Expanding the scope of the #[NoDiscard] attribute

Hi internals, 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. On the other hand, applying this to all array_* functions is more debatable. For example, functions like array_map() and array_filter() can be used with callbacks that have side effects (impure functions). In such cases, the return value might be intentionally discarded. Applying #[NoDiscard] to them could lead to false positives for legitimate code. 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 for existing code. This might be a type of change best reserved for a major version like PHP 9.0 to avoid backward compatibility breaks. Finally, I would love to hear the community's thoughts on the timeline. Should we aim to add these attributes for PHP 8.5, or should we introduce potentially breaking changes like these more gradually, perhaps leading up to PHP 9.0? Thanks, Kenta