[Go] Invalid code generation in version 2 with two files in multipart/form-data

Description

Swagger-codegen version

Version 2.4.12 against https://github.com/evankanderson/harbor/raw/walk-with-a/docs/build-customize-contribute/swagger.yaml
(corrected version of the harbor project's swagger definition)

Swagger declaration file content or url

The relevant part is this post (the entire file is 6000 lines long)

    post:
      summary: Upload a chart file to the specified project.
      description: 'Upload a chart file to the specified project. With this API, the corresponding provance file can be uploaded together with chart file at once.'
      tags:
        - Products
        - Chart Repository
      consumes:
        - multipart/form-data
      parameters:
        - name: repo
          in: path
          type: string
          required: true
          description: The project name
        - name: chart
          in: formData
          type: file
          required: true
          description: The chart file
        - name: prov
          in: formData
          type: file
          required: false
          description: The provance file

Command line used for generation

swagger-codegen generate -i https://github.com/evankanderson/harbor/raw/master/docs/build-customize-contribute/swagger.yaml -l go -o pkg/harbor -DpackageName=harbor

Steps to reproduce

Attempt to include the generated library; the build will fail with:

../pkg/harbor/api_chart_repository.go:85:6: localVarFile redeclared in this block
	previous declaration at ../pkg/harbor/api_chart_repository.go:78:6
../pkg/harbor/api_chart_repository.go:911:6: localVarFile redeclared in this block
	previous declaration at ../pkg/harbor/api_chart_repository.go:904:6

(and another 8 errors)

Note that this error may be masked by missing includes of "github.com/antihax/optional" in several files; I added these manually but the generated code is clearly incorrect:

	var localVarFile *os.File
	if localVarFile != nil {  // this is a no-op, but it's fixed by #10132
		fbs, _ := ioutil.ReadAll(localVarFile)
		localVarFileBytes = fbs  // Declared at the top of the block (singleton)
		localVarFileName = localVarFile.Name()
		localVarFile.Close()
	}
	var localVarFile *os.File  // Hey, look ma! I declared this above
	if localVarOptionals != nil && localVarOptionals.Prov.IsSet() {
		localVarFileOk := false  // Sort of odd, since this is reassigned immediately
		localVarFile, localVarFileOk = localVarOptionals.Prov.Value().(*os.File)
		if !localVarFileOk {
			return nil, reportError("prov should be *os.File")
		}
	}
	if localVarFile != nil {
		fbs, _ := ioutil.ReadAll(localVarFile)
		localVarFileBytes = fbs
		localVarFileName = localVarFile.Name()
		localVarFile.Close()
	}

Related issues/PRs

Related to:

• https://github.com/swagger-api/swagger-codegen/pull/8051
• https://github.com/swagger-api/swagger-codegen/pull/10132

Suggest a fix/enhancement

I'm not quite sure the best choice here, but I suspect it is to use the mime/multipart package in this case.

Also, it seems like api.mustache needs to conditionally import "github.com/antihax/optional".

Start with modules/swagger-codegen/src/main/resources/go/api.mustache and reproduce generation with the command and Swagger definition in the issue. Inspect the generated api_chart_repository.go and run the Go build; done means multipart/form-data with two files generates without localVarFile redeclarations and includes the optional dependency only when needed.