feat(NODE-5444)!: emit deprecation warning for useNewUrlParser and useUnifiedTopology

src/connection_string.ts

@@ -1223,9 +1223,17 @@ export const OPTIONS = {
   pfx: { type: 'any' },
   secureProtocol: { type: 'any' },
   index: { type: 'any' },
-  // Legacy Options, these are unused but left here to avoid errors with CSFLE lib
-  useNewUrlParser: { type: 'boolean' } as OptionDescriptor,
-  useUnifiedTopology: { type: 'boolean' } as OptionDescriptor,
+  // Legacy options from v3 era
+  useNewUrlParser: {
+    type: 'boolean',
+    deprecated:
+      'useNewUrlParser has no effect since Node.js Driver version 4.0.0 and will be removed in the next major version'
+  } as OptionDescriptor,
+  useUnifiedTopology: {
+    type: 'boolean',
+    deprecated:
+      'useUnifiedTopology has no effect since Node.js Driver version 4.0.0 and will be removed in the next major version'
+  } as OptionDescriptor,
   // MongoLogger
   // TODO(NODE-4849): Tighten the type of mongodbLogPath
   mongodbLogPath: { type: 'any' }

test/unit/connection_string.test.ts

@@ -1,3 +1,6 @@
+import { once } from 'node:events';
+import * as process from 'node:process';
+
 import { expect } from 'chai';
 import * as dns from 'dns';
 import * as sinon from 'sinon';
@@ -761,4 +764,40 @@ describe('Connection String', function () {
     expect(() => new MongoClient('mango://localhost:23')).to.throw(/Invalid scheme/i);
     expect(() => new MongoClient('mango+srv://localhost:23')).to.throw(/Invalid scheme/i);
   });
+
+  describe('when deprecated options are used', () => {
+    it('useNewUrlParser emits a warning', async () => {
+      let willBeWarning = once(process, 'warning');
+      parseOptions('mongodb://host?useNewUrlParser=true');
+      let [warning] = await willBeWarning;
+      expect(warning)
+        .to.have.property('message')
+        .that.matches(/useNewUrlParser has no effect/);
+
+      willBeWarning = once(process, 'warning');
+      //@ts-expect-error: using unsupported option on purpose
+      parseOptions('mongodb://host', { useNewUrlParser: true });
+      [warning] = await willBeWarning;
+      expect(warning)
+        .to.have.property('message')
+        .that.matches(/useNewUrlParser has no effect/);
+    });
+
+    it('useUnifiedTopology emits a warning', async () => {
+      let willBeWarning = once(process, 'warning');
+      parseOptions('mongodb://host?useUnifiedTopology=true');
+      let [warning] = await willBeWarning;
+      expect(warning)
+        .to.have.property('message')
+        .that.matches(/useUnifiedTopology has no effect/);
+
+      willBeWarning = once(process, 'warning');
+      //@ts-expect-error: using unsupported option on purpose
+      parseOptions('mongodb://host', { useUnifiedTopology: true });
+      [warning] = await willBeWarning;
+      expect(warning)
+        .to.have.property('message')
+        .that.matches(/useUnifiedTopology has no effect/);
+    });
+  });
 });