Use third party settings API for preview settings

There is some code in gatsby_form_alter that is editing node_type_edit_form

The submit handler gatsby_preview_form_submit reads and write to gatsby.settings

As you'd be aware, we just added a schema for that file based on the config form.

But this submit handler writes to keys that we didn't specify (by design) as follows:

* preview
* iframe
* target

These are per-node type.

Instead of abusing the global gatsby.settings, this should be writing to node.type.*.third_party_settings.gatsby.*

A good example of this is e.g. builder_notes module.

Instead of using a global config object, it writes to each node type.

Firstly it adds a schema entry for node-types

Then it uses an entity builder instead of a submit handler.

Then in the entity builder we save the values into the node-type itself.

The beauty of this is, if the node-type is deleted, the config lives in that node-type and is gone too.

With how its currently implemented in gatsby, those settings persist.

We'll obviously need to update how we read those values back in a few places.

We'll also need to write an update path for this, which is getting pretty deep once we add a test for it.

But if you get through this, really you could take on any issue in any module or core queue :)

There's an old lightning talk I did on this available on our website https://www.previousnext.com.au/blog/lightning-talk-drupal-8s-third-part... - full disclaimer it may be out of date now

See gatsby_preview_form_submit

Code looks great, now the fun starts

Next step is we need a config schema entry - here's an example for a node-type, we'd be doing similar for ours.

Then it starts to get a bit hairy, because we need an upgrade path and an upgrade path test.

Because existing sites have this config in their gatsby.settings.yml, we need to migrate it for them.

I'm happy to help guide on that, because its not simple.

I'll try to find some time this afternoon

Here's the steps I took

• drush si minimal -y
• drush en -y gatsby node
• drush uli to login as admin
• As admin, add two node-types from admin/structure/types/
• As admin, edit these node types and enable gatsby preview and configure settings
• Run the core DB export script php core/scripts/dump-database-d8-mysql.php|gzip > modules/gatsby/tests/update/fixtures/minimal-9-2-update-3160476.php.gz
• Write the update test
• Write the update hook

Also found #3204457: Show Gatsby fields on the node_type.add form while I was at it.

Remaining tasks:

• Add the missing schema per above
• Make the test pass - ran out of time locally to get it working today

Oh, the test might pass once we add a schema

There was 1 failure:

1) Drupal\Tests\gatsby\Functional\PreviewSettingsUpdateTest::testUpdatePath
There should be no errors in configuration 'node.type.article'. Errors:
Schema key node.type.article:third_party_settings.gatsby.preview failed with: missing schema
Schema key node.type.article:third_party_settings.gatsby.iframe failed with: missing schema
Schema key node.type.article:third_party_settings.gatsby.target failed with: missing schema

Failed asserting that Array &0 (
    'node.type.article:third_party_settings.gatsby.preview' => 'missing schema'
    'node.type.article:third_party_settings.gatsby.iframe' => 'missing schema'
    'node.type.article:third_party_settings.gatsby.target' => 'missing schema'
) is true.

https://dispatcher.drupalci.org/job/drupal8_contrib_patches/65042/testRe...

Pushed the schema

Ok, I think this is ready now, but would be good to get another reviewer who didn't work on it (@AJV009 and I have both worked on it)

No-one else came forward to review, putting this in and moving forward

#3210105: Gatsby Preview iframe isn't included when viewing nodes