Fix leak when the added previous exception is already in the chain

Zend/tests/exception_previous_already_in_chain_destructor.phpt

@@ -0,0 +1,29 @@
+--TEST--
+Exception thrown in a destructor during unwinding that already has the pending exception in its previous chain
+--FILE--
+<?php
+class ThrowsInDestructor {
+    public function __construct(private Throwable $pending) {}
+
+    public function __destruct() {
+        throw new LogicException("thrown", 0, $this->pending);
+    }
+}
+
+function f() {
+    $pending = new RuntimeException("pending");
+    $object = new ThrowsInDestructor($pending);
+    throw $pending;
+}
+
+try {
+    f();
+} catch (Throwable $t) {
+    for (; $t !== null; $t = $t->getPrevious()) {
+        echo $t->getMessage(), "\n";
+    }
+}
+?>
+--EXPECT--
+thrown
+pending

Zend/tests/fibers/gc-destructor-throw-previous-already-in-chain.phpt

@@ -0,0 +1,41 @@
+--TEST--
+Exception thrown by a GC destructor that already has the exception of a previous, suspended destructor in its previous chain
+--FILE--
+<?php
+class Cycle {
+    public static ?Throwable $pending = null;
+    public $self;
+
+    public function __construct() {
+        $this->self = $this;
+    }
+
+    public function __destruct() {
+        if (self::$pending === null) {
+            try {
+                Fiber::suspend();
+            } finally {
+                self::$pending = new RuntimeException("pending");
+                throw self::$pending;
+            }
+        }
+        throw new LogicException("thrown", 0, self::$pending);
+    }
+}
+
+$fiber = new Fiber(function () {
+    new Cycle;
+    new Cycle;
+    try {
+        gc_collect_cycles();
+    } catch (Throwable $t) {
+        for (; $t !== null; $t = $t->getPrevious()) {
+            echo $t->getMessage(), "\n";
+        }
+    }
+});
+$fiber->start();
+?>
+--EXPECT--
+thrown
+pending

Zend/tests/fibers/unfinished-fiber-with-throw-previous-already-in-chain.phpt

@@ -0,0 +1,28 @@
+--TEST--
+Exception thrown in finally of a fiber destroyed during unwinding that already has the pending exception in its previous chain
+--FILE--
+<?php
+function f() {
+    $pending = new RuntimeException("pending");
+    $fiber = new Fiber(function () use ($pending) {
+        try {
+            Fiber::suspend();
+        } finally {
+            throw new LogicException("thrown", 0, $pending);
+        }
+    });
+    $fiber->start();
+    throw $pending;
+}
+
+try {
+    f();
+} catch (Throwable $t) {
+    for (; $t !== null; $t = $t->getPrevious()) {
+        echo $t->getMessage(), "\n";
+    }
+}
+?>
+--EXPECT--
+thrown
+pending

Zend/tests/generators/finally/yield_throw_previous_already_in_chain.phpt

@@ -0,0 +1,30 @@
+--TEST--
+Exception thrown in finally of a generator destroyed during unwinding that already has the pending exception in its previous chain
+--FILE--
+<?php
+function gen(Throwable $pending) {
+    try {
+        yield;
+    } finally {
+        throw new LogicException("thrown", 0, $pending);
+    }
+}
+
+function f() {
+    $pending = new RuntimeException("pending");
+    $generator = gen($pending);
+    $generator->current();
+    throw $pending;
+}
+
+try {
+    f();
+} catch (Throwable $t) {
+    for (; $t !== null; $t = $t->getPrevious()) {
+        echo $t->getMessage(), "\n";
+    }
+}
+?>
+--EXPECT--
+thrown
+pending

Zend/tests/try/try_finally_previous_already_in_chain.phpt

@@ -0,0 +1,38 @@
+--TEST--
+Exception thrown in finally that already has the pending exception in its previous chain
+--FILE--
+<?php
+function direct() {
+    $e = new RuntimeException("pending");
+    try {
+        throw $e;
+    } finally {
+        throw new LogicException("thrown", 0, $e);
+    }
+}
+
+function nested() {
+    $e = new RuntimeException("pending");
+    try {
+        throw $e;
+    } finally {
+        throw new LogicException("thrown", 0, new Exception("middle", 0, $e));
+    }
+}
+
+foreach (['direct', 'nested'] as $function) {
+    try {
+        $function();
+    } catch (Throwable $t) {
+        for (; $t !== null; $t = $t->getPrevious()) {
+            echo $t->getMessage(), "\n";
+        }
+    }
+}
+?>
+--EXPECT--
+thrown
+pending
+thrown
+middle
+pending

Zend/zend_exceptions.c

@@ -135,6 +135,8 @@ void zend_exception_set_previous(zend_object *exception, zend_object *add_previo
 		}
 		ex = previous;
 	} while (Z_OBJ_P(ex) != add_previous);
+
+	OBJ_RELEASE(add_previous);
 }
 /* }}} */