Improve incompatible trait property error message

[bshaffer]

Description

The following code results in a PHP Fatal Error:

trait FooTrait
{
    private array $options = [];
}
class Foo
{
    use FooTrait;
    public function __construct(private array $options = []) {}
}

The error thrown is

PHP Fatal error:  Foo and FooTrait define the same property ($options) in the composition of Foo. However, the definition differs and is considered incompatible.

However, the same thing defined in the class instead of in the constructor works:

trait FooTrait
{
    private array $options = [];
}
class Foo
{
    use FooTrait;
    private array $options = [];
}

As does the same thing, but without setting a default value:

trait FooTrait
{
    private array $options;
}
class Foo
{
    use FooTrait;
    public function __construct(private array $options) {}
}

This seems to be ane rror

PHP Version

PHP 8.1.29 to PHP 8.4.0-dev

Operating System

MAC OSX 14.7

[iluuu1994]

Hi @bshaffer. Constructor promoted properties desugar to a property without a default value. This seems to be coming up a lot lately. 🙂 Hence, the equivalent is actually the following:

<?php

trait FooTrait
{
    private array $options = [];
}

class Foo
{
    use FooTrait;

    private array $options;

    public function __construct(array $options = []) {
        $this->options = $options;
    }
}

Hence your error.

[iluuu1994]

Anyway, I agree that the error alone is a bit cryptic. It might be worth improving the error to spell out how the property is incompatible, mentioning the default value in this case. So, converting to a feature request.