cli/command/system: add platformInfo type, and fix "omitempty"

The Platform field was defined with omitempty, but would always be shown
in the JSON output, because it was never nil.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Author: thaJeztah

cli/command/system/testdata/docker-client-version.json.golden

@@ -1 +1 @@
-{"Client":{"Platform":{"Name":""},"Version":"18.99.5-ce","ApiVersion":"1.38","DefaultAPIVersion":"1.38","GitCommit":"deadbeef","GoVersion":"go1.10.2","Os":"linux","Arch":"amd64","BuildTime":"Wed May 30 22:21:05 2018","Context":"my-context"},"Server":{"Platform":{"Name":"Docker Enterprise Edition (EE) 2.0"},"Components":[{"Name":"Engine","Version":"17.06.2-ee-15","Details":{"ApiVersion":"1.30","Arch":"amd64","BuildTime":"Mon Jul  9 23:38:38 2018","Experimental":"false","GitCommit":"64ddfa6","GoVersion":"go1.8.7","MinAPIVersion":"1.12","Os":"linux"}},{"Name":"Universal Control Plane","Version":"17.06.2-ee-15","Details":{"ApiVersion":"1.30","Arch":"amd64","BuildTime":"Mon Jul  2 21:24:07 UTC 2018","GitCommit":"4513922","GoVersion":"go1.9.4","MinApiVersion":"1.20","Os":"linux","Version":"3.0.3-tp2"}},{"Name":"Kubernetes","Version":"1.8+","Details":{"buildDate":"2018-04-26T16:51:21Z","compiler":"gc","gitCommit":"8d637aedf46b9c21dde723e29c645b9f27106fa5","gitTreeState":"clean","gitVersion":"v1.8.11-docker-8d637ae","goVersion":"go1.8.3","major":"1","minor":"8+","platform":"linux/amd64"}},{"Name":"Calico","Version":"v3.0.8","Details":{"cni":"v2.0.6","kube-controllers":"v2.0.5","node":"v3.0.8"}}],"Version":"","ApiVersion":"","GitCommit":"","GoVersion":"","Os":"","Arch":""}}
+{"Client":{"Version":"18.99.5-ce","ApiVersion":"1.38","DefaultAPIVersion":"1.38","GitCommit":"deadbeef","GoVersion":"go1.10.2","Os":"linux","Arch":"amd64","BuildTime":"Wed May 30 22:21:05 2018","Context":"my-context"},"Server":{"Platform":{"Name":"Docker Enterprise Edition (EE) 2.0"},"Components":[{"Name":"Engine","Version":"17.06.2-ee-15","Details":{"ApiVersion":"1.30","Arch":"amd64","BuildTime":"Mon Jul  9 23:38:38 2018","Experimental":"false","GitCommit":"64ddfa6","GoVersion":"go1.8.7","MinAPIVersion":"1.12","Os":"linux"}},{"Name":"Universal Control Plane","Version":"17.06.2-ee-15","Details":{"ApiVersion":"1.30","Arch":"amd64","BuildTime":"Mon Jul  2 21:24:07 UTC 2018","GitCommit":"4513922","GoVersion":"go1.9.4","MinApiVersion":"1.20","Os":"linux","Version":"3.0.3-tp2"}},{"Name":"Kubernetes","Version":"1.8+","Details":{"buildDate":"2018-04-26T16:51:21Z","compiler":"gc","gitCommit":"8d637aedf46b9c21dde723e29c645b9f27106fa5","gitTreeState":"clean","gitVersion":"v1.8.11-docker-8d637ae","goVersion":"go1.8.3","major":"1","minor":"8+","platform":"linux/amd64"}},{"Name":"Calico","Version":"v3.0.8","Details":{"cni":"v2.0.6","kube-controllers":"v2.0.5","node":"v3.0.8"}}],"Version":"","ApiVersion":"","GitCommit":"","GoVersion":"","Os":"","Arch":""}}

cli/command/system/version.go

@@ -23,7 +23,7 @@ import (
 )
 
 const defaultVersionTemplate = `{{with .Client -}}
-Client:{{if ne .Platform.Name ""}} {{.Platform.Name}}{{end}}
+Client:{{if ne .Platform nil}}{{if ne .Platform.Name ""}} {{.Platform.Name}}{{end}}{{end}}
  Version:	{{.Version}}
  API version:	{{.APIVersion}}{{if ne .APIVersion .DefaultAPIVersion}} (downgraded from {{.DefaultAPIVersion}}){{end}}
  Go version:	{{.GoVersion}}
@@ -66,9 +66,12 @@ type versionInfo struct {
 	Server *types.Version
 }
 
-type clientVersion struct {
-	Platform struct{ Name string } `json:",omitempty"`
+type platformInfo struct {
+	Name string `json:"Name,omitempty"`
+}
 
+type clientVersion struct {
+	Platform          *platformInfo `json:"Platform,omitempty"`
 	Version           string
 	APIVersion        string `json:"ApiVersion"`
 	DefaultAPIVersion string `json:"DefaultAPIVersion,omitempty"`
@@ -128,7 +131,6 @@ func runVersion(dockerCli command.Cli, opts *versionOptions) error {
 
 	vd := versionInfo{
 		Client: clientVersion{
-			Platform:          struct{ Name string }{version.PlatformName},
 			Version:           version.Version,
 			APIVersion:        dockerCli.CurrentVersion(),
 			DefaultAPIVersion: dockerCli.DefaultVersion(),
@@ -140,6 +142,9 @@ func runVersion(dockerCli command.Cli, opts *versionOptions) error {
 			Context:           dockerCli.CurrentContext(),
 		},
 	}
+	if version.PlatformName != "" {
+		vd.Client.Platform = &platformInfo{Name: version.PlatformName}
+	}
 
 	sv, err := dockerCli.Client().ServerVersion(context.Background())
 	if err == nil {