Move WebcilReader reflection to a helper; add lazy initialization

src/libraries/Microsoft.NET.WebAssembly.Webcil/src/Webcil/WebcilReader.Reflection.cs

@@ -0,0 +1,59 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Immutable;
+using System.IO;
+using System.Reflection;
+using System.Runtime.InteropServices;
+
+using System.Reflection.Metadata;
+using System.Reflection.PortableExecutable;
+
+namespace Microsoft.NET.WebAssembly.Webcil;
+
+
+public sealed partial class WebcilReader
+{
+
+    // Helpers to call into System.Reflection.Metadata internals
+    internal static class Reflection
+    {
+        private static Lazy<MethodInfo> _readUtf8NullTerminated = new Lazy<MethodInfo>(() =>
+        {
+            var mi = typeof(BlobReader).GetMethod("ReadUtf8NullTerminated", BindingFlags.NonPublic | BindingFlags.Instance);
+            if (mi == null)
+            {
+                throw new InvalidOperationException("Could not find BlobReader.ReadUtf8NullTerminated");
+            }
+            return mi;
+        });
+
+        internal static string? ReadUtf8NullTerminated(BlobReader reader) => (string?)_readUtf8NullTerminated.Value.Invoke(reader, null);
+
+        private static Lazy<ConstructorInfo> _codeViewDebugDirectoryDataCtor = new Lazy<ConstructorInfo>(() =>
+        {
+            var types = new Type[] { typeof(Guid), typeof(int), typeof(string) };
+            var mi = typeof(CodeViewDebugDirectoryData).GetConstructor(BindingFlags.NonPublic | BindingFlags.Instance, null, types, null);
+            if (mi == null)
+            {
+                throw new InvalidOperationException("Could not find CodeViewDebugDirectoryData constructor");
+            }
+            return mi;
+        });
+
+        internal static CodeViewDebugDirectoryData MakeCodeViewDebugDirectoryData(Guid guid, int age, string path) => (CodeViewDebugDirectoryData)_codeViewDebugDirectoryDataCtor.Value.Invoke(new object[] { guid, age, path });
+
+        private static Lazy<ConstructorInfo> _pdbChecksumDebugDirectoryDataCtor = new Lazy<ConstructorInfo>(() =>
+        {
+            var types = new Type[] { typeof(string), typeof(ImmutableArray<byte>) };
+            var mi = typeof(PdbChecksumDebugDirectoryData).GetConstructor(BindingFlags.NonPublic | BindingFlags.Instance, null, types, null);
+            if (mi == null)
+            {
+                throw new InvalidOperationException("Could not find PdbChecksumDebugDirectoryData constructor");
+            }
+            return mi;
+        });
+        internal static PdbChecksumDebugDirectoryData MakePdbChecksumDebugDirectoryData(string algorithmName, ImmutableArray<byte> checksum) => (PdbChecksumDebugDirectoryData)_pdbChecksumDebugDirectoryDataCtor.Value.Invoke(new object[] { algorithmName, checksum });
+    }
+}

src/libraries/Microsoft.NET.WebAssembly.Webcil/src/Webcil/WebcilReader.cs

@@ -13,7 +13,7 @@
 namespace Microsoft.NET.WebAssembly.Webcil;
 
 
-public sealed class WebcilReader : IDisposable
+public sealed partial class WebcilReader : IDisposable
 {
     // WISH:
     // This should be implemented in terms of System.Reflection.Internal.MemoryBlockProvider like the PEReader,
@@ -219,37 +219,11 @@ private static CodeViewDebugDirectoryData DecodeCodeViewDebugDirectoryData(BlobR
         return MakeCodeViewDebugDirectoryData(guid, age, path);
     }
 
-    private static string? ReadUtf8NullTerminated(BlobReader reader)
-    {
-        var mi = typeof(BlobReader).GetMethod("ReadUtf8NullTerminated", BindingFlags.NonPublic | BindingFlags.Instance);
-        if (mi == null)
-        {
-            throw new InvalidOperationException("Could not find BlobReader.ReadUtf8NullTerminated");
-        }
-        return (string?)mi.Invoke(reader, null);
-    }
+    private static string? ReadUtf8NullTerminated(BlobReader reader) => Reflection.ReadUtf8NullTerminated(reader);
 
-    private static CodeViewDebugDirectoryData MakeCodeViewDebugDirectoryData(Guid guid, int age, string path)
-    {
-        var types = new Type[] { typeof(Guid), typeof(int), typeof(string) };
-        var mi = typeof(CodeViewDebugDirectoryData).GetConstructor(BindingFlags.NonPublic | BindingFlags.Instance, null, types, null);
-        if (mi == null)
-        {
-            throw new InvalidOperationException("Could not find CodeViewDebugDirectoryData constructor");
-        }
-        return (CodeViewDebugDirectoryData)mi.Invoke(new object[] { guid, age, path });
-    }
+    private static CodeViewDebugDirectoryData MakeCodeViewDebugDirectoryData(Guid guid, int age, string path) => Reflection.MakeCodeViewDebugDirectoryData(guid, age, path);
 
-    private static PdbChecksumDebugDirectoryData MakePdbChecksumDebugDirectoryData(string algorithmName, ImmutableArray<byte> checksum)
-    {
-        var types = new Type[] { typeof(string), typeof(ImmutableArray<byte>) };
-        var mi = typeof(PdbChecksumDebugDirectoryData).GetConstructor(BindingFlags.NonPublic | BindingFlags.Instance, null, types, null);
-        if (mi == null)
-        {
-            throw new InvalidOperationException("Could not find PdbChecksumDebugDirectoryData constructor");
-        }
-        return (PdbChecksumDebugDirectoryData)mi.Invoke(new object[] { algorithmName, checksum });
-    }
+    private static PdbChecksumDebugDirectoryData MakePdbChecksumDebugDirectoryData(string algorithmName, ImmutableArray<byte> checksum) => Reflection.MakePdbChecksumDebugDirectoryData(algorithmName, checksum);
 
     public MetadataReaderProvider ReadEmbeddedPortablePdbDebugDirectoryData(DebugDirectoryEntry entry)
     {