fix(NODE-6764): incorrect negative bigint handling

package.json

@@ -111,7 +111,7 @@
     "build:bundle": "rollup -c rollup.config.mjs",
     "build": "npm run build:dts && npm run build:bundle",
     "check:lint": "ESLINT_USE_FLAT_CONFIG=false eslint -v && ESLINT_USE_FLAT_CONFIG=false eslint --ext '.js,.ts' --max-warnings=0 src test && npm run build:dts && npm run check:tsd",
-    "format": "eslint --ext '.js,.ts' src test --fix",
+    "format": "ESLINT_USE_FLAT_CONFIG=false eslint --ext '.js,.ts' src test --fix",
     "check:coverage": "nyc --check-coverage npm run check:node",
     "prepare": "node etc/prepare.js",
     "release": "standard-version -i HISTORY.md"

src/utils/number_utils.ts

@@ -87,10 +87,12 @@ export const NumberUtils: NumberUtils = {
     const hi = NumberUtils.getUint32LE(source, offset + 4);
 
     /*
-      eslint-disable-next-line no-restricted-globals
+      eslint-disable no-restricted-globals
       -- This is allowed since this helper should not be called unless bigint features are enabled
      */
-    return (BigInt(hi) << BigInt(32)) + BigInt(lo);
+    const intermediate = (BigInt(hi) << BigInt(32)) + BigInt(lo);
+    return BigInt.asIntN(64, intermediate);
+    /* eslint-enable no-restricted-globals */
   },
 
   /** Reads a little-endian 64-bit float from source */

test/node/bigint.test.ts

@@ -105,6 +105,39 @@ describe('BSON BigInt support', function () {
 
       it(description, test);
     }
+
+    describe('edge case tests', function () {
+      const tests = [
+        {
+          expectedResult: { a: -(2n ** 63n) },
+          input: Buffer.from('10000000126100000000000000008000', 'hex')
+        },
+        {
+          expectedResult: { a: -1n },
+          input: Buffer.from('10000000126100FFFFFFFFFFFFFFFF00', 'hex')
+        },
+        {
+          expectedResult: { a: 0n },
+          input: Buffer.from('10000000126100000000000000000000', 'hex')
+        },
+        {
+          expectedResult: { a: 1n },
+          input: Buffer.from('10000000126100010000000000000000', 'hex')
+        },
+        {
+          expectedResult: { a: 2n ** 63n - 1n },
+          input: Buffer.from('10000000126100FFFFFFFFFFFFFF7F00', 'hex')
+        }
+      ];
+
+      for (const test of tests) {
+        it(`correctly deserializes the bson document encoded in ${test.input.toString('hex')}`, function () {
+          expect(BSON.deserialize(test.input, { useBigInt64: true })).to.deep.equal(
+            test.expectedResult
+          );
+        });
+      }
+    });
   });
 
   describe('BSON.serialize()', function () {