[BUG][GO] `ineffectual assignment to err` in `decode`

Created by: brianlow

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?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Golang client ignores a potential error. Phabricator Arcanist reports: ineffectual assignment to err.

openapi-generator version

• 5.2.0
• latest-release (Jul 29) on dockerhub
• issue does not exist on 5.1.1

OpenAPI declaration file content or url

This is from the swagger homepage:

swagger: "2.0"
info:
  title: Sample API
  description: API description in Markdown.
  version: 1.0.0
host: api.example.com
basePath: /v1
schemes:
  - https
paths:
  /users:
    get:
      summary: Returns a list of users.
      description: Optional extended description in Markdown.
      produces:
        - application/json
      responses:
        200:
          description: OK

Generation Details

docker run --rm \
    -v $PWD:/local \
    openapitools/openapi-generator-cli:v5.2.0 generate \
    -i /local/swagger.yaml \
    -g go \
    -o /local/myclient

Steps to reproduce

The generated myclient/client.go has this code:

if f, ok := v.(**os.File); ok {
	*f, err = ioutil.TempFile("", "HttpClientFile")
	if err != nil {
		return
	}
	_, err = (*f).Write(b)                  // <--- ineffectual assignment to err
	_, err = (*f).Seek(0, io.SeekStart)
	return
}

The err assignment from the Write call is overwritten by the next call to Seek

Related issues/PRs

Introduced in #9812

Suggest a fix

  if f, ok := v.(**os.File); ok {
  	*f, err = ioutil.TempFile("", "HttpClientFile")
  	if err != nil {
  		return
  	}
  	_, err = (*f).Write(b)
+ 	if err != null {
+ 		return
+ 	}
  	_, err = (*f).Seek(0, io.SeekStart)
  	return
  }