Support never types

Zend/Optimizer/dce.c

@@ -155,6 +155,7 @@ static inline bool may_have_side_effects(
 		case ZEND_TICKS:
 		case ZEND_YIELD:
 		case ZEND_YIELD_FROM:
+		case ZEND_VERIFY_NEVER_TYPE:
 			/* Intrinsic side effects */
 			return 1;
 		case ZEND_DO_FCALL:

Zend/Optimizer/pass1.c

@@ -677,6 +677,7 @@ void zend_optimizer_pass1(zend_op_array *op_array, zend_optimizer_ctx *ctx)
 		case ZEND_COALESCE:
 		case ZEND_ASSERT_CHECK:
 		case ZEND_JMP_NULL:
+		case ZEND_VERIFY_NEVER_TYPE:
 			collect_constants = 0;
 			break;
 		}

Zend/Optimizer/zend_cfg.c

@@ -301,6 +301,7 @@ ZEND_API int zend_build_cfg(zend_arena **arena, const zend_op_array *op_array, u
 			case ZEND_GENERATOR_RETURN:
 			case ZEND_EXIT:
 			case ZEND_MATCH_ERROR:
+			case ZEND_VERIFY_NEVER_TYPE:
 				if (i + 1 < op_array->last) {
 					BB_START(i + 1);
 				}
@@ -515,6 +516,7 @@ ZEND_API int zend_build_cfg(zend_arena **arena, const zend_op_array *op_array, u
 			case ZEND_EXIT:
 			case ZEND_THROW:
 			case ZEND_MATCH_ERROR:
+			case ZEND_VERIFY_NEVER_TYPE:
 				break;
 			case ZEND_JMP:
 				block->successors_count = 1;

Zend/Optimizer/zend_dump.c

@@ -471,6 +471,9 @@ ZEND_API void zend_dump_op(const zend_op_array *op_array, const zend_basic_block
 			case IS_VOID:
 				fprintf(stderr, " (void)");
 				break;
+			case IS_NEVER:
+				fprintf(stderr, " (never)");
+				break;
 			default:
 				fprintf(stderr, " (\?\?\?)");
 				break;

Zend/tests/return_types/never_allowed.phpt

@@ -0,0 +1,29 @@
+--TEST--
+never return type: acceptable cases
+--FILE--
+<?php
+
+function foo(): never {
+    throw new Exception('bad');
+}
+
+try {
+    foo();
+} catch (Exception $e) {
+    // do nothing
+}
+
+function calls_foo(): never {
+    foo();
+}
+
+try {
+    calls_foo();
+} catch (Exception $e) {
+    // do nothing
+}
+
+echo "OK!", PHP_EOL;
+?>
+--EXPECT--
+OK!

Zend/tests/return_types/never_covariance.phpt

@@ -0,0 +1,78 @@
+--TEST--
+never return type: acceptable covariance cases
+--FILE--
+<?php
+
+class A
+{
+    public function foo(): string
+    {
+        return "hello";
+    }
+
+    public function bar(): never
+    {
+        throw new UnexpectedValueException('parent');
+    }
+
+    public function &baz()
+    {
+    }
+
+    public function someReturningStaticMethod() : static
+    {
+    }
+}
+
+class B extends A
+{
+    public function foo(): never
+    {
+        throw new UnexpectedValueException('bad');
+    }
+
+    public function bar(): never
+    {
+        throw new UnexpectedValueException('child');
+    }
+
+    public function &baz(): never
+    {
+        throw new UnexpectedValueException('child');
+    }
+
+    public function someReturningStaticMethod(): never
+    {
+        throw new UnexpectedValueException('child');
+    }
+}
+
+try {
+    (new B)->foo();
+} catch (UnexpectedValueException $e) {
+    // do nothing
+}
+
+try {
+    (new B)->bar();
+} catch (UnexpectedValueException $e) {
+    // do nothing
+}
+
+try {
+    (new B)->baz();
+} catch (UnexpectedValueException $e) {
+    // do nothing
+}
+
+try {
+    (new B)->someReturningStaticMethod();
+} catch (UnexpectedValueException $e) {
+    // do nothing
+}
+
+echo "OK!", PHP_EOL;
+
+?>
+--EXPECT--
+OK!

Zend/tests/return_types/never_disallowed1.phpt

@@ -0,0 +1,13 @@
+--TEST--
+never return type: unacceptable cases: any return
+--FILE--
+<?php
+
+function foo(): never {
+    return "hello"; // not permitted in a never function
+}
+
+// Note the lack of function call: function validated at compile-time
+?>
+--EXPECTF--
+Fatal error: A never function must not return in %s on line %d

Zend/tests/return_types/never_disallowed2.phpt

@@ -0,0 +1,13 @@
+--TEST--
+never return type: unacceptable cases: empty return
+--FILE--
+<?php
+
+function foo(): never {
+    return; // not permitted in a never function
+}
+
+// Note the lack of function call: function validated at compile-time
+?>
+--EXPECTF--
+Fatal error: A never function must not return in %s on line %d

Zend/tests/return_types/never_disallowed3.phpt

@@ -0,0 +1,19 @@
+--TEST--
+never return type: unacceptable cases: implicit return
+--FILE--
+<?php
+
+function foo(): never {
+    if (false) {
+        throw new Exception('bad');
+    }
+}
+
+foo();
+?>
+--EXPECTF--
+Fatal error: Uncaught TypeError: foo(): Nothing was expected to be returned in %s:%d
+Stack trace:
+#0 %s(%d): foo()
+#1 {main}
+  thrown in %s on line %d

Zend/tests/return_types/never_finally_return.phpt

@@ -0,0 +1,17 @@
+--TEST--
+never return type: never cannot return from finally
+--FILE--
+<?php
+
+function foo() : never {
+    try {
+        throw new Exception('bad');
+    } finally {
+        return;
+    }
+}
+
+// Note the lack of function call: function validated at compile-time
+?>
+--EXPECTF--
+Fatal error: A never function must not return in %s on line %d

Zend/tests/return_types/never_no_variance.phpt

@@ -0,0 +1,26 @@
+--TEST--
+never return type: prevent unacceptable cases
+--FILE--
+<?php
+
+class A
+{
+    public function bar(): never
+    {
+        throw new \Exception('parent');
+    }
+}
+
+class B extends A
+{
+    public function bar(): string
+    {
+        return "hello";
+    }
+}
+
+(new B)->bar();
+
+?>
+--EXPECTF--
+Fatal error: Declaration of B::bar(): string must be compatible with A::bar(): never in %s on line %d

Zend/tests/return_types/never_parameter.phpt

@@ -0,0 +1,9 @@
+--TEST--
+never return type: not valid as a parameter type
+--FILE--
+<?php
+
+function foobar(never $a) {}
+?>
+--EXPECTF--
+Fatal error: never cannot be used as a parameter type in %s on line %d

Zend/tests/return_types/never_reflected.phpt

@@ -0,0 +1,16 @@
+--TEST--
+never in reflection
+--FILE--
+<?php
+
+function foo(): never {}
+
+$neverType = (new ReflectionFunction('foo'))->getReturnType();
+
+echo $neverType->getName() . "\n";
+var_dump($neverType->isBuiltin());
+
+?>
+--EXPECT--
+never
+bool(true)

Zend/tests/return_types/never_return_throw.phpt

@@ -0,0 +1,13 @@
+--TEST--
+never return type: never cannot return from throw expression
+--FILE--
+<?php
+
+function foo() : never {
+    return throw new Exception('bad');
+}
+
+// Note the lack of function call: function validated at compile-time
+?>
+--EXPECTF--
+Fatal error: A never function must not return in %s on line %d

Zend/tests/return_types/never_tostring.phpt

@@ -0,0 +1,28 @@
+--TEST--
+never type of __toString method
+--FILE--
+<?php
+
+class A implements Stringable {
+    public function __toString(): string {
+        return "hello";
+    }
+}
+
+class B extends A {
+    public function __toString(): never {
+        throw new \Exception('not supported');
+    }
+}
+
+try {
+    echo (string) (new B());
+} catch (Exception $e) {
+    // do nothing
+}
+
+echo "done";
+
+?>
+--EXPECT--
+done

Zend/tests/type_declarations/typed_properties_109.phpt

@@ -0,0 +1,12 @@
+--TEST--
+Test typed properties disallow never
+--FILE--
+<?php
+class Foo {
+    public never $int;
+}
+
+$foo = new Foo();
+?>
+--EXPECTF--
+Fatal error: Property Foo::$int cannot have type never in %s on line 3

Zend/tests/type_declarations/union_types/never_with_class.phpt

@@ -0,0 +1,10 @@
+--TEST--
+Combining never with class type
+--FILE--
+<?php
+
+function test(): T|never {}
+
+?>
+--EXPECTF--
+Fatal error: never can only be used as a standalone type in %s on line %d