feat(discovery): skip discovery based on closure

packages/core/src/Kernel/LoadDiscoveryClasses.php

@@ -198,11 +198,22 @@ private function scan(DiscoveryLocation $location, array $discoveries, string $p
                 // Resolve `#[SkipDiscovery]` for this class
                 $skipDiscovery = $input->getAttribute(SkipDiscovery::class);
 
-                if ($skipDiscovery !== null && $skipDiscovery->except === []) {
-                    $this->shouldSkipForClass[$className] = true;
-                } elseif ($skipDiscovery !== null) {
-                    foreach ($skipDiscovery->except as $except) {
-                        $this->shouldSkipForClass[$className][$except] = true;
+                if ($skipDiscovery !== null) {
+                    // Evaluate conditional skip
+                    try {
+                        if ($skipDiscovery->when !== null && ($skipDiscovery->when)() !== true) {
+                            return;
+                        }
+                    } catch (Throwable) {
+                        return;
+                    }
+
+                    if ($skipDiscovery->except === []) {
+                        $this->shouldSkipForClass[$className] = true;
+                    } else {
+                        foreach ($skipDiscovery->except as $except) {
+                            $this->shouldSkipForClass[$className][$except] = true;
+                        }
                     }
                 }
 

packages/discovery/src/SkipDiscovery.php

@@ -5,6 +5,7 @@
 namespace Tempest\Discovery;
 
 use Attribute;
+use Closure;
 
 /**
  * Instruct Tempest to not discover this class.
@@ -15,8 +16,10 @@
     public function __construct(
         /**
          * Allows the specified `Discovery` classes to still discover this class.
-         * @var array<class-string<\Tempest\Discovery\Discovery>>
+         * @param array<class-string<\Tempest\Discovery\Discovery>>
+         * @param Closure|null
          */
         public array $except = [],
+        public ?Closure $when = null,
     ) {}
 }