Use parent image config in buildfile

buildfile.go

@@ -65,6 +65,9 @@ func (b *buildFile) CmdFrom(name string) error {
 	}
 	b.image = image.ID
 	b.config = &Config{}
+	if image.Config != nil {
+		b.config = image.Config
+	}
 	if b.config.Env == nil || len(b.config.Env) == 0 {
 		b.config.Env = append(b.config.Env, "HOME=/", "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin")
 	}

buildfile_test.go

@@ -542,3 +542,39 @@ func TestBuildADDFileNotFound(t *testing.T) {
 		t.Fail()
 	}
 }
+
+func TestBuildInheritance(t *testing.T) {
+	runtime, err := newTestRuntime("")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer nuke(runtime)
+
+	srv := &Server{
+		runtime:     runtime,
+		pullingPool: make(map[string]struct{}),
+		pushingPool: make(map[string]struct{}),
+	}
+
+	img := buildImage(testContextTemplate{`
+            from {IMAGE}
+            expose 4243
+            `,
+		nil, nil}, t, srv, true)
+
+	img2 := buildImage(testContextTemplate{fmt.Sprintf(`
+            from %s
+            entrypoint ["/bin/echo"]
+            `, img.ID),
+		nil, nil}, t, srv, true)
+
+	// from child
+	if img2.Config.Entrypoint[0] != "/bin/echo" {
+		t.Fail()
+	}
+
+	// from parent
+	if img.Config.PortSpecs[0] != "4243" {
+		t.Fail()
+	}
+}