Cant change the page template with PHP 8

[cb2004]

I have been scratching my head with this one for a while, on some installs I could change the page template no problem, on others I was having to go into the database as the other template options were not available to me in the dropdown. It turns out this could be a problem with PHP 8:

https://processwire.com/talk/topic/25400-cant-change-page-template-after-use-them/

[ryancramerdesign]

@cb2004 I am unable to get PHP8 to install successfully on my current development computer, so it may be awhile before I can track this one down. Though if you or anyone else has any idea on the source of it and can point me in the direction, I can investigate further and attempt to workaround it.

[adrianbj]

I am on PHP8 and can't seem to replicate this issue. That forum thread suggests something about changing the default language. I tried that and still couldn't reproduce it, but there are so many modules in the ML system that I wonder if it's some combination I don't have?

[cb2004]

I get it on all my PHP 8 sites and none of those have multi language. Let me know the best way to help track it down and I can find some time for you no problem.

[matjazpotocnik]

@cb2004 I am on PHP8 (windows) and also can't replicate this issue. Can you think of anything else that could cause this behaviour?

[sekru1]

I also can't enable PHP8 on my server because then the template can't be changed. This is very annoying.

I was able to narrow down the problem a bit:
There are still templates to choose from that are not currently used by any page.
Maybe this helps you, Ryan?

[ryancramerdesign]

@cb2004 @sekru1 I've been around here long enough to know that if adrianbj and matjazpotocnik can't duplicate the issue in PHP8 then I've got no hope to duplicate it myself. :) But I have had a look through the code to see if I can spot anything that might potentially affect behavior in PHP8. The code for this is all pretty simple and standard, and I haven't been able to spot any potential issues yet. But if you'd like to have a look at it, it's all in a method called ProcessPageEdit::getAllowedTemplates() and can be viewed here:

https://github.com/processwire/processwire/blob/dev/wire/modules/Process/ProcessPageEdit/ProcessPageEdit.module#L2660

Please let me know if you can spot anything? Or if you have a live server running PHP8 and exhibiting the issue, I could always attempt to debug it from there too.

[adrianbj]

@ryancramerdesign - I think I have it figured out. I run all my sites in advanced mode so didn't notice this initially, but it appears in normal mode. The issue is this line:
https://github.com/processwire/processwire/blob/896100100187ad25f9e49dad0c047b01909013f3/wire/modules/Process/ProcessPageEdit/ProcessPageEdit.module#L2709

PHP8 treats '' differently to 0 when doing comparison operators like < 0 and I see that $template->noParents equals ''.

https://www.php.net/manual/en/migration80.incompatible.php

Make sense?

[adrianbj]

PS - this more strict logic has broken some of my own code as well, but as yet I haven't noticed any other core PW issues, but it seems like there might be some others.

[ryancramerdesign]

@adrianbj Thanks, I'll have to have a closer look at it. So the suspect line is this one:

if(!$superAdvanced && $template->noParents < 0 && $template->getNumPages() > 0) {

I think it's definitely strange, but probably okay if it treats '' differently from 0. Though it makes me wonder what the point of strict comparison operators is anymore. But in this case it seems like it would have to be treating a blank string as having a negative integer value? I think this issue will definitely pop up in more places (after all, everything returned by MySQL is a string), but I'm glad to hear you've not seen it cause issues elsewhere yet though. So I'm thinking maybe we change the line to this?

if(!$superAdvanced && ((int) $template->noParents) < 0 && $template->getNumPages() > 0) {

Or will PHP8 typecast the blank string to some negative integer value? If so, maybe we'd need this:

$noParents = $template->noParents === '' ? 0 : intval($template->noParents); 
if(!$superAdvanced && $noParents < 0 && $template->getNumPages() > 0) {

I guess I'm a little afraid to change anything here until I better understand it, so going to do some more reading. Thanks.

[adrianbj]

Or will PHP8 typecast the blank string to some negative integer value?

It casts it to 0

[ryancramerdesign]

That's good. Strange how it compares with a negative number in an if() statement though. There's got to be more to it, I'll keep reading.

…

On Fri, Jul 16, 2021, 5:04 PM Adrian Jones ***@***.***> wrote: Or will PHP8 typecast the blank string to some negative integer value? It casts it to 0 — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#1363 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AACQEUECQ6COLKS4JDQPR5DTYCNHLANCNFSM423S53NQ> .

[teppokoivula]

It's explained here: http://docs.php.net/manual/en/language.operators.comparison.php.

Warning Prior to PHP 8.0.0, if a string is compared to a number or a numeric string then the string was converted to a number before performing the comparison. This can lead to surprising results as can be seen with the following example: [...]

The key is that strings are no longer converted to numbers in this type of comparison, which means that '' remains '' or is converted to null (not sure if that's specifically declared anywhere), both of which are technically smaller than 0 (and smaller than even PHP_INT_MIN for that matter) :)

[sekru1]

Thank you all.
I can confirm that this change by Ryan solves the problem:
if(!$superAdvanced && ((int) $template->noParents) < 0 && $template->getNumPages() > 0) {

I hope it will find its way into the next release.