Warn when direct package reference is unused

src/Analyzer/ReferenceTrimmerAnalyzer.cs

@@ -40,7 +40,7 @@ public class ReferenceTrimmerAnalyzer : DiagnosticAnalyzer
     private static readonly DiagnosticDescriptor RT0003Descriptor = new(
         "RT0003",
         "Unnecessary package reference",
-        "PackageReference {0} can be removed",
+        "PackageReference {0} can be removed{1}",
         "ReferenceTrimmer",
         DiagnosticSeverity.Warning,
         isEnabledByDefault: true);
@@ -140,6 +140,7 @@ private static void DumpUsedReferencesCore(CompilationAnalysisContext context)
         }
 
         Dictionary<string, List<string>> packageAssembliesDict = new(StringComparer.OrdinalIgnoreCase);
+        Dictionary<string, List<string>> topLevelPackageAssembliesDict = new(StringComparer.OrdinalIgnoreCase);
         foreach (DeclaredReference declaredReference in ReadDeclaredReferences(sourceText))
         {
             switch (declaredReference.Kind)
@@ -166,11 +167,23 @@ private static void DumpUsedReferencesCore(CompilationAnalysisContext context)
                 {
                     if (!packageAssembliesDict.TryGetValue(declaredReference.Spec, out List<string> packageAssemblies))
                     {
-                        packageAssemblies = new List<string>();
+                        packageAssemblies = [];
                         packageAssembliesDict.Add(declaredReference.Spec, packageAssemblies);
                     }
 
                     packageAssemblies.Add(declaredReference.AssemblyPath);
+
+                    bool isTopLevelPackageAssembly = string.Equals(declaredReference.Spec, declaredReference.AdditionalSpec, StringComparison.OrdinalIgnoreCase);
+                    if (isTopLevelPackageAssembly)
+                    {
+                        if (!topLevelPackageAssembliesDict.TryGetValue(declaredReference.Spec, out List<string> topLevelPackageAssemblies))
+                        {
+                            topLevelPackageAssemblies = [];
+                            topLevelPackageAssembliesDict.Add(declaredReference.Spec, topLevelPackageAssemblies);
+                        }
+
+                        topLevelPackageAssemblies.Add(declaredReference.AssemblyPath);
+                    }
                     break;
                 }
             }
@@ -183,7 +196,11 @@ private static void DumpUsedReferencesCore(CompilationAnalysisContext context)
             List<string> packageAssemblies = kvp.Value;
             if (!usedReferences.Overlaps(packageAssemblies))
             {
-                context.ReportDiagnostic(Diagnostic.Create(RT0003Descriptor, Location.None, packageName));
+                context.ReportDiagnostic(Diagnostic.Create(RT0003Descriptor, Location.None, packageName, string.Empty));
+            }
+            else if (!topLevelPackageAssembliesDict[packageName].Any(usedReferences.Contains))
+            {
+                context.ReportDiagnostic(Diagnostic.Create(RT0003Descriptor, Location.None, packageName, " (though some of its transitive dependent packages may be used)"));
             }
         }
     }
@@ -232,7 +249,7 @@ private static void WriteFile(string filePath, string text)
         return null;
     }
 
-    // File format: tab-separated fields (AssemblyPath, Kind, Spec), one reference per line.
+    // File format: tab-separated fields (AssemblyPath, Kind, Spec, AdditionalSpec), one reference per line.
     // Keep in sync with SaveDeclaredReferences in CollectDeclaredReferencesTask.cs.
     private static IEnumerable<DeclaredReference> ReadDeclaredReferences(SourceText sourceText)
     {
@@ -250,6 +267,7 @@ private static IEnumerable<DeclaredReference> ReadDeclaredReferences(SourceText
 
             int firstTab = -1;
             int secondTab = -1;
+            int thirdTab = -1;
             for (int i = start; i < end; i++)
             {
                 if (sourceText[i] == '\t')
@@ -258,21 +276,26 @@ private static IEnumerable<DeclaredReference> ReadDeclaredReferences(SourceText
                     {
                         firstTab = i;
                     }
-                    else
+                    else if (secondTab == -1)
                     {
                         secondTab = i;
+                    }
+                    else
+                    {
+                        thirdTab = i;
                         break;
                     }
                 }
             }
 
-            if (firstTab == -1 || secondTab == -1)
+            if (firstTab == -1 || secondTab == -1 || thirdTab == -1)
             {
                 yield break;
             }
 
             string assemblyPath = sourceText.ToString(TextSpan.FromBounds(start, firstTab));
-            string spec = sourceText.ToString(TextSpan.FromBounds(secondTab + 1, end));
+            string spec = sourceText.ToString(TextSpan.FromBounds(secondTab + 1, thirdTab));
+            string additionalSpec = sourceText.ToString(TextSpan.FromBounds(thirdTab + 1, end));
 
             // Determine kind without allocating a string. The three possible values are
             // "Reference" (len 9), "ProjectReference" (len 16), "PackageReference" (len 16).
@@ -295,7 +318,7 @@ private static IEnumerable<DeclaredReference> ReadDeclaredReferences(SourceText
                 continue;
             }
 
-            yield return new DeclaredReference(assemblyPath, kind, spec);
+            yield return new DeclaredReference(assemblyPath, kind, spec, additionalSpec);
         }
     }
 }

src/Shared/DeclaredReferences.cs

@@ -1,5 +1,5 @@
 namespace ReferenceTrimmer.Shared;
 
-internal readonly record struct DeclaredReference(string AssemblyPath, DeclaredReferenceKind Kind, string Spec);
+internal readonly record struct DeclaredReference(string AssemblyPath, DeclaredReferenceKind Kind, string Spec, string AdditionalSpec);
 
 internal enum DeclaredReferenceKind { Reference, ProjectReference, PackageReference }

src/Tasks/CollectDeclaredReferencesTask.cs

@@ -129,7 +129,7 @@ public override bool Execute()
 
                     if (referencePath is not null)
                     {
-                        declaredReferences.Add(new DeclaredReference(referencePath, DeclaredReferenceKind.Reference, referenceSpec));
+                        declaredReferences.Add(new DeclaredReference(referencePath, DeclaredReferenceKind.Reference, referenceSpec, string.Empty));
                     }
                 }
             }
@@ -162,7 +162,7 @@ public override bool Execute()
                     string projectReferenceAssemblyPath = Path.GetFullPath(projectReference.ItemSpec);
                     string referenceProjectFile = projectReference.GetMetadata("OriginalProjectReferenceItemSpec");
 
-                    declaredReferences.Add(new DeclaredReference(projectReferenceAssemblyPath, DeclaredReferenceKind.ProjectReference, referenceProjectFile));
+                    declaredReferences.Add(new DeclaredReference(projectReferenceAssemblyPath, DeclaredReferenceKind.ProjectReference, referenceProjectFile, string.Empty));
                 }
             }
             else
@@ -199,9 +199,9 @@ public override bool Execute()
                         continue;
                     }
 
-                    foreach (string assemblyPath in packageInfo.CompileTimeAssemblies)
+                    foreach (var assemblyPath in packageInfo.CompileTimeAssemblies)
                     {
-                        declaredReferences.Add(new DeclaredReference(assemblyPath, DeclaredReferenceKind.PackageReference, packageReference.ItemSpec));
+                        declaredReferences.Add(new DeclaredReference(assemblyPath.Item2, DeclaredReferenceKind.PackageReference, packageReference.ItemSpec, assemblyPath.Item1));
                     }
                 }
             }
@@ -347,7 +347,7 @@ private Dictionary<string, PackageInfo> GetPackageInfos()
                         packageInfoBuilders.Add(packageId, packageInfoBuilder);
                     }
 
-                    packageInfoBuilder.AddCompileTimeAssemblies(nugetLibraryAssemblies);
+                    packageInfoBuilder.AddCompileTimeAssemblies(nugetLibrary.Name, nugetLibraryAssemblies);
                     packageInfoBuilder.AddBuildFiles(buildFiles);
 
                     // Recurse though dependents
@@ -476,7 +476,7 @@ private static bool IsSuppressed(ITaskItem item, string warningId)
         return false;
     }
 
-    // File format: tab-separated fields (AssemblyPath, Kind, Spec), one reference per line.
+    // File format: tab-separated fields (AssemblyPath, Kind, Spec, AdditionalSpec), one reference per line.
     // Keep in sync with ReadDeclaredReferences in ReferenceTrimmerAnalyzer.cs.
     private static void SaveDeclaredReferences(IReadOnlyList<DeclaredReference> declaredReferences, string filePath)
     {
@@ -497,6 +497,8 @@ private static void SaveDeclaredReferences(IReadOnlyList<DeclaredReference> decl
             writer.Append(kindString);
             writer.Append(fieldDelimiter);
             writer.Append(reference.Spec);
+            writer.Append(fieldDelimiter);
+            writer.Append(reference.AdditionalSpec);
             writer.AppendLine();
         }
 
@@ -515,18 +517,18 @@ private static void SaveDeclaredReferences(IReadOnlyList<DeclaredReference> decl
 
     private sealed class PackageInfoBuilder
     {
-        private List<string>? _compileTimeAssemblies;
+        private List<Tuple<string, string>>? _compileTimeAssemblies;
         private List<string>? _buildFiles;
 
-        public void AddCompileTimeAssemblies(List<string> compileTimeAssemblies)
+        public void AddCompileTimeAssemblies(string packageName, List<string> compileTimeAssemblies)
         {
             if (compileTimeAssemblies.Count == 0)
             {
                 return;
             }
 
             _compileTimeAssemblies ??= new(compileTimeAssemblies.Count);
-            _compileTimeAssemblies.AddRange(compileTimeAssemblies);
+            _compileTimeAssemblies.AddRange(compileTimeAssemblies.Select(assemblyPath => Tuple.Create(packageName, assemblyPath)));
         }
 
         public void AddBuildFiles(List<string> buildFiles)
@@ -542,11 +544,11 @@ public void AddBuildFiles(List<string> buildFiles)
 
         public PackageInfo ToPackageInfo()
             => new(
-                (IReadOnlyCollection<string>?)_compileTimeAssemblies ?? Array.Empty<string>(),
-                (IReadOnlyCollection<string>?)_buildFiles ?? Array.Empty<string>());
+                (IReadOnlyCollection<Tuple<string, string>>?)_compileTimeAssemblies ?? [],
+                (IReadOnlyCollection<string>?)_buildFiles ?? []);
     }
 
     private readonly record struct PackageInfo(
-        IReadOnlyCollection<string> CompileTimeAssemblies,
+        IReadOnlyCollection<Tuple<string, string>> CompileTimeAssemblies,
         IReadOnlyCollection<string> BuildFiles);
 }

src/Tests/E2ETests.cs

@@ -307,6 +307,25 @@ public Task UnusedPackageReference()
             });
     }
 
+    [TestMethod]
+    public Task UnusedPackageReferenceWithSdk()
+    {
+        return RunMSBuildAsync(
+            projectFile: "Test/Test.csproj",
+            expectedWarnings:
+            [
+                new Warning("RT0003: PackageReference Moq can be removed (though some of its transitive dependent packages may be used)", "Test/Test.csproj")
+            ]);
+    }
+
+    [TestMethod]
+    public Task UnusedPackageReferenceWithMetaPackage()
+    {
+        return RunMSBuildAsync(
+            projectFile: "Test/Test.csproj",
+            expectedWarnings: []);
+    }
+
     [TestMethod]
     public Task UnusedPackageReferenceNoWarn()
     {

src/Tests/TestData/UnusedPackageReferenceWithMetaPackage/Test/Test.cs

@@ -0,0 +1,10 @@
+using System;
+using System.Collections.Frozen;
+
+namespace Test
+{
+    public class Foo
+    {
+        public static FrozenSet<int> SomeSet() => FrozenSet.ToFrozenSet(Array.Empty<int>());
+    }
+}

src/Tests/TestData/UnusedPackageReferenceWithMetaPackage/Test/Test.csproj

@@ -0,0 +1,12 @@
+<Project Sdk="MSTest.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ExplicitUsings>enable</ExplicitUsings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="MSTest" Version="4.1.0" />
+  </ItemGroup>
+
+</Project>

src/Tests/TestData/UnusedPackageReferenceWithSdk/Test/Test.cs

@@ -0,0 +1,9 @@
+using Castle.Core.Logging;
+
+namespace Test
+{
+    public class Foo
+    {
+        public static ILogger Logger() => NullLogger.Instance;
+    }
+}

src/Tests/TestData/UnusedPackageReferenceWithSdk/Test/Test.csproj

@@ -0,0 +1,12 @@
+<Project Sdk="MSTest.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ExplicitUsings>enable</ExplicitUsings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Moq" Version="4.20.72" />
+  </ItemGroup>
+
+</Project>