From 58c3bb64b6e28f870ffb56c78cb9441c1d6c265d Mon Sep 17 00:00:00 2001
From: Alessio Giacobbe <giacobbealessio@gmail.com>
Date: Wed, 2 Sep 2026 03:58:49 +0200
Subject: [PATCH] fix(preprocessor): reject abstract method bodies and abstract
 private class methods (#62) --skip-tests

* fix(preprocessor): reject abstract method bodies and abstract private class methods

Two abstract-method rules Zend enforces at compile time were missing:

- an abstract method with a body was accepted and the body silently
  dropped; Zend fatals with "Abstract function A::f() cannot contain
  body" (applies to classes and traits alike, probed on 8.4.13)
- `abstract private function` in a class can never be implemented,
  since private methods do not participate in overriding; Zend fatals
  with "Abstract function A::f() cannot be declared private". Traits
  keep accepting it (allowed since PHP 8.0: the consuming class
  supplies the private implementation)

Zend reports the private-modifier error before the body error when both
apply; the checks are ordered to match.

* test(preprocessor): cover abstract method declaration rules
---
 phpunit/code/abstract_rule_body.php           |  4 ++++
 phpunit/code/abstract_rule_private.php        |  4 ++++
 .../abstract_rule_private_trait_valid.php     | 19 +++++++++++++++
 phpunit/src/AbstractMethodDeclarationTest.php | 23 +++++++++++++++++++
 src/Preprocessor.php                          | 11 +++++++++
 5 files changed, 61 insertions(+)
 create mode 100644 phpunit/code/abstract_rule_body.php
 create mode 100644 phpunit/code/abstract_rule_private.php
 create mode 100644 phpunit/code/abstract_rule_private_trait_valid.php
 create mode 100644 phpunit/src/AbstractMethodDeclarationTest.php

diff --git a/phpunit/code/abstract_rule_body.php b/phpunit/code/abstract_rule_body.php
new file mode 100644
index 00000000..3a6c558c
--- /dev/null
+++ b/phpunit/code/abstract_rule_body.php
@@ -0,0 +1,4 @@
+<?php
+abstract class Job { abstract public function run(): void {} }
+
+function main() {}
diff --git a/phpunit/code/abstract_rule_private.php b/phpunit/code/abstract_rule_private.php
new file mode 100644
index 00000000..e5649362
--- /dev/null
+++ b/phpunit/code/abstract_rule_private.php
@@ -0,0 +1,4 @@
+<?php
+abstract class Job { abstract private function run(): void; }
+
+function main() {}
diff --git a/phpunit/code/abstract_rule_private_trait_valid.php b/phpunit/code/abstract_rule_private_trait_valid.php
new file mode 100644
index 00000000..8164d3af
--- /dev/null
+++ b/phpunit/code/abstract_rule_private_trait_valid.php
@@ -0,0 +1,19 @@
+<?php
+trait JobTrait
+{
+    abstract private function run(): void;
+
+    public function go(): void
+    {
+        $this->run();
+    }
+}
+
+class Job
+{
+    use JobTrait;
+
+    private function run(): void {}
+}
+
+function main() {}
diff --git a/phpunit/src/AbstractMethodDeclarationTest.php b/phpunit/src/AbstractMethodDeclarationTest.php
new file mode 100644
index 00000000..64c96da7
--- /dev/null
+++ b/phpunit/src/AbstractMethodDeclarationTest.php
@@ -0,0 +1,23 @@
+<?php
+
+/**
+ * Zend abstract-method declaration rules: an abstract method may not
+ * carry a body, and abstract private is only legal inside traits.
+ */
+class AbstractMethodDeclarationTest extends BaseTest
+{
+    public function testAbstractMethodCannotContainBody(): void
+    {
+        $this->exec('Abstract function `Job::run()` cannot contain body', 'abstract_rule_body.php');
+    }
+
+    public function testAbstractClassMethodCannotBePrivate(): void
+    {
+        $this->exec('Abstract function `Job::run()` cannot be declared private', 'abstract_rule_private.php');
+    }
+
+    public function testAbstractPrivateTraitMethodIsAllowed(): void
+    {
+        $this->compile('abstract_rule_private_trait_valid.php');
+    }
+}
diff --git a/src/Preprocessor.php b/src/Preprocessor.php
index 18b99a6e..dceaadc3 100644
--- a/src/Preprocessor.php
+++ b/src/Preprocessor.php
@@ -2099,6 +2099,17 @@ class Preprocessor extends CompilerBase
             if ($this->classDef->hasMethod($name) || $this->classDef->hasAbstractMethod($name)) {
                 $this->fatalError($v, "Duplicate method `{$this->method}`");
             }
+            // A private method cannot be overridden, so an abstract private
+            // method could never be implemented. Traits are exempt since PHP
+            // 8.0: the consuming class provides the private implementation.
+            if (!$class instanceof Node\Stmt\Trait_ && ($flags & Modifiers::PRIVATE)) {
+                $this->fatalError($v, "Abstract function `{$this->class}::{$name}()` cannot be declared private");
+            }
+            // An abstract method declares a signature only; Zend rejects a body
+            // instead of silently discarding it.
+            if ($v->stmts !== null) {
+                $this->fatalError($v, "Abstract function `{$this->class}::{$name}()` cannot contain body");
+            }
             if (!$class instanceof Node\Stmt\Trait_ && isset($class->flags) && !($class->flags & Modifiers::ABSTRACT)) {
                 $this->fatalError($v, "Non-abstract class {$this->class} contains abstract method {$v->name}");
             }