helper/resource: automatically validate resources

/cc @pearkes - So, just set a ConfigValidator struct up on your
resources and it'll now automatically validate.

helper/resource/map.go

@@ -13,6 +13,21 @@ type Map struct {
 	Mapping map[string]Resource
 }
 
+func (m *Map) Validate(
+	t string, c *terraform.ResourceConfig) ([]string, []error) {
+	r, ok := m.Mapping[t]
+	if !ok {
+		return nil, []error{fmt.Errorf("Unknown resource type: %s", t)}
+	}
+
+	// If there is no validator set, then it is valid
+	if r.ConfigValidator == nil {
+		return nil, nil
+	}
+
+	return r.ConfigValidator.Validate(c)
+}
+
 // Apply performs a create or update depending on the diff, and calls
 // the proper function on the matching Resource.
 func (m *Map) Apply(

helper/resource/map_test.go

@@ -4,6 +4,8 @@ import (
 	"reflect"
 	"testing"
 
+	tfconfig "github.com/hashicorp/terraform/config"
+	"github.com/hashicorp/terraform/helper/config"
 	"github.com/hashicorp/terraform/terraform"
 )
 
@@ -30,3 +32,50 @@ func TestMapResources(t *testing.T) {
 		t.Fatalf("bad: %#v", rts)
 	}
 }
+
+func TestMapValidate(t *testing.T) {
+	m := &Map{
+		Mapping: map[string]Resource{
+			"aws_elb": Resource{
+				ConfigValidator: &config.Validator{
+					Required: []string{"foo"},
+				},
+			},
+		},
+	}
+
+	var c *terraform.ResourceConfig
+	var ws []string
+	var es []error
+
+	// Valid
+	c = testConfig(t, map[string]interface{}{"foo": "bar"})
+	ws, es = m.Validate("aws_elb", c)
+	if len(ws) > 0 {
+		t.Fatalf("bad: %#v", ws)
+	}
+	if len(es) > 0 {
+		t.Fatalf("bad: %#v", es)
+	}
+
+	// Invalid
+	c = testConfig(t, map[string]interface{}{})
+	ws, es = m.Validate("aws_elb", c)
+	if len(ws) > 0 {
+		t.Fatalf("bad: %#v", ws)
+	}
+	if len(es) == 0 {
+		t.Fatalf("bad: %#v", es)
+	}
+}
+
+func testConfig(
+	t *testing.T,
+	c map[string]interface{}) *terraform.ResourceConfig {
+	r, err := tfconfig.NewRawConfig(c)
+	if err != nil {
+		t.Fatalf("bad: %s", err)
+	}
+
+	return terraform.NewResourceConfig(r)
+}

helper/resource/resource.go

@@ -1,10 +1,12 @@
 package resource
 
 import (
+	"github.com/hashicorp/terraform/helper/config"
 	"github.com/hashicorp/terraform/terraform"
 )
 
 type Resource struct {
+	ConfigValidator *config.Validator
 	Create          CreateFunc
 	Destroy         DestroyFunc
 	Diff            DiffFunc