Add analyzer warnings for command name issues

src/DemoApp/Services/IntermediateCaGenerator.cs

@@ -6,7 +6,7 @@ namespace DemoApp.Services;
 
 public class IntermediateCaGenerator
 {
-    ISerialNumberProvider _serialNumberProvider;
+    readonly ISerialNumberProvider _serialNumberProvider;
     public IntermediateCaGenerator(ISerialNumberProvider serialNumberProvider)
     {
         _serialNumberProvider = serialNumberProvider;

src/System.CommandLine.Minimal.SourceGenerator/CommandSourceGenerator.cs

@@ -1,6 +1,8 @@
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
+using System.Collections.Generic;
 using System.Collections.Immutable;
+using System.CommandLine.Minimal.SourceGenerator;
 using System.Threading;
 
 namespace System.CommandLine.Minimal.SourceGeneration;
@@ -22,17 +24,32 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
             ).Collect();
 
         context.RegisterSourceOutput(bindersProvider, (spc, binders) => {
-
+            HashSet<string> commandNames = new();
+
             // first generate and create all of the CommandOptions classes
             foreach (GeneratingCommandBinder? binder in binders)
             {
+                if(binder.CommandName is null || string.IsNullOrWhiteSpace(binder.CommandName))
+                {
+                    spc.ReportCommandNameEmptyError(binder.CommandNameLocation);
+                    continue;
+                }
+                if(commandNames.Contains(binder.CommandName))
+                {
+                    spc.ReportCommandNameConflict(binder.CommandNameLocation, binder.CommandName);
+                    continue;
+                }
+
+                // command name is validated so add to the hashset
+                commandNames.Add(binder.CommandName);
+
                 string? code = CommandOptionsWriter.GenerateOptions(binder);
                 if(code is not null)
                 {
                     spc.AddSource($"{binder.ClassName}_{binder.MethodName}_Command.g.cs", code);
                 }
             }
-
+            
             // Emit the aggregated Register method
             string? registryCode = MapAllCommandsExtensionWriter.GenerateMapAllCommandsExt(binders);
             if(registryCode is not null)

src/System.CommandLine.Minimal.SourceGenerator/DiagnosticErrors.cs

@@ -0,0 +1,45 @@
+using Microsoft.CodeAnalysis;
+
+namespace System.CommandLine.Minimal.SourceGenerator
+{
+    internal static class DiagnosticErrors
+    {
+        const string CommandNameCategory = "Command Name";
+        static readonly DiagnosticDescriptor CommandNameConflict =
+            new DiagnosticDescriptor(
+                "MIN0001",
+                "Command name conflict",
+                "Another Handler attribute already has this command name \"{0}\"",
+                CommandNameCategory,
+                DiagnosticSeverity.Error,
+                true
+            );
+        static readonly DiagnosticDescriptor CommandNameEmpty = 
+            new DiagnosticDescriptor(
+                "MIN0002",
+                "Command name empty",
+                "A command name is null or empty",
+                CommandNameCategory,
+                DiagnosticSeverity.Error,
+                true
+            );
+
+        /// <summary>
+        /// MIN0002 empty command name.
+        /// </summary>
+        internal static void ReportCommandNameEmptyError(
+            this SourceProductionContext ctx,
+            Location? location)
+            => ctx.ReportDiagnostic(Diagnostic.Create(CommandNameEmpty, location));
+
+        /// <summary>
+        /// MIN0001 duplicate command name.
+        /// </summary>
+        internal static void ReportCommandNameConflict(
+            this SourceProductionContext ctx, 
+            Location? location, 
+            string commandName)
+            => ctx.ReportDiagnostic(Diagnostic.Create(CommandNameConflict, location, commandName));
+
+    }
+}

src/System.CommandLine.Minimal.SourceGenerator/GeneratorBindingsProvider.cs

@@ -25,6 +25,31 @@ public static GeneratingCommandBinder Transform(GeneratorAttributeSyntaxContext
             && a.AttributeClass.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat) == "global::System.CommandLine.Minimal.HandlerAttribute");
         string? commandName = handlerAttribute?.ConstructorArguments.FirstOrDefault().Value as string;
 
+        Location? argumentLocation = null;
+        if (ctx.TargetNode is MethodDeclarationSyntax methodDecl)
+        {
+            AttributeSyntax? handlerAttrSyntax = methodDecl.AttributeLists
+                .SelectMany(attrs => attrs.Attributes)
+                .FirstOrDefault(attr => ctx.SemanticModel
+                    .GetTypeInfo(attr)
+                    .Type?
+                    .ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat) == "global::System.CommandLine.Minimal.HandlerAttribute"
+                );
+            argumentLocation = handlerAttrSyntax?.ArgumentList?.Arguments.FirstOrDefault()?.GetLocation();
+        }
+        //// Find the AttributeSyntax node for the HandlerAttribute
+        //AttributeSyntax? handlerAttributeSyntax = ctx.TargetNode switch
+        //{
+        //    MethodDeclarationSyntax methodDecl => methodDecl.AttributeLists
+        //        .SelectMany(list => list.Attributes)
+        //        .FirstOrDefault(attr =>
+        //            ctx.SemanticModel.GetTypeInfo(attr).Type?.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat)
+        //            == "global::System.CommandLine.Minimal.HandlerAttribute"),
+        //    _ => null
+        //};
+        //Location? argumentLocation = handlerAttributeSyntax?.ArgumentList?.Arguments.FirstOrDefault()?.GetLocation();
+
+
         string classNamespace = methodSymbol.ContainingNamespace.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat);
         string className = methodSymbol.ContainingType.Name;
         string methodName = methodSymbol.Name;
@@ -73,6 +98,7 @@ public static GeneratingCommandBinder Transform(GeneratorAttributeSyntaxContext
             MethodName: methodName,
             MethodReturnType: methodReturnType,
             MethodIsStatic: methodIsStatic,
+            CommandNameLocation: argumentLocation,
             Bindings: bindings.ToImmutableArray());
     }
 
@@ -221,6 +247,7 @@ internal record GeneratingCommandBinder(
     string MethodName,
     string MethodReturnType,
     bool MethodIsStatic,
+    Location? CommandNameLocation,
     ImmutableArray<ParameterBinding>? Bindings
 )
 {