update

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/ClientProvider.cs

@@ -7,6 +7,7 @@
 using System.Linq;
 using System.Threading;
 using Microsoft.TypeSpec.Generator.ClientModel.Primitives;
+using Microsoft.TypeSpec.Generator.EmitterRpc;
 using Microsoft.TypeSpec.Generator.Expressions;
 using Microsoft.TypeSpec.Generator.Input;
 using Microsoft.TypeSpec.Generator.Primitives;
@@ -147,9 +148,56 @@ public ClientProvider(InputClient inputClient)
             _subClients = new(GetSubClients);
         }
 
-        protected override string BuildNamespace() => string.IsNullOrEmpty(_inputClient.Namespace) ?
-            base.BuildNamespace() :
-            ScmCodeModelPlugin.Instance.TypeFactory.GetCleanNameSpace(_inputClient.Namespace);
+        private const string namespaceConflictCode = "client-namespace-conflict";
+
+        private string? _namespace;
+        protected override string BuildNamespace()
+        {
+            return _namespace ??= BuildNamespaceCore();
+        }
+
+        private string BuildNamespaceCore()
+        {
+            // if namespace is empty, we fallback to the root namespace
+            if (string.IsNullOrEmpty(_inputClient.Namespace))
+            {
+                return base.BuildNamespace();
+            }
+            var ns = ScmCodeModelPlugin.Instance.TypeFactory.GetCleanNameSpace(_inputClient.Namespace);
+
+            // figure out if this namespace has been changed for this client
+            if (!IsLastSegmentTheSame(ns, _inputClient.Namespace))
+            {
+                Emitter.Instance.ReportDiagnostic(namespaceConflictCode, $"namespace {_inputClient.Namespace} conflicts with client {_inputClient.Name}, please use `@clientName` to specify a different name for the client.", _inputClient.CrossLanguageDefinitionId);
+            }
+            return ns;
+        }
+
+        internal static bool IsLastSegmentTheSame(string left, string right)
+        {
+            // finish this via Span API
+            var leftSpan = left.AsSpan();
+            var rightSpan = right.AsSpan();
+            var count = Math.Min(leftSpan.Length, rightSpan.Length);
+            for (int i = 1; i <= count; i++)
+            {
+                var lc = leftSpan[^i];
+                var rc = rightSpan[^i];
+                // check if each char is the same from the right-most side
+                // if both of them are dot, we finished scanning the last segment - and if we could be here, meaning all of them are the same, return true.
+                if (lc == '.' && rc == '.')
+                {
+                    return true;
+                }
+                // if these are different - there is one different character, return false.
+                if (lc != rc)
+                {
+                    return false;
+                }
+            }
+
+            return leftSpan.Length == rightSpan.Length;
+        }
 
         private IReadOnlyList<ParameterProvider> GetSubClientInternalConstructorParameters()
         {

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.Input/src/InputLibrary.cs

@@ -3,7 +3,6 @@
 
 using System;
 using System.IO;
-using Microsoft.TypeSpec.Generator.Input.EmitterRpc;
 
 namespace Microsoft.TypeSpec.Generator.Input
 {
@@ -12,7 +11,6 @@ public class InputLibrary
         private const string CodeModelInputFileName = "tspCodeModel.json";
 
         private readonly string _codeModelPath;
-        private readonly Emitter _emitter;
 
         // for mocking
 #pragma warning disable CS8618 // Non-nullable field must contain a non-null value when exiting constructor. Consider declaring as nullable.
@@ -21,16 +19,15 @@ protected InputLibrary()
         {
         }
 
-        public InputLibrary(string codeModelPath, Emitter emitter)
+        public InputLibrary(string codeModelPath)
         {
             _codeModelPath = codeModelPath;
-            _emitter = emitter;
         }
 
         private InputNamespace? _inputNamespace;
-        public virtual InputNamespace InputNamespace => _inputNamespace ??= Load(_codeModelPath, _emitter);
+        public virtual InputNamespace InputNamespace => _inputNamespace ??= Load(_codeModelPath);
 
-        internal InputNamespace Load(string outputDirectory, Emitter emitter)
+        internal InputNamespace Load(string outputDirectory)
         {
             var codeModelFile = Path.Combine(outputDirectory, CodeModelInputFileName);
             if (!File.Exists(codeModelFile))
@@ -40,7 +37,7 @@ internal InputNamespace Load(string outputDirectory, Emitter emitter)
 
             // Read and deserialize tspCodeModel.json
             var json = File.ReadAllText(codeModelFile);
-            return TypeSpecSerialization.Deserialize(json, emitter) ?? throw new InvalidOperationException($"Deserializing {codeModelFile} has failed.");
+            return TypeSpecSerialization.Deserialize(json) ?? throw new InvalidOperationException($"Deserializing {codeModelFile} has failed.");
         }
 
         private bool? _hasMultipartFormDataOperation;

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.Input/src/InputTypes/Serialization/TypeSpecInputClientConverter.cs

@@ -5,20 +5,15 @@
 using System.Collections.Generic;
 using System.Text.Json;
 using System.Text.Json.Serialization;
-using Microsoft.TypeSpec.Generator.Input.EmitterRpc;
 
 namespace Microsoft.TypeSpec.Generator.Input
 {
     internal sealed class TypeSpecInputClientConverter : JsonConverter<InputClient>
     {
-        private const string namespaceConflictCode = "client-namespace-conflict";
-
-        private readonly Emitter _emitter;
         private readonly TypeSpecReferenceHandler _referenceHandler;
 
-        public TypeSpecInputClientConverter(TypeSpecReferenceHandler referenceHandler, Emitter emitter)
+        public TypeSpecInputClientConverter(TypeSpecReferenceHandler referenceHandler)
         {
-            _emitter = emitter;
             _referenceHandler = referenceHandler;
         }
 
@@ -80,11 +75,7 @@ public override void Write(Utf8JsonWriter writer, InputClient value, JsonSeriali
             var lastSegment = GetLastSegment(client.Namespace);
             if (lastSegment == client.Name)
             {
-                // invalid namespace segment found
-                // report the diagnostic
-                _emitter.ReportDiagnostic(namespaceConflictCode, $"namespace {client.Namespace} conflicts with client {client.Name}, please use `@clientName` to specify a different name for the client.", crossLanguageDefinitionId);
-                // check if the list is already there
-                // get the list out
+                // invalid namespace segment found, add it into the list
                 var invalidNamespaceSegments = (List<string>)resolver.ResolveReference(TypeSpecSerialization.InvalidNamespaceSegmentsKey);
                 invalidNamespaceSegments.Add(client.Name);
             }

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.Input/src/InputTypes/Serialization/TypeSpecSerialization.cs

@@ -4,14 +4,13 @@
 using System.Text.Json;
 using System.Text.Json.Serialization;
 using AutoRest.CSharp.Common.Input;
-using Microsoft.TypeSpec.Generator.Input.EmitterRpc;
 
 namespace Microsoft.TypeSpec.Generator.Input
 {
     public static class TypeSpecSerialization
     {
         internal const string InvalidNamespaceSegmentsKey = "InvalidNamespaceSegments";
-        public static InputNamespace? Deserialize(string json, Emitter emitter)
+        public static InputNamespace? Deserialize(string json)
         {
             var referenceHandler = new TypeSpecReferenceHandler();
             var options = new JsonSerializerOptions
@@ -32,7 +31,7 @@ public static class TypeSpecSerialization
                     new TypeSpecInputConstantConverter(referenceHandler),
                     new TypeSpecInputLiteralTypeConverter(referenceHandler),
                     new TypeSpecInputUnionTypeConverter(referenceHandler),
-                    new TypeSpecInputClientConverter(referenceHandler, emitter),
+                    new TypeSpecInputClientConverter(referenceHandler),
                     new TypeSpecInputOperationConverter(referenceHandler),
                     new TypeSpecInputParameterConverter(referenceHandler),
                     new TypeSpecInputPrimitiveTypeConverter(referenceHandler),

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/CSharpGen.cs

@@ -6,7 +6,7 @@
 using System.IO;
 using System.Linq;
 using System.Threading.Tasks;
-using Microsoft.TypeSpec.Generator.Input.EmitterRpc;
+using Microsoft.TypeSpec.Generator.EmitterRpc;
 using Microsoft.TypeSpec.Generator.SourceInput;
 
 namespace Microsoft.TypeSpec.Generator

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/CodeModelPlugin.cs

@@ -6,7 +6,6 @@
 using System.ComponentModel.Composition;
 using Microsoft.CodeAnalysis;
 using Microsoft.TypeSpec.Generator.Input;
-using Microsoft.TypeSpec.Generator.Input.EmitterRpc;
 using Microsoft.TypeSpec.Generator.Primitives;
 using Microsoft.TypeSpec.Generator.Providers;
 using Microsoft.TypeSpec.Generator.SourceInput;
@@ -45,7 +44,7 @@ internal static CodeModelPlugin Instance
         public CodeModelPlugin(GeneratorContext context)
         {
             Configuration = context.Configuration;
-            _inputLibrary = new InputLibrary(Configuration.OutputDirectory, Emitter.Instance);
+            _inputLibrary = new InputLibrary(Configuration.OutputDirectory);
             TypeFactory = new TypeFactory();
         }
 

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.Input/src/EmitterRpc/Emitter.cs → packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/EmitterRpc/Emitter.cs

@@ -5,7 +5,7 @@
 using System.IO;
 using System.Text.Json;
 
-namespace Microsoft.TypeSpec.Generator.Input.EmitterRpc
+namespace Microsoft.TypeSpec.Generator.EmitterRpc
 {
     public sealed class Emitter : IDisposable
     {

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/Providers/TypeProvider.cs

@@ -110,7 +110,7 @@ public string? Deprecated
         public CSharpType Type => _type ??=
             new(
                 _name ??= CustomCodeView?.Name ?? BuildName(),
-                CustomCodeView?.BuildNamespace() ?? BuildNamespace(),
+                CustomCodeView?.Type.Namespace ?? BuildNamespace(),
                 this is EnumProvider ||
                 DeclarationModifiers.HasFlag(TypeSignatureModifiers.Struct) ||
                 DeclarationModifiers.HasFlag(TypeSignatureModifiers.Enum),

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/StartUp/Program.cs

@@ -5,7 +5,7 @@
 using System.Diagnostics;
 using System.Threading.Tasks;
 using CommandLine;
-using Microsoft.TypeSpec.Generator.Input.EmitterRpc;
+using Microsoft.TypeSpec.Generator.EmitterRpc;
 
 namespace Microsoft.TypeSpec.Generator
 {