[BUG] [Csharp] Mustash templates remove explicit namespace for System.IO.Path

The newest version of the api generator v7.7.0 (#18915) removes specific namespaces (System.IO.Path) for templates on Csharp. This produces autogenerated code that may have conflict when imported to an existing project if there is an existing Path class.

To solve the problem, either the existing project has to rename their classes or add the missing namespaces in the autogenerated code.

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?

On the latest release the issue #18915 remove namespaces from the mustash templates ware added.

• What's the actual output vs expected output?

actual output:

ApiClient.cs

       internal object Deserialize(RestResponse response, Type type)
       {
           if (type == typeof(byte[])) // return byte array
           {
               return response.RawBytes;
           }

           // TODO: ? if (type.IsAssignableFrom(typeof(Stream)))
           if (type == typeof(Stream))
           {
               var bytes = response.RawBytes;
               if (response.Headers != null)
               {
                   var filePath = string.IsNullOrEmpty(_configuration.TempFolderPath)
                       ? Path.GetTempPath()
                       : _configuration.TempFolderPath;

Expected:

       internal object Deserialize(RestResponse response, Type type)
       {
           if (type == typeof(byte[])) // return byte array
           {
               return response.RawBytes;
           }

           // TODO: ? if (type.IsAssignableFrom(typeof(Stream)))
           if (type == typeof(Stream))
           {
               var bytes = response.RawBytes;
               if (response.Headers != null)
               {
                   var filePath = string.IsNullOrEmpty(_configuration.TempFolderPath)
                       ? global::System.IO.Path.GetTempPath()                     //Full namespace or import using Path = global::System.IO.Path; at the top
                       : _configuration.TempFolderPath;

• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

The newest version of the api generator v7.7.0 (#18915) removes specific namespaces (System.IO.Path) for templates on Csharp. This produces autogenerated code that may have conflict when imported to an existing project if there is an existing Path class.

openapi-generator version

v7.7.0

OpenAPI declaration file content or url

Using a single schema the generated code removes the namespaces

openapi: 3.0.1
info:
  title: Testing single
  version: 0.0.1
paths:
  /single/session/{userId}:
    get:
      summary: Single endpoint session
      parameters:
        - name: userId
          in: path
          description: The identity of the user.
          required: true
          schema:
            type: string
      responses:
        '200':
          description: Session found
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Session'
              example:
                userId: bob
                created: 1698256753
        '400':
          description: Bad Request.
        '404':
          description: If no session found
components:
  schemas:
    Session:
      type: object
      properties:
        userId:
          type: string
          description: Identify the user for the active session.
        created:
          type: integer
          description: Identify the creation of the session.
          format: int64
      additionalProperties: false
      description: Represents the active session of the user.

Generation Details

Executing the docker

Steps to reproduce

Execute the lastes version

docker run --rm openapitools/openapi-generator-cli:v7.7.0 generate -i ./swagger.json --package-name Sdk.Simple -g csharp -o ./Sdk/Simple --additional-properties targetFramework=net8.0

The output code in /Sdk.Simple /Client/ApiClient.cs does not have the namespaces

Related issues/PRs

#18915 removed namespaces for PATH

Suggest a fix

Fully qualify the autogenerate clases to avoid collision when importing on another project

Start with the generated Client/ApiClient.cs from the supplied Docker command and trace it back to the C# Mustache templates changed by #18915. Compare the output with the report’s expected System.IO.Path qualification; done means generated code remains usable when the consuming project defines its own Path class.