Allow exceptions in __toString()

RFC: https://wiki.php.net/rfc/tostring_exceptions

And convert some object to string conversion related recoverable
fatal errors into Error exceptions.

Improve exception safety of internal code performing string
conversions.

Author: nikic

UPGRADING

@@ -187,6 +187,11 @@ PHP 7.4 UPGRADE NOTES
   . Support for WeakReferences has been added.
     RFC: https://wiki.php.net/rfc/weakrefs
 
+  . Throwing exceptions from __toString() is now permitted. Previously this
+    resulted in a fatal error. Existing recoverable fatals in string conversions
+    have been converted to Error exceptions.
+    RFC: https://wiki.php.net/rfc/tostring_exceptions
+
 - CURL:
   . CURLFile now supports stream wrappers in addition to plain file names, if
     the extension has been built against libcurl >= 7.56.0.  The streams may

UPGRADING.INTERNALS

@@ -19,6 +19,8 @@ PHP 7.4 INTERNALS UPGRADE NOTES
   p. ZEND_EXT_FCALL_BEGIN can access arguments
   q. ZEND_COMPILE_IGNORE_USER_FUNCTIONS and ZEND_COMPILE_IGNORE_INTERNAL_FUNCTIONS
   r. TSRM environment locking
+  s. Typed references support
+  t. Exceptions thrown by string conversions.
 
 2. Build system changes
   a. Abstract
@@ -198,6 +200,14 @@ PHP 7.4 INTERNALS UPGRADE NOTES
      behave as if they are safe, care should still be taken in multi-threaded
      environments.
 
+  s. Correct support for typed properties requires the use of new macros to
+     assign values to references. For more information see
+     https://wiki.php.net/rfc/typed_properties_v2#impact_on_extensions.
+
+  t. convert_to_string() and zval_get_string() are now more likely to result in
+     an exception. For instructions on how to gracefully handle this see
+     https://wiki.php.net/rfc/tostring_exceptions#extension_guidelines.
+
 ========================
 2. Build system changes
 ========================

Zend/tests/bug26166.phpt

@@ -31,20 +31,18 @@ echo $o;
 
 echo "===NONE===\n";
 
-function my_error_handler($errno, $errstr, $errfile, $errline) {
-	var_dump($errstr);
-}
-
-set_error_handler('my_error_handler');
-
 class NoneTest
 {
 	function __toString() {
 	}
 }
 
 $o = new NoneTest;
-echo $o;
+try {
+    echo $o;
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
 
 echo "===THROW===\n";
 
@@ -58,17 +56,16 @@ class ErrorTest
 $o = new ErrorTest;
 try {
 	echo $o;
-}
-catch (Exception $e) {
-	echo "Got the exception\n";
+} catch (Exception $e) {
+	echo $e->getMessage(), "\n";
 }
 
 ?>
 ===DONE===
---EXPECTF--
+--EXPECT--
 Hello World!
 ===NONE===
-string(%d) "Method NoneTest::__toString() must return a string value"
+Method NoneTest::__toString() must return a string value
 ===THROW===
-
-Fatal error: Method ErrorTest::__toString() must not throw an exception, caught Exception: This is an error! in %sbug26166.php on line %d
+This is an error!
+===DONE===

Zend/tests/bug28444.phpt

@@ -3,12 +3,6 @@ Bug #28444 (Cannot access undefined property for object with overloaded property
 --FILE--
 <?php
 
-function my_error_handler($errno, $errstr, $errfile, $errline) {
-	var_dump($errstr);
-}
-
-set_error_handler('my_error_handler');
-
 class ObjectOne
 {
 	public $x;
@@ -17,6 +11,10 @@ class ObjectOne
 	{
 		$this->x = $x;
 	}
+
+	function __toString() {
+		return "Object";
+	}
 }
 
 class Overloaded
@@ -55,8 +53,8 @@ var_dump($y->z->x = 6);
 
 ?>
 ===DONE===
---EXPECTF--
-object(ObjectOne)#%d (1) {
+--EXPECT--
+object(ObjectOne)#2 (1) {
   ["x"]=>
   int(2)
 }
@@ -66,9 +64,8 @@ Overloaded::__set(y,3)
 int(3)
 Overloaded::__get(y)
 int(3)
-string(58) "Object of class ObjectOne could not be converted to string"
-Overloaded::__set(z,)
-object(ObjectOne)#%d (1) {
+Overloaded::__set(z,Object)
+object(ObjectOne)#3 (1) {
   ["x"]=>
   int(4)
 }

Zend/tests/bug30791.phpt

@@ -3,32 +3,25 @@ Bug #30791 (magic methods (__sleep/__wakeup/__toString) call __call if object is
 --FILE--
 <?php
 
-function my_error_handler($errno, $errstr, $errfile, $errline) {
-	var_dump($errstr);
-}
-
-set_error_handler('my_error_handler');
-
 class a
 {
-   public $a = 4;
-   function __call($a,$b) {
-       return "unknown method";
-   }
+    public $a = 4;
+    function __call($name, $args) {
+        echo __METHOD__, "\n";
+    }
 }
 
 $b = new a;
-echo $b,"\n";
+var_dump($b);
 $c = unserialize(serialize($b));
-echo $c,"\n";
 var_dump($c);
 
 ?>
 --EXPECT--
-string(50) "Object of class a could not be converted to string"
-
-string(50) "Object of class a could not be converted to string"
-
+object(a)#1 (1) {
+  ["a"]=>
+  int(4)
+}
 object(a)#2 (1) {
   ["a"]=>
   int(4)

Zend/tests/bug60909_2.phpt

@@ -3,18 +3,21 @@ Bug #60909 (custom error handler throwing Exception + fatal error = no shutdown
 --FILE--
 <?php
 register_shutdown_function(function(){echo("\n\n!!!shutdown!!!\n\n");});
-set_error_handler(function($errno, $errstr, $errfile, $errline){throw new Exception("Foo");});
 
 class Bad {
     public function __toString() {
-        throw new Exception('Oops, I cannot do this');
+        throw new Exception('I CAN DO THIS');
     }
 }
 
 $bad = new Bad();
 echo "$bad";
 --EXPECTF--
-Fatal error: Method Bad::__toString() must not throw an exception, caught Exception: Oops, I cannot do this in %sbug60909_2.php on line %d
+Fatal error: Uncaught Exception: I CAN DO THIS in %s:%d
+Stack trace:
+#0 %s(%d): Bad->__toString()
+#1 {main}
+  thrown in %s on line %d
 
 
 !!!shutdown!!!

Zend/tests/bug70967.phpt

@@ -11,4 +11,8 @@ class A {
 echo (new A);
 ?>
 --EXPECTF--
-Fatal error: Method A::__toString() must not throw an exception, caught Error: Call to undefined function undefined_function() in %sbug70967.php on line %d
+Fatal error: Uncaught Error: Call to undefined function undefined_function() in %s:%d
+Stack trace:
+#0 %s(%d): A->__toString()
+#1 {main}
+  thrown in %s on line %d

Zend/tests/bug72162.phpt

@@ -7,4 +7,8 @@ $var11 = new StdClass();
 $var16 = error_reporting($var11);
 ?>
 --EXPECTF--
-Recoverable fatal error: Object of class stdClass could not be converted to string in %sbug72162.php on line %d
+Fatal error: Uncaught Error: Object of class stdClass could not be converted to string in %s:%d
+Stack trace:
+#0 %s(%d): error_reporting(Object(stdClass))
+#1 {main}
+  thrown in %s on line %d

Zend/tests/call_with_refs.phpt

@@ -2,16 +2,17 @@
 Check call to non-ref function with call-time refs
 --FILE--
 <?php
-function my_errorhandler($errno,$errormsg) {
-  global $my_var;
-  $my_var=0x12345;
-  echo $errormsg."\n";
-  return true;
+class Test {
+    public function __toString() {
+        global $my_var;
+        $my_var=0x12345;
+        return "";
+    }
 }
-$oldhandler = set_error_handler("my_errorhandler");
+
 $my_var = str_repeat("A",64);
-$data = call_user_func_array("substr_replace",array(&$my_var, new StdClass(),1));
+$data = call_user_func_array("substr_replace",array(&$my_var, new Test(), 1));
 echo "OK!";
+?>
 --EXPECT--
-Object of class stdClass could not be converted to string
 OK!

Zend/tests/class_properties_const.phpt

@@ -22,4 +22,7 @@ NULL
 Notice: Undefined property: A::$1 in %sclass_properties_const.php on line %d
 NULL
 
-Recoverable fatal error: Object of class Closure could not be converted to string in %sclass_properties_const.php on line %d
+Fatal error: Uncaught Error: Object of class Closure could not be converted to string in %s:%d
+Stack trace:
+#0 {main}
+  thrown in %s on line %d

Zend/tests/closure_015.phpt

@@ -2,18 +2,20 @@
 Closure 015: converting to string/unicode
 --FILE--
 <?php
-set_error_handler('myErrorHandler', E_RECOVERABLE_ERROR);
-function myErrorHandler($errno, $errstr, $errfile, $errline) {
-  echo "Error: $errstr at $errfile($errline)\n";
-  return true;
-}
+
 $x = function() { return 1; };
-print (string) $x;
-print "\n";
-print $x;
-print "\n";
-?>
---EXPECTF--
-Error: Object of class Closure could not be converted to string at %sclosure_015.php(8)
+try {
+    print (string) $x;
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+try {
+    print $x;
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
 
-Error: Object of class Closure could not be converted to string at %sclosure_015.php(10)
+?>
+--EXPECT--
+Object of class Closure could not be converted to string
+Object of class Closure could not be converted to string

Zend/tests/exception_009.phpt

@@ -25,4 +25,8 @@ throw new my_exception;
 
 ?>
 --EXPECT--
-Recoverable fatal error: Object of class stdClass could not be converted to string in Unknown on line 0
+Fatal error: Uncaught Error: Object of class stdClass could not be converted to string in [no active file]:0
+Stack trace:
+#0 [internal function]: Exception->__toString()
+#1 {main}
+  thrown in [no active file] on line 0