Remove or add redundant readonly property modifier

[derrabus]

Feature request

In readonly classes, I can still flag individual properties as readonly, for example:

readonly class MyService
{
    private readonly Foo $foo;

    public function __construct(
        FooFactory $fooFactory,
        private readonly Bar $bar,
    ) {
        $this->foo = $fooFactory->create();
    }
}

In this context, the readonly modifiers on the properties are 100% redundant. However, in codebases where readonly and mutatable properties are mixed, these redundant modifiers can still provide explicitness to the reader.

Proposal

I'd like to propose a fixer that normalizes readonly property modifiers on read-only classes. That fixer should come with a boolean setting to let me choose between:

• Always add readonly to all properties of a readonly class. This is essential the code snippet above.
• Always remove readonly from all properties of a readonly class. This setting wold be my preferred default. Running the fixer with that setting on the code above would yield the following result:

readonly class MyService
{
    private Foo $foo;

    public function __construct(
        FooFactory $fooFactory,
        private Bar $bar,
    ) {
        $this->foo = $fooFactory->create();
    }
}

Related work

• The fixer I'm proposing could do the cleanup after the fixer proposed in [PHP8.2] mark class readonly if all props are readonly #6801.
• We already have a similar fixer that removes redundant final keywords.

[julienfalque]

in codebases where readonly and mutatable properties are mixed, these redundant modifiers can still provide explicitness to the reader.

While I see the value of removing the redundant readonly markers from properties, I don't understand what would be the value of the opposite. If you can add readonly to properties because the class itself is readonly, then you don't have a mix of mutable and readonly properties, you already have readonly properties only.

[derrabus]

If you can add readonly to properties because the class itself is readonly, then you don't have a mix of mutable and readonly properties, you already have readonly properties only.

Sure, but I have to look at the class definition to see that. I have to jump to a different line of code while reading a file.

That being said, I can totally live with a fixer that is not configurable and that is only able to remove redundant readonly from properties.

[Wirone]

If you can add readonly to properties because the class itself is readonly, then you don't have a mix of mutable and readonly properties, you already have readonly properties only.

Sure, but I have to look at the class definition to see that. I have to jump to a different line of code while reading a file.

You don't mark methods as final when class is final though, right? How's that different with readonly?

[derrabus]

You don't mark methods as final when class is final though, right?

But I could.

How's that different with readonly?

It isn't.