Fix Multipart file array support

src/Refitter.Core/ParameterExtractor.cs

@@ -194,8 +194,21 @@ private static string GetQueryParameterType(
         return type;
     }
 
-    private static string FindSupportedType(string typeName) =>
-        typeName is "FileResponse" or "FileParameter" ? "StreamPart" : typeName;
+    private static string FindSupportedType(string typeName)
+    {
+        if (typeName is "FileResponse" or "FileParameter")
+            return "StreamPart";
+
+        // Handle collections of FileParameter/FileResponse
+        if (typeName.Contains("FileParameter") || typeName.Contains("FileResponse"))
+        {
+            return typeName
+                .Replace("FileParameter", "StreamPart")
+                .Replace("FileResponse", "StreamPart");
+        }
+
+        return typeName;
+    }
 
     private static List<string> GetQueryParameters(CSharpOperationModel operationModel, RefitGeneratorSettings settings, string dynamicQuerystringParameterType, out string? dynamicQuerystringParameters)
     {

src/Refitter.Tests/Examples/MultiPartFormDataArrayTests.cs

@@ -0,0 +1,103 @@
+using FluentAssertions;
+using Refitter.Core;
+using Refitter.Tests.Build;
+using Refitter.Tests.TestUtilities;
+using Xunit;
+
+namespace Refitter.Tests.Examples;
+
+public class MultiPartFormDataArrayTests
+{
+    private const string OpenApiSpec = @"
+{
+    ""openapi"": ""3.0.2"",
+    ""paths"": {
+        ""/foo/{id}/files"": {
+            ""post"": {
+                ""summary"": ""uploads multiple files"",
+                ""operationId"": ""uploadFiles"",
+                ""parameters"": [
+                    {
+                        ""name"": ""id"",
+                        ""in"": ""path"",
+                        ""description"": ""Id of the foo resource"",
+                        ""required"": true,
+                        ""schema"": {
+                            ""type"": ""integer"",
+                            ""format"": ""int64""
+                        }
+                    }
+                ],
+                ""requestBody"": {
+                    ""content"": {
+                        ""multipart/form-data"": {
+                            ""schema"": {
+                                ""type"": ""object"",
+                                ""properties"": {
+                                    ""files"": {
+                                        ""type"": ""array"",
+                                        ""items"": {
+                                            ""type"": ""string"",
+                                            ""format"": ""binary""
+                                        }
+                                    }
+                                }
+                            }
+                        }
+                    }
+                },
+                ""responses"": {
+                    ""200"": {
+                        ""description"": ""successful operation""
+                    }
+                }
+            }
+        }
+    }
+}
+";
+
+    [Fact]
+    public async Task Can_Generate_Code()
+    {
+        string generatedCode = await GenerateCode();
+        generatedCode.Should().NotBeNullOrWhiteSpace();
+    }
+
+    [Fact]
+    public async Task Can_Build_Generated_Code()
+    {
+        string generatedCode = await GenerateCode();
+        BuildHelper
+            .BuildCSharp(generatedCode)
+            .Should()
+            .BeTrue();
+    }
+
+    [Fact]
+    public async Task Generated_Code_Contains_MultiPart_Attribute()
+    {
+        string generatedCode = await GenerateCode();
+        generatedCode.Should().Contain("[Multipart]");
+        generatedCode.Should().NotContain("Content-Type: multipart/form-data");
+    }
+
+    [Fact]
+    public async Task Generated_Code_Uses_IEnumerable_StreamPart_For_File_Array()
+    {
+        string generatedCode = await GenerateCode();
+        generatedCode.Should().Contain("long id, IEnumerable<StreamPart> files");
+        generatedCode.Should().NotContain("IEnumerable<FileParameter> files");
+    }
+
+    private static async Task<string> GenerateCode()
+    {
+        var swaggerFile = await SwaggerFileHelper.CreateSwaggerFile(OpenApiSpec);
+        var settings = new RefitGeneratorSettings { OpenApiPath = swaggerFile };
+
+        var sut = await RefitGenerator.CreateAsync(settings);
+        var generatedCode = sut.Generate();
+        return generatedCode;
+    }
+
+}