PHP 8.0: Fatal errors are no longer suppressed by `@`.

[costdev]

Overview

From ​PHP 8: Backward Incompatible Changes:

The @ operator will no longer silence fatal errors (E_ERROR, E_CORE_ERROR, E_COMPILE_ERROR, E_USER_ERROR, E_RECOVERABLE_ERROR, E_PARSE)

Example case

Initially reported by @swb1192 on Slack, a Fatal Error was thrown when disk_free_space() was called during a plugin update. disk_free_space() had been disabled by the host.

In earlier versions of PHP, if a function was unavailable (i.e. disabled via php.ini), this would silently fail. In PHP 8+, the Fatal Error is thrown.

Typical fix

This is typically fixed by using function_exists() before calling the function that may be unavailable. If the check fails, return the function's documented failure value. In the case of disk_free_space(), this value is false.

Notes

• disk_free_space() was reported on a popular plugin which also used the function. The issue was resolved by using the fix noted above. Other plugins have also used this fix for the same reason.
• I have reached out in the #hosting-community Slack channel to request functions that are commonly disabled on hosting platforms so that we can target these functions ahead of other instances being reported.
• Efforts are ongoing to reduce the use of @ in Core. However, until such time as that has been achieved, the fix above can be used, when appropriate, at least as a stop-gap fix.
• Other occurrences of Fatal Errors when using @ should be reported here so that we can target these, or related tickets linked in the comments below.
• There are currently ~269 uses of @. 239 of these occur in Core, and 30 occur upstream.

[costdev]

Related umbrella ticket: #54730

In PHP 8+, @ no longer suppresses fatal errors.

disk_free_space may be disabled by hosts, which will throw a Fatal Error on 'undefined function'.

This change prevents the Fatal Error, and falls back to false when disk_free_space() is unavailable.

Trac ticket:

The (int) cast is taken from the Rollback Update Failure plugin's ​usage. While I don't know the reason, I took the judgment to be sound.

I believe @SergeyBiryukov suggested the (int) for that usage. Sergey, can you clarify why this was suggested in the Rollback Update Failure plugin?

An int cast would only make sense if the fall back value was set to 0, which would effectively change the type of $available_space to always be an int.

Curious to hear the reasoning.

The (int) cast is taken from the Rollback Update Failure plugin's ​usage. While I don't know the reason, I took the judgment to be sound.

I believe @SergeyBiryukov suggested the (int) for that usage. Sergey, can you clarify why this was suggested in the Rollback Update Failure plugin?

If I recall correctly, my suggestion there was to use a function_exists() check instead of checking the disable_functions setting, see https://core.trac.wordpress.org/ticket/51857#comment:116 for more details. The (int) cast was pre-existing and was not a part of my comment,

I agree the (int) cast seems out of place here as is, we should either remove it completely, or use 0 as a fallback value to keep a consistent type.

IMO, removing the (int) cast is the preferred way forward, otherwise the "no space available" vs "failure to verify space available" cases can no longer be distinguished.
While it _may_ not seem important now to be able to distinguish between those cases, it may become important at a later date and I see no reason to deviate from the PHP native return types.

[costdev]

PR updated to remove the (int) cast. Ready for review.

[SergeyBiryukov]

In 52585:

Upgrade/Install: Check if the disk_free_space() function exists before calling it.

In PHP 8+, @ no longer suppresses fatal errors:

The @ operator will no longer silence fatal errors (E_ERROR, E_CORE_ERROR, E_COMPILE_ERROR, E_USER_ERROR, E_RECOVERABLE_ERROR, E_PARSE).

Reference: ​PHP 8: Backward Incompatible Changes.

disk_free_space() may be disabled by hosts, which will throw a fatal error on a call to undefined function.

This change prevents the fatal error, and falls back to false when disk_free_space() is unavailable.

Follow-up to [25540], [25774], [25776], [25831], [25869].

Props costdev, jrf, swb1192, SergeyBiryukov.
Fixes #54826. See #54730.

Thanks for the PR! Merged in https://core.trac.wordpress.org/changeset/52585.

Thanks @SergeyBiryukov ! Just checking - should an issue be opened in the plugin repo to remove the (int) cast there as well ?

Yes please! Looks like I don't have commit there, but I'm sure Andy would appreciate the PR.