php/php.editor/test/unit/data/testfiles/gotodeclaration/testArrowFunctions/testArrowFunctions.php

<?php
/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

const CONSTANT_INT = 1000;
$y = 5;

$fn0 = fn() => 100;

$fn1a = fn(int $x) => $x + $y;

$fn1b = function ($x) use ($y) {
    return $x + $y;
};

$fn2 = fn(int $a, ArrowFunctions $b) => $a + $b->getNumber() * $y;

fn (array $x) => $x; // parameter type

fn(int $x): int => $x; // return type

fn(?array $z, int $x): ?int => $x + count($z); // parameter and return type

fn($x = 100) => $x; // default value

fn(&$x) => $x; // reference

fn&($x) => $x; // reference

fn&(&$x) => $x; // reference

fn($x, ...$reset) => $reset; // variadics

fn($x, &...$reset) => $reset; // reference variadics

fn(): int => CONSTANT_INT;

fn(): ArrowFunctions => ArrowFunctions::new();

function (): ArrowFunctions {
    return ArrowFunctions::new();
};

// nest
$af = fn() => fn() => $y;
(fn() => fn() => $y)()();
(fn() => function() use ($y) {return $y;})()();

$af = fn(int $x): callable => fn(int $z): int => $x + $y * $z;
$af = fn(ArrowFunctions $x): callable => fn(?ArrowFunctions $z): ?ArrowFunctions => new ArrowFunctions();

$fn3 = function ($x) use ($y) {
    return fn() => $x + $y;
};
$fn4 = function ($x) use ($y) {
    return fn($x) => $x + $y;
};

function test(callable $f) {
    return fn(...$args) => !$f(...$args);
}

class ArrowFunctions
{

    public function test() {
        $y = 100;
        $af = fn(): ?ArrowFunctions => $this;
        $af = fn() => $$variable;
        $af = fn() => self::class;
        $af = fn($x): ?int => $x + $y;
        $af = static fn() => isset($this); // static
    }

    public function getNumber(): int {
        return 100;
    }

    public static function new() {
        return new ArrowFunctions();
    }
}