Test FindAndModify with replacement doc resembling a pipeline

Add a comment explaining how the conditional object cast in FindAndModify::createCommandDocument() affects BSON encoding for the update option.

Author: jmikola

src/Operation/FindAndModify.php

@@ -295,6 +295,14 @@ private function createCommandDocument(): array
         if (isset($this->options['update'])) {
             /** @psalm-var array|object */
             $update = $this->options['update'];
+            /* A non-empty pipeline will encode as a BSON array, so leave it
+             * as-is. Cast anything else to an object since a BSON document is
+             * likely expected. This includes empty arrays, which historically
+             * can be used to represent empty replacement documents.
+             *
+             * This also allows an empty pipeline expressed as a PackedArray or
+             * Serializable to still encode as a BSON array, since the object
+             * cast will have no effect. */
             $cmd['update'] = is_pipeline($update) ? $update : (object) $update;
         }
 

tests/Operation/FindAndModifyFunctionalTest.php

@@ -51,6 +51,7 @@ public function provideQueryDocuments(): array
      * @dataProvider provideReplacementDocuments
      * @dataProvider provideUpdateDocuments
      * @dataProvider provideUpdatePipelines
+     * @dataProvider provideReplacementDocumentLikePipeline
      */
     public function testUpdateDocuments($update, $expectedUpdate): void
     {
@@ -73,6 +74,16 @@ function (array $event) use ($expectedUpdate): void {
         );
     }
 
+    public function provideReplacementDocumentLikePipeline(): array
+    {
+        return [
+            'replacement_like_pipeline' => [
+                (object) ['0' => ['$set' => ['x' => 1]]],
+                (object) ['0' => (object) ['$set' => (object) ['x' => 1]]],
+            ],
+        ];
+    }
+
     /** @see https://jira.mongodb.org/browse/PHPLIB-344 */
     public function testManagerReadConcernIsOmitted(): void
     {