Revisions: only create autosave when content changed.

In the autosave REST API endpoint, avoid excessive database writes when an autosave is sent with content that is unchanged from the saved post. 

Before this fix, clicking "preview" in the editor (which uses the autosave feature) multiple times would cause an identical autosave entry to be deleted and re-created repeatedly.

Props inwerpsel, aduth, mukesh27, ironprogrammer.
Fixes #49532.



git-svn-id: https://develop.svn.wordpress.org/trunk@55154 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/rest-api/rest-autosaves-controller.php

@@ -674,4 +674,38 @@ class WP_Test_REST_Autosaves_Controller extends WP_Test_REST_Post_Type_Controlle
 
 		wp_delete_post( $post_id );
 	}
+
+	/**
+	 * @ticket 49532
+	 *
+	 * @covers WP_REST_Autosaves_Controller::create_post_autosave
+	 */
+	public function test_rest_autosave_do_not_create_autosave_when_post_is_unchanged() {
+		// Create a post by the editor.
+		$post_data = array(
+			'post_content' => 'Test post content',
+			'post_title'   => 'Test post title',
+			'post_excerpt' => 'Test post excerpt',
+			'post_author'  => self::$editor_id,
+			'post_status'  => 'publish',
+		);
+		$post_id   = wp_insert_post( $post_data );
+
+		wp_set_current_user( self::$editor_id );
+
+		$autosave_data = array(
+			'post_content' => $post_data['post_content'],
+		);
+
+		// Create autosaves response.
+		$request = new WP_REST_Request( 'POST', '/wp/v2/posts/' . $post_id . '/autosaves' );
+		$request->add_header( 'content-type', 'application/json' );
+		$request->set_body( wp_json_encode( $autosave_data ) );
+
+		$response = rest_get_server()->dispatch( $request );
+		$data     = $response->get_data();
+
+		$this->assertSame( 400, $response->get_status(), 'Response status is not 400.' );
+		$this->assertSame( 'rest_autosave_no_changes', $data['code'], 'Response "code" is not "rest_autosave_no_changes"' );
+	}
 }