[Go] Conform to Golang idioms and best practices

[neilotoole]

Description

There are several locations where the generated Go code does not conform to standard Go idioms / conventions / best practices. Taking CodeReviewComments as a primary source, and generally trying to follow the standards in the Go std lib and in popular OSS libraries.

For example:

• Use proper case: e.g. a generated object named ProjectApi should be ProjectAPI.
• The Configuration object should be named Config.
• Do we need to export APIClient at all? What's the use case for having this public?

Swagger-codegen version

master

[wing328]

@neilotoole sounds good to me as long as it conforms to the "Go Code Review Comments"

cc @guohuang

[vbatts]

discovered a small bit on swagger-codegen-cli-2.2.3.jar and fixed in #6669
There is still an issue of "how to populate the infoEmail field?" so there is not a trialing whitespace on that line as well.

But after building with master, it looks like the refactor for 2.3.0 introduced new issues.
A useful tool in checking is gofmt or go get golang.org/x/tools/cmd/goimports

1. indentation of imports, and placement of non-stdlib paths should be at the end of the import set:
   This is the diff of 2.2.3 -> 2.3.0-SNAPSHOT (96444d3)

@@ -12,22 +12,69 @@ package api
 
 import (
        "bytes"
+       "encoding/json"
+       "encoding/xml"
        "fmt"
-       "io/ioutil"
+       "errors"
+       "io"
+       "mime/multipart"
+    "golang.org/x/oauth2"
+    "golang.org/x/net/context"
+       "net/http"
        "net/url"
+       "time"
+       "os"
        "path/filepath"
        "reflect"
+       "regexp"
        "strings"
+       "unicode/utf8"
+       "strconv"
+)

it ought to be like

import (
        "bytes"
        "encoding/json"
        "encoding/xml"
        "errors"
        "fmt"
        "io"
        "mime/multipart"
        "net/http"
        "net/url"
        "os"
        "path/filepath"
        "reflect"
        "regexp"
        "strconv"
        "strings"
        "time"
        "unicode/utf8"

        "golang.org/x/net/context"
        "golang.org/x/oauth2"
)

2. alignment: these variable assignment align to the "=" sign.

+var (
+       jsonCheck = regexp.MustCompile("(?i:[application|text]/json)")
+       xmlCheck = regexp.MustCompile("(?i:[application|text]/xml)")
 )

it ought to be like

        jsonCheck = regexp.MustCompile("(?i:[application|text]/json)")
        xmlCheck  = regexp.MustCompile("(?i:[application|text]/xml)")

This is true for fields of a struct as well, they align to the type, as well as the tag on the field.
Here is a diff of the corrected output from 2.3.0-SNAPSHOT after goimports -w ...

 type Configuration struct {
-       BasePath      string                    `json:"basePath,omitempty"`
-       Host          string                    `json:"host,omitempty"`
-       Scheme        string                    `json:"scheme,omitempty"`
-       DefaultHeader map[string]string         `json:"defaultHeader,omitempty"`
-       UserAgent     string                    `json:"userAgent,omitempty"`
-       HTTPClient        *http.Client
+       BasePath      string            `json:"basePath,omitempty"`
+       Host          string            `json:"host,omitempty"`
+       Scheme        string            `json:"scheme,omitempty"`
+       DefaultHeader map[string]string `json:"defaultHeader,omitempty"`
+       UserAgent     string            `json:"userAgent,omitempty"`
+       HTTPClient    *http.Client
 }

3. no space between function name and parenthesis in function signature.
   Here is a diff from 2.3.0-SNAPSHOT after goimports -w ...:

 // Change base path to allow switching to mocks
-func (c *APIClient) ChangeBasePath (path string) {
+func (c *APIClient) ChangeBasePath(path string) {
        c.cfg.BasePath = path

4. single variable returns in a function do not need parenthesis:
   Here is a diff from 2.3.0-SNAPSHOT after goimports -w ...:

 // Prevent trying to import "fmt"
-func reportError(format string, a ...interface{}) (error) {
+func reportError(format string, a ...interface{}) error {
        return fmt.Errorf(format, a...)

5. initialized objects with empty curly brackets need no space.
   Here is a diff from 2.3.0-SNAPSHOT after goimports -w ...:

        // to determine the Content-Type header
-       localVarHttpContentTypes := []string{  }
+       localVarHttpContentTypes := []string{}
 
        // set Content-Type header
        localVarHttpContentType := selectHeaderContentType(localVarHttpContentTypes)
@@ -69,8 +69,7 @@ func (a *GrafeasApiService) CreateNote(projectsId string, localVarOptionals map[
        }
 
        // to determine the Accept header
-       localVarHttpHeaderAccepts := []string{
-               }
+       localVarHttpHeaderAccepts := []string{}

[wing328]

@vbatts I've filed #6695 to fix a few formatting issues.