LibJS: Implement the Temporal.PlainMonthDay constructor

And the simple Temporal.PlainMonthDay.prototype getters, so that the
constructed Temporal.PlainMonthDay may actually be validated.

Libraries/LibJS/Tests/builtins/Temporal/PlainMonthDay/PlainMonthDay.from.js

@@ -0,0 +1,104 @@
+describe("correct behavior", () => {
+    test("length is 1", () => {
+        expect(Temporal.PlainMonthDay.from).toHaveLength(1);
+    });
+
+    test("fields object argument", () => {
+        const object = {
+            month: 7,
+            day: 6,
+        };
+        const plainMonthDay = Temporal.PlainMonthDay.from(object);
+        expect(plainMonthDay.monthCode).toBe("M07");
+        expect(plainMonthDay.day).toBe(6);
+    });
+
+    test("from month day string", () => {
+        const plainMonthDay = Temporal.PlainMonthDay.from("--07-06");
+        expect(plainMonthDay.monthCode).toBe("M07");
+        expect(plainMonthDay.day).toBe(6);
+    });
+
+    test("from date time string", () => {
+        const plainMonthDay = Temporal.PlainMonthDay.from("2021-07-06T23:42:01");
+        expect(plainMonthDay.monthCode).toBe("M07");
+        expect(plainMonthDay.day).toBe(6);
+    });
+
+    test("compares calendar name in month day string in lowercase", () => {
+        const values = [
+            "02-10[u-ca=iso8601]",
+            "02-10[u-ca=isO8601]",
+            "02-10[u-ca=iSo8601]",
+            "02-10[u-ca=iSO8601]",
+            "02-10[u-ca=Iso8601]",
+            "02-10[u-ca=IsO8601]",
+            "02-10[u-ca=ISo8601]",
+            "02-10[u-ca=ISO8601]",
+        ];
+
+        for (const value of values) {
+            expect(() => {
+                Temporal.PlainMonthDay.from(value);
+            }).not.toThrowWithMessage(
+                RangeError,
+                "MM-DD string format can only be used with the iso8601 calendar"
+            );
+        }
+    });
+});
+
+describe("errors", () => {
+    test("missing fields", () => {
+        expect(() => {
+            Temporal.PlainMonthDay.from({});
+        }).toThrowWithMessage(TypeError, "Required property day is missing or undefined");
+        expect(() => {
+            Temporal.PlainMonthDay.from({ month: 1 });
+        }).toThrowWithMessage(TypeError, "Required property day is missing or undefined");
+        expect(() => {
+            Temporal.PlainMonthDay.from({ day: 1 });
+        }).toThrowWithMessage(TypeError, "Required property month is missing or undefined");
+    });
+
+    test("invalid month day string", () => {
+        expect(() => {
+            Temporal.PlainMonthDay.from("foo");
+        }).toThrowWithMessage(RangeError, "Invalid ISO date time");
+    });
+
+    test("string must not contain a UTC designator", () => {
+        expect(() => {
+            Temporal.PlainMonthDay.from("2021-07-06T23:42:01Z");
+        }).toThrowWithMessage(RangeError, "Invalid ISO date time");
+    });
+
+    test("extended year must not be negative zero", () => {
+        expect(() => {
+            Temporal.PlainMonthDay.from("-000000-01-01");
+        }).toThrowWithMessage(RangeError, "Invalid ISO date time");
+    });
+
+    test("can only use iso8601 calendar with month day strings", () => {
+        expect(() => {
+            Temporal.PlainMonthDay.from("02-10[u-ca=iso8602]");
+        }).toThrowWithMessage(RangeError, "Invalid calendar identifier 'iso8602'");
+
+        expect(() => {
+            Temporal.PlainMonthDay.from("02-10[u-ca=ladybird]");
+        }).toThrowWithMessage(RangeError, "Invalid calendar identifier 'ladybird'");
+    });
+
+    test("doesn't throw non-iso8601 calendar error when using a superset format string such as DateTime", () => {
+        // NOTE: This will still throw, but only because "ladybird" is not a recognised calendar, not because of the string format restriction.
+        try {
+            Temporal.PlainMonthDay.from("2023-02-10T22:56[u-ca=ladybird]");
+        } catch (e) {
+            expect(e).toBeInstanceOf(RangeError);
+            expect(e.message).not.toBe(
+                "MM-DD string format can only be used with the iso8601 calendar"
+            );
+            expect(e.message).toBe("Invalid calendar identifier 'ladybird'");
+        }
+    });
+});

Libraries/LibJS/Tests/builtins/Temporal/PlainMonthDay/PlainMonthDay.js

@@ -0,0 +1,66 @@
+describe("errors", () => {
+    test("called without new", () => {
+        expect(() => {
+            Temporal.PlainMonthDay();
+        }).toThrowWithMessage(
+            TypeError,
+            "Temporal.PlainMonthDay constructor must be called with 'new'"
+        );
+    });
+
+    test("cannot pass Infinity", () => {
+        expect(() => {
+            new Temporal.PlainMonthDay(Infinity);
+        }).toThrowWithMessage(RangeError, "Invalid plain month day");
+        expect(() => {
+            new Temporal.PlainMonthDay(1, Infinity);
+        }).toThrowWithMessage(RangeError, "Invalid plain month day");
+        expect(() => {
+            new Temporal.PlainMonthDay(1, 1, undefined, Infinity);
+        }).toThrowWithMessage(RangeError, "Invalid plain month day");
+        expect(() => {
+            new Temporal.PlainMonthDay(-Infinity);
+        }).toThrowWithMessage(RangeError, "Invalid plain month day");
+        expect(() => {
+            new Temporal.PlainMonthDay(1, -Infinity);
+        }).toThrowWithMessage(RangeError, "Invalid plain month day");
+        expect(() => {
+            new Temporal.PlainMonthDay(1, 1, undefined, -Infinity);
+        }).toThrowWithMessage(RangeError, "Invalid plain month day");
+    });
+
+    test("cannot pass invalid ISO month/day", () => {
+        expect(() => {
+            new Temporal.PlainMonthDay(0, 1);
+        }).toThrowWithMessage(RangeError, "Invalid plain month day");
+        expect(() => {
+            new Temporal.PlainMonthDay(1, 0);
+        }).toThrowWithMessage(RangeError, "Invalid plain month day");
+    });
+
+    test("not within iso date time limit", () => {
+        expect(() => {
+            new Temporal.PlainMonthDay(9, 30, "iso8601", 999_999_999_999_999);
+        }).toThrowWithMessage(RangeError, "Invalid plain month day");
+    });
+});
+
+describe("normal behavior", () => {
+    test("length is 2", () => {
+        expect(Temporal.PlainMonthDay).toHaveLength(2);
+    });
+
+    test("basic functionality", () => {
+        const plainMonthDay = new Temporal.PlainMonthDay(7, 6);
+        expect(typeof plainMonthDay).toBe("object");
+        expect(plainMonthDay).toBeInstanceOf(Temporal.PlainMonthDay);
+        expect(Object.getPrototypeOf(plainMonthDay)).toBe(Temporal.PlainMonthDay.prototype);
+    });
+
+    // FIXME: Re-implement this test with Temporal.PlainMonthDay.prototype.toString({ calendarName: "always" }).
+    // test("default reference year is 1972", () => {
+    //     const plainMonthDay = new Temporal.PlainMonthDay(7, 6);
+    //     const fields = plainMonthDay.getISOFields();
+    //     expect(fields.isoYear).toBe(1972);
+    // });
+});

Libraries/LibJS/Tests/builtins/Temporal/PlainMonthDay/PlainMonthDay.prototype.calendarId.js

@@ -0,0 +1,14 @@
+describe("correct behavior", () => {
+    test("calendarId basic functionality", () => {
+        const plainMonthDay = new Temporal.PlainMonthDay(5, 1, "iso8601");
+        expect(plainMonthDay.calendarId).toBe("iso8601");
+    });
+});
+
+describe("errors", () => {
+    test("this value must be a Temporal.PlainMonthDay object", () => {
+        expect(() => {
+            Reflect.get(Temporal.PlainMonthDay.prototype, "calendarId", "foo");
+        }).toThrowWithMessage(TypeError, "Not an object of type Temporal.PlainMonthDay");
+    });
+});

Libraries/LibJS/Tests/builtins/Temporal/PlainMonthDay/PlainMonthDay.prototype.day.js

@@ -0,0 +1,14 @@
+describe("correct behavior", () => {
+    test("basic functionality", () => {
+        const plainMonthDay = new Temporal.PlainMonthDay(7, 6);
+        expect(plainMonthDay.day).toBe(6);
+    });
+});
+
+describe("errors", () => {
+    test("this value must be a Temporal.PlainMonthDay object", () => {
+        expect(() => {
+            Reflect.get(Temporal.PlainMonthDay.prototype, "day", "foo");
+        }).toThrowWithMessage(TypeError, "Not an object of type Temporal.PlainMonthDay");
+    });
+});

Libraries/LibJS/Tests/builtins/Temporal/PlainMonthDay/PlainMonthDay.prototype.monthCode.js

@@ -0,0 +1,14 @@
+describe("correct behavior", () => {
+    test("basic functionality", () => {
+        const plainMonthDay = new Temporal.PlainMonthDay(7, 6);
+        expect(plainMonthDay.monthCode).toBe("M07");
+    });
+});
+
+describe("errors", () => {
+    test("this value must be a Temporal.PlainMonthDay object", () => {
+        expect(() => {
+            Reflect.get(Temporal.PlainMonthDay.prototype, "monthCode", "foo");
+        }).toThrowWithMessage(TypeError, "Not an object of type Temporal.PlainMonthDay");
+    });
+});