provider/terraform: remote state resource becomes a data source

As a first example of a real-world data source, the pre-existing
terraform_remote_state resource is adapted to be a data source. The
original resource is shimmed to wrap the data source for backward
compatibility.

data_source_state.go

@@ -8,23 +8,19 @@ import (
 	"github.com/hashicorp/terraform/state/remote"
 )
 
-func resourceRemoteState() *schema.Resource {
+func dataSourceRemoteState() *schema.Resource {
 	return &schema.Resource{
-		Create: resourceRemoteStateCreate,
-		Read:   resourceRemoteStateRead,
-		Delete: resourceRemoteStateDelete,
+		Read: dataSourceRemoteStateRead,
 
 		Schema: map[string]*schema.Schema{
 			"backend": &schema.Schema{
 				Type:     schema.TypeString,
 				Required: true,
-				ForceNew: true,
 			},
 
 			"config": &schema.Schema{
 				Type:     schema.TypeMap,
 				Optional: true,
-				ForceNew: true,
 			},
 
 			"output": &schema.Schema{
@@ -35,11 +31,7 @@ func resourceRemoteState() *schema.Resource {
 	}
 }
 
-func resourceRemoteStateCreate(d *schema.ResourceData, meta interface{}) error {
-	return resourceRemoteStateRead(d, meta)
-}
-
-func resourceRemoteStateRead(d *schema.ResourceData, meta interface{}) error {
+func dataSourceRemoteStateRead(d *schema.ResourceData, meta interface{}) error {
 	backend := d.Get("backend").(string)
 	config := make(map[string]string)
 	for k, v := range d.Get("config").(map[string]interface{}) {
@@ -69,8 +61,3 @@ func resourceRemoteStateRead(d *schema.ResourceData, meta interface{}) error {
 	d.Set("output", outputs)
 	return nil
 }
-
-func resourceRemoteStateDelete(d *schema.ResourceData, meta interface{}) error {
-	d.SetId("")
-	return nil
-}

provider.go

@@ -9,7 +9,12 @@ import (
 func Provider() terraform.ResourceProvider {
 	return &schema.Provider{
 		ResourcesMap: map[string]*schema.Resource{
-			"terraform_remote_state": resourceRemoteState(),
+			"terraform_remote_state": schema.DataSourceResourceShim(
+				dataSourceRemoteState(),
+			),
+		},
+		DataSourcesMap: map[string]*schema.Resource{
+			"terraform_remote_state": dataSourceRemoteState(),
 		},
 	}
 }