Automattic / Automattic/VIP-Coding-Standards
Check the hook callback parameter count ?
- Dominant language
- PHP
- Stars
- 261
- Forks
- 44
- Avg merge
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- Merged PRs (30d)
- 1
Description
## What problem would the enhancement address for VIP?
Prevent potential fatal `ArgumentCount` errors.
## Describe the solution you'd like
Inspired by the `AlwaysReturnInFilter` sniff, I was thinking that once the abstract hook/callback sniff exists, it wouldn't be that hard to create a sniff which would check synchronicity between the parameters requested from a hook-in and the callback function declaration.
This would apply to both `add_filter()` as well as `add_action()`.
Such a sniff would also be a candidate for (eventually moving to) WPCS, but I wanted to discuss the general idea here first, largely to see if the potential issue described above actually occurs in real life situations.
## What code should be reported as a violation?
```php
// Error: Two parameters expected, one (implicit) requested.
add_filter( 'the_title', function( $title, $id ) {
// Do something.
return $title;
} );
// Warning: One parameter expected, two requested.
add_filter( 'the_title', function( $title ) {
// Do something.
return $title;
}, 10, 2 );
```
## What code should *not* be reported as a violation?
```php
// OK: Two parameters expected, two requested.
add_filter( 'the_title', function( $title, $id ) {
// Do something.
return $title;
}, 10, 2 );
// OK: Three parameters expected, two requested, but third parameter is optional,
// which can be done by design to allow direct calls to the function to pass it.
function prefix_title_filter( $title, $id, $optional = null ) {
// Do something.
return $title;
}
add_filter( 'the_title', 'prefix_title_filter', 10, 2 );
```
## Additional context
### Future scope
* Once a list of WP native hooks + the amount of parameters they pass is known (via a trait in WPCS for instance), an additional check could be added that the `$accepted_args` parameter value is never higher than the number of passed parameters when the hook is called.
```php
function prefix_title_filter( $title, $id, $optional = null ) {
// Do something.
return $title;
}
// The `the_title` filter only passes two arguments max, so the code here is an error.
add_filter( 'the_title', 'prefix_title_filter', 10, 3 );
```
* For PHP native functions used in callbacks, reflection could be used to see how many (required) parameters these take and match that with the `$accepted_args` parameter.
* For WP native functions a list based solution would be needed to do the same.
## Relevant links
* https://developer.wordpress.org/reference/functions/add_action/
* https://developer.wordpress.org/reference/functions/add_filter/
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