From 23fdaa4d122a25a5f15354c8084d3fc89b1fe88b Mon Sep 17 00:00:00 2001
From: Dave Liddament <dave@lampbristol.com>
Date: Thu, 8 Aug 2024 11:34:19 +0100
Subject: [PATCH] ADD RestrictTraitTo

---
 README.md                                    | 28 ++++++++++
 examples/restrictTraitTo/restrictTraitTo.php | 56 ++++++++++++++++++++
 src/RestrictTraitTo.php                      | 39 ++++++++++++++
 3 files changed, 123 insertions(+)
 create mode 100644 examples/restrictTraitTo/restrictTraitTo.php
 create mode 100644 src/RestrictTraitTo.php

diff --git a/README.md b/README.md
index 1b7d511..389ea39 100644
--- a/README.md
+++ b/README.md
@@ -19,6 +19,7 @@ The intention, at least initially, is that these extra language features are enf
 - [NamespaceVisibility](#namespaceVisibility)
 - [InjectableVersion](#injectableVersion)
 - [Override](#override)
+- [RestrictTraitTo](#restricttraitto)
 - [Sealed](#sealed)
 - [TestTag](#testtag)
 
@@ -34,6 +35,7 @@ The intention, at least initially, is that these extra language features are enf
   - [NamespaceVisibility](#namespaceVisibility)
   - [InjectableVersion](#injectableVersion)
   - [Override](#override)
+  - [RestrictTraitTo](#restricttraitto)
   - [Sealed](#sealed)
   - [TestTag](#testtag)
   - Deprecated
@@ -417,6 +419,32 @@ NOTE:
 - If you are using PHP 8.3 then use the real `#[Override]` attribute.
 - This implementation doesn't consider traits. 
 
+## RestrictTraitTo
+
+This limits the use of a Trait to only be used by a specified class of a child of that class.
+
+E.g. this trait is limited to classes that are or extend `Controller`
+
+```php
+#[RestrictTraitTo(Controller::class)]
+trait ControllerHelpers {}
+```
+
+This would be allowed:
+```php
+class LoginController extends Controller {
+    use ControllerHelpers;
+}
+```
+
+But this would NOT be allowed:
+```php
+class Repository {
+    use ControllerHelpers;
+}
+```
+
+
 ## Sealed
 
 This is inspired by the rejected [sealed classes RFC](https://wiki.php.net/rfc/sealed_classes)
diff --git a/examples/restrictTraitTo/restrictTraitTo.php b/examples/restrictTraitTo/restrictTraitTo.php
new file mode 100644
index 0000000..cab54fd
--- /dev/null
+++ b/examples/restrictTraitTo/restrictTraitTo.php
@@ -0,0 +1,56 @@
+<?php
+
+declare(strict_types=1);
+
+namespace RestrictTraitTo;
+
+use DaveLiddament\PhpLanguageExtensions\RestrictTraitTo;
+
+trait UseAnywhere {}
+
+#[RestrictTraitTo(Interface1::class)]
+trait UseOnlyOnInterface1 {}
+
+#[RestrictTraitTo(AbstractClass1::class)]
+trait UseOnlyOnAbstractClass1 {}
+
+#[RestrictTraitTo(Class2::class)]
+trait UseOnlyOnClass2 {}
+
+
+interface Interface1 {}
+
+
+class AClass {
+    use UseAnywhere; // OK
+    use UseOnlyOnInterface1; // ERROR RestrictTraitTo\Interface1
+    use UseOnlyOnAbstractClass1; // ERROR RestrictTraitTo\AbstractClass1
+    use UseOnlyOnClass2; // ERROR RestrictTraitTo\Class2
+}
+
+
+class ImplementsInterface1 implements Interface1 {
+    use UseAnywhere; // OK
+    use UseOnlyOnInterface1; // OK
+    use UseOnlyOnAbstractClass1; // ERROR RestrictTraitTo\AbstractClass1
+    use UseOnlyOnClass2; // ERROR RestrictTraitTo\Class2
+}
+
+abstract class AbstractClass1
+{
+
+}
+
+class ExtendsAbstractClass1 extends AbstractClass1 {
+    use UseAnywhere; // OK
+    use UseOnlyOnInterface1; // ERROR RestrictTraitTo\Interface1
+    use UseOnlyOnAbstractClass1; // OK
+    use UseOnlyOnClass2; // ERROR RestrictTraitTo\Class2
+}
+
+class Class2 {
+    use UseAnywhere; // OK
+    use UseOnlyOnInterface1; // ERROR RestrictTraitTo\Interface1
+    use UseOnlyOnAbstractClass1; // ERROR RestrictTraitTo\AbstractClass1
+    use UseOnlyOnClass2; // OK
+}
\ No newline at end of file
diff --git a/src/RestrictTraitTo.php b/src/RestrictTraitTo.php
new file mode 100644
index 0000000..2147cf0
--- /dev/null
+++ b/src/RestrictTraitTo.php
@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DaveLiddament\PhpLanguageExtensions;
+
+/**
+ * Enforces that the trait can only be used on the specified class, or children of that class.
+ *
+ * E.g. this trait is limited to classes that are or extend `Controller`
+ *
+ * ```
+ * #[RestrictTraitTo(Controller::class)]
+ * trait ControllerHelpers {}
+ * ```
+ *
+ * This would be allowed:
+ * ```
+ * class LoginController extends Controller {
+ *     use ControllerHelpers;
+ * }
+ * ```
+ *
+ * But this would NOT be allowed:
+ * ```
+ * class Repository {
+ *     use ControllerHelpers;
+ * }
+ * ```
+ */
+#[\Attribute(\Attribute::TARGET_CLASS)]
+final class RestrictTraitTo
+{
+    /** @param class-string $className */
+    public function __construct(
+        public string $className,
+    ) {
+    }
+}