Write unused references to a log file

src/Analyzer/ReferenceTrimmerAnalyzer.cs

@@ -10,6 +10,7 @@ public class ReferenceTrimmerAnalyzer : DiagnosticAnalyzer
 {
     private const string DeclaredReferencesFileName = "_ReferenceTrimmer_DeclaredReferences.tsv";
     private const string UsedReferencesFileName = "_ReferenceTrimmer_UsedReferences.log";
+    private const string UnusedReferencesFileName = "_ReferenceTrimmer_UnusedReferences.log";
 
     private static readonly DiagnosticDescriptor RT0000Descriptor = new(
         "RT0000",
@@ -53,6 +54,7 @@ public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics
             RT0002Descriptor,
             RT0003Descriptor);
 
+    /// <inheritdoc/>
     public override void Initialize(AnalysisContext context)
     {
         context.EnableConcurrentExecution();
@@ -90,7 +92,21 @@ private static void DumpUsedReferences(CompilationAnalysisContext context)
             }
         }
 
-        WriteUsedReferencesToFile(usedReferences, declaredReferencesPath);
+        var globalOptions = context.Options.AnalyzerConfigOptionsProvider.GlobalOptions;
+        if (globalOptions.TryGetValue("build_property.EnableReferenceTrimmerDiagnostics", out string? enableDiagnostics)
+            && string.Equals(enableDiagnostics, "true", StringComparison.OrdinalIgnoreCase))
+        {
+            HashSet<string> unusedReferences = new(StringComparer.OrdinalIgnoreCase);
+            foreach (MetadataReference metadataReference in compilation.References)
+            {
+                if (metadataReference.Display != null && !usedReferences.Contains(metadataReference.Display))
+                {
+                    unusedReferences.Add(metadataReference.Display);
+                }
+            }
+
+            DumpReferencesInfo(usedReferences, unusedReferences, declaredReferencesPath);
+        }
 
         Dictionary<string, List<string>> packageAssembliesDict = new(StringComparer.OrdinalIgnoreCase);
         foreach (DeclaredReference declaredReference in declaredReferences.References)
@@ -141,12 +157,19 @@ private static void DumpUsedReferences(CompilationAnalysisContext context)
         }
     }
 
-    private static void WriteUsedReferencesToFile(HashSet<string> usedReferences, string declaredReferencesPath)
+    private static void DumpReferencesInfo(HashSet<string> usedReferences, HashSet<string> unusedReferences, string declaredReferencesPath)
     {
-        string filePath = Path.Combine(Path.GetDirectoryName(declaredReferencesPath), UsedReferencesFileName);
-
+        string dir = Path.GetDirectoryName(declaredReferencesPath);
+        string filePath = Path.Combine(dir, UsedReferencesFileName);
         string text = string.Join(Environment.NewLine, usedReferences.OrderBy(s => s));
+        WriteFile(filePath, text);
+        filePath = Path.Combine(dir, UnusedReferencesFileName);
+        text = string.Join(Environment.NewLine, unusedReferences.OrderBy(s => s));
+        WriteFile(filePath, text);
+    }
 
+    private static void WriteFile(string filePath, string text)
+    {
         try
         {
             if (File.Exists(filePath))

src/Package/build/ReferenceTrimmer.targets

@@ -5,10 +5,15 @@
   <PropertyGroup>
     <CoreCompileDependsOn Condition="'$(EnableReferenceTrimmer)' != 'false'">$(CoreCompileDependsOn);CollectDeclaredReferences</CoreCompileDependsOn>
   </PropertyGroup>
+  <ItemGroup>
+    <CompilerVisibleProperty Include="EnableReferenceTrimmerDiagnostics"/>
+  </ItemGroup>
 
   <Target Name="CollectDeclaredReferences" DependsOnTargets="ResolveAssemblyReferences;PrepareProjectReferences">
     <PropertyGroup>
       <_ReferenceTrimmerDeclaredReferencesFile>$(IntermediateOutputPath)\_ReferenceTrimmer_DeclaredReferences.tsv</_ReferenceTrimmerDeclaredReferencesFile>
+      <_ReferenceTrimmerUsedReferencesFile>$(IntermediateOutputPath)\_ReferenceTrimmer_UsedReferences.log</_ReferenceTrimmerUsedReferencesFile>
+      <_ReferenceTrimmerUnusedReferencesFile>$(IntermediateOutputPath)\_ReferenceTrimmer_UnusedReferences.log</_ReferenceTrimmerUnusedReferencesFile>
     </PropertyGroup>
     <ItemGroup>
       <!--
@@ -42,6 +47,8 @@
       <!-- https://github.com/dotnet/roslyn/blob/main/docs/analyzers/Using%20Additional%20Files.md#in-a-project-file -->
       <AdditionalFiles Include="$(_ReferenceTrimmerDeclaredReferencesFile)" />
       <FileWrites Include="$(_ReferenceTrimmerDeclaredReferencesFile)" />
+      <FileWrites Include="$(_ReferenceTrimmerUsedReferencesFile)" Condition="'$(EnableReferenceTrimmerDiagnostics)'=='true'" />
+      <FileWrites Include="$(_ReferenceTrimmerUnusedReferencesFile)" Condition="'$(EnableReferenceTrimmerDiagnostics)'=='true'" />
     </ItemGroup>
   </Target>
 </Project>

src/Tests/E2ETests.cs

@@ -54,14 +54,17 @@ public Task UsedProjectReferenceNoReferenceAssembly()
     }
 
     [TestMethod]
-    public Task UnusedProjectReference()
+    [DataRow(true)]
+    [DataRow(false)]
+    public Task UnusedProjectReference(bool enableReferenceTrimmerDiagnostics)
     {
         return RunMSBuildAsync(
             projectFile: "Library/Library.csproj",
             expectedWarnings: new[]
             {
                 new Warning("RT0002: ProjectReference ../Dependency/Dependency.csproj can be removed", "Library/Library.csproj"),
-            });
+            },
+            enableReferenceTrimmerDiagnostics: enableReferenceTrimmerDiagnostics);
     }
 
     [TestMethod]
@@ -524,7 +527,8 @@ private static void DirectoryCopy(string sourceDirName, string destDirName)
         }
     }
 
-    private async Task RunMSBuildAsync(string projectFile, Warning[] expectedWarnings, string[]? expectedConsoleOutputs = null, bool expectUnusedMsvcLibrariesLog = false)
+    private async Task RunMSBuildAsync(string projectFile, Warning[] expectedWarnings, string[]? expectedConsoleOutputs = null, bool expectUnusedMsvcLibrariesLog = false,
+                                       bool enableReferenceTrimmerDiagnostics = false)
     {
         var testDataSourcePath = Path.GetFullPath(Path.Combine("TestData", TestContext?.TestName ?? string.Empty));
 
@@ -548,7 +552,8 @@ private async Task RunMSBuildAsync(string projectFile, Warning[] expectedWarning
                              $"-bl:\"{binlogFilePath}\" " +
                              $"-flp1:logfile=\"{errorsFilePath}\";errorsonly " +
                              $"-flp2:logfile=\"{warningsFilePath}\";warningsonly " +
-                             $"-distributedlogger:CentralLogger,\"{loggersAssemblyPath}\"*ForwardingLogger,\"{loggersAssemblyPath}\"";
+                             $"-distributedlogger:CentralLogger,\"{loggersAssemblyPath}\"*ForwardingLogger,\"{loggersAssemblyPath}\" " +
+                             (enableReferenceTrimmerDiagnostics ? "-p:EnableReferenceTrimmerDiagnostics=true" : string.Empty);
 
         Process? process = Process.Start(
             new ProcessStartInfo
@@ -620,5 +625,11 @@ private async Task RunMSBuildAsync(string projectFile, Warning[] expectedWarning
                 Assert.IsTrue(stdOut.Contains(expectedLogOutput, StringComparison.OrdinalIgnoreCase), $"Expected log output '{expectedLogOutput}' was not found. Full console stdout: {stdOut}{Environment.NewLine}Console stderr: {stdErr}");
             }
         }
+
+        // local tests run debug, CI builds run release, thus the assertion needs to look for the file
+        var usedReferencesFiles = Directory.GetFiles(testDataSourcePath, "_ReferenceTrimmer_UsedReferences.log", SearchOption.AllDirectories);
+        var unusedReferencesFiles = Directory.GetFiles(testDataSourcePath, "_ReferenceTrimmer_UnusedReferences.log", SearchOption.AllDirectories);
+        Assert.AreEqual(enableReferenceTrimmerDiagnostics, usedReferencesFiles.Length > 0);
+        Assert.AreEqual(enableReferenceTrimmerDiagnostics, unusedReferencesFiles.Length > 0);
     }
 }