Fix graying out of unused members in LSP

src/Analyzers/CSharp/Analyzers/RemoveUnusedMembers/CSharpRemoveUnusedMembersDiagnosticAnalyzer.cs

@@ -8,11 +8,12 @@
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Diagnostics;
 using Microsoft.CodeAnalysis.RemoveUnusedMembers;
+using Microsoft.CodeAnalysis.Shared.Extensions;
 
 namespace Microsoft.CodeAnalysis.CSharp.RemoveUnusedMembers;
 
 [DiagnosticAnalyzer(LanguageNames.CSharp)]
-internal class CSharpRemoveUnusedMembersDiagnosticAnalyzer
+internal sealed class CSharpRemoveUnusedMembersDiagnosticAnalyzer
     : AbstractRemoveUnusedMembersDiagnosticAnalyzer<
         DocumentationCommentTriviaSyntax,
         IdentifierNameSyntax,
@@ -28,4 +29,18 @@ protected override IEnumerable<TypeDeclarationSyntax> GetTypeDeclarations(INamed
 
     protected override SyntaxList<MemberDeclarationSyntax> GetMembers(TypeDeclarationSyntax typeDeclaration)
         => typeDeclaration.Members;
+
+    protected override SyntaxNode GetParentIfSoleDeclarator(SyntaxNode node)
+    {
+        return node switch
+        {
+            VariableDeclaratorSyntax variableDeclarator
+                => variableDeclarator.Parent is VariableDeclarationSyntax
+                {
+                    Parent: FieldDeclarationSyntax { Declaration.Variables.Count: 0 } or
+                            EventFieldDeclarationSyntax { Declaration.Variables.Count: 0 }
+                } declaration ? declaration.GetRequiredParent() : node,
+            _ => node,
+        };
+    }
 }

src/Analyzers/CSharp/Tests/RemoveUnusedMembers/RemoveUnusedMembersTests.cs

@@ -1745,7 +1745,7 @@ class MyClass
     }
 
     [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/43191")]
-    public async Task PropertyIsIncrementedAndValueDropped_VerifyAnalizerMessage()
+    public async Task PropertyIsIncrementedAndValueDropped_VerifyAnalyzerMessage()
     {
         var code = """
             class MyClass
@@ -1805,7 +1805,7 @@ class MyClass
     }
 
     [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/43191")]
-    public async Task IndexerIsIncrementedAndValueDropped_VerifyAnalizerMessage()
+    public async Task IndexerIsIncrementedAndValueDropped_VerifyAnalyzerMessage()
     {
         var code = """
             class MyClass
@@ -3176,8 +3176,8 @@ class C
                 private C(int i) { }
             }
             """,
-// /0/Test0.cs(3,13): info IDE0051: Private member 'C.C' is unused
-VerifyCS.Diagnostic("IDE0051").WithSpan(3, 13, 3, 14).WithArguments("C.C"));
+            // /0/Test0.cs(3,13): info IDE0051: Private member 'C.C' is unused
+            VerifyCS.Diagnostic("IDE0051").WithSpan(3, 5, 3, 25).WithArguments("C.C"));
     }
 
     [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/62856")]

src/Analyzers/Core/Analyzers/Helpers/DiagnosticHelper.cs

@@ -47,21 +47,22 @@ public static Diagnostic Create(
         params object[] messageArgs)
     {
         if (descriptor == null)
-        {
             throw new ArgumentNullException(nameof(descriptor));
-        }
 
-        LocalizableString message;
+        var message = CreateMessage(descriptor, messageArgs);
+        return CreateWithMessage(descriptor, location, notificationOption, analyzerOptions, additionalLocations, properties, message);
+    }
+
+    private static LocalizableString CreateMessage(DiagnosticDescriptor descriptor, object[] messageArgs)
+    {
         if (messageArgs == null || messageArgs.Length == 0)
         {
-            message = descriptor.MessageFormat;
+            return descriptor.MessageFormat;
         }
         else
         {
-            message = new LocalizableStringWithArguments(descriptor.MessageFormat, messageArgs);
+            return new LocalizableStringWithArguments(descriptor.MessageFormat, messageArgs);
         }
-
-        return CreateWithMessage(descriptor, location, notificationOption, analyzerOptions, additionalLocations, properties, message);
     }
 
     /// <summary>
@@ -92,11 +93,28 @@ public static Diagnostic CreateWithLocationTags(
         ImmutableArray<Location> additionalLocations,
         ImmutableArray<Location> additionalUnnecessaryLocations,
         params object[] messageArgs)
+    {
+        return CreateWithLocationTags(
+            descriptor,
+            location,
+            notificationOption,
+            analyzerOptions,
+            CreateMessage(descriptor, messageArgs),
+            additionalLocations,
+            additionalUnnecessaryLocations);
+    }
+
+    private static Diagnostic CreateWithLocationTags(
+        DiagnosticDescriptor descriptor,
+        Location location,
+        NotificationOption2 notificationOption,
+        AnalyzerOptions analyzerOptions,
+        LocalizableString message,
+        ImmutableArray<Location> additionalLocations,
+        ImmutableArray<Location> additionalUnnecessaryLocations)
     {
         if (additionalUnnecessaryLocations.IsEmpty)
-        {
-            return Create(descriptor, location, notificationOption, analyzerOptions, additionalLocations, ImmutableDictionary<string, string?>.Empty, messageArgs);
-        }
+            return CreateWithMessage(descriptor, location, notificationOption, analyzerOptions, additionalLocations, ImmutableDictionary<string, string?>.Empty, message);
 
         var tagIndices = ImmutableDictionary<string, IEnumerable<int>>.Empty
             .Add(WellKnownDiagnosticTags.Unnecessary, Enumerable.Range(additionalLocations.Length, additionalUnnecessaryLocations.Length));
@@ -105,10 +123,10 @@ public static Diagnostic CreateWithLocationTags(
             location,
             notificationOption,
             analyzerOptions,
+            message,
             additionalLocations.AddRange(additionalUnnecessaryLocations),
             tagIndices,
-            ImmutableDictionary<string, string?>.Empty,
-            messageArgs);
+            ImmutableDictionary<string, string?>.Empty);
     }
 
     /// <summary>
@@ -144,11 +162,30 @@ public static Diagnostic CreateWithLocationTags(
         ImmutableArray<Location> additionalUnnecessaryLocations,
         ImmutableDictionary<string, string?>? properties,
         params object[] messageArgs)
+    {
+        return CreateWithLocationTags(
+            descriptor,
+            location,
+            notificationOption,
+            analyzerOptions,
+            CreateMessage(descriptor, messageArgs),
+            additionalLocations,
+            additionalUnnecessaryLocations,
+            properties);
+    }
+
+    public static Diagnostic CreateWithLocationTags(
+        DiagnosticDescriptor descriptor,
+        Location location,
+        NotificationOption2 notificationOption,
+        AnalyzerOptions analyzerOptions,
+        LocalizableString message,
+        ImmutableArray<Location> additionalLocations,
+        ImmutableArray<Location> additionalUnnecessaryLocations,
+        ImmutableDictionary<string, string?>? properties)
     {
         if (additionalUnnecessaryLocations.IsEmpty)
-        {
-            return Create(descriptor, location, notificationOption, analyzerOptions, additionalLocations, properties, messageArgs);
-        }
+            return CreateWithMessage(descriptor, location, notificationOption, analyzerOptions, additionalLocations, properties, message);
 
         var tagIndices = ImmutableDictionary<string, IEnumerable<int>>.Empty
             .Add(WellKnownDiagnosticTags.Unnecessary, Enumerable.Range(additionalLocations.Length, additionalUnnecessaryLocations.Length));
@@ -157,49 +194,29 @@ public static Diagnostic CreateWithLocationTags(
             location,
             notificationOption,
             analyzerOptions,
+            message,
             additionalLocations.AddRange(additionalUnnecessaryLocations),
             tagIndices,
-            properties,
-            messageArgs);
+            properties);
     }
 
-    /// <summary>
-    /// Create a diagnostic that adds properties specifying a tag for a set of locations.
-    /// </summary>
-    /// <param name="descriptor">A <see cref="DiagnosticDescriptor"/> describing the diagnostic.</param>
-    /// <param name="location">An optional primary location of the diagnostic. If null, <see cref="Location"/> will return <see cref="Location.None"/>.</param>
-    /// <param name="notificationOption">Notification option for the diagnostic.</param>
-    /// <param name="additionalLocations">
-    /// An optional set of additional locations related to the diagnostic.
-    /// Typically, these are locations of other items referenced in the message.
-    /// </param>
-    /// <param name="tagIndices">
-    /// a map of location tag to index in additional locations.
-    /// "AbstractRemoveUnnecessaryParenthesesDiagnosticAnalyzer" for an example of usage.
-    /// </param>
-    /// <param name="properties">
-    /// An optional set of name-value pairs by means of which the analyzer that creates the diagnostic
-    /// can convey more detailed information to the fixer.
-    /// </param>
-    /// <param name="messageArgs">Arguments to the message of the diagnostic.</param>
-    /// <returns>The <see cref="Diagnostic"/> instance.</returns>
     private static Diagnostic CreateWithLocationTags(
         DiagnosticDescriptor descriptor,
         Location location,
         NotificationOption2 notificationOption,
         AnalyzerOptions analyzerOptions,
+        LocalizableString message,
         IEnumerable<Location> additionalLocations,
         IDictionary<string, IEnumerable<int>> tagIndices,
-        ImmutableDictionary<string, string?>? properties,
-        params object[] messageArgs)
+        ImmutableDictionary<string, string?>? properties)
     {
         Contract.ThrowIfTrue(additionalLocations.IsEmpty());
         Contract.ThrowIfTrue(tagIndices.IsEmpty());
 
         properties ??= ImmutableDictionary<string, string?>.Empty;
         properties = properties.AddRange(tagIndices.Select(kvp => new KeyValuePair<string, string?>(kvp.Key, EncodeIndices(kvp.Value, additionalLocations.Count()))));
 
-        return Create(descriptor, location, notificationOption, analyzerOptions, additionalLocations, properties, messageArgs);
+        return CreateWithMessage(descriptor, location, notificationOption, analyzerOptions, additionalLocations, properties, message);
 
         static string EncodeIndices(IEnumerable<int> indices, int additionalLocationsLength)
         {

src/Analyzers/Core/Analyzers/RemoveUnusedMembers/AbstractRemoveUnusedMembersDiagnosticAnalyzer.cs

@@ -45,7 +45,7 @@ internal abstract class AbstractRemoveUnusedMembersDiagnosticAnalyzer<
         EnforceOnBuildValues.RemoveUnusedMembers,
         new LocalizableResourceString(nameof(AnalyzersResources.Remove_unused_private_members), AnalyzersResources.ResourceManager, typeof(AnalyzersResources)),
         new LocalizableResourceString(nameof(AnalyzersResources.Private_member_0_is_unused), AnalyzersResources.ResourceManager, typeof(AnalyzersResources)),
-        hasAnyCodeStyleOption: false, isUnnecessary: true);
+        hasAnyCodeStyleOption: false, isUnnecessary: false);
 
     // IDE0052: "Remove unread members" (Value is written and/or symbol is referenced, but the assigned value is never read)
     // Internal for testing
@@ -54,7 +54,7 @@ internal abstract class AbstractRemoveUnusedMembersDiagnosticAnalyzer<
         EnforceOnBuildValues.RemoveUnreadMembers,
         new LocalizableResourceString(nameof(AnalyzersResources.Remove_unread_private_members), AnalyzersResources.ResourceManager, typeof(AnalyzersResources)),
         new LocalizableResourceString(nameof(AnalyzersResources.Private_member_0_can_be_removed_as_the_value_assigned_to_it_is_never_read), AnalyzersResources.ResourceManager, typeof(AnalyzersResources)),
-        hasAnyCodeStyleOption: false, isUnnecessary: true);
+        hasAnyCodeStyleOption: false, isUnnecessary: false);
 
     protected AbstractRemoveUnusedMembersDiagnosticAnalyzer()
         : base([s_removeUnusedMembersRule, s_removeUnreadMembersRule],
@@ -64,6 +64,7 @@ protected AbstractRemoveUnusedMembersDiagnosticAnalyzer()
 
     protected abstract IEnumerable<TTypeDeclarationSyntax> GetTypeDeclarations(INamedTypeSymbol namedType, CancellationToken cancellationToken);
     protected abstract SyntaxList<TMemberDeclarationSyntax> GetMembers(TTypeDeclarationSyntax typeDeclaration);
+    protected abstract SyntaxNode GetParentIfSoleDeclarator(SyntaxNode declaration);
 
     // We need to analyze the whole document even for edits within a method body,
     // because we might add or remove references to members in executable code.
@@ -428,6 +429,7 @@ private void AnalyzeObjectCreationOperation(OperationAnalysisContext operationCo
 
         private void OnSymbolEnd(SymbolAnalysisContext symbolEndContext, bool hasUnsupportedOperation)
         {
+            var cancellationToken = symbolEndContext.CancellationToken;
             if (hasUnsupportedOperation)
             {
                 return;
@@ -445,7 +447,7 @@ private void OnSymbolEnd(SymbolAnalysisContext symbolEndContext, bool hasUnsuppo
             using var _1 = PooledHashSet<ISymbol>.GetInstance(out var symbolsReferencedInDocComments);
             using var _2 = ArrayBuilder<string>.GetInstance(out var debuggerDisplayAttributeArguments);
 
-            var entryPoint = symbolEndContext.Compilation.GetEntryPoint(symbolEndContext.CancellationToken);
+            var entryPoint = symbolEndContext.Compilation.GetEntryPoint(cancellationToken);
 
             var namedType = (INamedTypeSymbol)symbolEndContext.Symbol;
             foreach (var member in namedType.GetMembers())
@@ -467,15 +469,15 @@ private void OnSymbolEnd(SymbolAnalysisContext symbolEndContext, bool hasUnsuppo
                     {
                         // Bail out if there are syntax errors in any of the declarations of the containing type.
                         // Note that we check this only for the first time that we report an unused or unread member for the containing type.
-                        if (HasSyntaxErrors(namedType, symbolEndContext.CancellationToken))
+                        if (HasSyntaxErrors(namedType, cancellationToken))
                         {
                             return;
                         }
 
                         // Compute the set of candidate symbols referenced in all the documentation comments within the named type declarations.
                         // This set is computed once and used for all the iterations of the loop.
                         AddCandidateSymbolsReferencedInDocComments(
-                            namedType, symbolEndContext.Compilation, symbolsReferencedInDocComments, symbolEndContext.CancellationToken);
+                            namedType, symbolEndContext.Compilation, symbolsReferencedInDocComments, cancellationToken);
 
                         // Compute the set of string arguments to DebuggerDisplay attributes applied to any symbol within the named type declaration.
                         // These strings may have an embedded reference to the symbol.
@@ -509,17 +511,24 @@ member is IPropertySymbol property &&
                         continue;
                     }
 
+                    var diagnosticLocation = GetDiagnosticLocation(member);
+                    var fadingLocation = member.DeclaringSyntaxReferences.FirstOrDefault(
+                        r => r.SyntaxTree == diagnosticLocation.SourceTree && r.Span.Contains(diagnosticLocation.SourceSpan));
+
+                    var fadingNode = fadingLocation?.GetSyntax(cancellationToken) ?? diagnosticLocation.FindNode(cancellationToken);
+                    fadingNode = fadingNode != null ? this._analyzer.GetParentIfSoleDeclarator(fadingNode) : null;
+
                     // Most of the members should have a single location, except for partial methods.
                     // We report the diagnostic on the first location of the member.
-                    var diagnostic = DiagnosticHelper.CreateWithMessage(
+                    symbolEndContext.ReportDiagnostic(DiagnosticHelper.CreateWithLocationTags(
                         rule,
-                        GetDiagnosticLocation(member),
+                        diagnosticLocation,
                         NotificationOption2.ForSeverity(rule.DefaultSeverity),
                         symbolEndContext.Options,
-                        additionalLocations: null,
-                        properties: null,
-                        GetMessage(rule, member));
-                    symbolEndContext.ReportDiagnostic(diagnostic);
+                        message: GetMessage(rule, member),
+                        additionalLocations: [],
+                        additionalUnnecessaryLocations: fadingNode is null ? [] : [fadingNode.GetLocation()],
+                        properties: null));
                 }
             }
         }

src/Analyzers/VisualBasic/Analyzers/RemoveUnusedMembers/VisualBasicRemoveUnusedMembersDiagnosticAnalyzer.vb

@@ -59,5 +59,17 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.RemoveUnusedMembers
         Protected Overrides Function GetMembers(typeDeclaration As TypeBlockSyntax) As SyntaxList(Of StatementSyntax)
             Return typeDeclaration.Members
         End Function
+
+        Protected Overrides Function GetParentIfSoleDeclarator(node As SyntaxNode) As SyntaxNode
+            Dim modifiedIdentifier = TryCast(node, ModifiedIdentifierSyntax)
+            Dim declarator = TryCast(modifiedIdentifier?.Parent, VariableDeclaratorSyntax)
+            Dim field = TryCast(declarator?.Parent, FieldDeclarationSyntax)
+
+            If declarator?.Names.Count = 1 AndAlso field?.Declarators.Count = 1 Then
+                Return field
+            End If
+
+            Return node
+        End Function
     End Class
 End Namespace