diff --git a/phpunit/code/constructor_visibility_inherited_private.php b/phpunit/code/constructor_visibility_inherited_private.php
new file mode 100644
index 00000000..53ace63a
--- /dev/null
+++ b/phpunit/code/constructor_visibility_inherited_private.php
@@ -0,0 +1,17 @@
+<?php
+
+class PrivateConstructorParent
+{
+    private function __construct()
+    {
+    }
+}
+
+class PrivateConstructorChild extends PrivateConstructorParent
+{
+}
+
+function main()
+{
+    new PrivateConstructorChild();
+}
diff --git a/phpunit/code/constructor_visibility_internal_private.php b/phpunit/code/constructor_visibility_internal_private.php
new file mode 100644
index 00000000..afe70b6e
--- /dev/null
+++ b/phpunit/code/constructor_visibility_internal_private.php
@@ -0,0 +1,6 @@
+<?php
+
+function main()
+{
+    new Closure();
+}
diff --git a/phpunit/code/constructor_visibility_namespaced.php b/phpunit/code/constructor_visibility_namespaced.php
new file mode 100644
index 00000000..cc4afb76
--- /dev/null
+++ b/phpunit/code/constructor_visibility_namespaced.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace ConstructorVisibility;
+
+class Hidden
+{
+    private function __construct()
+    {
+    }
+}
+
+function main()
+{
+    new Hidden();
+}
diff --git a/phpunit/code/constructor_visibility_private.php b/phpunit/code/constructor_visibility_private.php
new file mode 100644
index 00000000..89f7c1aa
--- /dev/null
+++ b/phpunit/code/constructor_visibility_private.php
@@ -0,0 +1,11 @@
+<?php
+
+class TestClass
+{
+    private function __construct(){}
+}
+
+function main()
+{
+    new TestClass;
+}
diff --git a/phpunit/code/constructor_visibility_protected.php b/phpunit/code/constructor_visibility_protected.php
new file mode 100644
index 00000000..64e31b55
--- /dev/null
+++ b/phpunit/code/constructor_visibility_protected.php
@@ -0,0 +1,11 @@
+<?php
+
+class TestClass
+{
+    protected function __construct(){}
+}
+
+function main()
+{
+    new TestClass;
+}
diff --git a/phpunit/code/constructor_visibility_protected_foreign_class.php b/phpunit/code/constructor_visibility_protected_foreign_class.php
new file mode 100644
index 00000000..d158987b
--- /dev/null
+++ b/phpunit/code/constructor_visibility_protected_foreign_class.php
@@ -0,0 +1,19 @@
+<?php
+
+class Base
+{
+    protected function __construct(){}
+}
+
+class Other
+{
+    public static function make(): Base
+    {
+        return new Base();
+    }
+}
+
+function main()
+{
+    Other::make();
+}
diff --git a/phpunit/code/inheritance_error_generator_return_widened.php b/phpunit/code/inheritance_error_generator_return_widened.php
new file mode 100644
index 00000000..cccf6ae1
--- /dev/null
+++ b/phpunit/code/inheritance_error_generator_return_widened.php
@@ -0,0 +1,14 @@
+<?php
+
+interface GeneratorReturnContract
+{
+    public function values(): \Generator;
+}
+
+class GeneratorReturnImplementation implements GeneratorReturnContract
+{
+    public function values(): iterable
+    {
+        yield 1;
+    }
+}
diff --git a/phpunit/code/inheritance_error_return_intersection_missing.php b/phpunit/code/inheritance_error_return_intersection_missing.php
new file mode 100644
index 00000000..03ac56c2
--- /dev/null
+++ b/phpunit/code/inheritance_error_return_intersection_missing.php
@@ -0,0 +1,23 @@
+<?php
+
+interface IntersectionLeft
+{
+}
+
+interface IntersectionRight
+{
+}
+
+interface IntersectionReturnParent
+{
+    public function value(): IntersectionLeft&IntersectionRight;
+}
+
+class IntersectionReturnChild implements IntersectionReturnParent
+{
+    public function value(): IntersectionLeft
+    {
+        return new class implements IntersectionLeft {
+        };
+    }
+}
diff --git a/phpunit/code/inheritance_error_return_never_widened.php b/phpunit/code/inheritance_error_return_never_widened.php
new file mode 100644
index 00000000..f453f333
--- /dev/null
+++ b/phpunit/code/inheritance_error_return_never_widened.php
@@ -0,0 +1,13 @@
+<?php
+
+abstract class NeverReturnParent
+{
+    abstract public function stop(): never;
+}
+
+abstract class NeverReturnChild extends NeverReturnParent
+{
+    public function stop(): void
+    {
+    }
+}
diff --git a/phpunit/code/inheritance_error_return_static_widened.php b/phpunit/code/inheritance_error_return_static_widened.php
new file mode 100644
index 00000000..c1377fdb
--- /dev/null
+++ b/phpunit/code/inheritance_error_return_static_widened.php
@@ -0,0 +1,17 @@
+<?php
+
+class StaticReturnParent
+{
+    public function value(): static
+    {
+        return $this;
+    }
+}
+
+class StaticReturnChild extends StaticReturnParent
+{
+    public function value(): self
+    {
+        return $this;
+    }
+}
diff --git a/phpunit/code/inheritance_error_return_union_widened.php b/phpunit/code/inheritance_error_return_union_widened.php
new file mode 100644
index 00000000..2db69e1a
--- /dev/null
+++ b/phpunit/code/inheritance_error_return_union_widened.php
@@ -0,0 +1,14 @@
+<?php
+
+interface UnionReturnParent
+{
+    public function value(): int|string;
+}
+
+class UnionReturnChild implements UnionReturnParent
+{
+    public function value(): bool
+    {
+        return true;
+    }
+}
diff --git a/phpunit/code/preprocessor/namespace_ending_comment_unbracketed.php b/phpunit/code/preprocessor/namespace_ending_comment_unbracketed.php
new file mode 100644
index 00000000..7ad8b333
--- /dev/null
+++ b/phpunit/code/preprocessor/namespace_ending_comment_unbracketed.php
@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace NamespaceEndingComment;
+
+const VALUE = 42;
+
+function value(): int
+{
+    return VALUE;
+}
+
+// unbracketed namespace trailing comment
diff --git a/phpunit/code/return_type_covariance_intersection.php b/phpunit/code/return_type_covariance_intersection.php
new file mode 100644
index 00000000..2c26a062
--- /dev/null
+++ b/phpunit/code/return_type_covariance_intersection.php
@@ -0,0 +1,39 @@
+<?php
+
+interface CovarianceLeft
+{
+}
+
+interface CovarianceRight
+{
+}
+
+class CovarianceBoth implements CovarianceLeft, CovarianceRight
+{
+}
+
+interface IntersectionNarrowingContract
+{
+    public function intersection(): CovarianceLeft;
+}
+
+class IntersectionNarrowingImpl implements IntersectionNarrowingContract
+{
+    public function intersection(): CovarianceLeft&CovarianceRight
+    {
+        return new CovarianceBoth();
+    }
+}
+
+interface IntersectionContract
+{
+    public function concrete(): CovarianceLeft&CovarianceRight;
+}
+
+class IntersectionImpl implements IntersectionContract
+{
+    public function concrete(): CovarianceBoth
+    {
+        return new CovarianceBoth();
+    }
+}
diff --git a/phpunit/code/trait_constructor_conflict.php b/phpunit/code/trait_constructor_conflict.php
new file mode 100644
index 00000000..695eee02
--- /dev/null
+++ b/phpunit/code/trait_constructor_conflict.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+trait TraitA
+{
+    public function __construct()
+    {
+        echo "A\n";
+    }
+}
+
+trait TraitB
+{
+    public function __construct()
+    {
+        echo "B\n";
+    }
+}
+
+class TestClass
+{
+    use TraitA, TraitB;
+}
+
+function main()
+{
+    new TestClass();
+}
diff --git a/phpunit/code/trait_constructor_private.php b/phpunit/code/trait_constructor_private.php
new file mode 100644
index 00000000..2dc1db14
--- /dev/null
+++ b/phpunit/code/trait_constructor_private.php
@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+trait TestTrait
+{
+    private function __construct()
+    {
+        echo "trait ctor\n";
+    }
+}
+
+class TestClass
+{
+    use TestTrait;
+}
+
+function main()
+{
+    new TestClass();
+}
diff --git a/phpunit/code/trait_constructor_protected.php b/phpunit/code/trait_constructor_protected.php
new file mode 100644
index 00000000..be585075
--- /dev/null
+++ b/phpunit/code/trait_constructor_protected.php
@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+trait TestTrait
+{
+    protected function __construct()
+    {
+        echo "trait ctor\n";
+    }
+}
+
+class TestClass
+{
+    use TestTrait;
+}
+
+function main()
+{
+    new TestClass();
+}
diff --git a/phpunit/src/ConstructorVisibilityTest.php b/phpunit/src/ConstructorVisibilityTest.php
new file mode 100644
index 00000000..fa0fd311
--- /dev/null
+++ b/phpunit/src/ConstructorVisibilityTest.php
@@ -0,0 +1,78 @@
+<?php
+
+use TypePhp\Exception\TestError;
+
+class ConstructorVisibilityTest extends BaseTest
+{
+    /**
+     * 编译期错误在转换阶段直接以 TestError 抛出，而在桩文件生成阶段
+     * (gen_stub.php) 会被包成 RuntimeException，这里两者都要捕获。
+     */
+    protected function exec(string $expected, string $file): void
+    {
+        try {
+            $this->compile($file);
+        } catch (TestError|RuntimeException $exception) {
+            $this->assertStringContainsString($expected, $exception->getMessage());
+            return;
+        }
+        $this->fail('Expected compile-time error was not thrown');
+    }
+
+    public function testPrivateConstructorCannotBeCalledFromOutside(): void
+    {
+        // 私有构造器不能从类外部通过 `new` 调用
+        $this->exec('Cannot call private TestClass::__construct()', 'constructor_visibility_private.php');
+    }
+
+    public function testProtectedConstructorCannotBeCalledFromGlobalScope(): void
+    {
+        // 保护构造器不能从全局作用域调用
+        $this->exec('Cannot call protected TestClass::__construct()', 'constructor_visibility_protected.php');
+    }
+
+    public function testProtectedConstructorCannotBeCalledFromNonSubclass(): void
+    {
+        // 保护构造器不能从非子类的其它类内部调用
+        $this->exec('Cannot call protected Base::__construct()', 'constructor_visibility_protected_foreign_class.php');
+    }
+
+    public function testInheritedPrivateConstructorCannotBeCalledFromChildScope(): void
+    {
+        $this->exec(
+            'Cannot call private PrivateConstructorParent::__construct()',
+            'constructor_visibility_inherited_private.php'
+        );
+    }
+
+    public function testInternalPrivateConstructorCannotBeCalled(): void
+    {
+        $this->exec('Cannot call private Closure::__construct()', 'constructor_visibility_internal_private.php');
+    }
+
+    public function testNamespacedConstructorUsesPhpClassNameInDiagnostic(): void
+    {
+        $this->exec(
+            'Cannot call private ConstructorVisibility\Hidden::__construct()',
+            'constructor_visibility_namespaced.php'
+        );
+    }
+
+    public function testTraitPrivateConstructorCannotBeCalledFromGlobalScope(): void
+    {
+        // trait 提供的私有构造器扁平化后等价于类的私有构造器
+        $this->exec('Cannot call private TestClass::__construct()', 'trait_constructor_private.php');
+    }
+
+    public function testTraitProtectedConstructorCannotBeCalledFromGlobalScope(): void
+    {
+        // trait 提供的保护构造器扁平化后等价于类的保护构造器
+        $this->exec('Cannot call protected TestClass::__construct()', 'trait_constructor_protected.php');
+    }
+
+    public function testConflictingTraitConstructorMustBeResolved(): void
+    {
+        // 两个 trait 各自声明 __construct 时必须显式解决冲突
+        $this->exec('Trait `TraitB` method `__construct` already exists', 'trait_constructor_conflict.php');
+    }
+}
diff --git a/phpunit/src/InheritanceErrorTest.php b/phpunit/src/InheritanceErrorTest.php
index 59c07e14..0190376c 100644
--- a/phpunit/src/InheritanceErrorTest.php
+++ b/phpunit/src/InheritanceErrorTest.php
@@ -53,6 +53,36 @@ class InheritanceErrorTest extends TestCase
         $this->exec('must be compatible', 'inheritance_error_return_contravariant_class.php');
     }
 
+    public function testUnionReturnTypeCannotBeWidenedToUnrelatedType(): void
+    {
+        $this->exec('must be compatible', 'inheritance_error_return_union_widened.php');
+    }
+
+    public function testIntersectionReturnTypeCannotDropAMember(): void
+    {
+        $this->exec('must be compatible', 'inheritance_error_return_intersection_missing.php');
+    }
+
+    public function testStaticReturnTypeCannotBeWidenedToSelf(): void
+    {
+        $this->exec('must be compatible', 'inheritance_error_return_static_widened.php');
+    }
+
+    public function testNeverReturnTypeCannotBeWidenedToVoid(): void
+    {
+        $this->exec('must be compatible', 'inheritance_error_return_never_widened.php');
+    }
+
+    public function testGeneratorReturnTypeCannotBeWidenedToIterable(): void
+    {
+        $this->exec('must be compatible', 'inheritance_error_generator_return_widened.php');
+    }
+
+    public function testIntersectionReturnTypeCanNarrowToIntersectionOrConcreteSubtype(): void
+    {
+        $this->assertCompiles('return_type_covariance_intersection.php');
+    }
+
     public function testParameterTypeCannotBeCovariant()
     {
         $this->exec('must be compatible', 'inheritance_error_param_covariant_class.php');
diff --git a/phpunit/src/PreprocessorTest.php b/phpunit/src/PreprocessorTest.php
index 8e7eeee0..86984f93 100644
--- a/phpunit/src/PreprocessorTest.php
+++ b/phpunit/src/PreprocessorTest.php
@@ -321,6 +321,25 @@ class PreprocessorTest extends TestCase
         $this->assertSame('App\\VERSION', $constants['_const_var_App__VERSION']->name);
     }
 
+    public function testNamespaceEndingCommentWithUnbracketedSyntaxIsIgnored(): void
+    {
+        global $translator;
+        $file = __DIR__ . '/../code/preprocessor/namespace_ending_comment_unbracketed.php';
+        $previousTranslator = $translator ?? null;
+        $translator = $this->compiler;
+
+        try {
+            $this->compiler->addFiles([$file]);
+            $this->compiler->prepareFile($file);
+            $this->compiler->convertFile($file);
+        } finally {
+            $translator = $previousTranslator;
+        }
+
+        $constants = $this->getProperty('constants');
+        $this->assertArrayHasKey('_const_var_NamespaceEndingComment__VALUE', $constants);
+    }
+
     public function testSortFilesUsesImplementsAndTraitDependencies(): void
     {
         $classFile = realpath(__DIR__ . '/../code/preprocessor/deps_class_implements.php');
diff --git a/src/CompilerBase.php b/src/CompilerBase.php
index c183b5a9..5a2f709a 100644
--- a/src/CompilerBase.php
+++ b/src/CompilerBase.php
@@ -3172,11 +3172,17 @@ class CompilerBase implements PropertyAccessContext
                         $className = $this->getNamespacedClassName($className);
                     }
                     $ctorClassName = $className;
-                    if ($this->hasClass($className)) {
-                        $classDef = $this->getClass($className);
-                        if ($classDef->flags & Modifiers::ABSTRACT) {
-                            $this->fatalError($expr, "abstract class `{$className}` cannot be instantiated");
-                        }
+                    if ($this->isAbstractClass($className)) {
+                        $this->fatalError($expr, "abstract class `{$className}` cannot be instantiated");
+                    }
+                    $constructor = $this->findConstructor($className);
+                    if ($constructor !== null
+                        && !$this->checkAccessibleByClassName($constructor['className'], $constructor['flags'])) {
+                        $this->fatalError(
+                            $expr,
+                            'Cannot call ' . $this->visibilityLabel($constructor['flags']) . ' '
+                            . $constructor['className'] . '::__construct()'
+                        );
                     }
                     $cePtr = $this->getClassEntryPtr($className);
                 }
@@ -3833,6 +3839,11 @@ class CompilerBase implements PropertyAccessContext
     }
 
     protected function checkAccessible(ClassDef $classDef, int $flags): bool
+    {
+        return $this->checkAccessibleByClassName($classDef->getNamespacedName(false), $flags);
+    }
+
+    protected function checkAccessibleByClassName(string $declaringClass, int $flags): bool
     {
         $scopeClassDef = $this->classDef;
         if ($this->functionDef !== null
@@ -3843,7 +3854,7 @@ class CompilerBase implements PropertyAccessContext
         // 私有方法，只能当前的类使用
         if ($flags & Modifiers::PRIVATE) {
             return $scopeClassDef !== null
-                && strcasecmp($classDef->getNamespacedName(false), $scopeClassDef->getNamespacedName(false)) === 0;
+                && $this->isSameClassName($declaringClass, $scopeClassDef->getNamespacedName(false));
         }
         // 保护方法，只能当前类和子类使用
         if ($flags & Modifiers::PROTECTED) {
@@ -3852,13 +3863,60 @@ class CompilerBase implements PropertyAccessContext
             }
             return $this->canAccessProtectedProperty(
                 $scopeClassDef->getNamespacedName(false),
-                $classDef->getNamespacedName(false)
+                $declaringClass
             );
         }
         // 类外部调用，只允许调用 public 方法
         return true;
     }
 
+    /**
+     * 沿继承链查找实际调用的构造函数，包括项目类继承的内部类构造函数。
+     *
+     * @return array{className: string, flags: int}|null
+     */
+    protected function findConstructor(string $className): ?array
+    {
+        $current = $className;
+        while ($current !== '') {
+            if ($this->hasClass($current)) {
+                $classDef = $this->getClass($current);
+                if ($classDef->hasMethod('__construct')) {
+                    return [
+                        'className' => $classDef->getNamespacedName(false),
+                        'flags' => $classDef->getMethod('__construct')->flags,
+                    ];
+                }
+                $current = $classDef->extends;
+                continue;
+            }
+            if (!$this->isInternalClass($current)) {
+                return null;
+            }
+
+            $constructor = Reflection::getClass($current)?->getConstructor();
+            if ($constructor === null) {
+                return null;
+            }
+            return [
+                'className' => $constructor->getDeclaringClass()->getName(),
+                'flags' => $constructor->getModifiers(),
+            ];
+        }
+        return null;
+    }
+
+    protected function visibilityLabel(int $flags): string
+    {
+        if ($flags & Modifiers::PRIVATE) {
+            return 'private';
+        }
+        if ($flags & Modifiers::PROTECTED) {
+            return 'protected';
+        }
+        return 'public';
+    }
+
     protected function genDebugInfo(?NodeAbstract $stmt = null, string $functionName = '', int $startLine = 0): string
     {
         $code = '';
diff --git a/src/Entity/FunctionDef.php b/src/Entity/FunctionDef.php
index 78e8c01b..028b69f9 100644
--- a/src/Entity/FunctionDef.php
+++ b/src/Entity/FunctionDef.php
@@ -74,6 +74,20 @@ class FunctionDef
     /** Original union/nullable return type AST node. */
     public ?NodeAbstract $returnTypeNode = null;
 
+    /**
+     * Source-level return type declared on a generator method, preserved after
+     * `prepareGeneratorFunction()` neutralizes the runtime return type. A
+     * generator actually returns a `\FiberGenerator` (which implements
+     * `Iterator`), so the C++ return type and runtime type check are left
+     * neutral; this copy is only used by interface/abstract return-type
+     * covariance checks so a generator method can still satisfy a contract such
+     * as `: \Generator`.
+     */
+    public ?string $declaredReturnType = null;
+    public string $declaredReturnClass = '';
+    public ?array $declaredReturnTypeCheck = null;
+    public string $declaredReturnTypeStr = '';
+
     public function __construct(string $name, string $returnType, string $namespace)
     {
         $this->name = $name;
diff --git a/src/Generator/FiberGenerator.php b/src/Generator/FiberGenerator.php
index 9e766fd2..9aa44dbd 100644
--- a/src/Generator/FiberGenerator.php
+++ b/src/Generator/FiberGenerator.php
@@ -72,6 +72,18 @@ trait FiberGenerator
         if (!$this->generatorReturnTypeAcceptsFiber($v->returnType)) {
             $this->fatalError($v, 'Generator return type must accept \\FiberGenerator; use Iterator, Traversable, iterable, object, mixed, or omit the return type');
         }
+        // Preserve the source-level declared return type before neutralizing the
+        // runtime return type. The override compatibility check still needs it so
+        // a generator method can satisfy an interface/abstract contract such as
+        // `: \Generator` (the runtime object is a `\FiberGenerator`, not a Zend
+        // `Generator`, so the C++ return type and runtime check stay neutral).
+        if ($v->returnType !== null) {
+            $declared = $this->buildTypeCheckFromNode($v->returnType);
+            $functionDef->declaredReturnTypeCheck = $declared['check'] ?: null;
+        }
+        $functionDef->declaredReturnType = $functionDef->returnType;
+        $functionDef->declaredReturnClass = $functionDef->returnClass;
+        $functionDef->declaredReturnTypeStr = $functionDef->returnTypeStr;
         $functionDef->generator = true;
         $functionDef->returnType = Type::VAR;
         $functionDef->returnClass = '';
diff --git a/src/Generator/TypeCheckGenerator.php b/src/Generator/TypeCheckGenerator.php
index 292967a1..66dbb2e2 100644
--- a/src/Generator/TypeCheckGenerator.php
+++ b/src/Generator/TypeCheckGenerator.php
@@ -116,7 +116,7 @@ trait TypeCheckGenerator
         return $class ? [['kind' => 'instanceof', 'class' => $class]] : [];
     }
 
-    private function typeCheckNodeToString(NodeAbstract $typeNode): string
+    protected function typeCheckNodeToString(NodeAbstract $typeNode): string
     {
         if ($typeNode instanceof Node\Identifier) {
             return $typeNode->name;
diff --git a/src/Preprocessor.php b/src/Preprocessor.php
index 2d311e00..877cc4f2 100644
--- a/src/Preprocessor.php
+++ b/src/Preprocessor.php
@@ -321,6 +321,8 @@ class Preprocessor extends CompilerBase
                 case 'Stmt_Interface':
                     $this->parseInterface($v2);
                     break;
+                case 'Stmt_Nop':
+                    break;
                 default:
                     $this->foundStrayCode($v2);
                     break;
@@ -542,6 +544,9 @@ class Preprocessor extends CompilerBase
         }
         $functionDef->exported = !($this->classDef?->exported === false || $this->hasNoExportAttribute($v));
         $functionDef->returnClass = $class;
+        $functionDef->returnTypeStr = $v->returnType === null
+            ? ''
+            : $this->typeCheckNodeToString($v->returnType);
         // Record late-bound return type keywords so they can be re-resolved to
         // the consuming class when a trait method is flattened into a class.
         $functionDef->returnTypeKeyword = $returnTypeKeyword;
@@ -560,7 +565,6 @@ class Preprocessor extends CompilerBase
             $typeInfo = $this->buildTypeCheckFromNode($v->returnType);
             if (!empty($typeInfo['check'])) {
                 $functionDef->returnTypeCheck = $typeInfo['check'];
-                $functionDef->returnTypeStr = $typeInfo['typeStr'];
                 $functionDef->returnTypeNode = $v->returnType;
             }
         }
diff --git a/src/Translator.php b/src/Translator.php
index 14916aec..66568139 100644
--- a/src/Translator.php
+++ b/src/Translator.php
@@ -2514,6 +2514,8 @@ CODE;
                 case 'Stmt_Interface':
                     $this->validateInterfaceOverrideAttributes($v2);
                     break;
+                case 'Stmt_Nop':
+                    break;
                 default:
                     abort($v2);
                     break;
@@ -3624,7 +3626,12 @@ CODE;
             ));
         }
 
-        if (!$this->isReturnTypeOverrideCompatible($childFuncDef, $parentFuncDef)) {
+        if (!$this->isReturnTypeOverrideCompatible(
+            $childFuncDef,
+            $parentFuncDef,
+            $className,
+            $parentClass,
+        )) {
             $this->fatalMethodOverrideIncompatible($v, $className, $methodName, $parentClass);
         }
         if ($childFuncDef->returnsByRef !== $parentFuncDef->returnsByRef) {
@@ -3709,33 +3716,176 @@ CODE;
         ));
     }
 
-    private function isReturnTypeOverrideCompatible(FunctionDef $childFuncDef, FunctionDef $parentFuncDef): bool
-    {
+    private function isReturnTypeOverrideCompatible(
+        FunctionDef $childFuncDef,
+        FunctionDef $parentFuncDef,
+        string $childClass,
+        string $parentClass,
+    ): bool {
         if ($parentFuncDef->returnTypeUndeclared) {
             return true;
         }
         if ($childFuncDef->returnTypeUndeclared) {
             return false;
         }
-        if ($parentFuncDef->returnTypeCheck || $childFuncDef->returnTypeCheck) {
-            return $parentFuncDef->returnTypeStr === $childFuncDef->returnTypeStr;
+
+        $parentTypes = $this->getReturnAcceptedTypes($parentFuncDef, $parentClass);
+        $childTypes = $this->getReturnAcceptedTypes($childFuncDef, $childClass);
+
+        // Type checks are stored in disjunctive normal form: the outer list is
+        // a union, while an allOf entry is an intersection. Every child union
+        // branch must imply at least one complete parent branch.
+        foreach ($childTypes as $childType) {
+            if (!$this->isReturnTypeCoveredBy($childType, $parentTypes)) {
+                return false;
+            }
         }
-        if ($parentFuncDef->returnType === Type::VAR) {
-            return true;
+        return true;
+    }
+
+    private function getReturnAcceptedTypes(FunctionDef $functionDef, string $declaringClass): array
+    {
+        $returnTypeCheck = $functionDef->generator
+            ? $functionDef->declaredReturnTypeCheck
+            : $functionDef->returnTypeCheck;
+        $returnType = $functionDef->generator
+            ? $functionDef->declaredReturnType
+            : $functionDef->returnType;
+        $returnClass = $functionDef->generator
+            ? $functionDef->declaredReturnClass
+            : $functionDef->returnClass;
+        $returnTypeStr = $functionDef->generator
+            ? $functionDef->declaredReturnTypeStr
+            : $functionDef->returnTypeStr;
+
+        if (!empty($returnTypeCheck)) {
+            return array_map(
+                fn (array $type): array => $this->normalizeReturnTypeEntry($type, $declaringClass),
+                $returnTypeCheck,
+            );
         }
-        if ($childFuncDef->returnType !== $parentFuncDef->returnType) {
-            return false;
+
+        if ($functionDef->returnTypeKeyword === 'static') {
+            return [['kind' => 'isStatic', 'class' => $declaringClass]];
+        }
+        if ($returnType === Type::OBJECT && $returnClass !== '') {
+            return [['kind' => 'instanceof', 'class' => $returnClass]];
+        }
+
+        $declaredType = strtolower($returnTypeStr);
+        return match ($declaredType) {
+            'mixed' => [['kind' => 'isMixed']],
+            'never' => [['kind' => 'isNever']],
+            'void' => [['kind' => 'isVoid']],
+            'null' => [['kind' => 'isNull']],
+            'true' => [['kind' => 'isTrue']],
+            'false' => [['kind' => 'isFalse']],
+            'callable' => [['kind' => 'callable']],
+            'iterable' => [['kind' => 'iterable']],
+            'object' => [['kind' => 'isObject']],
+            default => match ($returnType) {
+                Type::INT => [['kind' => 'isInt']],
+                Type::FLOAT => [['kind' => 'isFloat']],
+                Type::BOOL => [['kind' => 'isBool']],
+                Type::STR => [['kind' => 'isString']],
+                Type::ARRAY => [['kind' => 'isArray']],
+                Type::RESOURCE => [['kind' => 'isResource']],
+                Type::OBJECT => [['kind' => 'isObject']],
+                default => [['kind' => 'isMixed']],
+            },
+        };
+    }
+
+    private function normalizeReturnTypeEntry(array $type, string $declaringClass): array
+    {
+        if (($type['kind'] ?? null) === 'allOf') {
+            $type['types'] = array_map(
+                fn (array $member): array => $this->normalizeReturnTypeEntry($member, $declaringClass),
+                $type['types'],
+            );
+        } elseif (($type['kind'] ?? null) === 'instanceof' && ($type['class'] ?? null) === 'static') {
+            $type = ['kind' => 'isStatic', 'class' => $declaringClass];
+        }
+        return $type;
+    }
+
+    private function isReturnTypeCoveredBy(array $childType, array $parentTypes): bool
+    {
+        $childClause = ($childType['kind'] ?? null) === 'allOf'
+            ? $childType['types']
+            : [$childType];
+
+        foreach ($parentTypes as $parentType) {
+            $parentClause = ($parentType['kind'] ?? null) === 'allOf'
+                ? $parentType['types']
+                : [$parentType];
+            if ($this->isReturnTypeClauseSubtype($childClause, $parentClause)) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    private function isReturnTypeClauseSubtype(array $childClause, array $parentClause): bool
+    {
+        foreach ($parentClause as $parentType) {
+            $covered = false;
+            foreach ($childClause as $childType) {
+                if ($this->isReturnTypeEntryCompatible($childType, $parentType)) {
+                    $covered = true;
+                    break;
+                }
+            }
+            if (!$covered) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private function isReturnTypeEntryCompatible(array $childType, array $parentType): bool
+    {
+        $childKind = $childType['kind'] ?? null;
+        $parentKind = $parentType['kind'] ?? null;
+
+        if ($childKind === 'isNever' || $parentKind === 'isMixed') {
+            return true;
         }
-        if ($parentFuncDef->returnType !== Type::OBJECT) {
+        if (($childKind === 'isTrue' || $childKind === 'isFalse') && $parentKind === 'isBool') {
             return true;
         }
-        if ($childFuncDef->returnClass === $parentFuncDef->returnClass) {
+        if ($childKind === 'isArray' && $parentKind === 'iterable') {
             return true;
         }
-        if (!$childFuncDef->returnClass || !$parentFuncDef->returnClass) {
+        if ($childKind === 'isStatic') {
+            if ($parentKind === 'isObject' || $parentKind === 'isStatic') {
+                return true;
+            }
+            if ($parentKind === 'instanceof') {
+                return $this->isInheritedFrom(
+                    $childType['class'] ?? '',
+                    $parentType['class'] ?? '',
+                );
+            }
+            return false;
+        }
+        if ($childKind === 'instanceof') {
+            if ($parentKind === 'isObject') {
+                return true;
+            }
+            $childClass = $childType['class'] ?? '';
+            if ($parentKind === 'iterable') {
+                return $childClass !== '' && $this->isInheritedFrom($childClass, 'Traversable');
+            }
+            if ($parentKind === 'instanceof') {
+                $parentClass = $parentType['class'] ?? '';
+                return $childClass !== ''
+                    && $parentClass !== ''
+                    && $this->isInheritedFrom($childClass, $parentClass);
+            }
             return false;
         }
-        return $this->isInheritedFrom($childFuncDef->returnClass, $parentFuncDef->returnClass);
+        return $childKind !== null && $childKind === $parentKind;
     }
 
     private function isParameterTypeOverrideCompatible(ArgInfo $childArg, ArgInfo $parentArg): bool
diff --git a/tests/compiler/class/interface-return-covariance.phpt b/tests/compiler/class/interface-return-covariance.phpt
new file mode 100644
index 00000000..792c3c76
--- /dev/null
+++ b/tests/compiler/class/interface-return-covariance.phpt
@@ -0,0 +1,47 @@
+--TEST--
+Interface return type covariance with nullable interface and anonymous class
+--FILE--
+<?php
+
+declare(strict_types=1);
+
+interface TestInterface1
+{
+}
+
+interface TestInterface2 extends TestInterface1
+{
+}
+
+interface TestInterface3
+{
+    public function test(): ?TestInterface1;
+}
+
+class TestClass implements TestInterface3
+{
+    // Covariant: ?TestInterface2 is a subtype of ?TestInterface1 because
+    // TestInterface2 extends TestInterface1.
+    public function test(): ?TestInterface2
+    {
+        return new class() implements TestInterface2 {
+            public function hello(): string {
+                return "anon";
+            }
+        };
+    }
+}
+
+function main()
+{
+    $test = new TestClass;
+    $result = $test->test();
+    var_dump($result instanceof TestInterface1);
+    var_dump($result instanceof TestInterface2);
+    var_dump($result === null);
+}
+?>
+--EXPECT--
+bool(true)
+bool(true)
+bool(false)
diff --git a/tests/compiler/generator/interface-return-type-variants.phpt b/tests/compiler/generator/interface-return-type-variants.phpt
new file mode 100644
index 00000000..d36b61e0
--- /dev/null
+++ b/tests/compiler/generator/interface-return-type-variants.phpt
@@ -0,0 +1,96 @@
+--TEST--
+generator methods implementing interfaces with iterable, nullable and union return types
+--FILE--
+<?php
+interface GenInterface
+{
+    public function gen(array $array): \Generator;
+}
+
+interface IterableInterface
+{
+    public function it(array $array): iterable;
+
+    public function narrowed(array $array): iterable;
+}
+
+interface NullableInterface
+{
+    public function nullable(array $array): ?\Generator;
+}
+
+interface UnionInterface
+{
+    public function union(array $array): \Generator|\Iterator;
+}
+
+class Box implements GenInterface, IterableInterface, NullableInterface, UnionInterface
+{
+    public function gen(array $array): \Generator
+    {
+        foreach ($array as $value) {
+            yield $value * 2;
+        }
+    }
+
+    public function it(array $array): iterable
+    {
+        foreach ($array as $value) {
+            yield $value;
+        }
+    }
+
+    public function narrowed(array $array): \Generator
+    {
+        foreach ($array as $value) {
+            yield $value;
+        }
+    }
+
+    public function nullable(array $array): ?\Generator
+    {
+        foreach ($array as $value) {
+            yield $value;
+        }
+    }
+
+    public function union(array $array): \Generator|\Iterator
+    {
+        foreach ($array as $value) {
+            yield $value;
+        }
+    }
+}
+
+function main()
+{
+    $box = new Box();
+    foreach ($box->gen([1, 2, 3]) as $v) {
+        var_dump($v);
+    }
+    foreach ($box->it([4, 5]) as $v) {
+        var_dump($v);
+    }
+    foreach ($box->narrowed([10, 11]) as $v) {
+        var_dump($v);
+    }
+    foreach ($box->nullable([6, 7]) as $v) {
+        var_dump($v);
+    }
+    foreach ($box->union([8, 9]) as $v) {
+        var_dump($v);
+    }
+}
+?>
+--EXPECT--
+int(2)
+int(4)
+int(6)
+int(4)
+int(5)
+int(10)
+int(11)
+int(6)
+int(7)
+int(8)
+int(9)
diff --git a/tests/compiler/generator/interface-return-type.phpt b/tests/compiler/generator/interface-return-type.phpt
new file mode 100644
index 00000000..82eb4ca4
--- /dev/null
+++ b/tests/compiler/generator/interface-return-type.phpt
@@ -0,0 +1,38 @@
+--TEST--
+generator method implementing an interface that declares \Generator return type
+--FILE--
+<?php
+interface T
+{
+    public function test(array $array): \Generator;
+}
+
+class TestClass implements T
+{
+    public function test(array $array): \Generator
+    {
+        foreach ($array as $value) {
+            yield $value;
+        }
+    }
+}
+
+function main()
+{
+    $test = new TestClass;
+    $g = $test->test([1, 2, 3]);
+    // TypePHP generators return a \FiberGenerator which implements Iterator
+    // but is NOT the Zend \Generator class.
+    var_dump($g instanceof \Generator);
+    var_dump($g instanceof \Iterator);
+    foreach ($g as $value) {
+        var_dump($value);
+    }
+}
+?>
+--EXPECT--
+bool(false)
+bool(true)
+int(1)
+int(2)
+int(3)
diff --git a/tests/compiler/namespace/namespace-ending-comment.phpt b/tests/compiler/namespace/namespace-ending-comment.phpt
new file mode 100644
index 00000000..e937a711
--- /dev/null
+++ b/tests/compiler/namespace/namespace-ending-comment.phpt
@@ -0,0 +1,22 @@
+--TEST--
+A namespace block ending with a comment must not be treated as stray code
+--FILE--
+<?php
+
+declare(strict_types=1);
+
+namespace Test {
+    /* named namespace trailing block comment */
+}
+
+namespace {
+    function main()
+    {
+        var_dump('done');
+    }
+
+    // global namespace trailing line comment
+}
+?>
+--EXPECT--
+string(4) "done"
diff --git a/tests/compiler/object_ctor/ctor-visibility-protected-subclass.phpt b/tests/compiler/object_ctor/ctor-visibility-protected-subclass.phpt
new file mode 100644
index 00000000..a1db317b
--- /dev/null
+++ b/tests/compiler/object_ctor/ctor-visibility-protected-subclass.phpt
@@ -0,0 +1,26 @@
+--TEST--
+Constructor visibility - protected constructor accessible from subclass
+--FILE--
+<?php
+
+class Base
+{
+    protected function __construct(){}
+}
+
+class Sub extends Base
+{
+    public static function make(): Base
+    {
+        return new Base();
+    }
+}
+
+function main()
+{
+    $obj = Sub::make();
+    var_dump($obj instanceof Base);
+}
+?>
+--EXPECT--
+bool(true)
diff --git a/tests/compiler/trait/trait-ctor-basic.phpt b/tests/compiler/trait/trait-ctor-basic.phpt
new file mode 100644
index 00000000..1cf76b71
--- /dev/null
+++ b/tests/compiler/trait/trait-ctor-basic.phpt
@@ -0,0 +1,27 @@
+--TEST--
+Trait __construct is used by the composing class
+--FILE--
+<?php
+
+declare(strict_types=1);
+
+trait TestTrait
+{
+    public function __construct()
+    {
+        echo "trait ctor\n";
+    }
+}
+
+class TestClass
+{
+    use TestTrait;
+}
+
+function main()
+{
+    new TestClass();
+}
+?>
+--EXPECT--
+trait ctor
diff --git a/tests/compiler/trait/trait-ctor-override.phpt b/tests/compiler/trait/trait-ctor-override.phpt
new file mode 100644
index 00000000..5b40f487
--- /dev/null
+++ b/tests/compiler/trait/trait-ctor-override.phpt
@@ -0,0 +1,32 @@
+--TEST--
+Class __construct overrides the one provided by a trait
+--FILE--
+<?php
+
+declare(strict_types=1);
+
+trait TestTrait
+{
+    public function __construct()
+    {
+        echo "trait ctor\n";
+    }
+}
+
+class TestClass
+{
+    use TestTrait;
+
+    public function __construct()
+    {
+        echo "class ctor\n";
+    }
+}
+
+function main()
+{
+    new TestClass();
+}
+?>
+--EXPECT--
+class ctor
diff --git a/tests/compiler/trait/trait-ctor-protected-subclass.phpt b/tests/compiler/trait/trait-ctor-protected-subclass.phpt
new file mode 100644
index 00000000..319fd2f3
--- /dev/null
+++ b/tests/compiler/trait/trait-ctor-protected-subclass.phpt
@@ -0,0 +1,37 @@
+--TEST--
+Trait protected __construct is accessible from a subclass
+--FILE--
+<?php
+
+declare(strict_types=1);
+
+trait TestTrait
+{
+    protected function __construct()
+    {
+        echo "base ctor\n";
+    }
+}
+
+class BaseClass
+{
+    use TestTrait;
+}
+
+class SubClass extends BaseClass
+{
+    public function __construct()
+    {
+        new BaseClass();
+        echo "sub ctor\n";
+    }
+}
+
+function main()
+{
+    new SubClass();
+}
+?>
+--EXPECT--
+base ctor
+sub ctor
diff --git a/tests/compiler/trait/trait-ctor-with-args.phpt b/tests/compiler/trait/trait-ctor-with-args.phpt
new file mode 100644
index 00000000..5177cb28
--- /dev/null
+++ b/tests/compiler/trait/trait-ctor-with-args.phpt
@@ -0,0 +1,30 @@
+--TEST--
+Trait __construct with arguments and $this property access
+--FILE--
+<?php
+
+declare(strict_types=1);
+
+trait TestTrait
+{
+    private int $value = 0;
+
+    public function __construct(int $value)
+    {
+        $this->value = $value;
+        echo "value=" . $this->value . "\n";
+    }
+}
+
+class TestClass
+{
+    use TestTrait;
+}
+
+function main()
+{
+    new TestClass(42);
+}
+?>
+--EXPECT--
+value=42
diff --git a/tests/compiler/type_decl/return-type-covariance.phpt b/tests/compiler/type_decl/return-type-covariance.phpt
new file mode 100644
index 00000000..68883ac3
--- /dev/null
+++ b/tests/compiler/type_decl/return-type-covariance.phpt
@@ -0,0 +1,120 @@
+--TEST--
+Return type covariance: union narrowing and object subtype
+--FILE--
+<?php
+
+interface UnionReturnContract
+{
+    public function make(): int|string;
+}
+
+class UnionReturnImpl implements UnionReturnContract
+{
+    // Covariant: narrowing a union return type (int|string -> int) is allowed.
+    public function make(): int
+    {
+        return 42;
+    }
+}
+
+class BaseType {}
+class ChildType extends BaseType {}
+
+interface ObjectReturnContract
+{
+    public function build(): BaseType;
+}
+
+class ObjectReturnImpl implements ObjectReturnContract
+{
+    // Covariant: returning a subtype (ChildType) for a BaseType return is allowed.
+    public function build(): ChildType
+    {
+        return new ChildType();
+    }
+}
+
+class StaticBase
+{
+    public function copy(): ?self
+    {
+        return $this;
+    }
+}
+
+class StaticChild extends StaticBase
+{
+    public function copy(): ?static
+    {
+        return $this;
+    }
+}
+
+interface IterableContract
+{
+    public function values(): iterable;
+}
+
+class IterableImpl implements IterableContract
+{
+    public function values(): array
+    {
+        return [1, 2];
+    }
+}
+
+interface BoolContract
+{
+    public function enabled(): bool;
+}
+
+class LiteralBoolImpl implements BoolContract
+{
+    public function enabled(): true
+    {
+        return true;
+    }
+}
+
+abstract class VoidContract
+{
+    abstract public function stop(): void;
+}
+
+abstract class NeverImpl extends VoidContract
+{
+    public function stop(): never
+    {
+        throw new RuntimeException('stop');
+    }
+}
+
+function main()
+{
+    $impl = new UnionReturnImpl();
+    var_dump($impl->make());
+
+    $obj = new ObjectReturnImpl();
+    $built = $obj->build();
+    var_dump($built instanceof BaseType);
+    var_dump($built instanceof ChildType);
+
+    $static = new StaticChild();
+    var_dump($static->copy() instanceof StaticChild);
+
+    var_dump((new IterableImpl())->values());
+    var_dump((new LiteralBoolImpl())->enabled());
+}
+?>
+--EXPECT--
+int(42)
+bool(true)
+bool(true)
+bool(true)
+array(2) {
+  [0]=>
+  int(1)
+  [1]=>
+  int(2)
+}
+bool(true)