Make creating CSharpDecompiler easier.

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -209,6 +209,11 @@ namespace ICSharpCode.Decompiler.CSharp
 			get { return astTransforms; }
 		}
 
+		public CSharpDecompiler(string fileName, DecompilerSettings settings)
+			: this(CreateTypeSystemFromFile(fileName, settings), settings)
+		{
+		}
+
 		public CSharpDecompiler(string fileName, IAssemblyResolver assemblyResolver, DecompilerSettings settings)
 			: this(LoadPEFile(fileName, settings), assemblyResolver, settings)
 		{
@@ -340,6 +345,15 @@ namespace ICSharpCode.Decompiler.CSharp
 			);
 		}
 
+		static DecompilerTypeSystem CreateTypeSystemFromFile(string fileName, DecompilerSettings settings)
+		{
+			var file = LoadPEFile(fileName, settings);
+			var resolver = new UniversalAssemblyResolver(fileName, settings.ThrowOnAssemblyResolveErrors,
+				file.Reader.DetectTargetFrameworkId(),
+				settings.LoadInMemory ? PEStreamOptions.PrefetchMetadata : PEStreamOptions.Default);
+			return new DecompilerTypeSystem(file, resolver);
+		}
+
 		TypeSystemAstBuilder CreateAstBuilder(ITypeResolveContext decompilationContext)
 		{
 			var typeSystemAstBuilder = new TypeSystemAstBuilder();

ICSharpCode.Decompiler/Metadata/PEFile.cs

@@ -47,9 +47,8 @@ namespace ICSharpCode.Decompiler.Metadata
 		public PEReader Reader { get; }
 		public MetadataReader Metadata { get; }
 
-		public PEFile(string fileName, bool metadataOnly = false)
-			: this(fileName, new PEReader(new FileStream(fileName, FileMode.Open, FileAccess.Read),
-				metadataOnly ? PEStreamOptions.PrefetchMetadata : PEStreamOptions.PrefetchEntireImage))
+		public PEFile(string fileName, PEStreamOptions options = PEStreamOptions.Default)
+			: this(fileName, new PEReader(new FileStream(fileName, FileMode.Open, FileAccess.Read), options))
 		{
 		}