Fix incorrect arguments for google_compute_instance data source (#2874)

Fixes #2535

Author: lawliet89

google/data_source_google_compute_instance.go

@@ -2,18 +2,16 @@ package google
 
 import (
 	"fmt"
+
 	"github.com/hashicorp/terraform/helper/schema"
 )
 
 func dataSourceGoogleComputeInstance() *schema.Resource {
 	// Generate datasource schema from resource
 	dsSchema := datasourceSchemaFromResourceSchema(resourceComputeInstance().Schema)
 
-	// Set 'Required' schema elements
-	addRequiredFieldsToSchema(dsSchema, "name")
-
 	// Set 'Optional' schema elements
-	addOptionalFieldsToSchema(dsSchema, "project", "zone")
+	addOptionalFieldsToSchema(dsSchema, "name", "self_link", "project", "zone")
 
 	return &schema.Resource{
 		Read:   dataSourceGoogleComputeInstanceRead,

google/data_source_google_compute_instance_test.go

@@ -129,5 +129,9 @@ data "google_compute_instance" "bar" {
 	name = "${google_compute_instance.foo.name}"
 	zone = "us-central1-a"
 }
+
+data "google_compute_instance" "baz" {
+	self_link = "${google_compute_instance.foo.self_link}"
+}
 `, instanceName)
 }