Quote constraint name in MySQL DROP FOREIGN KEY statement (#1088)

The MySQL adapter built `DROP FOREIGN KEY <name>` without quoting the
constraint identifier. That produces invalid SQL whenever the constraint
name is not a bare identifier, e.g. names containing whitespace, or the
numeric names ("1", "2", ...) that MariaDB 12 auto-assigns to foreign
keys created without an explicit name.

Quote the identifier via quoteColumnName(), matching the Postgres and
SQL Server adapters, which already quote the dropped constraint name.

Author: dereuromark

src/Db/Adapter/MysqlAdapter.php

@@ -1061,7 +1061,7 @@ protected function getDropForeignKeyInstructions(string $tableName, string $cons
     {
         $alter = sprintf(
             'DROP FOREIGN KEY %s',
-            $constraint,
+            $this->quoteColumnName($constraint),
         );
 
         return new AlterInstructions([$alter]);

tests/TestCase/Db/Adapter/MysqlAdapterTest.php

@@ -1848,6 +1848,32 @@ public function testDropForeignKeyWithIdenticalMultipleColumns(): void
         $this->assertFalse($this->adapter->hasForeignKey($table->getName(), [], 'ref_table_fk_2'));
     }
 
+    public function testDropForeignKeyWithNameContainingWhitespace(): void
+    {
+        $refTable = new Table('ref_table', [], $this->adapter);
+        $refTable->addColumn('field1', 'string')->save();
+
+        $table = new Table('table', [], $this->adapter);
+        $key = (new ForeignKey())
+            ->setName('ref table fk')
+            ->setColumns(['ref_table_id'])
+            ->setReferencedTable('ref_table')
+            ->setReferencedColumns(['id']);
+        $table
+            ->addColumn('ref_table_id', 'integer', ['signed' => false])
+            ->addForeignKey($key)
+            ->save();
+
+        $this->assertTrue($this->adapter->hasForeignKey($table->getName(), [], 'ref table fk'));
+
+        // The constraint name must be quoted in the DROP statement, otherwise
+        // names with whitespace (or numeric names auto-assigned by MariaDB 12)
+        // produce invalid SQL.
+        $this->adapter->dropForeignKey($table->getName(), [], 'ref table fk');
+
+        $this->assertFalse($this->adapter->hasForeignKey($table->getName(), [], 'ref table fk'));
+    }
+
     public static function nonExistentForeignKeyColumnsProvider(): array
     {
         return [