LibJS: Implement Temporal.Instant.fromEpochSeconds()

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -143,6 +143,7 @@ namespace JS {
     P(fromCharCode)                          \
     P(fromCodePoint)                         \
     P(fromEntries)                           \
+    P(fromEpochSeconds)                      \
     P(fround)                                \
     P(gc)                                    \
     P(get)                                   \

Userland/Libraries/LibJS/Runtime/Temporal/InstantConstructor.cpp

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <LibCrypto/BigInt/UnsignedBigInteger.h>
 #include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/Temporal/Instant.h>
 #include <LibJS/Runtime/Temporal/InstantConstructor.h>
@@ -25,6 +26,9 @@ void InstantConstructor::initialize(GlobalObject& global_object)
     // 8.2.1 Temporal.Instant.prototype, https://tc39.es/proposal-temporal/#sec-temporal-instant-prototype
     define_direct_property(vm.names.prototype, global_object.temporal_instant_prototype(), 0);
 
+    u8 attr = Attribute::Writable | Attribute::Configurable;
+    define_native_function(vm.names.fromEpochSeconds, from_epoch_seconds, 1, attr);
+
     define_direct_property(vm.names.length, Value(1), Attribute::Configurable);
 }
 
@@ -60,4 +64,30 @@ Value InstantConstructor::construct(FunctionObject& new_target)
     return create_temporal_instant(global_object, *epoch_nanoseconds, &new_target);
 }
 
+// 8.2.3 Temporal.Instant.fromEpochSeconds ( epochSeconds ), https://tc39.es/proposal-temporal/#sec-temporal.instant.fromepochseconds
+JS_DEFINE_NATIVE_FUNCTION(InstantConstructor::from_epoch_seconds)
+{
+    // 1. Set epochSeconds to ? ToNumber(epochSeconds).
+    auto epoch_seconds_value = vm.argument(0).to_number(global_object);
+    if (vm.exception())
+        return {};
+
+    // 2. Set epochSeconds to ? NumberToBigInt(epochSeconds).
+    auto* epoch_seconds = number_to_bigint(global_object, epoch_seconds_value);
+    if (vm.exception())
+        return {};
+
+    // 3. Let epochNanoseconds be epochSeconds × 10^9ℤ.
+    auto* epoch_nanoseconds = js_bigint(vm.heap(), epoch_seconds->big_integer().multiplied_by(Crypto::UnsignedBigInteger { 1'000'000'000 }));
+
+    // 4. If ! IsValidEpochNanoseconds(epochNanoseconds) is false, throw a RangeError exception.
+    if (!is_valid_epoch_nanoseconds(*epoch_nanoseconds)) {
+        vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidEpochNanoseconds);
+        return {};
+    }
+
+    // 5. Return ? CreateTemporalInstant(epochNanoseconds).
+    return create_temporal_instant(global_object, *epoch_nanoseconds);
+}
+
 }

Userland/Libraries/LibJS/Runtime/Temporal/InstantConstructor.h

@@ -23,6 +23,8 @@ public:
 
 private:
     virtual bool has_constructor() const override { return true; }
+
+    JS_DECLARE_NATIVE_FUNCTION(from_epoch_seconds);
 };
 
 }

Userland/Libraries/LibJS/Tests/builtins/Temporal/Instant/Instant.fromEpochSeconds.js

@@ -0,0 +1,48 @@
+describe("correct behavior", () => {
+    test("length is 1", () => {
+        expect(Temporal.Instant.fromEpochSeconds).toHaveLength(1);
+    });
+
+    test("basic functionality", () => {
+        expect(Temporal.Instant.fromEpochSeconds(0).epochSeconds).toBe(0);
+        expect(Temporal.Instant.fromEpochSeconds(1).epochSeconds).toBe(1);
+        expect(Temporal.Instant.fromEpochSeconds(999_999_999).epochSeconds).toBe(999_999_999);
+        expect(Temporal.Instant.fromEpochSeconds(8_640_000_000_000).epochSeconds).toBe(
+            8_640_000_000_000
+        );
+
+        expect(Temporal.Instant.fromEpochSeconds(-0).epochSeconds).toBe(0);
+        expect(Temporal.Instant.fromEpochSeconds(-1).epochSeconds).toBe(-1);
+        expect(Temporal.Instant.fromEpochSeconds(-999_999_999).epochSeconds).toBe(-999_999_999);
+        expect(Temporal.Instant.fromEpochSeconds(-8_640_000_000_000).epochSeconds).toBe(
+            -8_640_000_000_000
+        );
+    });
+});
+
+test("errors", () => {
+    test("argument must be coercible to BigInt", () => {
+        expect(() => {
+            Temporal.Instant.fromEpochSeconds(1.23);
+        }).toThrowWithMessage(RangeError, "Cannot convert non-integral number to BigInt");
+        // NOTE: ToNumber is called on the argument first, so this is effectively NaN.
+        expect(() => {
+            Temporal.Instant.fromEpochSeconds("foo");
+        }).toThrowWithMessage(RangeError, "Cannot convert non-integral number to BigInt");
+    });
+
+    test("out-of-range epoch seconds value", () => {
+        expect(() => {
+            Temporal.Instant.fromEpochSeconds(8_640_000_000_001);
+        }).toThrowWithMessage(
+            RangeError,
+            "Invalid epoch nanoseconds value, must be in range -86400 * 10^17 to 86400 * 10^17"
+        );
+        expect(() => {
+            Temporal.Instant.fromEpochSeconds(-8_640_000_000_001);
+        }).toThrowWithMessage(
+            RangeError,
+            "Invalid epoch nanoseconds value, must be in range -86400 * 10^17 to 86400 * 10^17"
+        );
+    });
+});