[Go] Bug generating nested imports

Description

Go client generator generates nested imports when --import-mappings is specified

Swagger-codegen version

swagger-codegen-cli-2.4.27.jar

Swagger declaration file content or url

swagger.json

Command line used for generation

java -jar swagger-codegen-cli-2.4.27.jar generate -i pet.json -l go --import-mappings uuid.UUID='github.com/google/uuid' --type-mappings UUID=uuid.UUID -o go-client

Steps to reproduce

1. Execute the swagger-codegen-cli specified above.
2. Check the generated pet_dto.go

Result

package swagger

import (
import (
        "github.com/google/uuid"
        "time"
)

)

type PetDto struct {

        // The creation timestamp
        CreatedAt time.Time `json:"createdAt,omitempty"`

        // The user who created
        CreatedBy uuid.UUID `json:"createdBy,omitempty"`

        // The ID
        Id uuid.UUID `json:"id,omitempty"`

        // The name of the pet
        Name string `json:"name,omitempty"`
}

Related issues/PRs

#11776

Suggest a fix/enhancement

Reproduce the issue with swagger-codegen-cli-2.4.27.jar, the linked swagger.json, and the shown Go generation command. Inspect the generated pet_dto.go and the Go generator templates or entry points responsible for imports. Done means generation no longer produces a nested import block and the resulting file has the expected imports.