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Date: Wed, 28 Jan 2015 09:43:47 +0100
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To: Rowan Collins <rowan.collins@gmail.com>
Cc: PHP Internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Proposal: Raise severity of undefined constants
From: kontakt@beberlei.de (Benjamin Eberlei)

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On Tue, Jan 27, 2015 at 11:21 PM, Rowan Collins <rowan.collins@gmail.com>
wrote:

> Hi All,
>
> I would like to propose that the error given for an undefined constant
> should be raised from E_NOTICE, probably to E_RECOVERABLE_ERROR, in PHP 7.
>
> I'm happy to expand this into a proper RFC, and work on patches for the
> engine, tests, and spec, but want to see if initial reception to the idea
> is favourable first.
>
> Current behaviour: any bare word which is not a defined constant is
> treated as though it were a quoted string, with an E_NOTICE issued.
>
> Proposed behaviour: an E_RECOVERABLE_ERROR is issued; if the error is
> caught, either the existing string behaviour could be retained, or the
> value could be treated as NULL. (I'm open to other alternatives.)
>
> PROS
>
> 1. Consistency.
>
> An undefined class constant (e.g. Foo::BAR) gives a fatal error, but a
> normal global constant gives only a notice. Class constants being "more
> modern" made this seem reasonable, but with namespaces, it's even worse - a
> qualified namespace constant (e.g. Foo\BAR) gives a fatal error, as does a
> global constant in namespace notation (e.g. \BAR); but a namespace constant
> referenced relative to the current namespace is a bare word, and gives only
> a notice (e.g. namespace Foo; const BAR=42; echo BAAR;).
>
> Functions and classes also give fatal errors if used without declaring;
> variables do not, but this is more useful, because they can meaningfully be
> created as null, and there isn't a syntax to declare a local variable, only
> to initialise it.
>
> 2. Inherent severity.
>
> It's probably relatively common to turn off E_NOTICE in error_reporting,
> or to miss one notice among many others. But an undefined constant
> magically turning into a string could cause relatively major problems.
>
> Firstly, a constant is likely to have some value which needs to be used or
> matched somewhere else. A READ_ONLY flag mis-typed as REED_ONLY could be
> interpreted as int(0) (i.e. intval('REED_ONLY')) and cause a catastrophic
> error.
>
> Secondly, keywords are also bare words, and any expression can be a
> statement. Thus the following is an infinite loop, no matter what
> blahblah() returns:
> while(true) {
> if ( blahblah() ) {
> brek;
> }
> }
>
> Obviously, there are other mistakes which could cause such errors, but
> this is one that the engine could easily pick up on and protect the user.
>
>
> CONS
>
> Like most changes, the downside is a break in compatibility.
>
> As far as I can make out, the current behaviour is actually for
> compatibility back as far as PHP 3 (correct me if I'm wrong, I didn't dig
> far).
>
> I'm not aware of any notice officially deprecating barewords-as-strings,
> but nor can I find many references to it in the manual at all. Its use for
> array keys has been explicitly discouraged in the manual since some time in
> 2001. [1]
>
> Outside code golf, I'd be very surprised if any code written or updated in
> the last 10 years deliberately uses this "feature", and I think changing it
> in PHP 7 is justifiable given the benefits to maintainers of even the
> simplest non-OO, non-namespaced code.
>
>
> What do people think?
>

I think this is too big a BC break.

The usage of $array[key] = 0 instead of "key" is widespread.

>
> [1] http://web.archive.org/web/20010614144157/http://www.php.
> net/manual/en/language.types.array.php#language.types.array.donts
>
> Regards,
>
> --
> Rowan Collins
> [IMSoP]
>
>
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