[5.7] Support custom accessor on whenPivotLoaded()

[staudenmeir]

whenPivotLoaded() doesn't work if the relationship uses a custom accessor with ->as('accessor').

You can now specify it as the fourth parameter:

return [
    'expires_at' => $this->whenPivotLoaded('role_user', function () {
        return $this->accessor->expires_at;
    }, new MissingValue, 'accessor'),
];

new MissingValue is necessary as the third parameter ($default = null) because whenPivotLoaded() behaves differently depending on the number of parameters:

'key' => $this->whenPivotLoaded($table, $value)       // "key" missing
'key' => $this->whenPivotLoaded($table, $value, null) // "key": null

I don't think this requires a separate test. The existing one already tests the default pivot accessor.

Fixes #25596.

[sisve]

You're changing a method signature which is a breaking change. This should target the 5.8 release.

[taylorotwell]

I would also maybe rather add a function like whenPivotLoadedAs($accessor... etc) to make this syntax a little cleaner. But, yes, will probably have to go on master branch. Thanks!

[staudenmeir]

@sisve In the past, changes to protected methods haven't been considered breaking.

[sisve]

@staudenmeir Can you give a link that describes when this has happened, and if that decision was intentional or just that no one said anything?

[staudenmeir]

@sisve I've seen multiple cases, but I can't find one right now. I can't remember an explicit "protected methods can be changed" comment, so they could have been mistakes.

[staudenmeir]

@sisve I found an example: Taylor renamed a protected method in 9a912d6.

[sisve]

It's hard to provide any argument other than the linked commit was not part of a PR, and was not reviewed by anyone. Someone would have to read every commit to catch these.