Improve error_handing replacement functions

[twose]

It looks that it's unnecessary to make user_error_handler UNDEF.
The usage of zend_replace_error_handling() is to convert warnings to exceptions, it does not involve the call to user_error_handler.

And it also breaks the security of coroutine switching, following is an example:

// 0
set_error_handler(function () {
    // 9
    var_dump(func_get_args());
});

// 1
$wr = new WaitReference();

// 2
Coroutine::run(function () use ($wr) {
    // 3
    // zend_replace_error_handling() was called
    // then stream_connect() was called
    // it yield from __construct
    new PDO('mysql:host=127.0.0.1;charset=utf8', 'root', 'root');
    // 6
});

// error handler is UNDEF here
// 4
trigger_error('foo', E_USER_WARNING);

// 5
// it's same with WaitGroup
$wr::wait($wr);
// 7

// 8
// after PDO __construct() done
// zend_restore_error_handling() was restored
// user error handler will be called
trigger_error('foo', E_USER_WARNING);

// 10

[nikic]

Hm, interesting... The thing is that we explicitly skip calls to user_error_handler in EH_THROW mode (so this change is fine), but I am wondering if we really should fully skip them. EH_THROW only converts warnings, not notices and deprecations. This means that calling of the user error handler will be skipped for them, which seems maybe not right?

[twose]

Is it necessary to merge it into 7.3?
this patch will not break anything except struct zend_error_handling.

[twose]

The use of EH_THROW is very limited...perhaps this is not a real problem.
It's a hack way, when we use this API, we should have considered its risks, in my opinion.

[twose]

It's the new trend that throwing exceptions instead of warnings, I do hope we don’t use this API anymore... (Including other things that involve global vars)
Otherwise, the context switch of the coroutine will be affected.

[nikic]

@twose At least in this form, it cannot go into PHP 7.3 (it changes an exported structure). I think we should stick to master only.

[twose]

It is a bugfix under the coroutine model...
it's better for me to merge it into PHP 7.3.
How about only merge the part of function implementation? it seems to have only benefits.
I am also glad to only merge it into master, but I am obligated to consider it for my users.

[nikic]

@twose Could you please submit another patch against PHP-7.3 to show how it would look like? I guess it should keep the structure the same but just always set the field to UNDEF.

[twose]

Goto #6050