Add support of --squash flag on build params

main.go

@@ -113,6 +113,11 @@ func main() {
 			Usage:  "build args",
 			EnvVar: "PLUGIN_BUILD_ARGS",
 		},
+		cli.BoolFlag{
+			Name:   "squash",
+			Usage:  "squash the layers at build time",
+			EnvVar: "PLUGIN_SQUASH",
+		},
 		cli.StringFlag{
 			Name:   "repo",
 			Usage:  "docker repository",
@@ -161,6 +166,7 @@ func run(c *cli.Context) error {
 			Context:    c.String("context"),
 			Tags:       c.StringSlice("tags"),
 			Args:       c.StringSlice("args"),
+			Squash:     c.Bool("squash"),
 			Repo:       c.String("repo"),
 		},
 		Daemon: Daemon{

plugin.go

@@ -46,6 +46,7 @@ type (
 		Context    string   // Docker build context
 		Tags       []string // Docker build tags
 		Args       []string // Docker build args
+		Squash     bool     // Docker build squash
 		Repo       string   // Docker build repository
 	}
 
@@ -109,6 +110,11 @@ func (p Plugin) Exec() error {
 		fmt.Println("Registry credentials not provided. Guest mode enabled.")
 	}
 
+	if p.Build.Squash && !p.Daemon.Experimental {
+		fmt.Println("Squash build flag is only available when Docker deamon is started with experimental flag. Ignoring...")
+		p.Build.Squash = false
+	}
+
 	// add proxy build args
 	addProxyBuildArgs(&p.Build)
 
@@ -177,19 +183,23 @@ func commandInfo() *exec.Cmd {
 
 // helper function to create the docker build command.
 func commandBuild(build Build) *exec.Cmd {
-	cmd := exec.Command(
-		dockerExe, "build",
-		"--pull=true",
-		"--rm=true",
-		"-f", build.Dockerfile,
-		"-t", build.Name,
-	)
-
+	args := []string {
+	  "build",
+	  "--pull=true",
+	  "--rm=true",
+	  "-f", build.Dockerfile,
+	  "-t", build.Name,
+  }
+
+	args = append(args, build.Context)
+	if build.Squash {
+		args = append(args, "--squash")
+	}
 	for _, arg := range build.Args {
-		cmd.Args = append(cmd.Args, "--build-arg", arg)
+		args = append(args, "--build-arg", arg)
 	}
-	cmd.Args = append(cmd.Args, build.Context)
-	return cmd
+
+	return exec.Command(dockerExe, args...)
 }
 
 // helper function to add proxy values from the environment