add method to build an on-demand filesystem

the `build` method allows the user to create an on-demand filesystem disk.

a string passed to the method will be treated as the "root" of a local driver (99% use case).

passing an array allows full customization of the disk config.

src/Illuminate/Filesystem/FilesystemManager.php

@@ -90,6 +90,19 @@ public function cloud()
         return $this->disks[$name] = $this->get($name);
     }
 
+    /**
+     * Build an on-demand disk.
+     *
+     * @param  string|array  $root
+     * @return \Illuminate\Contracts\Filesystem\Filesystem
+     */
+    public function build($root)
+    {
+        $config = is_array($root) ? $root : ['driver' => 'local', 'root' => $root];
+
+        return $this->disks['ondemand'] = $this->resolve('ondemand', $config);
+    }
+
     /**
      * Attempt to get the disk from the local cache.
      *
@@ -109,9 +122,9 @@ protected function get($name)
      *
      * @throws \InvalidArgumentException
      */
-    protected function resolve($name)
+    protected function resolve($name, $config = null)
     {
-        $config = $this->getConfig($name);
+        $config = $config ?? $this->getConfig($name);
 
         if (empty($config['driver'])) {
             throw new InvalidArgumentException("Disk [{$name}] does not have a configured driver.");

src/Illuminate/Support/Facades/Storage.php

@@ -8,6 +8,7 @@
  * @method static \Illuminate\Contracts\Filesystem\Filesystem assertExists(string|array $path)
  * @method static \Illuminate\Contracts\Filesystem\Filesystem assertMissing(string|array $path)
  * @method static \Illuminate\Contracts\Filesystem\Filesystem cloud()
+ * @method static \Illuminate\Contracts\Filesystem\Filesystem build(string|array $root)
  * @method static \Illuminate\Contracts\Filesystem\Filesystem disk(string|null $name = null)
  * @method static \Illuminate\Filesystem\FilesystemManager extend(string $driver, \Closure $callback)
  * @method static \Symfony\Component\HttpFoundation\StreamedResponse download(string $path, string|null $name = null, array|null $headers = [])

tests/Filesystem/FilesystemManagerTest.php

@@ -2,6 +2,7 @@
 
 namespace Illuminate\Tests\Filesystem;
 
+use Illuminate\Contracts\Filesystem\Filesystem;
 use Illuminate\Filesystem\FilesystemManager;
 use Illuminate\Foundation\Application;
 use InvalidArgumentException;
@@ -20,4 +21,18 @@ public function testExceptionThrownOnUnsupportedDriver()
 
         $filesystem->disk('local');
     }
+
+    public function testCanBuildOnDemandDisk()
+    {
+        $filesystem = new FilesystemManager(new Application);
+
+        $this->assertInstanceOf(Filesystem::class, $filesystem->build('my-custom-path'));
+
+        $this->assertInstanceOf(Filesystem::class, $filesystem->build([
+            'driver'     => 'local',
+            'root'       => 'my-custom-path',
+            'url'        => 'my-custom-url',
+            'visibility' => 'public',
+        ]));
+    }
 }