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Date: Mon, 23 May 2016 10:12:34 +0200
Message-ID: <CAMUwpuR=ES4eWTofrAcfC434nFQOrAyp5cy-wVdAykVr3BwE-A@mail.gmail.com>
To: Rasmus Schultz <rasmus@mindplay.dk>
Cc: Rowan Collins <rowan.collins@gmail.com>, PHP internals <internals@lists.php.net>
Content-Type: text/plain; charset=UTF-8
Subject: Re: [PHP-DEV] Exception::getLine()
From: jpauli@php.net (Julien Pauli)

On Sat, May 21, 2016 at 8:16 PM, Rasmus Schultz <rasmus@mindplay.dk> wrote:
> Alright, so forget my comparison with other languages.
>
> My other points remain:
>
> Presently, "throw new" is treated as though it was one statement.
> That's not the case. We have deferred throws and factory methods for
> exceptions, and we have re-throws, so collecting the stack-trace at
> construction time doesn't work.
>
> The construction site would only be relevant if "throw new" was in
> deed a single statement.
>
> Recording the actual throw site is clearly the goal - the current
> implementation is betting on "throw" and "new" happening at the same
> site, which is merely circumstance.
>
> Ideally, an Exception should collect another stack trace for each
> successive throw, which would enable you to trace not only the
> original site, but the flow through any exception-handlers that might
> have re-thrown the same Exception.
>
> As is, there is no information collected on throw, and thereby no
> evidence or record of possible re-throws - on top of the fact that you
> may be collecting and looking at bogus stack-traces from factory
> methods or exception mappers.
>
>
> On Fri, May 20, 2016 at 11:06 AM, Rowan Collins <rowan.collins@gmail.com> wrote:
>> On 20/05/2016 08:22, Niklas Keller wrote:
>>>
>>> 2016-05-20 4:13 GMT+02:00 Jesse Schalken <me@jesseschalken.com>:
>>>>
>>>> The top frame is the construction (get_error) and the site of the throw
>>>> (do_throw) doesn't appear in the stack at all.
>>>>
>>>
>>> The comparison with JavaScript isn't a good one, since you can throw
>>> everything in JS. If they didn't provide the stack trace upon throw, you
>>> would not have a stack trace at all if you throw a plain string.
>>>
>>
>>
>> That explanation justifies completely the opposite behaviour to what Jesse
>> described.
>>
>> According to MDN [1] the "stack" property is completley unstandardised, and
>> some engines may indeed populate it on throw, but there's no hint on that
>> page that they'll attach it to anything not constructed as an Error.
>>
>> So it's not a great comparison for either side (note that it was originally
>> brought up by Rasmus as an example where it *does* come from the throw site)
>> because the language doesn't actually guarantee you a stack trace at all.
>>
>> [1]
>> https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/stack
>>
>> Regards,
>> --
>> Rowan Collins
>> [IMSoP]
>>
>> --
>> PHP Internals - PHP Runtime Development Mailing List
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>
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>

Hi.

I explained that in my article detailing Exceptions from internal ,
http://jpauli.github.io/2015/04/09/exceptional-php.html

I admit it would be more logical to collect the trace in the
ZEND_THROW Opcode instead of in the create_handler of the Exception
class.

That would break backtraces, but we already broke them in PHP 7.0
So we could think about it for a 8.0 ideally , or a 7.1 ; I'm not
sure. Anyway, that needs more debate ;-)



Julien.Pauli