add another roslyn analyzer for context menu commands that can use emoji

SourceGenerators/AttributeUsageAnalyzer.cs

@@ -1,4 +1,5 @@
-using System.Collections.Immutable;
+using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Linq;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
@@ -31,10 +32,20 @@ public class AttributeUsageAnalyzer : DiagnosticAnalyzer
         isEnabledByDefault: true,
         description: "Description must be less than or equal to 100 characters."
     );
+    private static readonly DiagnosticDescriptor CommandWithEmojiVariationSelector = new(
+        "DSP0003",
+        "Emoji with variation selector",
+        "Command name has an emoji character with VS{0} ({1}), which may not work as a command name",
+        "Usage",
+        DiagnosticSeverity.Warning,
+        isEnabledByDefault: true,
+        description: "Commands should avoid using variation selectors for emoji characters in command names."
+    );
 
     public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } = [
         AccessCheckAttributeOnGroupCommandRule,
         DescriptionLengthRule,
+        CommandWithEmojiVariationSelector,
     ];
 
     public override void Initialize(AnalysisContext context)
@@ -46,6 +57,7 @@ public class AttributeUsageAnalyzer : DiagnosticAnalyzer
         // See https://github.com/dotnet/roslyn/blob/master/docs/analyzers/Analyzer%20Actions%20Semantics.md for more information
         context.RegisterSymbolAction(AnalyzeMethod, SymbolKind.Method);
         context.RegisterOperationAction(AnalyzeDescriptionAttribute, OperationKind.Attribute);
+        context.RegisterOperationAction(AnalyzeCommandAttribute, OperationKind.Attribute);
     }
 
     private static void AnalyzeMethod(SymbolAnalysisContext context)
@@ -135,6 +147,70 @@ public class AttributeUsageAnalyzer : DiagnosticAnalyzer
         // Reporting a diagnostic is the primary outcome of analyzers.
         context.ReportDiagnostic(diagnostic);
     }
+    
+    private void AnalyzeCommandAttribute(OperationAnalysisContext context)
+    {
+        // The Roslyn architecture is based on inheritance.
+        // To get the required metadata, we should match the 'Operation' and 'Syntax' objects to the particular types,
+        // which are based on the 'OperationKind' parameter specified in the 'Register...' method.
+        if (context.Operation is not IAttributeOperation attributeOperation
+            || context.Operation.Syntax is not AttributeSyntax attributeSyntax)
+            return;
+
+        if (attributeOperation.Kind != OperationKind.Attribute
+            || attributeOperation.Operation is not IObjectCreationOperation
+            {
+                Kind: OperationKind.ObjectCreation,
+                Type:
+                {
+                    ContainingNamespace:
+                    {
+                        ContainingNamespace.Name: "DSharpPlus",
+                        Name: "Commands"
+                    },
+                    Name: "CommandAttribute"
+                }
+            } attrCtorOp)
+            return;
+
+        if (attrCtorOp.Arguments.Length is 0
+            || attrCtorOp.Arguments.FirstOrDefault(arg => arg is
+            {
+                Parameter:
+                {
+                    Name: "name",
+                    Type: {ContainingNamespace.Name: "System", Name: "String"}
+                }
+            }) is not
+            {
+                Value: ILiteralOperation
+                {
+                    ConstantValue:
+                    {
+                        HasValue: true,
+                        Value: string actualName
+                    }
+                }
+            })
+            return;
+
+        if (actualName is not {Length: >0})
+            return;
+
+        var vs = actualName.ToCharArray().FirstOrDefault(VariationSelectors.Contains);
+        if (vs is default(char))
+            return;
+        
+        var diagnostic = Diagnostic.Create(CommandWithEmojiVariationSelector,
+            // The highlighted area in the analyzed source code. Keep it as specific as possible.
+            attributeSyntax.GetLocation(),
+            // The value is passed to the 'MessageFormat' argument of your rule.
+            vs - 0xFE00 + 1, $"0x{(int)vs:X4}"
+        );
+
+        // Reporting a diagnostic is the primary outcome of analyzers.
+        context.ReportDiagnostic(diagnostic);
+    }
 
     private static bool IsDescendantOfAttribute(AttributeData attributeData, string baseAttributeClassNameWithNamespace)
     {
@@ -148,4 +224,6 @@ public class AttributeUsageAnalyzer : DiagnosticAnalyzer
         } 
         return false;
     }
+
+    private static readonly HashSet<char> VariationSelectors = [.. Enumerable.Range(0xFE00, 16).Select(i => (char)i)];
 }