Fix Multipart file array support

[christianhelle]

This fixes #783

The changes here add support for multipart file arrays.

The following OpenAPI spec:

{
    "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"
                    }
                }
            }
        }
    }
}

will now generated

public partial interface IApiClient
{
    /// <summary>uploads multiple files</summary>
    /// <param name="id">Id of the foo resource</param>
    /// <returns>A <see cref="Task"/> that completes when the request is finished.</returns>
    /// <exception cref="ApiException">Thrown when the request returns a non-success status code.</exception>
    [Multipart]
    [Post("/foo/{id}/files")]
    Task UploadFiles(long id, IEnumerable<StreamPart> files);
}

CoPilot Generated Description

This pull request improves support for multipart form data file arrays in the code generator. The main change is an enhancement to the type mapping logic for file parameters, ensuring that arrays of files are correctly mapped to IEnumerable<StreamPart>. Additionally, new tests have been added to verify the correct code generation for multipart file uploads.

Multipart form data support improvements

• Enhanced the FindSupportedType method in ParameterExtractor.cs to replace occurrences of FileParameter and FileResponse within collection types, ensuring arrays of files are mapped to StreamPart.

Testing enhancements

• Added MultiPartFormDataArrayTests.cs to verify that code generation for OpenAPI specs with multipart file arrays produces the correct parameter types and attributes, and that the generated code builds successfully.

Summary by CodeRabbit

• Bug Fixes

  • Improved type normalization for multipart/form-data file parameters so generated code correctly maps file arrays to appropriate stream-part collections.

• Tests

  • Added unit tests validating multipart file-array code generation, build success, and expected use of stream-part collections.

[coderabbitai]

Note

Other AI code review bot(s) detected

CodeRabbit has detected other AI code review bot(s) in this pull request and will avoid duplicating their findings in the review comments. This may lead to a less comprehensive review.

Walkthrough

ParameterExtractor.FindSupportedType was expanded to normalize type names containing "FileParameter" or "FileResponse" by mapping them (including within collections/composites) to StreamPart. A new unit test file verifies generated multipart/form-data endpoints with file arrays use IEnumerable<StreamPart> and build successfully.

Changes

Cohort / File(s)	Summary
Type Resolution Logic src/Refitter.Core/ParameterExtractor.cs	Expands FindSupportedType to detect FileResponse/FileParameter occurrences inside type names (including collections/composites) and replace those substrings with StreamPart; preserves original mapping for direct FileResponse/FileParameter and falls back to the original name when no match.
Multipart File Array Tests src/Refitter.Tests/Examples/MultiPartFormDataArrayTests.cs	Adds tests that generate a client for a multipart/form-data endpoint with a files array, asserting generated output is non-empty, builds, includes [Multipart], and uses IEnumerable<StreamPart> (no FileParameter).

Sequence Diagram(s)

sequenceDiagram
    participant Generator as RefitGenerator
    participant Extractor as ParameterExtractor
    participant TypeName as TypeName(string)

    Generator->>Extractor: Request supported type for parameter (typeName)
    Extractor->>TypeName: Inspect typeName
    alt typeName == "FileResponse" or "FileParameter"
        Extractor-->>Generator: return "StreamPart"
    else typeName contains "FileResponse" or "FileParameter"
        Extractor-->>Generator: replace occurrences -> return modified typeName (e.g., IEnumerable\<StreamPart\>)
    else
        Extractor-->>Generator: return original typeName
    end
    Note over Generator,Extractor: Generated method signatures use returned type names (e.g., IEnumerable\<StreamPart\>)

Loading

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰 Files in arrays no longer tarry,
StreamPart hops through every carry,
Parameters tidy, signatures bright,
Multipart singing through the night,
Build passes—code takes flight! ✨

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title Check	✅ Passed	The pull request title "Fix Multipart file array support" is concise, clear, and directly related to the main change in the changeset. The title accurately summarizes the primary objective: addressing the issue where multipart file arrays were being mapped to IEnumerable instead of the correct IEnumerable. The title is specific enough that developers scanning the history would understand the focus area without needing to read the full description.
Linked Issues Check	✅ Passed	The pull request successfully addresses the requirements from linked issue #783. The changes to ParameterExtractor.cs implement the type-mapping logic to replace occurrences of FileParameter and FileResponse within collection types with StreamPart, which directly resolves the issue. The new test file MultiPartFormDataArrayTests.cs validates that the generated code produces the expected method signature with IEnumerable and includes the [Multipart] attribute while excluding FileParameter, confirming the fix meets the stated objectives. The changes are complete and validate that generated code compiles successfully.
Out of Scope Changes Check	✅ Passed	All changes in this pull request are directly related to the stated objective of fixing multipart file array support. The modifications to ParameterExtractor.cs implement the necessary type-mapping logic for the fix, and the new MultiPartFormDataArrayTests.cs file provides test coverage to validate the solution. Both the code changes and tests are focused on resolving the issue where file arrays were incorrectly mapped to FileParameter instead of StreamPart, with no extraneous modifications detected.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch multipart-file-array

---

📜 Recent review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 4c90aae and 9d48542.

📒 Files selected for processing (1)

• src/Refitter.Tests/Examples/MultiPartFormDataArrayTests.cs (1 hunks)

🧰 Additional context used

📓 Path-based instructions (2)

src/**/*.cs

📄 CodeRabbit inference engine (.github/copilot-instructions.md)

src/**/*.cs: Follow existing C# coding conventions defined in .editorconfig
Use PascalCase for public members
Use camelCase for parameters and local variables
Include XML documentation for public APIs
Use meaningful variable and method names

Files:

• src/Refitter.Tests/Examples/MultiPartFormDataArrayTests.cs

src/Refitter.Tests/Examples/**/*.cs

📄 CodeRabbit inference engine (.github/copilot-instructions.md)

All new code must include unit tests following the Refitter.Tests.Examples pattern

Files:

• src/Refitter.Tests/Examples/MultiPartFormDataArrayTests.cs

🧠 Learnings (1)

📚 Learning: 2025-09-17T20:15:55.708Z

Learnt from: CR
PR: christianhelle/refitter#0
File: .github/copilot-instructions.md:0-0
Timestamp: 2025-09-17T20:15:55.708Z
Learning: Applies to src/Refitter.Tests/Examples/**/*.cs : All new code must include unit tests following the Refitter.Tests.Examples pattern

Applied to files:

• src/Refitter.Tests/Examples/MultiPartFormDataArrayTests.cs

🧬 Code graph analysis (1)

src/Refitter.Tests/Examples/MultiPartFormDataArrayTests.cs (3)

src/Refitter.Tests/Build/BuildHelper.cs (2)

• BuildHelper (6-53)
• BuildCSharp (8-45)

src/Refitter.Tests/TestUtilities/SwaggerFileHelper.cs (1)

• SwaggerFileHelper (9-25)

src/Refitter.Core/RefitGenerator.cs (1)

• RefitGenerator (10-284)

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (5)

• GitHub Check: 👌 Verify build
• GitHub Check: 👌 Verify build
• GitHub Check: 👌 Verify build
• GitHub Check: script
• GitHub Check: Analyze (csharp)

🔇 Additional comments (1)

src/Refitter.Tests/Examples/MultiPartFormDataArrayTests.cs (1)

9-101: Well-structured test coverage for multipart file array support.

The test suite comprehensively validates the fix for issue #783:

• Verifies code generation succeeds and builds
• Confirms [Multipart] attribute is generated correctly
• Validates IEnumerable replaces FileParameter for file arrays
• Helper method appropriately reduces duplication

The OpenAPI spec accurately represents the reproduction scenario from the issue. The tests follow the Refitter.Tests.Examples pattern and naming conventions as per coding guidelines.

---

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[Copilot]

Pull Request Overview

Fix multipart file array support in the code generator by mapping file arrays to IEnumerable and adding targeted tests to validate generation and build.

• Extend type mapping to replace FileParameter/FileResponse within collection types.
• Add tests ensuring [Multipart] is used and file array parameters are generated as IEnumerable.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/Refitter.Core/ParameterExtractor.cs	Enhances FindSupportedType to replace FileParameter/FileResponse within collection/generic types, enabling IEnumerable for file arrays.
src/Refitter.Tests/Examples/MultiPartFormDataArrayTests.cs	Adds tests validating multipart code generation, parameter types, and successful build of generated code.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.27%. Comparing base (40db6cc) to head (9d48542).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #784      +/-   ##
==========================================
+ Coverage   92.24%   92.27%   +0.02%     
==========================================
  Files          24       24              
  Lines        1767     1773       +6     
  Branches      273      274       +1     
==========================================
+ Hits         1630     1636       +6     
  Misses        101      101              
  Partials       36       36              

Flag	Coverage Δ
unittests	92.27% <100.00%> (+0.02%)	⬆️

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