ladybird/Tests/LibJS/Runtime/syntax/generators.js

describe("parsing freestanding generators", () => {
    test("simple", () => {
        expect(`function* foo() {}`).toEval();
        expect(`function *foo() {}`).toEval();
        expect(`function
            *foo() {}`).toEval();

        expect(`function *await() {}`).toEval();
        expect(`function *yield() {}`).toEval();
    });
    test("yield expression", () => {
        expect(`function* foo() { yield; }`).toEval();
        expect(`function* foo() { yield (yield); }`).toEval();
        expect(`function* foo() { yield (yield foo); }`).toEval();
        expect(`function foo() { yield; }`).toEval();
        expect(`function foo() { yield 3; }`).not.toEval();
    });

    test("yield expression only gets the first expression", () => {
        expect("function* foo() { yield 2,3 }").toEval();
        expect("function* foo() { ({...yield yield, }) }").toEval();
    });

    test("yield expression preserves for-loop no-In context", () => {
        expect("function* foo() { for (yield '' in {}; ;); }").not.toEval();
        expect("function* foo() { for (yield * '' in {}; ;); }").not.toEval();
    });

    test("yield-from expression", () => {
        expect(`function* foo() { yield *bar; }`).toEval();
        expect(`function* foo() { yield *(yield); }`).toEval();
        expect(`function* foo() { yield
            *bar; }`).not.toEval();
        expect(`function foo() { yield
            *bar; }`).toEval();
    });
});

describe("parsing object literal generator functions", () => {
    test("simple", () => {
        expect(`x = { *foo() { } }`).toEval();
        expect(`x = { * foo() { } }`).toEval();
        expect(`x = { *
                foo() { } }`).toEval();
    });
    test("yield", () => {
        expect(`x = { foo() { yield; } }`).toEval();
        expect(`x = { *foo() { yield; } }`).toEval();
        expect(`x = { *foo() { yield 42; } }`).toEval();
        expect(`x = { foo() { yield 42; } }`).not.toEval();
        expect(`x = { *foo() { yield (yield); } }`).toEval();
        expect(`x = { *
                foo() { yield (yield); } }`).toEval();
    });
});

describe("parsing classes with generator methods", () => {
    test("simple", () => {
        expect(`class Foo { *foo() {} }`).toEval();
        expect(`class Foo { static *foo() {} }`).toEval();
        expect(`class Foo { *foo() { yield; } }`).toEval();
        expect(`class Foo { *foo() { yield 42; } }`).toEval();
        expect(`class Foo { *constructor() { yield 42; } }`).not.toEval();
    });
});

test("function expression names equal to 'yield'", () => {
    expect(`function *foo() { (function yield() {}); }`).toEval();
    expect(`function f() { (function* yield() {}); }`).not.toEval();
    expect(`var g = function* yield() {};`).not.toEval();
    expect(`function *foo() { function yield() {} }`).not.toEval();
});

test("generator instances use the intrinsic prototype when function prototype is not an object", () => {
    function* generator() {}
    const GeneratorPrototype = Object.getPrototypeOf(generator).prototype;

    for (const prototype of [undefined, null, false, "", Symbol(), 1]) {
        generator.prototype = prototype;
        expect(Object.getPrototypeOf(generator())).toBe(GeneratorPrototype);
    }
});

test("yield-star yields delegated iterator results directly", () => {
    const firstResult = { value: 1 };
    const terminalResult = { value: 34, done: true };
    const iterator = {
        index: 0,
        next() {
            return this.index++ === 0 ? firstResult : terminalResult;
        },
    };
    const iterable = {
        [Symbol.iterator]() {
            return iterator;
        },
    };

    function* generator() {
        return yield* iterable;
    }

    const outer = generator();
    expect(outer.next()).toBe(firstResult);
    expect(outer.next()).toEqual({ value: 34, done: true });
});

test("yield-star does not get value from non-terminal sync results", () => {
    let log = "";
    let count = 1;
    const iterator = {
        next() {
            log += "n";
            return {
                get done() {
                    log += "d";
                    return count-- === 0;
                },
                get value() {
                    log += "v";
                    return 42;
                },
            };
        },
        [Symbol.iterator]() {
            log += "i";
            return this;
        },
    };

    function* generator() {
        return yield* iterator;
    }

    const outer = generator();
    const firstResult = outer.next();
    expect(log).toBe("ind");
    expect(firstResult.value).toBe(42);
    expect(log).toBe("indv");
    expect(outer.next()).toEqual({ value: 42, done: true });
    expect(log).toBe("indvndv");
});