Allow `null and false` as standalone types (#7546)

RFC: https://wiki.php.net/rfc/null-standalone-type

Also a drive-by consistency fix for error messages.

Zend/tests/type_declarations/standalone_null.phpt

@@ -0,0 +1,14 @@
+--TEST--
+Null can be used as a standalone type
+--FILE--
+<?php
+
+function test(null $v): null {
+    return $v;
+}
+
+var_dump(test(null));
+
+?>
+--EXPECT--
+NULL

Zend/tests/type_declarations/typed_properties_110.phpt

@@ -0,0 +1,20 @@
+--TEST--
+Test typed properties allow null
+--FILE--
+<?php
+class Foo {
+    public null $value;
+}
+
+$foo = new Foo();
+$foo->value = null;
+
+try {
+    $foo->value = 1;
+} catch (\TypeError $e) {
+    echo $e->getMessage();
+}
+
+?>
+--EXPECT--
+Cannot assign int to property Foo::$value of type null

Zend/tests/type_declarations/typed_properties_111.phpt

@@ -0,0 +1,20 @@
+--TEST--
+Test typed properties allow false
+--FILE--
+<?php
+class Foo {
+    public false $value;
+}
+
+$foo = new Foo();
+$foo->value = false;
+
+try {
+    $foo->value = true;
+} catch (\TypeError $e) {
+    echo $e->getMessage();
+}
+
+?>
+--EXPECT--
+Cannot assign bool to property Foo::$value of type false

Zend/tests/type_declarations/typed_return_null_false_without_value.phpt

@@ -0,0 +1,14 @@
+--TEST--
+Typed null|false return without value generates compile-time error
+--FILE--
+<?php
+
+function test() : null|false {
+    return;
+}
+
+test();
+
+?>
+--EXPECTF--
+Fatal error: A function with return type must return a value (did you mean "return null;" instead of "return;"?) in %s on line %d

Zend/tests/type_declarations/typed_return_null_without_value.phpt

@@ -0,0 +1,14 @@
+--TEST--
+Typed null return without value generates compile-time error
+--FILE--
+<?php
+
+function test() : null {
+    return;
+}
+
+test();
+
+?>
+--EXPECTF--
+Fatal error: A function with return type must return a value (did you mean "return null;" instead of "return;"?) in %s on line %d

Zend/tests/type_declarations/union_types/null_false_union.phpt

@@ -0,0 +1,12 @@
+--TEST--
+Null and false can be used in a union type
+--FILE--
+<?php
+
+function test1(): null|false {}
+function test2(): false|null {}
+
+?>
+===DONE===
+--EXPECT--
+===DONE===

Zend/tests/type_declarations/union_types/redundant_types/nullable_null.phpt

@@ -8,4 +8,4 @@ function test(): ?null {
 
 ?>
 --EXPECTF--
-Fatal error: Null cannot be used as a standalone type in %s on line %d
+Fatal error: null cannot be marked as nullable in %s on line %d

Zend/tests/type_declarations/union_types/standalone_false.phpt

@@ -1,10 +1,11 @@
 --TEST--
-False cannot be used as a standalone type
+False can be used as a standalone type
 --FILE--
 <?php
 
 function test(): false {}
 
 ?>
---EXPECTF--
-Fatal error: False cannot be used as a standalone type in %s on line %d
+===DONE===
+--EXPECT--
+===DONE===

Zend/tests/type_declarations/union_types/standalone_false_implicit_nullability.phpt

@@ -0,0 +1,11 @@
+--TEST--
+False can be used as a standalone type even with implicit nullability
+--FILE--
+<?php
+
+function test(false $v = null) {}
+
+?>
+===DONE===
+--EXPECT--
+===DONE===

Zend/tests/type_declarations/union_types/standalone_null.phpt

@@ -1,10 +1,11 @@
 --TEST--
-Null cannot be used as a standalone type
+Null can be used as a standalone type
 --FILE--
 <?php
 
 function test(): null {}
 
 ?>
---EXPECTF--
-Fatal error: Null cannot be used as a standalone type in %s on line %d
+===DONE===
+--EXPECT--
+===DONE===

Zend/tests/type_declarations/union_types/standalone_nullable_false.phpt

@@ -1,10 +1,11 @@
 --TEST--
-Nullable false cannot be used as a standalone type
+Nullable false can be used as a standalone type
 --FILE--
 <?php
 
 function test(): ?false {}
 
 ?>
---EXPECTF--
-Fatal error: False cannot be used as a standalone type in %s on line %d
+===DONE===
+--EXPECT--
+===DONE===

Zend/zend_compile.c

@@ -6186,11 +6186,11 @@ static bool zend_type_contains_traversable(zend_type type) {
 static zend_type zend_compile_typename(
 		zend_ast *ast, bool force_allow_null) /* {{{ */
 {
-	bool allow_null = force_allow_null;
+	bool is_marked_nullable = ast->attr & ZEND_TYPE_NULLABLE;
 	zend_ast_attr orig_ast_attr = ast->attr;
 	zend_type type = ZEND_TYPE_INIT_NONE(0);
-	if (ast->attr & ZEND_TYPE_NULLABLE) {
-		allow_null = 1;
+
+	if (is_marked_nullable) {
 		ast->attr &= ~ZEND_TYPE_NULLABLE;
 	}
 
@@ -6314,10 +6314,6 @@ static zend_type zend_compile_typename(
 		type = zend_compile_single_typename(ast);
 	}
 
-	if (allow_null) {
-		ZEND_TYPE_FULL_MASK(type) |= MAY_BE_NULL;
-	}
-
 	uint32_t type_mask = ZEND_TYPE_PURE_MASK(type);
 	if ((type_mask & (MAY_BE_ARRAY|MAY_BE_ITERABLE)) == (MAY_BE_ARRAY|MAY_BE_ITERABLE)) {
 		zend_string *type_str = zend_type_to_string(type);
@@ -6332,7 +6328,7 @@ static zend_type zend_compile_typename(
 			ZSTR_VAL(type_str));
 	}
 
-	if (type_mask == MAY_BE_ANY && (orig_ast_attr & ZEND_TYPE_NULLABLE)) {
+	if (type_mask == MAY_BE_ANY && is_marked_nullable) {
 		zend_error_noreturn(E_COMPILE_ERROR, "Type mixed cannot be marked as nullable since mixed already includes null");
 	}
 
@@ -6343,6 +6339,15 @@ static zend_type zend_compile_typename(
 			ZSTR_VAL(type_str));
 	}
 
+	if ((type_mask & MAY_BE_NULL) && is_marked_nullable) {
+		zend_error_noreturn(E_COMPILE_ERROR, "null cannot be marked as nullable");
+	}
+
+	if (is_marked_nullable || force_allow_null) {
+		ZEND_TYPE_FULL_MASK(type) |= MAY_BE_NULL;
+		type_mask = ZEND_TYPE_PURE_MASK(type);
+	}
+
 	if ((type_mask & MAY_BE_VOID) && (ZEND_TYPE_IS_COMPLEX(type) || type_mask != MAY_BE_VOID)) {
 		zend_error_noreturn(E_COMPILE_ERROR, "Void can only be used as a standalone type");
 	}
@@ -6351,15 +6356,6 @@ static zend_type zend_compile_typename(
 		zend_error_noreturn(E_COMPILE_ERROR, "never can only be used as a standalone type");
 	}
 
-	if ((type_mask & (MAY_BE_NULL|MAY_BE_FALSE))
-			&& !ZEND_TYPE_IS_COMPLEX(type) && !(type_mask & ~(MAY_BE_NULL|MAY_BE_FALSE))) {
-		if (type_mask == MAY_BE_NULL) {
-			zend_error_noreturn(E_COMPILE_ERROR, "Null cannot be used as a standalone type");
-		} else {
-			zend_error_noreturn(E_COMPILE_ERROR, "False cannot be used as a standalone type");
-		}
-	}
-
 	ast->attr = orig_ast_attr;
 	return type;
 }

ext/reflection/php_reflection.c

@@ -1356,6 +1356,7 @@ static void reflection_type_factory(zend_type type, zval *object, bool legacy_be
 	type_reference *reference;
 	reflection_type_kind type_kind = get_type_kind(type);
 	bool is_mixed = ZEND_TYPE_PURE_MASK(type) == MAY_BE_ANY;
+	bool is_only_null = (ZEND_TYPE_PURE_MASK(type) == MAY_BE_NULL && !ZEND_TYPE_IS_COMPLEX(type));
 
 	switch (type_kind) {
 		case INTERSECTION_TYPE:
@@ -1373,7 +1374,7 @@ static void reflection_type_factory(zend_type type, zval *object, bool legacy_be
 	intern = Z_REFLECTION_P(object);
 	reference = (type_reference*) emalloc(sizeof(type_reference));
 	reference->type = type;
-	reference->legacy_behavior = legacy_behavior && type_kind == NAMED_TYPE && !is_mixed;
+	reference->legacy_behavior = legacy_behavior && type_kind == NAMED_TYPE && !is_mixed && !is_only_null;
 	intern->ptr = reference;
 	intern->ref_type = REF_TYPE_TYPE;
 

ext/reflection/tests/ReflectionType_possible_types.phpt

@@ -12,6 +12,8 @@ $functions = [
     function(): array {},
     function(): callable {},
     function(): iterable {},
+    function(): null {},
+    function(): false {},
     function(): StdClass {}
 ];
 
@@ -30,4 +32,6 @@ string(4) "bool"
 string(5) "array"
 string(8) "callable"
 string(8) "iterable"
+string(4) "null"
+string(5) "false"
 string(8) "StdClass"

ext/reflection/tests/union_types.phpt

@@ -13,8 +13,17 @@ function dumpType(ReflectionUnionType $rt) {
     }
 }
 
+function dumpBCType(ReflectionNamedType $rt) {
+    echo "Type $rt:\n";
+    echo "  Name: " . $rt->getName() . "\n";
+    echo "  String: " . (string) $rt . "\n";
+    echo "  Allows Null: " . ($rt->allowsNull() ? "true" : "false") . "\n";
+}
+
 function test1(): X|Y|int|float|false|null { }
 function test2(): X|iterable|bool { }
+function test3(): null|false { }
+function test4(): ?false { }
 
 class Test {
     public X|Y|int $prop;
@@ -22,6 +31,8 @@ class Test {
 
 dumpType((new ReflectionFunction('test1'))->getReturnType());
 dumpType((new ReflectionFunction('test2'))->getReturnType());
+dumpBCType((new ReflectionFunction('test3'))->getReturnType());
+dumpBCType((new ReflectionFunction('test4'))->getReturnType());
 
 $rc = new ReflectionClass(Test::class);
 $rp = $rc->getProperty('prop');
@@ -75,6 +86,14 @@ Allows null: false
   Name: bool
   String: bool
   Allows Null: false
+Type ?false:
+  Name: false
+  String: ?false
+  Allows Null: true
+Type ?false:
+  Name: false
+  String: ?false
+  Allows Null: true
 Type X|Y|int:
 Allows null: false
   Name: X