Hard to figure out from an error message where incompatible method declarations meet

[ondrejmirtes]

Description

When we launch a PHP application, we might get a similar message:

Fatal error: Declaration of Baz::getId(): mixed must be compatible with Foo::getId(): int in /tmp/preview on line 13

When we look up the declarations of these methods, we get this:

interface Foo
{
    
    public function getId(): int;
    
}

abstract class Baz
{
    
    public function getId(): mixed
    {
        //...
    }
    
}

They have nothing in common, their existence on their own shouldn't be a problem for our application.

The problem is when they meet via a common child that both extends Baz and implements Foo:

class Lorem extends Baz implements Foo
{
    
}

The problem is that we don't learn about Lorem from the PHP error message which makes it really hard to find Loremin a large application.

Personally I solved it by enabling Xdebug in develop mode and looking at the stack trace. One (or both) of these two things would help to debug this problem in the future:

1. Show fatal error stack trace in PHP out of the box, without requiring Xdebug.
2. Somehow include Lorem too in this error message: Fatal error: Declaration of Baz::getId(): mixed must be compatible with Foo::getId(): int in /tmp/preview on line 13

3v4l.org link: https://3v4l.org/4iOYG

[iluuu1994]

Maybe "Foo::getId() (from Lorem)" would be an option. Edit: Actually, the other way around may make more sense.

[derickr]

Assigning this to me, as this sounds like a good thing to look into.

[ondrejmirtes]

This gets a bit more interesting with traits. When they're involved I think the part in parentheses should mention both the class that uses the trait and the trait with the method declaration.

Because if we mention only the class, it might use a lot of traits and the declaration might be hard to find.

If we mention only the trait, it might be used by a lot of classes and it might be hard to find the violating class that uses the trait.

[derickr]

@ondrejmirtes If you have example code for that, please add that as examples here. There might be many other situations that I didn't think of (yet).

[ondrejmirtes]

Simple example that still might be hard to figure out when the class uses many traits (the trait name is missing from the message): https://3v4l.org/Vupib

The original complicated example but with a trait: https://3v4l.org/q9e2j (in this example it'd be useful to know about Lorem, but also about BazTrait)

[derickr]

I have a draft PR up at https://github.com/php/php-src/pull/12129/files — it's likely not the best and final solution.