Override ApiException.Message getter to include ResponseStatusCode

src/Kiota.Builder/Writers/CSharp/CodePropertyWriter.cs

@@ -62,7 +62,7 @@ private void WritePropertyInternal(CodeProperty codeElement, LanguageWriter writ
                 if (parentClass.GetPrimaryMessageCodePath(static x => x.Name.ToFirstCharacterUpperCase(), static x => x.Name.ToFirstCharacterUpperCase(), "?.") is string primaryMessageCodePath && !string.IsNullOrEmpty(primaryMessageCodePath))
                     writer.WriteLine($"public override {propertyType} {codeElement.Name.ToFirstCharacterUpperCase()} {{ get => {primaryMessageCodePath} ?? string.Empty; }}");
                 else
-                    writer.WriteLine($"public override {propertyType} {codeElement.Name.ToFirstCharacterUpperCase()} {{ get => base.Message; }}");
+                    writer.WriteLine($"public override {propertyType} {codeElement.Name.ToFirstCharacterUpperCase()} {{ get => $\"{{ResponseStatusCode}}: {{base.Message}}\"; }}");
                 break;
             case CodePropertyKind.QueryParameter when codeElement.IsNameEscaped:
                 writer.WriteLine($"[QueryParameter(\"{codeElement.SerializationName}\")]");

src/Kiota.Builder/Writers/Dart/CodePropertyWriter.cs

@@ -59,7 +59,8 @@ private void WritePropertyInternal(CodeProperty codeElement, LanguageWriter writ
                 break;
             case CodePropertyKind.ErrorMessageOverride when parentClass.IsErrorDefinition:
                 writer.WriteLine("@override");
-                goto default;
+                writer.WriteLine($"{propertyType} get {codeElement.Name} => '$responseStatusCode: ${{super.message}}';");
+                break;
             case CodePropertyKind.QueryParameter when codeElement.IsNameEscaped:
                 writer.WriteLine($"/// @QueryParameter('{codeElement.SerializationName}')");
                 goto default;

src/Kiota.Builder/Writers/Go/CodeMethodWriter.cs

@@ -101,7 +101,7 @@ private static void WriteErrorMethodOverride(CodeClass parentClass, LanguageWrit
         }
         else
         {
-            writer.WriteLine("return m.ApiError.Error()");
+            writer.WriteLine("return fmt.Sprintf(\"%d: %s\", m.ResponseStatusCode, m.ApiError.Error())");
         }
     }
     private void WriteRawUrlBuilderBody(CodeClass parentClass, CodeMethod codeElement, LanguageWriter writer)

src/Kiota.Builder/Writers/Java/CodeMethodWriter.cs

@@ -105,7 +105,7 @@ private static void WriteErrorMethodOverride(CodeClass parentClass, LanguageWrit
         }
         else
         {
-            writer.WriteLine("return super.getMessage();");
+            writer.WriteLine("return getResponseStatusCode() + \": \" + super.getMessage();");
         }
     }
     private void WriteRawUrlBuilderBody(CodeClass parentClass, CodeMethod codeElement, LanguageWriter writer)

src/Kiota.Builder/Writers/Php/CodeMethodWriter.cs

@@ -98,7 +98,7 @@ private void WriteErrorMessageOverride(CodeClass parentClass, LanguageWriter wri
         }
         else
         {
-            writer.WriteLine("return parent::getMessage();");
+            writer.WriteLine("return $this->getResponseStatusCode() . ': ' . parent::getMessage();");
         }
     }
     private const string UrlTemplateTempVarName = "$urlTplParams";

src/Kiota.Builder/Writers/Python/CodePropertyWriter.cs

@@ -65,7 +65,7 @@ public override void WriteCodeElement(CodeProperty codeElement, LanguageWriter w
                     writer.WriteLine("return ''");
                 }
                 else
-                    writer.WriteLine("return super().message");
+                    writer.WriteLine("return f'{self.response_status_code}: {super().message}'");
                 writer.DecreaseIndent();
                 break;
         }

src/Kiota.Builder/Writers/TypeScript/CodeFunctionWriter.cs

@@ -621,6 +621,13 @@ private void WriteDeserializerFunctionProperties(CodeParameter param, CodeInterf
             WritePropertyDeserializationBlock(otherProp, param, primaryErrorMapping, primaryErrorMappingKey, codeFile, writer);
         }
 
+        // Fallback: If no primaryErrorMappingKey, emit error message assignment here
+        if (string.IsNullOrEmpty(primaryErrorMappingKey) && !string.IsNullOrEmpty(primaryErrorMapping))
+        {
+            writer.WriteLine("// Fallback error message assignment for error definitions without primary message");
+            writer.WriteLine(primaryErrorMapping.Trim());
+        }
+
         writer.CloseBlock();
     }
 
@@ -630,10 +637,17 @@ private static (string, string) GetPrimaryErrorMapping(CodeFunction codeFunction
         var primaryErrorMappingKey = string.Empty;
         var parentClass = codeFunction.OriginalMethodParentClass;
 
-        if (parentClass.IsErrorDefinition && parentClass.AssociatedInterface is not null && parentClass.AssociatedInterface.GetPrimaryMessageCodePath(static x => x.Name.ToFirstCharacterLowerCase(), static x => x.Name.ToFirstCharacterLowerCase(), "?.") is string primaryMessageCodePath && !string.IsNullOrEmpty(primaryMessageCodePath))
+        if (parentClass.IsErrorDefinition)
         {
-            primaryErrorMapping = $" {param.Name.ToFirstCharacterLowerCase()}.message = {param.Name.ToFirstCharacterLowerCase()}.{primaryMessageCodePath} ?? \"\";";
-            primaryErrorMappingKey = primaryMessageCodePath.Split("?.", StringSplitOptions.RemoveEmptyEntries)[0];
+            if (parentClass.AssociatedInterface is not null && parentClass.AssociatedInterface.GetPrimaryMessageCodePath(static x => x.Name.ToFirstCharacterLowerCase(), static x => x.Name.ToFirstCharacterLowerCase(), "?.") is string primaryMessageCodePath && !string.IsNullOrEmpty(primaryMessageCodePath))
+            {
+                primaryErrorMapping = $" {param.Name.ToFirstCharacterLowerCase()}.message = {param.Name.ToFirstCharacterLowerCase()}.{primaryMessageCodePath} ?? \"\";";
+                primaryErrorMappingKey = primaryMessageCodePath.Split("?.", StringSplitOptions.RemoveEmptyEntries)[0];
+            }
+            else
+            {
+                primaryErrorMapping = $" {param.Name.ToFirstCharacterLowerCase()}.message = `${{{param.Name.ToFirstCharacterLowerCase()}.responseStatusCode}}: ${{super.message ?? \"\"}}`;";
+            }
         }
 
         return (primaryErrorMapping, primaryErrorMappingKey);

tests/Kiota.Builder.Tests/Writers/CSharp/CodePropertyWriterTests.cs

@@ -249,5 +249,29 @@ public void WritesMessageOverrideOnPrimary()
         // Then
         Assert.Contains("public override string Message { get => Prop1 ?? string.Empty; }", result);
     }
+
+    [Fact]
+    public void WritesMessageOverrideWithStatusCodeWhenNoPrimaryMessage()
+    {
+        // Given
+        parentClass.IsErrorDefinition = true;
+        // No primary error message property added
+        var overrideProperty = parentClass.AddProperty(new CodeProperty
+        {
+            Name = "Message",
+            Kind = CodePropertyKind.ErrorMessageOverride,
+            Type = new CodeType
+            {
+                Name = "string",
+            },
+        }).First();
+
+        // When
+        writer.Write(overrideProperty);
+        var result = tw.ToString();
+
+        // Then
+        Assert.Contains("public override string Message { get => $\"{ResponseStatusCode}: {base.Message}\"; }", result);
+    }
 }
 

tests/Kiota.Builder.Tests/Writers/Dart/CodePropertyWriterTests.cs

@@ -131,4 +131,15 @@ public void DoesntWritePropertiesExistingInParentType()
         var result = tw.ToString();
         Assert.Empty(result);
     }
+
+    [Fact]
+    public void WriteErrorMessageOverrideWithStatusCodeWhenNoPrimary()
+    {
+        property.Kind = CodePropertyKind.ErrorMessageOverride;
+        parentClass.IsErrorDefinition = true;
+        writer.Write(property);
+        var result = tw.ToString();
+        Assert.Contains("@override", result);
+        Assert.Contains("get propertyName => '$responseStatusCode: ${super.message}';", result);
+    }
 }

tests/Kiota.Builder.Tests/Writers/Go/CodeMethodWriterTests.cs

@@ -2304,6 +2304,39 @@ public void WritesMessageOverrideOnPrimary()
         Assert.Contains("return *(m.GetProp1()", result);
     }
 
+    [Fact]
+    public void WritesMessageOverrideWithStatusCodeWhenNoPrimary()
+    {
+        // Given
+        parentClass = root.AddClass(new CodeClass
+        {
+            Name = "parentClass",
+            IsErrorDefinition = true,
+            Kind = CodeClassKind.Model,
+        }).First();
+        // No primary error message property added
+        var method = parentClass.AddMethod(new CodeMethod
+        {
+            Kind = CodeMethodKind.ErrorMessageOverride,
+            ReturnType = new CodeType
+            {
+                Name = "string",
+                IsNullable = false,
+            },
+            IsAsync = false,
+            IsStatic = false,
+            Name = "Error"
+        }).First();
+
+        // When
+        writer.Write(method);
+        var result = tw.ToString();
+
+        // Then
+        Assert.Contains("Error()(string) {", result);
+        Assert.Contains("return fmt.Sprintf(\"%d: %s\", m.ResponseStatusCode, m.ApiError.Error())", result);
+    }
+
     [Fact]
     public void WritesRequestGeneratorAcceptHeaderQuotes()
     {

tests/Kiota.Builder.Tests/Writers/Java/CodeMethodWriterTests.cs

@@ -2165,6 +2165,40 @@ public void WritesMessageOverrideOnPrimary()
         Assert.Contains("return this.getProp1()", result);
     }
 
+    [Fact]
+    public void WritesMessageOverrideWithStatusCodeWhenNoPrimary()
+    {
+        // Given
+        parentClass = root.AddClass(new CodeClass
+        {
+            Name = "parentClass",
+            IsErrorDefinition = true,
+            Kind = CodeClassKind.Model,
+        }).First();
+        // No primary error message property added
+        var method = parentClass.AddMethod(new CodeMethod
+        {
+            Kind = CodeMethodKind.ErrorMessageOverride,
+            ReturnType = new CodeType
+            {
+                Name = "String",
+                IsNullable = false,
+            },
+            IsAsync = false,
+            IsStatic = false,
+            Name = "getErrorMessage"
+        }).First();
+
+        // When
+        writer.Write(method);
+        var result = tw.ToString();
+
+        // Then
+        Assert.Contains("@Override", result);
+        Assert.Contains("String getErrorMessage() ", result);
+        Assert.Contains("return getResponseStatusCode() + \": \" + super.getMessage();", result);
+    }
+
     [Fact]
     public void WritesRequestGeneratorAcceptHeaderQuotes()
     {

tests/Kiota.Builder.Tests/Writers/Php/CodeMethodWriterTests.cs

@@ -318,6 +318,32 @@ public async Task WriteErrorMessageOverrideAsync()
 
         Assert.Contains("return $primaryError->getMessage() ?? '';", result);
     }
+
+    [Fact]
+    public async Task WriteErrorMessageOverrideWithStatusCodeWhenNoPrimaryAsync()
+    {
+        setup();
+        var error401 = root.AddClass(new CodeClass
+        {
+            Name = "Error401",
+            IsErrorDefinition = true
+        }).First();
+        // No primary error message property added
+
+        var codeMethod = new CodeMethod
+        {
+            Kind = CodeMethodKind.ErrorMessageOverride,
+            ReturnType = new CodeType { Name = "string" },
+            SimpleName = "getPrimaryErrorMessage",
+        };
+        error401.AddMethod(codeMethod);
+        await ILanguageRefiner.RefineAsync(new GenerationConfiguration { Language = GenerationLanguage.PHP }, root);
+        _codeMethodWriter.WriteCodeElement(codeMethod, languageWriter);
+        var result = stringWriter.ToString();
+
+        Assert.Contains("return $this->getResponseStatusCode() . ': ' . parent::getMessage();", result);
+    }
+
     [Fact]
     public async Task WritesRequestExecutorForEnumTypesAsync()
     {

tests/Kiota.Builder.Tests/Writers/Python/CodePropertyWriterTests.cs

@@ -132,6 +132,17 @@ public void WritePrimaryErrorMessagePropertyOption1()
         var result = tw.ToString();
         Assert.Contains("super().message", result);
     }
+
+    [Fact]
+    public void WriteMessageOverrideWithStatusCodeWhenNoPrimary()
+    {
+        property.Kind = CodePropertyKind.ErrorMessageOverride;
+        parentClass.IsErrorDefinition = true;
+        writer.Write(property);
+        var result = tw.ToString();
+        Assert.Contains("return f'{self.response_status_code}: {super().message}'", result);
+    }
+
     [Fact]
     public void WritePrimaryErrorMessagePropertyOption2()
     {

tests/Kiota.Builder.Tests/Writers/TypeScript/CodeFunctionWriterTests.cs

@@ -1717,5 +1717,86 @@ public void WritesByteArrayPropertyDeserialization()
         var result = tw.ToString();
         Assert.Contains("\"property\": n => { model.property = n.getByteArrayValue(); }", result, StringComparison.Ordinal);
     }
+
+    [Fact]
+    public void WritesErrorMessageAssignmentWithStatusCodeWhenNoPrimary()
+    {
+        var errorClass = root.AddClass(new CodeClass
+        {
+            Name = "Error4XX",
+            IsErrorDefinition = true,
+            Kind = CodeClassKind.Model,
+        }).First();
+
+        // Create associated interface (required for TypeScript)
+        var errorInterface = root.AddInterface(new CodeInterface
+        {
+            Name = "Error4XXInterface",
+            Kind = CodeInterfaceKind.Model,
+            OriginalClass = errorClass
+        }).First();
+
+        // Add the same property to both class and interface
+        var codeProperty = new CodeProperty
+        {
+            Name = "code",
+            Kind = CodePropertyKind.Custom,
+            Type = new CodeType { Name = "string" },
+        };
+        errorClass.AddProperty(codeProperty);
+        errorInterface.AddProperty(new CodeProperty
+        {
+            Name = "code",
+            Kind = CodePropertyKind.Custom,
+            Type = new CodeType { Name = "string" },
+        });
+
+        // Link class to interface
+        errorClass.AssociatedInterface = errorInterface;
+
+        // No primary error message property added - this should trigger our fallback
+
+        // Create deserializer method manually (like the refiner would)
+        var deserializerMethod = errorClass.AddMethod(new CodeMethod
+        {
+            Name = "deserializeIntoError4XX",
+            Kind = CodeMethodKind.Deserializer,
+            IsStatic = true,
+            ReturnType = new CodeType
+            {
+                Name = "Record<string, (node: ParseNode) => void>",
+            },
+        }).First();
+
+        deserializerMethod.AddParameter(new CodeParameter
+        {
+            Name = "error4XX",
+            Kind = CodeParameterKind.RequestBody,
+            Type = new CodeType
+            {
+                Name = "Error4XXInterface",
+                TypeDefinition = errorInterface,
+            },
+        });
+
+        var function = new CodeFunction(deserializerMethod);
+        root.TryAddCodeFile("error4XX", function);
+        writer.Write(function);
+        var result = tw.ToString();
+
+        // The result should contain deserializer properties and the error message assignment
+        Assert.Contains("error4XX.code = n.getStringValue()", result); // Basic property assignment should exist
+
+        // The error message assignment should be generated because this is an error definition without primary message
+        // It should contain our enhancement that includes the status code
+        var expectedErrorMessage = "error4XX.message = `${error4XX.responseStatusCode}: ${super.message ?? \"\"}`";
+        Assert.Contains(expectedErrorMessage, result);
+
+        // Verify the error message assignment appears exactly once
+        var occurrences = result.Split(new[] { expectedErrorMessage }, StringSplitOptions.None).Length - 1;
+        Assert.Equal(1, occurrences);
+
+        Assert.Contains("deserializeIntoError4XX", result);
+    }
 }