fix: change result type based on nameOnly option

Author: nbbeeken

src/db.ts

@@ -34,7 +34,11 @@ import {
   DropDatabaseOptions,
   DropCollectionOptions
 } from './operations/drop';
-import { ListCollectionsCursor, ListCollectionsOptions } from './operations/list_collections';
+import {
+  CollectionInfo,
+  ListCollectionsCursor,
+  ListCollectionsOptions
+} from './operations/list_collections';
 import { ProfilingLevelOperation, ProfilingLevelOptions } from './operations/profiling_level';
 import { RemoveUserOperation, RemoveUserOptions } from './operations/remove_user';
 import { RenameOperation, RenameOptions } from './operations/rename';
@@ -358,8 +362,25 @@ export class Db {
    * @param filter - Query to filter collections by
    * @param options - Optional settings for the command
    */
-  listCollections(filter?: Document, options?: ListCollectionsOptions): ListCollectionsCursor {
-    return new ListCollectionsCursor(this, filter ?? {}, resolveOptions(this, options));
+  listCollections(
+    filter: Document,
+    options: Exclude<ListCollectionsOptions, 'nameOnly'> & { nameOnly: true }
+  ): ListCollectionsCursor<Pick<CollectionInfo, 'name' | 'type'>>;
+  listCollections(
+    filter: Document,
+    options: Exclude<ListCollectionsOptions, 'nameOnly'> & { nameOnly: false }
+  ): ListCollectionsCursor<CollectionInfo>;
+  listCollections<
+    T extends Pick<CollectionInfo, 'name' | 'type'> | CollectionInfo =
+      | Pick<CollectionInfo, 'name' | 'type'>
+      | CollectionInfo
+  >(filter?: Document, options?: ListCollectionsOptions): ListCollectionsCursor<T>;
+  listCollections<
+    T extends Pick<CollectionInfo, 'name' | 'type'> | CollectionInfo =
+      | Pick<CollectionInfo, 'name' | 'type'>
+      | CollectionInfo
+  >(filter: Document = {}, options: ListCollectionsOptions = {}): ListCollectionsCursor<T> {
+    return new ListCollectionsCursor<T>(this, filter, resolveOptions(this, options));
   }
 
   /**

src/operations/list_collections.ts

@@ -118,7 +118,7 @@ export interface CollectionInfo extends Document {
 
 /** @public */
 export class ListCollectionsCursor<
-  T extends string | CollectionInfo = CollectionInfo
+  T extends Pick<CollectionInfo, 'name' | 'type'> | CollectionInfo = CollectionInfo
 > extends AbstractCursor<T> {
   parent: Db;
   filter: Document;

test/types/list_collections.test-d.ts

@@ -6,14 +6,38 @@ import type { CollectionInfo, ListCollectionsCursor } from '../../src/operations
 const db = new MongoClient('').db();
 
 // We default to the CollectionInfo result type
-expectType<ListCollectionsCursor<CollectionInfo>>(db.listCollections());
-// We do not return the string result, and since its a runtime option there's not a great TS way to capture this
-expectNotType<ListCollectionsCursor<string>>(db.listCollections());
+expectType<ListCollectionsCursor<Pick<CollectionInfo, 'name' | 'type'> | CollectionInfo>>(
+  db.listCollections()
+);
+// By default it isn't narrowed to either type
+expectNotType<ListCollectionsCursor<Pick<CollectionInfo, 'name' | 'type'>>>(db.listCollections());
+expectNotType<ListCollectionsCursor<CollectionInfo>>(db.listCollections());
+
+// Testings each argument variation
+db.listCollections();
+db.listCollections({ a: 2 });
+db.listCollections({ a: 2 }, { batchSize: 2 });
 
-// toArray is a good way for TS users to keep their code simple
 const collections = await db.listCollections().toArray();
-expectType<CollectionInfo[]>(collections);
+expectType<(CollectionInfo | string)[]>(collections);
+
+const nameOnly = await db.listCollections({}, { nameOnly: true }).toArray();
+expectType<Pick<CollectionInfo, 'name' | 'type'>[]>(nameOnly);
+
+const fullInfo = await db.listCollections({}, { nameOnly: false }).toArray();
+expectType<CollectionInfo[]>(fullInfo);
+
+const couldBeEither = await db.listCollections({}, { nameOnly: Math.random() > 0.5 }).toArray();
+expectType<(CollectionInfo | string)[]>(couldBeEither);
 
-// toArray takes an override so here we can get an array of strings easily
-const collectionNames = await db.listCollections({}, { nameOnly: true }).toArray<string>();
-expectType<string[]>(collectionNames);
+// Showing here that:
+// regardless of the option the generic parameter can be used to coerce the result if need be
+// note the nameOnly: false, yet strings are returned
+const overridden = await db
+  .listCollections<Pick<CollectionInfo, 'name' | 'type'>>({}, { nameOnly: false })
+  .toArray();
+expectType<Pick<CollectionInfo, 'name' | 'type'>[]>(overridden);
+const overriddenWithToArray = await db
+  .listCollections({}, { nameOnly: false })
+  .toArray<Pick<CollectionInfo, 'name' | 'type'>>();
+expectType<Pick<CollectionInfo, 'name' | 'type'>[]>(overriddenWithToArray);