Use McMaster.NETCore.Plugins for assembly loading

* Tasks deprecate `GeneratorAssemblySearchPaths` usage
* Tasks use `CodeGenerationRoslynPlugin` Item instead, which contains
  concrete assembly paths
* Engine targets `netcoreapp2.0` to reference McMaster package
* Tests use Amadevus.RecordGenerator NuGet generator for
  back-compat checks
* Tests.Generators use Bogus NuGet for NuGet dependency resolution check

src/CodeGeneration.Roslyn.BuildTime/build/CodeGeneration.Roslyn.BuildTime.targets

@@ -8,6 +8,8 @@
       PrepareGenerateCodeFromAttributes;
       GenerateCodeFromAttributesCore
     </GenerateCodeFromAttributesDependsOn>
+    <CgrUrl>https://github.com/AArnott/CodeGeneration.Roslyn</CgrUrl>
+    <WarnOnGeneratorAssemblySearchPaths Condition=" '$(WarnOnGeneratorAssemblySearchPaths)' == '' ">true</WarnOnGeneratorAssemblySearchPaths>
   </PropertyGroup>
 
   <Target
@@ -22,7 +24,21 @@
         Include="@(Compile)"
         Condition=" '%(Compile.Generator)' == 'MSBuild:GenerateCodeFromAttributes' " />
       <DefineConstantsItems Include="$(DefineConstants)" />
+      <!-- Map GeneratorAssemblySearchPaths to actual DLLs until support is removed -->
+      <GeneratorAssemblySearchPaths
+        Update="@(GeneratorAssemblySearchPaths)"
+        PathWithTrailingSlash="$([MSBuild]::EnsureTrailingSlash(%(Identity)))" />
+      <_GeneratorAssemblySearchPathsResolved
+        Include="%(GeneratorAssemblySearchPaths.PathWithTrailingSlash)*.dll" />
+      <!-- Include resolved DLLs into CodeGenerationRoslynPlugin -->
+      <CodeGenerationRoslynPlugin
+        Include="@(_GeneratorAssemblySearchPathsResolved)"
+        Condition="Exists('%(Identity)')" />
     </ItemGroup>
+    <!-- Warning for the time GeneratorAssemblySearchPaths are deprecated but supported -->
+    <Warning
+      Text="Using GeneratorAssemblySearchPaths is deprecated, please use CodeGenerationRoslynPlugin ItemGroup. See $(CgrUrl) for more info. Disable this warning by setting 'WarnOnGeneratorAssemblySearchPaths' property to false."
+      Condition=" '@(GeneratorAssemblySearchPaths)' != '' and '$(WarnOnGeneratorAssemblySearchPaths)' != 'false' " />
     <PropertyGroup>
       <GenerateCodeFromAttributesToolPathOverride
         Condition="'$(GenerateCodeFromAttributesToolPathOverride)' == ''">codegen</GenerateCodeFromAttributesToolPathOverride>
@@ -32,7 +48,7 @@
       <_CodeGenToolResponseFileLines>
         @(ReferencePath->'-r;%(Identity)');
         @(DefineConstantsItems->'-d;%(Identity)');
-        @(GeneratorAssemblySearchPaths->'--generatorSearchPath;%(Identity)');
+        @(CodeGenerationRoslynPlugin->'--plugin;%(Identity)');
         --out;
         $(IntermediateOutputPath);
         --projectDir;
@@ -72,7 +88,7 @@
       Condition="'$(_GenerateCodeToolVersionExitCode)' == '0'" />
     <Error
       Code="CGR1001"
-      Text="CodeGeneration.Roslyn.Tool (dotnet-codegen) is not available, code generation won't run. Please check https://github.com/AArnott/CodeGeneration.Roslyn for usage instructions."
+      Text="CodeGeneration.Roslyn.Tool (dotnet-codegen) is not available, code generation won't run. Please check $(CgrUrl) for usage instructions."
       Condition="'$(_GenerateCodeToolVersionExitCode)' != '0'" />
     <ItemGroup>
       <FileWrites Include="$(_CodeGenToolResponseFileFullPath)" />
@@ -86,7 +102,7 @@
       StandardOutputImportance="normal" />
     <Error
       Code="CGR1000"
-      Text="CodeGeneration.Roslyn.Tool (dotnet-codegen) failed to generate the list of generated files. The tool didn't run successfully. Please check https://github.com/AArnott/CodeGeneration.Roslyn for usage instructions."
+      Text="CodeGeneration.Roslyn.Tool (dotnet-codegen) failed to generate the list of generated files. The tool didn't run successfully. Please check $(CgrUrl) for usage instructions."
       Condition="Exists('$(_CodeGenToolGeneratedFileListFullPath)') != 'true'" />
     <ReadLinesFromFile File="$(_CodeGenToolGeneratedFileListFullPath)">
       <Output TaskParameter="Lines" ItemName="CodeGenerationRoslynOutput_Compile"/>

src/CodeGeneration.Roslyn.Engine/CodeGeneration.Roslyn.Engine.csproj

@@ -1,13 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netstandard2.0</TargetFramework>
+    <TargetFramework>netcoreapp2.0</TargetFramework>
     <Description>The engine of source code generation used by `dotnet-codegen` tool.</Description>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.DependencyModel" Version="2.0.4" />
-    <PackageReference Include="System.Runtime.Loader" Version="4.3.0" />
+    <PackageReference Include="McMaster.NETCore.Plugins" Version="0.2.4" />
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="[$(RoslynNugetVersion)]" />
     <PackageReference Include="Validation" Version="2.4.18" />
   </ItemGroup>

src/CodeGeneration.Roslyn.Engine/CompilationGenerator.cs

@@ -8,16 +8,14 @@ namespace CodeGeneration.Roslyn.Engine
     using System.IO;
     using System.Linq;
     using System.Reflection;
-    using System.Runtime.Loader;
     using System.Text;
     using System.Threading;
     using System.Threading.Tasks;
+    using McMaster.NETCore.Plugins;
     using Microsoft.CodeAnalysis;
     using Microsoft.CodeAnalysis.CSharp;
     using Microsoft.CodeAnalysis.CSharp.Syntax;
     using Microsoft.CodeAnalysis.Text;
-    using Microsoft.Extensions.DependencyModel;
-    using Microsoft.Extensions.DependencyModel.Resolution;
     using Validation;
 
     /// <summary>
@@ -28,16 +26,12 @@ public class CompilationGenerator
     {
         private const string InputAssembliesIntermediateOutputFileName = "CodeGeneration.Roslyn.InputAssemblies.txt";
         private const int ProcessCannotAccessFileHR = unchecked((int)0x80070020);
-        private static readonly HashSet<string> AllowedAssemblyExtensions = new HashSet<string>(StringComparer.OrdinalIgnoreCase) { ".dll" };
 
         private readonly List<string> emptyGeneratedFiles = new List<string>();
         private readonly List<string> generatedFiles = new List<string>();
         private readonly List<string> additionalWrittenFiles = new List<string>();
         private readonly List<string> loadedAssemblies = new List<string>();
-        private readonly Dictionary<string, Assembly> assembliesByPath = new Dictionary<string, Assembly>();
-        private readonly HashSet<string> directoriesWithResolver = new HashSet<string>();
-        private CompositeCompilationAssemblyResolver assemblyResolver;
-        private DependencyContext dependencyContext;
+        private readonly Dictionary<string, (PluginLoader loader, Assembly assembly)> plugins = new Dictionary<string, (PluginLoader, Assembly)>(StringComparer.OrdinalIgnoreCase);
 
         /// <summary>
         /// Gets or sets the list of paths of files to be compiled.
@@ -55,9 +49,9 @@ public class CompilationGenerator
         public IEnumerable<string> PreprocessorSymbols { get; set; }
 
         /// <summary>
-        /// Gets or sets the paths to directories to search for generator assemblies.
+        /// Gets or sets the paths to plugins.
         /// </summary>
-        public IReadOnlyList<string> GeneratorAssemblySearchPaths { get; set; }
+        public IReadOnlyList<string> PluginPaths { get; set; } = new List<string>();
 
         /// <summary>
         /// Gets or sets the path to the directory that contains generated source files.
@@ -84,23 +78,6 @@ public class CompilationGenerator
         /// </summary>
         public string ProjectDirectory { get; set; }
 
-        /// <summary>
-        /// Initializes a new instance of the <see cref="CompilationGenerator"/> class
-        /// with default dependency resolution and loading.
-        /// </summary>
-        public CompilationGenerator()
-        {
-            this.assemblyResolver = new CompositeCompilationAssemblyResolver(new ICompilationAssemblyResolver[]
-            {
-                new ReferenceAssemblyPathResolver(),
-                new PackageCompilationAssemblyResolver(),
-            });
-            this.dependencyContext = DependencyContext.Default;
-
-            var loadContext = AssemblyLoadContext.GetLoadContext(this.GetType().GetTypeInfo().Assembly);
-            loadContext.Resolving += this.ResolveAssembly;
-        }
-
         /// <summary>
         /// Runs the code generation as configured using this instance's properties.
         /// </summary>
@@ -110,8 +87,8 @@ public void Generate(IProgress<Diagnostic> progress = null, CancellationToken ca
         {
             Verify.Operation(this.Compile != null, $"{nameof(Compile)} must be set first.");
             Verify.Operation(this.ReferencePath != null, $"{nameof(ReferencePath)} must be set first.");
+            Verify.Operation(this.PluginPaths != null, $"{nameof(PluginPaths)} must be set first.");
             Verify.Operation(this.IntermediateOutputDirectory != null, $"{nameof(IntermediateOutputDirectory)} must be set first.");
-            Verify.Operation(this.GeneratorAssemblySearchPaths != null, $"{nameof(GeneratorAssemblySearchPaths)} must be set first.");
 
             var compilation = this.CreateCompilation(cancellationToken);
 
@@ -146,7 +123,7 @@ public void Generate(IProgress<Diagnostic> progress = null, CancellationToken ca
                                     compilation,
                                     inputSyntaxTree,
                                     this.ProjectDirectory,
-                                    this.LoadAssembly,
+                                    this.LoadPlugin,
                                     progress).GetAwaiter().GetResult();
 
                                 var outputText = generatedSyntaxTree.GetText(cancellationToken);
@@ -195,79 +172,31 @@ public void Generate(IProgress<Diagnostic> progress = null, CancellationToken ca
             }
         }
 
-        private Assembly LoadAssembly(string path)
+        private Assembly LoadPlugin(AssemblyName assemblyName)
         {
-            if (this.assembliesByPath.ContainsKey(path))
-                return this.assembliesByPath[path];
-
-            var loadContext = AssemblyLoadContext.GetLoadContext(this.GetType().GetTypeInfo().Assembly);
-            var assembly = loadContext.LoadFromAssemblyPath(path);
-
-            var newDependencyContext = DependencyContext.Load(assembly);
-            if (newDependencyContext != null)
-                this.dependencyContext = this.dependencyContext.Merge(newDependencyContext);
-            var basePath = Path.GetDirectoryName(path);
-            if (!this.directoriesWithResolver.Contains(basePath))
+            if (plugins.TryGetValue(assemblyName.Name, out var cached))
             {
-                this.assemblyResolver = new CompositeCompilationAssemblyResolver(new ICompilationAssemblyResolver[]
-                {
-                    new AppBaseCompilationAssemblyResolver(basePath),
-                    this.assemblyResolver,
-                });
-                this.directoriesWithResolver.Add(basePath);
+                Logger.Info($"CGR retrieved cached plugin for {assemblyName.Name}: {cached.assembly.Location}");
+                return cached.assembly;
             }
-
-            this.assembliesByPath.Add(path, assembly);
-            return assembly;
-        }
-
-        private Assembly ResolveAssembly(AssemblyLoadContext context, AssemblyName name)
-        {
-            var library = FindMatchingLibrary(this.dependencyContext.RuntimeLibraries, name);
-            if (library == null)
-                return null;
-            var wrapper = new CompilationLibrary(
-                library.Type,
-                library.Name,
-                library.Version,
-                library.Hash,
-                library.RuntimeAssemblyGroups.SelectMany(g => g.AssetPaths),
-                library.Dependencies,
-                library.Serviceable);
-
-            var assemblyPaths = new List<string>();
-            this.assemblyResolver.TryResolveAssemblyPaths(wrapper, assemblyPaths);
-
-            if (assemblyPaths.Count == 0)
+            var pluginPath = PluginPaths.FirstOrDefault(IsRequestedPlugin);
+            if (pluginPath is null)
             {
-                var matches = from refAssemblyPath in this.ReferencePath
-                              where Path.GetFileNameWithoutExtension(refAssemblyPath).Equals(name.Name, StringComparison.OrdinalIgnoreCase)
-                              select context.LoadFromAssemblyPath(refAssemblyPath);
-                return matches.FirstOrDefault();
+                Logger.Info($"CGR didn't find plugin for {assemblyName.Name}");
+                return null;
             }
+            var loader = PluginLoader.CreateFromAssemblyFile(pluginPath, PluginLoaderOptions.PreferSharedTypes);
+            var assembly = loader.LoadDefaultAssembly();
+            plugins[assemblyName.Name] = (loader, assembly);
+            this.loadedAssemblies.Add(pluginPath);
+            Logger.Info($"CGR loaded plugin for {assemblyName.Name}: {assembly.Location}");
+            return assembly;
 
-            return assemblyPaths.Select(context.LoadFromAssemblyPath).FirstOrDefault();
-        }
-
-        private static RuntimeLibrary FindMatchingLibrary(IEnumerable<RuntimeLibrary> libraries, AssemblyName name)
-        {
-            foreach (var runtime in libraries)
+            bool IsRequestedPlugin(string path)
             {
-                if (string.Equals(runtime.Name, name.Name, StringComparison.OrdinalIgnoreCase))
-                {
-                    return runtime;
-                }
-
-                // If the NuGet package name does not exactly match the AssemblyName,
-                // we check whether the assembly file name is matching
-                if (runtime.RuntimeAssemblyGroups.Any(
-                        g => g.AssetPaths.Any(
-                            p => string.Equals(Path.GetFileNameWithoutExtension(p), name.Name, StringComparison.OrdinalIgnoreCase))))
-                {
-                    return runtime;
-                }
+                var fileName = Path.GetFileNameWithoutExtension(path);
+                return string.Equals(assemblyName.Name, fileName, StringComparison.OrdinalIgnoreCase);
             }
-            return null;
         }
 
         private static DateTime GetLastModifiedAssemblyTime(string assemblyListPath)
@@ -315,26 +244,6 @@ private static void ReportError(IProgress<Diagnostic> progress, string id, Synta
             progress.Report(reportDiagnostic);
         }
 
-        private Assembly LoadAssembly(AssemblyName assemblyName)
-        {
-            var matchingRefAssemblies = from refPath in this.ReferencePath
-                                        where Path.GetFileNameWithoutExtension(refPath).Equals(assemblyName.Name, StringComparison.OrdinalIgnoreCase)
-                                        select refPath;
-            var matchingAssemblies = from path in this.GeneratorAssemblySearchPaths
-                                     from file in Directory.EnumerateFiles(path, $"{assemblyName.Name}.dll", SearchOption.TopDirectoryOnly)
-                                     where AllowedAssemblyExtensions.Contains(Path.GetExtension(file))
-                                     select file;
-
-            string matchingRefAssembly = matchingRefAssemblies.Concat(matchingAssemblies).FirstOrDefault();
-            if (matchingRefAssembly != null)
-            {
-                this.loadedAssemblies.Add(matchingRefAssembly);
-                return this.LoadAssembly(matchingRefAssembly);
-            }
-
-            return Assembly.Load(assemblyName);
-        }
-
         private void SaveGeneratorAssemblyList(string assemblyListPath)
         {
             // Union our current list with the one on disk, since our incremental code generation

src/CodeGeneration.Roslyn.Tests.Generators/CodeGeneration.Roslyn.Tests.Generators.csproj

@@ -1,10 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
-
+  
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="Bogus" Version="28.0.2" />
     <PackageReference Include="Validation" Version="2.4.18" />
   </ItemGroup>
 

src/CodeGeneration.Roslyn.Tests.Generators/ExternalDuplicateWithSuffixGenerator.cs

@@ -40,7 +40,8 @@ public Task<SyntaxList<MemberDeclarationSyntax>> GenerateAsync(TransformationCon
             if (applyToClass != null)
             {
                 copy = applyToClass
-                    .WithIdentifier(SyntaxFactory.Identifier(NameGenerator.Combine(applyToClass.Identifier.ValueText, this.suffix)));
+                    .WithIdentifier(SyntaxFactory.Identifier(NameGenerator.Combine(applyToClass.Identifier.ValueText, this.suffix)))
+                    .WithLeadingTrivia(SyntaxFactory.Comment($"// Bogus content: {new Bogus.Faker().Hacker.Phrase()}"));
             }
 
             if (copy != null)

src/CodeGeneration.Roslyn.Tests/CodeGeneration.Roslyn.Tests.csproj

@@ -3,11 +3,14 @@
   <Import Project="..\CodeGeneration.Roslyn.BuildTime\build\CodeGeneration.Roslyn.BuildTime.props" />
 
   <PropertyGroup>
-    <TargetFrameworks>net462;netcoreapp2.1</TargetFrameworks>
+    <TargetFrameworks>netcoreapp2.1</TargetFrameworks>
     <GenerateCodeFromAttributesToolPathOverride>$(OutputPath)..\..\CodeGeneration.Roslyn.Tool\$(Configuration)\netcoreapp2.1\dotnet-codegen.dll</GenerateCodeFromAttributesToolPathOverride>
+    <WarnOnGeneratorAssemblySearchPaths>false</WarnOnGeneratorAssemblySearchPaths>
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="Amadevus.RecordGenerator.Attributes" Version="0.4.1" PrivateAssets="all" />
+    <PackageReference Include="Amadevus.RecordGenerator.Generators" Version="0.4.1" PrivateAssets="all" />
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Workspaces" Version="$(RoslynNugetVersion)" />
     <PackageReference Include="Microsoft.CSharp" Version="4.5.0" />
     <PackageReference Include="Xunit" Version="2.4.1" />
@@ -20,7 +23,8 @@
 
   <ItemGroup>
     <ProjectReference Include="..\CodeGeneration.Roslyn.Engine\CodeGeneration.Roslyn.Engine.csproj" />
-    <ProjectReference Include="..\CodeGeneration.Roslyn.Tests.Generators\CodeGeneration.Roslyn.Tests.Generators.csproj" />
+    <ProjectReference Include="..\CodeGeneration.Roslyn.Tests.Generators\CodeGeneration.Roslyn.Tests.Generators.csproj"
+                      OutputItemType="CodeGenerationRoslynPlugin" />
     <ProjectReference Include="..\CodeGeneration.Roslyn.Tool\CodeGeneration.Roslyn.Tool.csproj">
       <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
       <SkipGetTargetFrameworkProperties>true</SkipGetTargetFrameworkProperties>

src/CodeGeneration.Roslyn.Tests/CodeGenerationTests.cs

@@ -31,6 +31,13 @@ public void ExternalDependencyFound()
         d.TestMethodSuffix();
     }
 
+    [Fact]
+    public void NuGetRecordGeneratorWorks()
+    {
+        var record = new MyRecord(1, "id");
+        record.ToBuilder();
+    }
+
     public partial class Wrapper
     {
         [ExternalDuplicateWithSuffixByName("Suffix")]
@@ -39,6 +46,14 @@ public void TestMethod()
         }
     }
 
+    [Record]
+    public partial class MyRecord
+    {
+        public int Id { get; }
+
+        public string Name { get; }
+    }
+
     [DuplicateWithSuffixByName("A")]
     [DuplicateWithSuffixByType("B")]
     public class Foo