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Thread-Topic: [RFC] Allow calls to global functions in constant expressions
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Date: Fri, 14 Feb 2020 15:18:17 +0000
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Subject: Re: [RFC] Allow calls to global functions in constant expressions
From: tysonandre775@hotmail.com (tyson andre)

Hi internals,=0A=
=0A=
https://wiki.php.net/rfc/calls_in_constant_expressions=A0has hit some roadb=
locks in the implementation shortly after the last email.=0A=
I've been blocked on how to resolve them in the implementation in a way I'm=
 certain would work.=0A=
I had assumed the calling scope wouldn't have the below issues when I start=
ed working on this RFC, but was mistaken.=0A=
=0A=
=A0- The helper method the C code uses, `zend_call_function()`, will always=
 act as though `strict_types=3D0`. I'd consider this a blocker for `declare=
(strict_types=3D1); const X =3D intdiv("123", 2);`. (Internally, zend_call_=
function adds a fake call frame without a function, similar to what=A0__get=
, invocations of error handlers, etc do, and that call frame makes the para=
meter parsing helper macros of the invoked function treat it like strict_ty=
pes=3D0)=0A=
=0A=
    It may also be desirable to specify calls in constants always work like=
 strict_types=3D1, to avoid issues such as `strpos($float, '.')` being loca=
le-dependent)=0A=
 - Getting the class scope *of the constant declaration* to work properly w=
ith `callable` (e.g. `public $x =3D array_map('self::helperMethod', VALUES)=
;`).=0A=
    This isn't an issue with only a whitelist.=0A=
 - Solving the above two issues while continuing to throw for func_get_args=
(), get_defined_vars(), etc.=0A=
   get_defined_vars() would throw for dynamic calls, but the above approach=
es would act like =0A=
=0A=
Currently, my best ideas to fix some of the 3 issues were:=0A=
 - Create a fake zend_function placeholder in C with a placeholder name and=
 add it to the internal stack of calls (EG(current_execute_data)).=0A=
   Currently, though, it's only possible to set strict_types=3D1 for user-d=
efined functions.=0A=
 - Create an actual closure when compiling the code, which would be evaluat=
ed the same way as `public $x =3D (static function() { return array_map('se=
lf::helperMethod', VALUES); })()`=0A=
    (i.e. a closure without any `use` variables. The )=0A=
=0A=
    This would solve it, but the performance would be unexpectedly worse th=
an expected, and that would interfere with optimizations.=0A=
 - Create an alternative to zend_call_function, but that would duplicate co=
de and be error prone.=0A=
   I'm not familiar enough with XDebug, NewRelic, uopz, and other replaceme=
nts of zend_vm_execute to know if those would be able to support that,=0A=
   or if there would be even more issues I haven't thought up yet that woul=
d prevent .=0A=
=0A=
Second, I realize it doesn't make much sense to restrain the constant expre=
ssions for parameter defaults and class constants in the same way.=0A=
The RFC was coherent proposing allowing any function call in 5 places, but =
less coherent proposing a whitelist of functions, even where those restrict=
ions weren't necessary.=0A=
=0A=
- It may be desirable to support many extra expression types in parameter d=
efaults and static property defaults=0A=
  (`function myFunc(object $x =3D new DefaultObject()) {}`)=0A=
  but still limit class constants to the proposed whitelist of functions.=
=0A=
=0A=
Third, I was considering a straw poll for this,=0A=
but don't know what's required to set one up.=0A=
It also didn't make sense to me without a solution to the roadblocks.=0A=
=0A=
1. Desired expressions in param defaults (No change/Whitelisted functions/A=
ny function/Any method + new X()+others)=0A=
2. ... in static property defaults=0A=
3. ... in static variable defaults=0A=
4. ... in class constant values=0A=
5. ... in const X =3D ...=0A=
=0A=
Thanks,=0A=
- Tyson=