Hi
Am 2025-07-01 16:41, schrieb Kenta Usami:
I'm writing to start a discussion about expanding the use of the newly
accepted #[NoDiscard] attribute.
I believe this attribute is a fantastic addition that will help
prevent many subtle bugs, and we can make it even more effective by
applying it to a broader set of core functions.
My initial thoughts for strong candidates are:
- All is_* prefixed functions
- The password_*() functions
- Most string functions: Many string functions like strlen(),
substr(), trim(), and str_replace() are also clear candidates.
We would naturally exclude functions with output side effects, such
as the printf() family.
- Mathematical functions
- Pure array_*() functions: Functions that don't accept callbacks,
such as array_keys(), array_values(), array_reverse(), and
array_unique(), are also strong candidates. Their return value is
their only result.
As one of the RFC authors, adding `#[\NoDiscard]` to every pure function
was an explicit non-goal of the RFC. Please let me refer to:
https://wiki.php.net/rfc/marking_return_value_as_important#recommended_usage
The goal of the attribute is to prevent
hard-to-detect-but-easy-to-create bugs. Forgetting to use the return
value of `str_contains()` is not particularly easy to do
unintentionally.
This nuance extends to other areas, like many filesystem functions
which require case-by-case evaluation. A tricky example is
file_get_contents(). At first glance, it seems like an obvious
candidate. However, despite its name, it can be used to send external
HTTP requests where the primary goal might be the side effect of the
request itself (like a webhook ping), and the returned content is
intentionally ignored. Adding #[NoDiscard] here could create issues
`file_get_contents()` on the other hand might be a good candidate, since
even for a “ping” request you are generally interested in finding out
whether or not the request succeeded. However `file_get_contents()`
already emits warnings and notices in this case (and would probably
throw an Exception if it was newly introduced).
Best regards
Tim Düsterhus
