Fix #2068: ILSpy can't find referenced library even though it's open

ICSharpCode.Decompiler/Metadata/DotNetCorePathFinder.cs

@@ -61,29 +61,30 @@ namespace ICSharpCode.Decompiler.Metadata
 		};
 
 		readonly DotNetCorePackageInfo[] packages;
-		ISet<string> packageBasePaths = new HashSet<string>(StringComparer.Ordinal);
-		readonly Version version;
+		readonly List<string> searchPaths = new List<string>();
+		readonly List<string> packageBasePaths = new List<string>();
+		readonly Version targetFrameworkVersion;
 		readonly string dotnetBasePath = FindDotNetExeDirectory();
 
-		public DotNetCorePathFinder(Version version)
+		public DotNetCorePathFinder(Version targetFrameworkVersion)
 		{
-			this.version = version;
+			this.targetFrameworkVersion = targetFrameworkVersion;
 		}
 
-		public DotNetCorePathFinder(string parentAssemblyFileName, string targetFrameworkIdString, TargetFrameworkIdentifier targetFramework, Version version, ReferenceLoadInfo loadInfo = null)
+		public DotNetCorePathFinder(string parentAssemblyFileName, string targetFrameworkIdString, TargetFrameworkIdentifier targetFramework, Version targetFrameworkVersion, ReferenceLoadInfo loadInfo = null)
 		{
 			string assemblyName = Path.GetFileNameWithoutExtension(parentAssemblyFileName);
 			string basePath = Path.GetDirectoryName(parentAssemblyFileName);
-			this.version = version;
+			this.targetFrameworkVersion = targetFrameworkVersion;
 
 			if (targetFramework == TargetFrameworkIdentifier.NETStandard) {
 				// .NET Standard 2.1 is implemented by .NET Core 3.0 or higher
-				if (version.Major == 2 && version.Minor == 1) {
-					this.version = new Version(3, 0, 0);
+				if (targetFrameworkVersion.Major == 2 && targetFrameworkVersion.Minor == 1) {
+					this.targetFrameworkVersion = new Version(3, 0, 0);
 				}
 			}
 
-			packageBasePaths.Add(basePath);
+			searchPaths.Add(basePath);
 
 			var depsJsonFileName = Path.Combine(basePath, $"{assemblyName}.deps.json");
 			if (File.Exists(depsJsonFileName)) {
@@ -106,17 +107,17 @@ namespace ICSharpCode.Decompiler.Metadata
 
 		public void AddSearchDirectory(string path)
 		{
-			this.packageBasePaths.Add(path);
+			this.searchPaths.Add(path);
 		}
 
 		public void RemoveSearchDirectory(string path)
 		{
-			this.packageBasePaths.Remove(path);
+			this.searchPaths.Remove(path);
 		}
 
 		public string TryResolveDotNetCore(IAssemblyReference name)
 		{
-			foreach (var basePath in packageBasePaths) {
+			foreach (var basePath in searchPaths.Concat(packageBasePaths)) {
 				if (File.Exists(Path.Combine(basePath, name.Name + ".dll"))) {
 					return Path.Combine(basePath, name.Name + ".dll");
 				} else if (File.Exists(Path.Combine(basePath, name.Name + ".exe"))) {
@@ -124,7 +125,7 @@ namespace ICSharpCode.Decompiler.Metadata
 				}
 			}
 
-			return FallbackToDotNetSharedDirectory(name, version);
+			return FallbackToDotNetSharedDirectory(name);
 		}
 
 		internal string GetReferenceAssemblyPath(string targetFramework)
@@ -169,7 +170,7 @@ namespace ICSharpCode.Decompiler.Metadata
 			}
 		}
 
-		string FallbackToDotNetSharedDirectory(IAssemblyReference name, Version version)
+		string FallbackToDotNetSharedDirectory(IAssemblyReference name)
 		{
 			if (dotnetBasePath == null)
 				return null;
@@ -177,7 +178,7 @@ namespace ICSharpCode.Decompiler.Metadata
 			foreach (var basePath in basePaths) {
 				if (!Directory.Exists(basePath))
 					continue;
-				var closestVersion = GetClosestVersionFolder(basePath, version);
+				var closestVersion = GetClosestVersionFolder(basePath, targetFrameworkVersion);
 				if (File.Exists(Path.Combine(basePath, closestVersion, name.Name + ".dll"))) {
 					return Path.Combine(basePath, closestVersion, name.Name + ".dll");
 				} else if (File.Exists(Path.Combine(basePath, closestVersion, name.Name + ".exe"))) {
@@ -189,15 +190,17 @@ namespace ICSharpCode.Decompiler.Metadata
 
 		static string GetClosestVersionFolder(string basePath, Version version)
 		{
-			string result = null;
-			foreach (var folder in new DirectoryInfo(basePath).GetDirectories().Select(d => ConvertToVersion(d.Name)).Where(v => v.Item1 != null).OrderByDescending(v => v.Item1)) {
-				if (folder.Item1 >= version)
-					result = folder.Item2;
+			var foundVersions = new DirectoryInfo(basePath).GetDirectories()
+				.Select(d => ConvertToVersion(d.Name))
+				.Where(v => v.version != null);
+			foreach (var folder in foundVersions.OrderBy(v => v.Item1)) {
+				if (folder.version >= version)
+					return folder.directoryName;
 			}
-			return result ?? version.ToString();
+			return version.ToString();
 		}
 
-		internal static (Version, string) ConvertToVersion(string name)
+		internal static (Version version, string directoryName) ConvertToVersion(string name)
 		{
 			string RemoveTrailingVersionInfo()
 			{

ICSharpCode.Decompiler/Metadata/UniversalAssemblyResolver.cs

@@ -327,9 +327,13 @@ namespace ICSharpCode.Decompiler.Metadata
 			if (assembly != null)
 				return assembly;
 
-			assembly = SearchDirectory(name, framework_dirs);
-			if (assembly != null)
-				return assembly;
+			// when decompiling assemblies that target frameworks prior to 4.0, we can fall back to the 4.0 assemblies in case the target framework is not installed.
+			// but when looking for Microsoft.Build.Framework, Version=15.0.0.0 we should not use the version 4.0 assembly here so that the LoadedAssembly logic can instead fall back to version 15.1.0.0
+			if (name.Version <= new Version(4, 0, 0, 0)) {
+				assembly = SearchDirectory(name, framework_dirs);
+				if (assembly != null)
+					return assembly;
+			}
 
 			if (throwOnError)
 				throw new AssemblyResolutionException(name);

ILSpy/LoadedAssembly.cs

@@ -20,6 +20,7 @@ using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
+using System.Linq;
 using System.Reflection.Metadata;
 using System.Reflection.PortableExecutable;
 using System.Runtime.CompilerServices;
@@ -31,6 +32,7 @@ using ICSharpCode.Decompiler.Metadata;
 using ICSharpCode.Decompiler.PdbProvider;
 using ICSharpCode.Decompiler.TypeSystem;
 using ICSharpCode.Decompiler.TypeSystem.Implementation;
+using ICSharpCode.Decompiler.Util;
 using ICSharpCode.ILSpy.Options;
 
 namespace ICSharpCode.ILSpy
@@ -318,6 +320,17 @@ namespace ICSharpCode.ILSpy
 		static readonly Dictionary<string, LoadedAssembly> loadingAssemblies = new Dictionary<string, LoadedAssembly>();
 		MyUniversalResolver universalResolver;
 
+		/// <summary>
+		/// 1) try to find exact match by tfm + full asm name in loaded assemblies
+		/// 2) try to find match in search paths
+		/// 3) if a.deps.json is found: search %USERPROFILE%/.nuget/packages/* as well
+		/// 4) look in /dotnet/shared/{runtime-pack}/{closest-version}
+		/// 5) if the version is retargetable or all zeros or ones, search C:\Windows\Microsoft.NET\Framework64\v4.0.30319
+		/// 6) For "mscorlib.dll" we use the exact same assembly with which ILSpy runs
+		/// 7) Search the GAC
+		/// 8) search C:\Windows\Microsoft.NET\Framework64\v4.0.30319
+		/// 9) try to find match by asm name (no tfm/version) in loaded assemblies
+		/// </summary>
 		LoadedAssembly LookupReferencedAssemblyInternal(IAssemblyReference fullName, bool isWinRT, string tfm)
 		{
 			string key = tfm + ";" + (isWinRT ? fullName.Name : fullName.FullName);
@@ -359,8 +372,29 @@ namespace ICSharpCode.ILSpy
 					LoadedAssemblyReferencesInfo.AddMessage(fullName.ToString(), MessageKind.Info, "Success - Loading from: " + file);
 					asm = new LoadedAssembly(assemblyList, file) { IsAutoLoaded = true };
 				} else {
-					LoadedAssemblyReferencesInfo.AddMessageOnce(fullName.ToString(), MessageKind.Error, "Could not find reference: " + fullName);
-					return null;
+					var candidates = new List<(LoadedAssembly assembly, Version version)>();
+
+					foreach (LoadedAssembly loaded in assemblyList.GetAssemblies()) {
+						var module = loaded.GetPEFileOrNull();
+						var reader = module?.Metadata;
+						if (reader == null || !reader.IsAssembly) continue;
+						var asmDef = reader.GetAssemblyDefinition();
+						var asmDefName = reader.GetString(asmDef.Name);
+						if (fullName.Name.Equals(asmDefName, StringComparison.OrdinalIgnoreCase)) {
+							candidates.Add((loaded, asmDef.Version));
+						}
+					}
+
+					if (candidates.Count == 0) {
+						LoadedAssemblyReferencesInfo.AddMessageOnce(fullName.ToString(), MessageKind.Error, "Could not find reference: " + fullName);
+						return null;
+					}
+
+					candidates.SortBy(c => c.version);
+
+					var bestCandidate = candidates.FirstOrDefault(c => c.version >= fullName.Version).assembly ?? candidates.Last().assembly;
+					LoadedAssemblyReferencesInfo.AddMessageOnce(fullName.ToString(), MessageKind.Info, "Success - Found in Assembly List with different TFM or version: " + bestCandidate.fileName);
+					return bestCandidate;
 				}
 				loadingAssemblies.Add(file, asm);
 			}