ParamNameMismatch

Emitted when method overrides a parent method but renames a param.

<?php

class A {
    public function foo(string $str, bool $b = false) : void {}
}

class AChild extends A {
    public function foo(string $string, bool $b = false) : void {}
}

Why is this bad?

PHP 8 introduces named parameters which allow developers to call methods with explicitly-named parameters;

<?php

function callFoo(A $a) {
    $a->foo(str: "hello");
}

In the first example passing new AChild() to callFoo() results in a fatal error, as AChild's definition of the method foo() doesn't have a parameter named $str.

How to fix

You can change the child method param name to match:

<?php

class A {
    public function foo(string $str, bool $b = false) : void {}
}

class AChild extends A {
    public function foo(string $str, bool $b = false) : void {}
}

Workarounds

@no-named-params

Alternatively you can ignore this issue by adding a @no-named-params annotation to the parent method:

<?php

class A {
    /** @no-named-params */
    public function foo(string $str, bool $b = false) : void {}
}

class AChild extends A {
    public function foo(string $string, bool $b = false) : void {}
}

Any method with this annotation will be prevented (by Psalm) from being called with named parameters, so the original issue does not matter.

Config allowNamedParamCalls="false"

This prevents any use of named params in your codebase. Ideal for self-contained projects, but less ideal for libraries.

It means the original code above will not emit any errors as long as the class A is defined in a directory that Psalm can scan.

Config allowInternalNamedParamCalls="false"

For library authors Psalm supports a more nuanced flag that tells Psalm to prohibit any named parameter calls on @internal classes or methods.

With that config value, this is now allowed:

<?php

/**
 * @internal
 */
class A {
    public function foo(string $str, bool $b = false) : void {}
}

class AChild extends A {
    public function foo(string $string, bool $b = false) : void {}
}

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