Make exclusion contexts return their parent on change

lib/Context/Context.php

@@ -27,7 +27,7 @@ class Context extends ExclusionContext {
     public $notMarkedSince;
 
     public function __construct() {
-        $this->not = new ExclusionContext;
+        $this->not = new ExclusionContext($this);
     }
 
     public function __clone() {
@@ -35,6 +35,10 @@ class Context extends ExclusionContext {
         $this->not = clone $this->not;
     }
 
+    public function __destruct() {
+        unset($this->not);
+    }
+
     public function reverse(bool $spec = null) {
         return $this->act(__FUNCTION__, func_num_args(), $spec);
     }

lib/Context/ExclusionContext.php

@@ -24,6 +24,24 @@ class ExclusionContext {
     public $authorTerms;
 
     protected $props = [];
+    protected $parent;
+
+    public function __construct(self $c = null) {
+        $this->parent = $c;
+    }
+
+    public function __clone() {
+        if ($this->parent) {
+            $p = debug_backtrace(\DEBUG_BACKTRACE_IGNORE_ARGS | \DEBUG_BACKTRACE_PROVIDE_OBJECT, 2)[1]['object'] ?? null;
+            if ($p instanceof self) {
+                $this->parent = $p;
+            }
+        }
+    }
+
+    public function __destruct() {
+        unset($this->parent);
+    }
 
     protected function act(string $prop, int $set, $value) {
         if ($set) {
@@ -34,7 +52,7 @@ class ExclusionContext {
                 $this->props[$prop] = true;
                 $this->$prop = $value;
             }
-            return $this;
+            return $this->parent ?? $this;
         } else {
             return isset($this->props[$prop]);
         }

tests/cases/Misc/TestContext.php

@@ -104,5 +104,7 @@ class TestContext extends \JKingWeb\Arsse\Test\AbstractTest {
         $this->assertEquals($c1->not, $c2->not);
         $this->assertNotSame($c1, $c2);
         $this->assertNotSame($c1->not, $c2->not);
+        $this->assertSame($c1, $c1->not->article(null));
+        $this->assertSame($c2, $c2->not->article(null));
     }
 }