Add 'build' to types.go

This adds 'build' to types.go in order for projects that use docker/cli
to parse Docker Compose files to correctly retrieve `build` keys.

Signed-off-by: Charlie Drage <charlie@charliedrage.com>

cli/compose/loader/full-example.yml

@@ -2,6 +2,13 @@ version: "3.4"
 
 services:
   foo:
+
+    build:
+      context: ./dir
+      dockerfile: Dockerfile-alternate
+      args:
+        foo: bar
+
     cap_add:
       - ALL
 

cli/compose/loader/loader_test.go

@@ -686,6 +686,11 @@ func TestFullExample(t *testing.T) {
 	expectedServiceConfig := types.ServiceConfig{
 		Name: "foo",
 
+		Build: types.BuildConfig{
+			Context:    "./dir",
+			Dockerfile: "Dockerfile-alternative",
+			Args:       map[string]*string{"foo": strPtr("bar")},
+		},
 		CapAdd:        []string{"ALL"},
 		CapDrop:       []string{"NET_ADMIN", "SYS_ADMIN"},
 		CgroupParent:  "m-executor-abcd",

cli/compose/types/types.go

@@ -78,9 +78,10 @@ type Config struct {
 type ServiceConfig struct {
 	Name string
 
-	CapAdd          []string `mapstructure:"cap_add"`
-	CapDrop         []string `mapstructure:"cap_drop"`
-	CgroupParent    string   `mapstructure:"cgroup_parent"`
+	Build           BuildConfig `mapstructure:"build"`
+	CapAdd          []string    `mapstructure:"cap_add"`
+	CapDrop         []string    `mapstructure:"cap_drop"`
+	CgroupParent    string      `mapstructure:"cgroup_parent"`
 	Command         ShellCommand
 	Configs         []ServiceConfigObjConfig
 	ContainerName   string               `mapstructure:"container_name"`
@@ -125,6 +126,14 @@ type ServiceConfig struct {
 	WorkingDir      string `mapstructure:"working_dir"`
 }
 
+// BuildConfig is a type for build
+// using the same format at libcompose: https://github.com/docker/libcompose/blob/master/yaml/build.go#L12
+type BuildConfig struct {
+	Context    string
+	Dockerfile string
+	Args       map[string]*string
+}
+
 // ShellCommand is a string or list of string args
 type ShellCommand []string