Add YAML as an optional entity storage format

@betz There wasn't really - I just wasn't sure if core's normalization supported YAML as a format. If it does I'd be happy to review a patch.

I just looked into this, it looks like there is no Symphony serializer support for YML, so I don't think I'm going to support it in Tome. Core's test coverage for entity serialization also uses JSON (and XML, and HAL-JSON), so I don't want to go into uncharted territory with using YML.

The good news is that contrib, or a sub-module of Tome, could override the tome.storage.content service (using service decorators, I think?) to use any format they want (including remote storage!), so there are options going forward.

I'm going to close this issue, but if you can come up with a patch that adds a sub-module that uses YML I'll look into adding it. For now I'm sticking with JSON going forward. Thanks!

This is possible now

Here's a start to this, which appears to work. Core doesn't have an encoder for Yaml yet which is what I thought originally, but it turns out making out own makes sense for controlling the output.

Added importer tests as well.

+++ b/modules/tome_sync/tests/src/Kernel/ExporterTest.php
@@ -208,4 +208,48 @@ class ExporterTest extends TestBase {
+    $this->assertFileExists($yml_file);

should you assert something about the contents of the file too?

Looks good, but from memory we didn't use YAML as an export format in core for security reasons.

@larowlan YAML is scarier but AFAIK Symfony's encoder with the flags I'm using should be fine, no object or constant parsing, but I'll double check that.

For the test coverage - this is mimicking the JSON test coverage in the same file, basically the fact that the file storage works and the entity is denormalized is good enough for me. However I am doing some tricky (and likely stupid) things with the YAML so I could check that mullti-line strings work.

Also just saw that https://www.drupal.org/project/default_content uses Yaml as of 2.0 - our modules have a lot of overlap lol!

I tested the patch and things were smooth, I have to admit though that I tested with demo content on a site still under development.

As for default_content it does use YAML, but it has a different scope (to provide default content, not to import/export content).
tome_sync has an overlapping scope with default_content_deploy, but I find tome more straightforward :)

Also just saw that https://www.drupal.org/project/default_content uses Yaml as of 2.0 - our modules have a lot of overlap lol!

But this is an actively maintained solution ;)

Thanks all, let's ship it! I'll do a release this month.