Add ability to ignore build files in packages

README.md

@@ -54,6 +54,16 @@ You can turn off specific docxml related warnings and errors while defaulting Re
 
 Note: To get better results, enable the [`IDE0005`](https://learn.microsoft.com/en-us/dotnet/fundamentals/code-analysis/style-rules/ide0005) unnecessary `using` rule. This avoids the C# compiler seeing a false positive assembly usage from unneeded `using` directives causing it to miss a removable dependency. 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).
 
+Packages are prevented from being trimmed if they contain build files, as there's no reliable way to determine whether it's safe to do so. You can explicitly ignore specific packages' build files and cause them to be solely judged based on whther the libraries are used by adding the package to the `ReferenceTrimmerIgnorePackageBuildFiles` item on a project level, or in `Directory.Build.props`.
+
+Example:
+```xml
+  <ItemGroup>
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Logging.Abstractions" />
+  </ItemGroup>
+```
+A default set of `ReferenceTrimmerIgnorePackageBuildFiles` items is already included for well-known package, notably various `Microsoft.Extensions.*` packages.
+
 ### C++ (.vcxproj projects)
 ReferenceTrimmer for C++ is an MSBuild [distributed logger](https://learn.microsoft.com/en-us/visualstudio/msbuild/logging-in-a-multi-processor-environment?view=vs-2022). It writes guidance to the MSBuild stdout stream (not to the MSBuild internal logger at this time) and writes `ReferenceTrimmerUnusedMSVCLibraries.json.log` to the build working directory.
 

src/Package/build/ReferenceTrimmer.props

@@ -22,4 +22,42 @@
     </Link>
   </ItemDefinitionGroup>
 
+  <ItemGroup>
+    <!--
+      List of commonly used packages that contain build files that are not consequential, but they're preventing the reference from being trimmed.
+    -->
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Caching.Abstractions" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Caching.Memory" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Configuration" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Configuration.Abstractions" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Configuration.Binder" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Configuration.CommandLine" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Configuration.EnvironmentVariables" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Configuration.FileExtensions" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Configuration.Json" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Configuration.UserSecrets" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.DependencyInjection" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.DependencyModel" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Diagnostics" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Diagnostics.Abstractions" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.FileProviders.Abstractions" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.FileProviders.Composite" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.FileProviders.Physical" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.FileSystemGlobbing" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Hosting" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Hosting.Abstractions" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Http" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Logging" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Logging.Abstractions" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Logging.Configuration" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Logging.Console" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Logging.Debug" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Logging.EventLog" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Logging.EventSource" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Options" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Options.ConfigurationExtensions" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Primitives" />
+  </ItemGroup>
+
 </Project>

src/Package/build/ReferenceTrimmer.targets

@@ -41,6 +41,7 @@
       RuntimeIdentifier="$(RuntimeIdentifier)"
       NuGetRestoreTargets="$(NuGetRestoreTargets)"
       TargetFrameworkDirectories="$(TargetFrameworkDirectory)"
+      IgnorePackageBuildFiles="@(ReferenceTrimmerIgnorePackageBuildFiles)"
       NuGetPackageRoot="$(NuGetPackageRoot)" />
 
     <ItemGroup>

src/Tasks/CollectDeclaredReferencesTask.cs

@@ -40,6 +40,8 @@ public sealed class CollectDeclaredReferencesTask : MSBuildTask
 
     public ITaskItem[]? PackageReferences { get; set; }
 
+    public ITaskItem[]? IgnorePackageBuildFiles { get; set; }
+
     public string? ProjectAssetsFile { get; set; }
 
     public string? TargetFrameworkMoniker { get; set; }
@@ -170,7 +172,6 @@ public override bool Execute()
                         continue;
                     }
 
-                    // Ignore packages with build logic as we cannot easily evaluate whether the build logic is necessary or not.
                     if (packageInfo.BuildFiles.Count > 0)
                     {
                         continue;
@@ -245,6 +246,12 @@ private Dictionary<string, PackageInfo> GetPackageInfos()
             }
         }
 
+        HashSet<string> packageToIgnoreBuildFiles = new(StringComparer.OrdinalIgnoreCase);
+        foreach (ITaskItem item in IgnorePackageBuildFiles ?? [])
+        {
+            packageToIgnoreBuildFiles.Add(item.ItemSpec);
+        }
+
         // Get the transitive closure of assemblies included by each package
         foreach (LockFileTargetLibrary nugetLibrary in nugetLibraries)
         {
@@ -274,11 +281,13 @@ private Dictionary<string, PackageInfo> GetPackageInfos()
                 })
                 .ToList();
 
-            List<string> buildFiles = nugetLibrary.Build
-                .Select(item => item.Path)
-                .Where(IsValidFile)
-                .Select(path => Path.Combine(nugetLibraryAbsolutePath, path))
-                .ToList();
+            List<string> buildFiles = packageToIgnoreBuildFiles.Contains(nugetLibrary.Name)
+                ? []
+                : nugetLibrary.Build
+                    .Select(item => item.Path)
+                    .Where(IsValidFile)
+                    .Select(path => Path.Combine(nugetLibraryAbsolutePath, path))
+                    .ToList();
 
             // Add this package's assets, if there are any
             if (nugetLibraryAssemblies.Count > 0 || buildFiles.Count > 0)

src/Tests/E2ETests.cs

@@ -491,6 +491,29 @@ public Task PackageReferenceWithFakeBuildFile()
             ]);
     }
 
+    [TestMethod]
+    public async Task IgnorePackageBuildFiles()
+    {
+        await RunMSBuildAsync(
+            projectFile: "Library/Library.csproj",
+            expectedWarnings: [],
+            globalProperties: new Dictionary<string, string>
+            {
+                { "IgnorePackageBuildFiles", "false" },
+            });
+
+        await RunMSBuildAsync(
+            projectFile: "Library/Library.csproj",
+            expectedWarnings:
+            [
+                new Warning("RT0003: PackageReference Microsoft.Extensions.Logging can be removed", "Library/Library.csproj"),
+            ],
+            globalProperties: new Dictionary<string, string>
+            {
+                { "IgnorePackageBuildFiles", "true" },
+            });
+    }
+
     private static (string ExePath, string Verb, string? VsInstallDir) GetMsBuildExeAndVerb()
     {
         // On Windows, try to find Visual Studio using vswhere
@@ -614,7 +637,13 @@ private static (string ExePath, string Verb, string? VsInstallDir) GetMsBuildExe
         return env;
     }
 
-    private async Task RunMSBuildAsync(string projectFile, Warning[] expectedWarnings, string[]? expectedConsoleOutputs = null, bool expectUnusedMsvcLibrariesLog = false, bool enableReferenceTrimmerDiagnostics = false)
+    private async Task RunMSBuildAsync(
+        string projectFile,
+        Warning[] expectedWarnings,
+        string[]? expectedConsoleOutputs = null,
+        bool expectUnusedMsvcLibrariesLog = false,
+        bool enableReferenceTrimmerDiagnostics = false,
+        IReadOnlyDictionary<string, string>? globalProperties = null)
     {
         var testDataSourcePath = Path.GetFullPath(Path.Combine("TestData", TestContext?.TestName ?? string.Empty));
 
@@ -641,6 +670,14 @@ private async Task RunMSBuildAsync(string projectFile, Warning[] expectedWarning
                              $"-distributedlogger:CentralLogger,\"{loggersAssemblyPath}\"*ForwardingLogger,\"{loggersAssemblyPath}\" " +
                              (enableReferenceTrimmerDiagnostics ? "-p:EnableReferenceTrimmerDiagnostics=true" : string.Empty);
 
+        if (globalProperties is not null)
+        {
+            foreach ((string key, string value) in globalProperties)
+            {
+                msbuildArgs += $" -p:{key}={value}";
+            }
+        }
+
         Process? process = Process.Start(
             new ProcessStartInfo
             {

src/Tests/TestData/IgnorePackageBuildFiles/Library/Library.cs

@@ -0,0 +1,7 @@
+namespace Library
+{
+    public static class Foo
+    {
+        public static string Bar() => "Baz";
+    }
+}

src/Tests/TestData/IgnorePackageBuildFiles/Library/Library.csproj

@@ -0,0 +1,23 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Library</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.Logging" Version="8.0.0" />
+  </ItemGroup>
+
+  <!-- Clear out the defaults so we can test -->
+  <ItemGroup>
+    <ReferenceTrimmerIgnorePackageBuildFiles Remove="@(ReferenceTrimmerIgnorePackageBuildFiles)" />
+  </ItemGroup>
+
+  <ItemGroup Condition="'$(IgnorePackageBuildFiles)' == 'true'">
+    <!-- Microsoft.Extensions.Logging is the reference, but its dependencies are the ones with the build files. -->
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Logging.Abstractions" />
+    <ReferenceTrimmerIgnorePackageBuildFiles Include="Microsoft.Extensions.Options" />
+  </ItemGroup>
+
+</Project>

version.json

@@ -1,7 +1,7 @@
 {
     "$schema": "https://raw.githubusercontent.com/AArnott/Nerdbank.GitVersioning/master/src/NerdBank.GitVersioning/version.schema.json",
-    "version": "3.3",
-    "assemblyVersion": "3.3",
+    "version": "3.4",
+    "assemblyVersion": "3.4",
     "buildNumberOffset": -1,
     "publicReleaseRefSpec": [
         "^refs/tags/v\\d+\\.\\d+\\.\\d+"