rewrite mod assembly loading (#229)

This greatly simplifies mod loading, eliminates the .cache folders by loading assemblies in memory, ensures DLLs are loaded in leaf-to-root order, and reduces log verbosity. These changes should address a range of issues, notably #221 and #226.

1 files changed, 239 insertions, 0 deletions

diff --git a/src/StardewModdingAPI/Framework/AssemblyLoader.cs b/src/StardewModdingAPI/Framework/AssemblyLoader.cs
new file mode 100644
index 00000000..37f2764a
--- /dev/null
+++ b/src/StardewModdingAPI/Framework/AssemblyLoader.cs
@@ -0,0 +1,239 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Reflection;
+using Mono.Cecil;
+using Mono.Cecil.Cil;
+using Mono.Cecil.Rocks;
+using StardewModdingAPI.AssemblyRewriters;
+
+namespace StardewModdingAPI.Framework
+{
+    /// <summary>Preprocesses and loads mod assemblies.</summary>
+    internal class AssemblyLoader
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>Metadata for mapping assemblies to the current platform.</summary>
+        private readonly PlatformAssemblyMap AssemblyMap;
+
+        /// <summary>A type => assembly lookup for types which should be rewritten.</summary>
+        private readonly IDictionary<string, Assembly> TypeAssemblies;
+
+        /// <summary>Encapsulates monitoring and logging.</summary>
+        private readonly IMonitor Monitor;
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="targetPlatform">The current game platform.</param>
+        /// <param name="monitor">Encapsulates monitoring and logging.</param>
+        public AssemblyLoader(Platform targetPlatform, IMonitor monitor)
+        {
+            this.Monitor = monitor;
+            this.AssemblyMap = Constants.GetAssemblyMap(targetPlatform);
+
+            // generate type => assembly lookup for types which should be rewritten
+            this.TypeAssemblies = new Dictionary<string, Assembly>();
+            foreach (Assembly assembly in this.AssemblyMap.Targets)
+            {
+                ModuleDefinition module = this.AssemblyMap.TargetModules[assembly];
+                foreach (TypeDefinition type in module.GetTypes())
+                {
+                    if (!type.IsPublic)
+                        continue; // no need to rewrite
+                    if (type.Namespace.Contains("<"))
+                        continue; // ignore assembly metadata
+                    this.TypeAssemblies[type.FullName] = assembly;
+                }
+            }
+        }
+
+        /// <summary>Preprocess and load an assembly, writing modified assemblies to the cache folder if needed.</summary>
+        /// <param name="assemblyPath">The assembly file path.</param>
+        /// <returns>Returns the rewrite metadata for the preprocessed assembly.</returns>
+        public Assembly Load(string assemblyPath)
+        {
+            // get referenced local assemblies
+            AssemblyParseResult[] assemblies;
+            {
+                AssemblyDefinitionResolver resolver = new AssemblyDefinitionResolver();
+                assemblies = this.GetReferencedLocalAssemblies(new FileInfo(assemblyPath), new HashSet<string>(), resolver).ToArray();
+                if (!assemblies.Any())
+                    throw new InvalidOperationException($"Could not load '{assemblyPath}' because it doesn't exist.");
+                resolver.Add(assemblies.Select(p => p.Definition).ToArray());
+            }
+
+            // rewrite & load assemblies in leaf-to-root order
+            Assembly lastAssembly = null;
+            foreach (AssemblyParseResult assembly in assemblies)
+            {
+                this.Monitor.Log($"Loading {assembly.File.FullName}...", LogLevel.Trace);
+                this.RewriteAssembly(assembly.Definition);
+                using (MemoryStream outStream = new MemoryStream())
+                {
+                    assembly.Definition.Write(outStream);
+                    byte[] bytes = outStream.ToArray();
+                    lastAssembly = Assembly.Load(bytes);
+                }
+            }
+
+            // last assembly loaded is the root
+            return lastAssembly;
+        }
+
+        /// <summary>Resolve an assembly by its name.</summary>
+        /// <param name="name">The assembly name.</param>
+        /// <remarks>
+        /// This implementation returns the first loaded assembly which matches the short form of
+        /// the assembly name, to resolve assembly resolution issues when rewriting
+        /// assemblies (especially with Mono). Since this is meant to be called on <see cref="AppDomain.AssemblyResolve"/>,
+        /// the implicit assumption is that loading the exact assembly failed.
+        /// </remarks>
+        public Assembly ResolveAssembly(string name)
+        {
+            string shortName = name.Split(new[] { ',' }, 2).First(); // get simple name (without version and culture)
+            return AppDomain.CurrentDomain
+                .GetAssemblies()
+                .FirstOrDefault(p => p.GetName().Name == shortName);
+        }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /****
+        ** Assembly parsing
+        ****/
+        /// <summary>Get a list of referenced local assemblies starting from the mod assembly, ordered from leaf to root.</summary>
+        /// <param name="file">The assembly file to load.</param>
+        /// <param name="visitedAssemblyPaths">The assembly paths that should be skipped.</param>
+        /// <returns>Returns the rewrite metadata for the preprocessed assembly.</returns>
+        private IEnumerable<AssemblyParseResult> GetReferencedLocalAssemblies(FileInfo file, HashSet<string> visitedAssemblyPaths, IAssemblyResolver assemblyResolver)
+        {
+            // validate
+            if (file.Directory == null)
+                throw new InvalidOperationException($"Could not get directory from file path '{file.FullName}'.");
+            if (visitedAssemblyPaths.Contains(file.FullName))
+                yield break; // already visited
+            if (!file.Exists)
+                yield break; // not a local assembly
+            visitedAssemblyPaths.Add(file.FullName);
+
+            // read assembly
+            byte[] assemblyBytes = File.ReadAllBytes(file.FullName);
+            AssemblyDefinition assembly;
+            using (Stream readStream = new MemoryStream(assemblyBytes))
+                assembly = AssemblyDefinition.ReadAssembly(readStream, new ReaderParameters(ReadingMode.Deferred) { AssemblyResolver = assemblyResolver });
+
+            // yield referenced assemblies
+            foreach (AssemblyNameReference dependency in assembly.MainModule.AssemblyReferences)
+            {
+                FileInfo dependencyFile = new FileInfo(Path.Combine(file.Directory.FullName, $"{dependency.Name}.dll"));
+                foreach (AssemblyParseResult result in this.GetReferencedLocalAssemblies(dependencyFile, visitedAssemblyPaths, assemblyResolver))
+                    yield return result;
+            }
+
+            // yield assembly
+            yield return new AssemblyParseResult(file, assembly);
+        }
+
+        /****
+        ** Assembly rewriting
+        ****/
+        /// <summary>Rewrite the types referenced by an assembly.</summary>
+        /// <param name="assembly">The assembly to rewrite.</param>
+        /// <returns>Returns whether the assembly was modified.</returns>
+        private bool RewriteAssembly(AssemblyDefinition assembly)
+        {
+            ModuleDefinition module = assembly.Modules.Single(); // technically an assembly can have multiple modules, but none of the build tools (including MSBuild) support it; simplify by assuming one module
+
+            // remove old assembly references
+            bool shouldRewrite = false;
+            for (int i = 0; i < module.AssemblyReferences.Count; i++)
+            {
+                if (this.AssemblyMap.RemoveNames.Any(name => module.AssemblyReferences[i].Name == name))
+                {
+                    shouldRewrite = true;
+                    module.AssemblyReferences.RemoveAt(i);
+                    i--;
+                }
+            }
+            if (!shouldRewrite)
+                return false;
+
+            // add target assembly references
+            foreach (AssemblyNameReference target in this.AssemblyMap.TargetReferences.Values)
+                module.AssemblyReferences.Add(target);
+
+            // rewrite type scopes to use target assemblies
+            IEnumerable<TypeReference> typeReferences = module.GetTypeReferences().OrderBy(p => p.FullName);
+            foreach (TypeReference type in typeReferences)
+                this.ChangeTypeScope(type);
+
+            // rewrite incompatible methods
+            IMethodRewriter[] methodRewriters = Constants.GetMethodRewriters().ToArray();
+            foreach (MethodDefinition method in this.GetMethods(module))
+            {
+                // skip methods with no rewritable method
+                bool hasMethodToRewrite = method.Body.Instructions.Any(op => (op.OpCode == OpCodes.Call || op.OpCode == OpCodes.Callvirt) && methodRewriters.Any(rewriter => rewriter.ShouldRewrite((MethodReference)op.Operand)));
+                if (!hasMethodToRewrite)
+                    continue;
+
+                // rewrite method references
+                method.Body.SimplifyMacros();
+                ILProcessor cil = method.Body.GetILProcessor();
+                Instruction[] instructions = cil.Body.Instructions.ToArray();
+                foreach (Instruction op in instructions)
+                {
+                    if (op.OpCode == OpCodes.Call || op.OpCode == OpCodes.Callvirt)
+                    {
+                        IMethodRewriter rewriter = methodRewriters.FirstOrDefault(p => p.ShouldRewrite((MethodReference)op.Operand));
+                        if (rewriter != null)
+                        {
+                            MethodReference methodRef = (MethodReference)op.Operand;
+                            rewriter.Rewrite(module, cil, op, methodRef, this.AssemblyMap);
+                        }
+                    }
+                }
+                method.Body.OptimizeMacros();
+            }
+            return true;
+        }
+
+        /// <summary>Get the correct reference to use for compatibility with the current platform.</summary>
+        /// <param name="type">The type reference to rewrite.</param>
+        private void ChangeTypeScope(TypeReference type)
+        {
+            // check skip conditions
+            if (type == null || type.FullName.StartsWith("System."))
+                return;
+
+            // get assembly
+            Assembly assembly;
+            if (!this.TypeAssemblies.TryGetValue(type.FullName, out assembly))
+                return;
+
+            // replace scope
+            AssemblyNameReference assemblyRef = this.AssemblyMap.TargetReferences[assembly];
+            type.Scope = assemblyRef;
+        }
+
+        /// <summary>Get all methods in a module.</summary>
+        /// <param name="module">The module to search.</param>
+        private IEnumerable<MethodDefinition> GetMethods(ModuleDefinition module)
+        {
+            return (
+                from type in module.GetTypes()
+                where type.HasMethods
+                from method in type.Methods
+                where method.HasBody
+                select method
+            );
+        }
+    }
+}