[5.3] Allow wrapping schema changes in a transaction if the database supports it

src/Illuminate/Database/Migrations/Migrator.php

@@ -2,6 +2,7 @@
 
 namespace Illuminate\Database\Migrations;
 
+use Closure;
 use Illuminate\Support\Arr;
 use Illuminate\Support\Str;
 use Illuminate\Support\Collection;
@@ -159,7 +160,9 @@ protected function runUp($file, $batch, $pretend)
             return $this->pretendToRun($migration, 'up');
         }
 
-        $migration->up();
+        $this->runMigration(function () use ($migration) {
+            $migration->up();
+        });
 
         // Once we have run a migrations class, we will log that it was run in this
         // repository so that we don't try to run it next time we do a migration
@@ -279,7 +282,9 @@ protected function runDown($file, $migration, $pretend)
             return $this->pretendToRun($instance, 'down');
         }
 
-        $instance->down();
+        $this->runMigration(function () use ($instance) {
+            $instance->down();
+        });
 
         // Once we have successfully run the migration "down" we will remove it from
         // the migration repository so it will be considered to have not been run
@@ -356,6 +361,26 @@ protected function getQueries($migration, $method)
         });
     }
 
+    /**
+     * Run a migration, inside a transaction if the database supports it.
+     *
+     * @param  \Closure  $callback
+     * @return void
+     */
+    protected function runMigration(Closure $callback)
+    {
+        // To deal with potential errors during migrations that may leave a database
+        // in an invalid state, we wrap everything in a transaction so all changes
+        // are rolled back, and the developer need not manually repair errors.
+        $connection = $this->resolveConnection($this->connection);
+
+        $grammar = $connection->getSchemaGrammar();
+
+        $grammar->supportsSchemaTransactions()
+            ? $connection->transaction($callback)
+            : $callback();
+    }
+
     /**
      * Resolve a migration instance from a file.
      *

src/Illuminate/Database/Schema/Grammars/Grammar.php

@@ -17,6 +17,13 @@
 
 abstract class Grammar extends BaseGrammar
 {
+    /**
+     * If this Grammar supports schema changes wrapped in a transaction.
+     *
+     * @var bool
+     */
+    protected $transactions = false;
+
     /**
      * Compile a rename column command.
      *
@@ -456,4 +463,14 @@ protected function mapFluentValueToDoctrine($option, $value)
     {
         return $option == 'notnull' ? ! $value : $value;
     }
+
+    /**
+     * Check if this Grammar supports schema changes wrapped in a transaction.
+     *
+     * @return bool
+     */
+    public function supportsSchemaTransactions()
+    {
+        return $this->transactions;
+    }
 }

src/Illuminate/Database/Schema/Grammars/PostgresGrammar.php

@@ -7,6 +7,13 @@
 
 class PostgresGrammar extends Grammar
 {
+    /**
+     * If this Grammar supports schema changes wrapped in a transaction.
+     *
+     * @var bool
+     */
+    protected $transactions = true;
+
     /**
      * The possible column modifiers.
      *