Rely on GetUsedAssemblyReferences

Directory.Build.props

@@ -11,6 +11,10 @@
     <EnforceCodeStyleInBuild>true</EnforceCodeStyleInBuild>
     <AnalysisMode>Recommended</AnalysisMode>
 
+    <!-- See https://learn.microsoft.com/en-us/dotnet/fundamentals/code-analysis/style-rules/ide0005 -->
+    <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    <NoWarn>$(NoWarn);1591</NoWarn>
+
     <!-- Enable implicit usings -->
     <ImplicitUsings>Enable</ImplicitUsings>
 

README.md

@@ -7,7 +7,13 @@ Easily identify which dependencies can be removed from an MSBuild project.
 ## How to use
 Simply add a `PackageReference` to the [ReferenceTrimmer](https://www.nuget.org/packages/ReferenceTrimmer) package in your projects. You can add the package reference to your `Directory.Build.props` or `Directory.Build.targets` instead to apply to the entire repo.
 
-The package contains build logic to emit warnings when unused dependencies are detected.
+The package contains build logic to emit warnings when unused dependencies are detected. The logic relies on [`GetUsedAssemblyReferences`](https://learn.microsoft.com/en-us/dotnet/api/microsoft.codeanalysis.compilation.getusedassemblyreferences) analyzer API which is available starting with Roslyn compiler that shipped with Visual Studio 2019 version 16.10, .NET 5. (see https://github.com/dotnet/roslyn/blob/main/docs/wiki/NuGet-packages.md#versioning).
+
+Note: to get better effects, enable [`IDE0005`](https://learn.microsoft.com/en-us/dotnet/fundamentals/code-analysis/style-rules/ide0005) unnecessary code rule. See also the note for why IDE0005 code analysis rule requires `<GenerateDocumentationFile>` property to be enabled. Documentation generation is also required for accuracy of used references detection (based on https://github.com/dotnet/roslyn/issues/66188).
 
 ## Configuration
 `$(EnableReferenceTrimmer)` - Controls whether the build logic should run for a given project. Defaults to `true`.
+
+## Future development
+
+The outcome of https://github.com/dotnet/sdk/issues/10414 may be of use for `ReferenceTrimmer` future updates.

ReferenceTrimmer.sln

@@ -1,4 +1,4 @@
-
+
 Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio Version 17
 VisualStudioVersion = 17.2.32317.152
@@ -23,6 +23,10 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "test", "test", "{16768D5E-9
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "src", "src", "{D49A052F-6C94-4B71-81D4-4D1871858F6D}"
 EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "analyzer", "analyzer", "{20D61165-FED7-496A-9F83-AAD2CA32CFA5}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "ReferenceTrimmerAnalyzer", "analyzer\ReferenceTrimmerAnalyzer.csproj", "{2C295A5A-5889-494B-8893-66381B000102}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -37,13 +41,18 @@ Global
 		{9F80F05C-91EA-4D15-B96C-128E7E5E93CB}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{9F80F05C-91EA-4D15-B96C-128E7E5E93CB}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{9F80F05C-91EA-4D15-B96C-128E7E5E93CB}.Release|Any CPU.Build.0 = Release|Any CPU
+		{2C295A5A-5889-494B-8893-66381B000102}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{2C295A5A-5889-494B-8893-66381B000102}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{2C295A5A-5889-494B-8893-66381B000102}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{2C295A5A-5889-494B-8893-66381B000102}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
 	EndGlobalSection
 	GlobalSection(NestedProjects) = preSolution
 		{D0410117-6DF9-4E70-91BD-312FEDD51299} = {D49A052F-6C94-4B71-81D4-4D1871858F6D}
 		{9F80F05C-91EA-4D15-B96C-128E7E5E93CB} = {16768D5E-9929-45B8-9222-A4A83C40B005}
+		{2C295A5A-5889-494B-8893-66381B000102} = {20D61165-FED7-496A-9F83-AAD2CA32CFA5}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {BD73DFDB-4A6B-49B2-B544-7F071454A46A}

analyzer/AnalyzerReleases.Shipped.md

@@ -0,0 +1,10 @@
+; Shipped analyzer releases
+; https://github.com/dotnet/roslyn-analyzers/blob/master/src/Microsoft.CodeAnalysis.Analyzers/ReleaseTrackingAnalyzers.Help.md
+
+## Release 3.1.0
+
+### New Rules
+
+Rule ID | Category | Severity | Notes
+--------|----------|----------|--------------------
+DOC001  | Documentation |  Warning | See https://github.com/dotnet/roslyn/issues/66188

analyzer/AnalyzerReleases.Unshipped.md

@@ -0,0 +1,2 @@
+; Unshipped analyzer release
+; https://github.com/dotnet/roslyn-analyzers/blob/master/src/Microsoft.CodeAnalysis.Analyzers/ReleaseTrackingAnalyzers.Help.md

analyzer/ReferenceTrimmerAnalyzer.csproj

@@ -0,0 +1,16 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>netstandard2.0</TargetFramework>
+    <IsPackable>false</IsPackable>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+  <ItemGroup>
+    <!-- 3.10 is the lowest version the GetUsedAssemblyReferences API is available in.
+         Upgrading this package automatically upgrades the minimum compiler version this analyzer will work with, so upgrade with care and update README.md accordingly -->
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" PrivateAssets="all" Version="3.10" />
+  </ItemGroup>
+  <ItemGroup>
+    <AdditionalFiles Include="AnalyzerReleases.Shipped.md" />
+    <AdditionalFiles Include="AnalyzerReleases.Unshipped.md" />
+  </ItemGroup>
+</Project>

analyzer/UsedAssemblyReferencesDumper.cs

@@ -0,0 +1,48 @@
+using System.Collections.Immutable;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace ReferenceTrimmer
+{
+    [DiagnosticAnalyzer(LanguageNames.CSharp, LanguageNames.VisualBasic, LanguageNames.FSharp)]
+    public class UsedAssemblyReferencesDumper : DiagnosticAnalyzer
+    {
+        private static readonly string Title = "Enable documentation generation for accuracy of used references detection";
+        private static readonly string Message = "Enable /doc parameter or in MSBuild set <GenerateDocumentationFile>true</GenerateDocumentationFile> for accuracy of used references detection";
+        private static DiagnosticDescriptor Rule = new DiagnosticDescriptor("DOC001", Title, Message, "Documentation", DiagnosticSeverity.Warning, true);
+
+        /// <summary>
+        /// The supported diagnosticts.
+        /// </summary>
+        public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => ImmutableArray.Create(Rule);
+
+        public override void Initialize(AnalysisContext context)
+        {
+            context.EnableConcurrentExecution();
+            context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
+            context.RegisterCompilationAction(DumpUsedReferences);
+        }
+
+        private static void DumpUsedReferences(CompilationAnalysisContext context)
+        {
+            Compilation compilation = context.Compilation;
+            if (compilation.SyntaxTrees.FirstOrDefault()?.Options.DocumentationMode == DocumentationMode.None)
+            {
+                string? nameOrPath = compilation.Options.ModuleName;
+                Location location = Location.None;
+                context.ReportDiagnostic(Diagnostic.Create(Rule, location, nameOrPath));
+            }
+
+            if (compilation.Options.Errors.IsEmpty)
+            {
+                AdditionalText? analyzerOutputFile = context.Options.AdditionalFiles.FirstOrDefault(file => file.Path.EndsWith("_ReferenceTrimmer_GetUsedAssemblyReferences.txt", StringComparison.OrdinalIgnoreCase));
+                if (analyzerOutputFile != null)
+                {
+                    IEnumerable<MetadataReference> usedReferences = compilation.GetUsedAssemblyReferences();
+                    Directory.CreateDirectory(Path.GetDirectoryName(analyzerOutputFile.Path));
+                    File.WriteAllLines(analyzerOutputFile.Path, usedReferences.Select(reference => reference.Display));
+                }
+            }
+        }
+    }
+}

src/ReferenceTrimmer.csproj

@@ -3,13 +3,16 @@
     <TargetFramework>netstandard2.0</TargetFramework>
     <BuildOutputTargetFolder>build\</BuildOutputTargetFolder>
     <DevelopmentDependency>true</DevelopmentDependency>
-    <!-- This package contains MSBuild tasks only, so avoid dependencies. -->
+    <!-- This package contains MSBuild task and an analyzer, so no need for extra dependencies. -->
     <SuppressDependenciesWhenPacking>true</SuppressDependenciesWhenPacking>
+    <TargetsForTfmSpecificContentInPackage>$(TargetsForTfmSpecificContentInPackage);_AddAnalyzersToOutput</TargetsForTfmSpecificContentInPackage>
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.Build.Utilities.Core" Version="17.3.1" />
     <PackageReference Include="NuGet.ProjectModel" Version="6.3.0" />
-    <PackageReference Include="System.Reflection.Metadata" Version="6.0.1" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\analyzer\ReferenceTrimmerAnalyzer.csproj" ReferenceOutputAssembly="false" />
   </ItemGroup>
   <ItemGroup>
     <None Include="build\*">
@@ -22,8 +25,19 @@
       <Pack>true</Pack>
       <PackagePath>buildMultiTargeting\</PackagePath>
     </None>
+    <None Update="tools\*.ps1">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+      <Pack>true</Pack>
+      <PackagePath>tools\</PackagePath>
+    </None>
   </ItemGroup>
   <ItemGroup>
     <InternalsVisibleTo Include="ReferenceTrimmer.Tests" />
   </ItemGroup>
+
+  <Target Name="_AddAnalyzersToOutput">
+    <ItemGroup>
+      <TfmSpecificPackageFile Include="..\analyzer\$(IntermediateOutputPath)ReferenceTrimmerAnalyzer.dll" PackagePath="analyzers/dotnet" />
+    </ItemGroup>
+  </Target>
 </Project>

src/ReferenceTrimmerTask.cs

@@ -1,6 +1,4 @@
-using System.Reflection;
-using System.Reflection.Metadata;
-using System.Reflection.PortableExecutable;
+using System.Reflection;
 using System.Xml.Linq;
 using Microsoft.Build.Framework;
 using NuGet.Common;
@@ -16,7 +14,7 @@ public sealed class ReferenceTrimmerTask : MSBuildTask
         {
             // Direct dependency
             "NuGet.ProjectModel",
-            
+
             // Indirect dependencies
             "NuGet.Common",
             "NuGet.Frameworks",
@@ -25,9 +23,9 @@ public sealed class ReferenceTrimmerTask : MSBuildTask
         };
 
         [Required]
-        public string OutputAssembly { get; set; }
+        public string MSBuildProjectFile { get; set; }
 
-        public bool NeedsTransitiveAssemblyReferences { get; set; }
+        public ITaskItem[] UsedReferences { get; set; }
 
         public ITaskItem[] References { get; set; }
 
@@ -102,7 +100,7 @@ public override bool Execute()
 
                         if (!assemblyReferences.Contains(referenceAssemblyName))
                         {
-                            Log.LogWarning($"Reference {referenceSpec} can be removed");
+                            LogWarning("Reference {0} can be removed", referenceSpec);
                         }
                     }
                 }
@@ -115,7 +113,7 @@ public override bool Execute()
                         if (!assemblyReferences.Contains(projectReferenceAssemblyName.Name))
                         {
                             string referenceProjectFile = projectReference.GetMetadata("OriginalProjectReferenceItemSpec");
-                            Log.LogWarning($"ProjectReference {referenceProjectFile} can be removed");
+                            LogWarning("ProjectReference {0} can be removed", referenceProjectFile);
                         }
                     }
                 }
@@ -132,45 +130,22 @@ public override bool Execute()
 
                         if (!packageAssemblies.Any(packageAssembly => assemblyReferences.Contains(packageAssembly)))
                         {
-                            Log.LogWarning($"PackageReference {packageReference} can be removed");
+                            LogWarning("PackageReference {0} can be removed", packageReference);
                         }
                     }
                 }
-
-                return !Log.HasLoggedErrors;
             }
             finally
             {
                 AppDomain.CurrentDomain.AssemblyResolve -= ResolveAssembly;
             }
-        }
 
-        private HashSet<string> GetAssemblyReferences()
-        {
-            var assemblyReferences = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
-            using (var stream = File.OpenRead(OutputAssembly))
-            using (var peReader = new PEReader(stream))
-            {
-                var metadata = peReader.GetMetadataReader(MetadataReaderOptions.ApplyWindowsRuntimeProjections);
-                if (!metadata.IsAssembly)
-                {
-                    Log.LogError($"{OutputAssembly} is not an assembly");
-                    return null;
-                }
+            return !Log.HasLoggedErrors;
+        }
 
-                foreach (var assemblyReferenceHandle in metadata.AssemblyReferences)
-                {
-                    AssemblyReference reference = metadata.GetAssemblyReference(assemblyReferenceHandle);
-                    string name = metadata.GetString(reference.Name);
-                    if (!string.IsNullOrEmpty(name))
-                    {
-                        assemblyReferences.Add(name);
-                    }
-                }
-            }
+        private void LogWarning(string message, params object[] messageArgs) => Log.LogWarning(null, null, null, MSBuildProjectFile, 0, 0, 0, 0, message, messageArgs);
 
-            return assemblyReferences;
-        }
+        private HashSet<string> GetAssemblyReferences() => new(UsedReferences.Select(usedReference => AssemblyName.GetAssemblyName(usedReference.ItemSpec).Name), StringComparer.OrdinalIgnoreCase);
 
         private Dictionary<string, List<string>> GetPackageAssemblies()
         {
@@ -218,6 +193,12 @@ private Dictionary<string, List<string>> GetPackageAssemblies()
                     })
                     .ToList();
 
+                // Add this package's assemblies, if there are any
+                if (nugetLibraryAssemblies.Count == 0)
+                {
+                    continue;
+                }
+
                 // Walk up to add assemblies to all packages which directly or indirectly depend on this one.
                 var seenDependants = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
                 var queue = new Queue<string>();
@@ -226,18 +207,14 @@ private Dictionary<string, List<string>> GetPackageAssemblies()
                 {
                     var packageId = queue.Dequeue();
 
-                    // Add this package's assemblies, if there are any
-                    if (nugetLibraryAssemblies.Count > 0)
+                    if (!packageAssemblies.TryGetValue(packageId, out var assemblies))
                     {
-                        if (!packageAssemblies.TryGetValue(packageId, out var assemblies))
-                        {
-                            assemblies = new List<string>();
-                            packageAssemblies.Add(packageId, assemblies);
-                        }
-
-                        assemblies.AddRange(nugetLibraryAssemblies);
+                        assemblies = new List<string>();
+                        packageAssemblies.Add(packageId, assemblies);
                     }
 
+                    assemblies.AddRange(nugetLibraryAssemblies);
+
                     // Recurse though dependants
                     if (nugetDependants.TryGetValue(packageId, out var dependants))
                     {
@@ -285,14 +262,16 @@ internal HashSet<string> GetTargetFrameworkAssemblyNames()
                         {
                             targetFrameworkAssemblyNames.Add(assemblyName);
                         }
-
                     }
                 }
             }
 
             return targetFrameworkAssemblyNames;
         }
 
+        /// <summary>
+        /// Assembly resolution needed for parsing the lock file, needed if the version the task depends on is a different version than MSBuild's
+        /// </summary>
         private Assembly ResolveAssembly(object sender, ResolveEventArgs args)
         {
             AssemblyName assemblyName = new(args.Name);

src/build/ReferenceTrimmer.targets

@@ -2,21 +2,38 @@
 <Project>
   <UsingTask TaskName="ReferenceTrimmerTask" AssemblyFile="$(ReferenceTrimmerTaskAssembly)" />
 
+  <PropertyGroup>
+    <ReferenceTrimmerGetUsedAssemblyReferencesFile>$(MSBuildProjectDirectory)\$(IntermediateOutputPath)_ReferenceTrimmer_GetUsedAssemblyReferences.txt</ReferenceTrimmerGetUsedAssemblyReferencesFile>
+    <CoreCompileDependsOn>$(CoreCompileDependsOn);DeleteReferenceTrimmerGetUsedAssemblyReferencesFile</CoreCompileDependsOn>
+  </PropertyGroup>
+
+  <ItemGroup Condition="'$(EnableReferenceTrimmer)' != 'false'">
+    <!-- https://github.com/dotnet/roslyn/blob/main/docs/analyzers/Using%20Additional%20Files.md#in-a-project-file -->
+    <AdditionalFiles Include="$(ReferenceTrimmerGetUsedAssemblyReferencesFile)" />
+    <FileWrites Include="$(ReferenceTrimmerGetUsedAssemblyReferencesFile)" />
+  </ItemGroup>
+
+  <Target Name="DeleteReferenceTrimmerGetUsedAssemblyReferencesFile" Condition="'$(EnableReferenceTrimmer)' != 'false'" BeforeTargets="BeforeBuild" >
+    <Delete Files="$(ReferenceTrimmerGetUsedAssemblyReferencesFile)" Condition="Exists('$(ReferenceTrimmerGetUsedAssemblyReferencesFile)')" />
+  </Target>
+
   <Target Name="VerifyReferences"
           Condition="'$(EnableReferenceTrimmer)' != 'false'"
           AfterTargets="AfterBuild"
           DependsOnTargets="ResolveProjectReferences">
-    <PropertyGroup>
-       <!-- Certain project types may require references simply to copy them to the output folder to satisfy transitive dependencies. -->
-       <_ReferenceTrimmerNeedsTransitiveAssemblyReferences Condition="'$(OutputType)' == 'Exe'">true</_ReferenceTrimmerNeedsTransitiveAssemblyReferences>
-    </PropertyGroup>
     <ItemGroup>
       <_ReferenceTrimmerProjectReferences Include="@(ReferencePath)" Condition="'%(ReferencePath.ReferenceSourceTarget)' == 'ProjectReference'" />
     </ItemGroup>
 
+    <ReadLinesFromFile File="$(ReferenceTrimmerGetUsedAssemblyReferencesFile)">
+      <Output TaskParameter="Lines" ItemName="UsedReference" />
+    </ReadLinesFromFile>
+    <Warning Text="Skipping ReferenceTrimmerTask due to empty file $(ReferenceTrimmerGetUsedAssemblyReferencesFile)" Condition=" '@(UsedReference)' == '' "/>
+
     <ReferenceTrimmerTask
-      OutputAssembly="$(TargetPath)"
-      NeedsTransitiveAssemblyReferences="$(_ReferenceTrimmerNeedsTransitiveAssemblyReferences)"
+      Condition=" '@(UsedReference)' != '' "
+      MSBuildProjectFile="$(MSBuildProjectFile)"
+      UsedReferences="@(UsedReference)"
       References="@(Reference)"
       ProjectReferences="@(_ReferenceTrimmerProjectReferences)"
       PackageReferences="@(PackageReference)"