb.Capacity, out _, out _, out _, out _, out _, out _, out _);
+            hr = importHolder.Value.GetFieldProps(fieldToken, out _, sb, sb.Capacity, out _, out _, out _, out _, out _, out _, out _);
             if (hr != S_OK)
             {
                 throw new DkmException((DkmExceptionCode)hr);

src/ExpressionEvaluator/Core/Test/ResultProvider/Debugger/Engine/DkmClrModuleInstance.cs

@@ -66,7 +66,7 @@ internal int ResolveTypeNameFailures
             get { return _resolveTypeNameFailures; }
         }
 
-        public object GetMetaDataImport() => new MetadataImportMock(Assembly);
+        public DkmMetadataImportHolder GetMetaDataImportHolder() => new DkmMetadataImportHolder(new MetadataImportMock(Assembly));
 
         private class MetadataImportMock : IMetadataImport
         {

src/ExpressionEvaluator/Core/Test/ResultProvider/Debugger/Engine/DkmMetadataImportHolder.cs

@@ -0,0 +1,38 @@
+// 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 Microsoft.MetadataReader;
+
+#nullable enable
+
+namespace Microsoft.VisualStudio.Debugger.Clr
+{
+    /// <summary>
+    /// Wrapper around a <see cref="Microsoft.MetadataReader.IMetadataImport"/> interface
+    /// reference that provides a easy way to release the reference to the underlying
+    /// COM object. Instances of this struct should always be disposed.
+    /// </summary>
+    public readonly struct DkmMetadataImportHolder : IDisposable
+    {
+        /// <summary>
+        /// The underlying IMetaDataImport interface reference
+        /// </summary>
+        public IMetadataImport Value { get; }
+
+        /// <summary>
+        /// Creates a new instance of <see cref="DkmMetadataImportHolder"/>.
+        /// </summary>
+        /// <param name="value">[In] Implementation of IMetadataImport to wrap</param>
+        public DkmMetadataImportHolder(IMetadataImport value)
+        {
+            this.Value = value ?? throw new ArgumentNullException(nameof(value));
+        }
+
+        void IDisposable.Dispose()
+        {
+            // Mock implementation does nothing
+        }
+    }
+}