Update based off review

builtin/providers/postgresql/provider.go

@@ -45,6 +45,7 @@ func Provider() terraform.ResourceProvider {
 		ResourcesMap: map[string]*schema.Resource{
 			"postgresql_database": resourcePostgreSQLDatabase(),
 			"postgresql_role":     resourcePostgreSQLRole(),
+      "postgresql_extension": resourcePostgreSQLExtension(),
 		},
 
 		ConfigureFunc: providerConfigure,

builtin/providers/postgresql/resource_postgresql_extension.go

@@ -1,6 +1,7 @@
 package postgresql
 
 import (
+	"database/sql"
 	"fmt"
 
 	"github.com/hashicorp/errwrap"
@@ -11,6 +12,7 @@ import (
 func resourcePostgreSQLExtension() *schema.Resource {
 	return &schema.Resource{
 		Create: resourcePostgreSQLExtensionCreate,
+		Read:   resourcePostgreSQLExtensionRead,
 		Delete: resourcePostgreSQLExtensionDelete,
 
 		Schema: map[string]*schema.Schema{
@@ -41,7 +43,31 @@ func resourcePostgreSQLExtensionCreate(d *schema.ResourceData, meta interface{})
 
 	d.SetId(extensionName)
 
-	return resourcePostgreSQLRoleRead(d, meta)
+	return resourcePostgreSQLExtensionRead(d, meta)
+}
+
+func resourcePostgreSQLExtensionRead(d *schema.ResourceData, meta interface{}) error {
+	client := meta.(*Client)
+	conn, err := client.Connect()
+	if err != nil {
+		return err
+	}
+	defer conn.Close()
+
+	extensionName := d.Get("name").(string)
+
+	var hasExtension bool
+	err = conn.QueryRow("SELECT 1 from pg_extension d WHERE extname=$1", extensionName).Scan(&hasExtension)
+	switch {
+	case err == sql.ErrNoRows:
+		d.SetId("")
+		return nil
+	case err != nil:
+		return errwrap.Wrapf("Error reading extension: {{err}}", err)
+	default:
+		d.Set("extension", hasExtension)
+		return nil
+	}
 }
 
 func resourcePostgreSQLExtensionDelete(d *schema.ResourceData, meta interface{}) error {

website/source/layouts/postgresql.erb

@@ -19,6 +19,9 @@
                     <li<%= sidebar_current("docs-postgresql-resource-postgresql_role") %>>
                         <a href="/docs/providers/postgresql/r/postgresql_role.html">postgresql_role</a>
                     </li>
+                    <li<%= sidebar_current("docs-postgresql-resource-postgresql_extension") %>>
+                        <a href="/docs/providers/postgresql/r/postgresql_extension.html">postgresql_extensions</a>
+                    </li>
                 </ul>
         </li>
       </ul>