From fa6bce5087618f8b8bb321e0ade082019d5dd7a7 Mon Sep 17 00:00:00 2001
From: Linus Groh <mail@linusgroh.de>
Date: Tue, 16 Mar 2021 20:35:55 +0100
Subject: [PATCH] LibJS: Throw RangeError on BigInt exponentiation with
 negative exponent

https://tc39.es/ecma262/#sec-numeric-types-bigint-exponentiate
---
 Userland/Libraries/LibJS/Runtime/ErrorTypes.h              | 1 +
 Userland/Libraries/LibJS/Runtime/Value.cpp                 | 7 ++++++-
 .../Libraries/LibJS/Tests/builtins/BigInt/bigint-basic.js  | 6 ++++++
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/Userland/Libraries/LibJS/Runtime/ErrorTypes.h b/Userland/Libraries/LibJS/Runtime/ErrorTypes.h
index 58bb2f2929c..f55314261df 100644
--- a/Userland/Libraries/LibJS/Runtime/ErrorTypes.h
+++ b/Userland/Libraries/LibJS/Runtime/ErrorTypes.h
@@ -60,6 +60,7 @@
     M(JsonBigInt, "Cannot serialize BigInt value to JSON")                                                                              \
     M(JsonCircular, "Cannot stringify circular object")                                                                                 \
     M(JsonMalformed, "Malformed JSON string")                                                                                           \
+    M(NegativeExponent, "Exponent must be positive")                                                                                    \
     M(NotA, "Not a {} object")                                                                                                          \
     M(NotAConstructor, "{} is not a constructor")                                                                                       \
     M(NotAFunction, "{} is not a function")                                                                                             \
diff --git a/Userland/Libraries/LibJS/Runtime/Value.cpp b/Userland/Libraries/LibJS/Runtime/Value.cpp
index e29d40aa403..328d53c9145 100644
--- a/Userland/Libraries/LibJS/Runtime/Value.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Value.cpp
@@ -941,8 +941,13 @@ Value exp(GlobalObject& global_object, Value lhs, Value rhs)
         return {};
     if (both_number(lhs_numeric, rhs_numeric))
         return Value(pow(lhs_numeric.as_double(), rhs_numeric.as_double()));
-    if (both_bigint(lhs_numeric, rhs_numeric))
+    if (both_bigint(lhs_numeric, rhs_numeric)) {
+        if (rhs_numeric.as_bigint().big_integer().is_negative()) {
+            vm.throw_exception<RangeError>(global_object, ErrorType::NegativeExponent);
+            return {};
+        }
         return js_bigint(vm.heap(), Crypto::NumberTheory::Power(lhs_numeric.as_bigint().big_integer(), rhs_numeric.as_bigint().big_integer()));
+    }
     vm.throw_exception<TypeError>(global_object, ErrorType::BigIntBadOperatorOtherType, "exponentiation");
     return {};
 }
diff --git a/Userland/Libraries/LibJS/Tests/builtins/BigInt/bigint-basic.js b/Userland/Libraries/LibJS/Tests/builtins/BigInt/bigint-basic.js
index eb96764d4f3..eb957020bfa 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/BigInt/bigint-basic.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/BigInt/bigint-basic.js
@@ -96,4 +96,10 @@ describe("errors", () => {
             1n % 0n;
         }).toThrowWithMessage(RangeError, "Division by zero");
     });
+
+    test("negative exponent", () => {
+        expect(() => {
+            1n ** -1n;
+        }).toThrowWithMessage(RangeError, "Exponent must be positive");
+    });
 });