PHP Internals News: Episode 101: More Partially Supported Callable Deprecations

PHP Internals News: Episode 101: More Partially Supported Callable Deprecations

Thursday, May 19th 2022, 09:05 BST London, UK

In this episode of "PHP Internals News" I talk with Juliette Reinders Folmer (Website, Twitter, GitHub) about the "More Partially Supported Callable Deprecations" RFC that she has proposed.

The RSS feed for this podcast is https://derickrethans.nl/feed-phpinternalsnews.xml, you can download this episode's MP3 file, and it's available on Spotify and iTunes. There is a dedicated website: https://phpinternals.news

Transcript

Derick Rethans 0:14

Hi, I'm Derick. Welcome to PHP internals news, the podcast dedicated to explaining the latest developments in the PHP language. This is episode 101. Today I'm talking with Juliette Reinders Folmer, about the Expand Deprecation Notice Scope for Partially supported Callables RFC that she's proposing. That's quite a mouthful. I think you should shorten the title. Juliette, would you please introduce yourself?

Juliette Reinders Folmer 0:37

You're starting with the hardest questions, because introducing myself is something I never know how to do. So let's just say I'm a PHP developer and I work in open source, nearly all the time.

Derick Rethans 0:50

Mostly related to WordPress as far as I understand?

Juliette Reinders Folmer 0:52

Nope, mostly related to actually CLI tools. Things like PHP Unit polyfills. Things like PHP Code Sniffer, PHP parallel Lint. I spend the majority of my time on CLI tools, and only a small portion of my time consulting on the things for WordPress, like keeping that cross version compatible.

Derick Rethans 1:12

All right, very well. I actually did not know that. So I learned something new already.

Juliette Reinders Folmer 1:16

Yeah, but it's nice. You give me the chance now to correct that image. Because I notice a lot of people see me in within the PHP world as the voice of WordPress and vice versa, by the way in WordPress world to see me as far as PHP. And in reality, I do completely different things. There is a perception bias there somewhere and which has slipped in.

Derick Rethans 1:38

It's good to clear that up then.

Juliette Reinders Folmer 1:39

Yeah, thank you.

Derick Rethans 1:40

Let's have a chat about the RFC itself then. What is the problem that is RFC is trying to solve?

Juliette Reinders Folmer 1:46

There was an RFC or 8.2 which has already been approved in October, which deprecates partially supported callables. Now for those people listening who do not know enough about that RFC, partially supported callables are callables which you can call via a function like call_user_func that which you can't assign to variable and then call as a variable. Sometimes you can call them just by using the syntax which you used for defining the callable, so not as variable but as the actual literal.

Derick Rethans 2:20

And as an example here, that is, for example, static colon colon function name, for example.

Juliette Reinders Folmer 2:26

Absolutely, yeah.

Derick Rethans 2:27

Which you can use with call_user_func by having two array elements. You can call it with literal syntax, but you can't assign it to a variable and then call it. Do I get that, right?

Juliette Reinders Folmer 2:36

Absolutely. That's it. There's eight of those. And basically, the original RFC from Nikita proposed to deprecate support for them in 8.2, add deprecation notices and remove support for them altogether in PHP nine. And the original RFC explicitly excluded two particular things from those deprecation notices. That's the callable type and using the syntaxes in combination with the is_callable function, where you're checking if the syntax is callable. The argument used in the original RFC was to keep those side effect free. The problem with this is that with the callable type, this means you go from absolutely no notice or nothing, to a fatal error in PHP 9. Everything works, and you're not getting any notification. But in PHP 9, its fatal error at the moment that callable is being passed to a function.

Derick Rethans 3:31

This is the callable type in function declarations.

Juliette Reinders Folmer 3:33

Yeah, absolutely. And with is_callable, I discovered a pattern in my wanderings across the world where people use the syntax in is_callable, but then use it in a literal call. So not using call_user_func, not using a variable to call it, but it's callable static double colon method name, and then called static double colon method name as literal. And that pattern basically, for valid calls would mean that that function would no longer be called in PHP 9 without any notification whatsoever.

Derick Rethans 4:13

So it's a silent change that you can't detect at all.

Juliette Reinders Folmer 4:17

Yeah, which to me sounded dangerous. I started asking some questions about that. But six weeks ago, the conclusion was, well, maybe this should be changed. But as this was explicit in the original RFC, we can't just change it. We need to have a new RFC to basically amend the original RFC and remove the exception for these two situations and allow them to throw deprecation notices.

Derick Rethans 4:44

What are you proposing to change with this RFC than?

Juliette Reinders Folmer 4:47

What this RFC is proposing is simply to remove the exception that the callable type and is_callable are not throwing a deprecation notice. This RFC is proposing that they should throw a deprecation notice, so that more of these type situations can be discovered in time for PHP 9 to prevent users getting fatal errors.

Derick Rethans 5:08

Now, of course, we have no idea when PHP nine is actually showing up, but I don't think it will be this year. Well, I know it won't be this year, and it certainly won't be be next year neither, I think.

Juliette Reinders Folmer 5:17

That's all the same. I mean, it makes there'll be two, three years ahead, but it doesn't really make sense to have the main deprecation in 8.2 and then have the additional deprecation in 8.4 or something.

Derick Rethans 5:29

Absolutely.

Juliette Reinders Folmer 5:30

It's a lot more logical to have it all in in the same version. Because it's all related. It's basically the same thing without the exception for callable type. And is_callable.

Derick Rethans 5:42

Although there is no current application, would this be able to be found if you had like a comprehensive test suite?

Juliette Reinders Folmer 5:48

Yes and no. Yes, you can find this with a test suite. But one, you're presuming that there are tests. Two, that the tests covered the effected code with enough path coverage. Three, imagine a test you've written yourself at some point in the past where which affected callables, you might have, you know, a data provider where you say: Okay, valid callable function, which you've mocked or, you know, closure, which you've put in and second, this function does not exist. Okay, so now you're testing this function, which at some point in its logic has a callable, and expects that type to receive that type. But are you actually testing with the specific deprecated partially supported callables? Even if you have a test, and the test covers the affected code, if you do not test with one of these eight syntaxes, which has been deprecated, you still cannot detect it. And then, four, you s