Regression: Error when using nested properties in `_fields` with `getEntityRecord()`

[kraftner]

Description

When requesting something from the REST API using wp.data.select('core').getEntityRecord() this can result in an uncaught Type Error.

I noticed this when trying to get back the routes field removed in https://github.com/WordPress/gutenberg/pull/39256/files#diff-38a74d088ea018dbbea00d8f5bd5c03ea54bfc099d1d1836686c24a5582bf579R27-R39 using the _fields parameter.

Here is an example. Just run this code in the console when editing a post:

wp.data.select('core').getEntityRecord()'root', '__unstableBase', undefined, { _fields: [ 'routes./wp/v2/posts' ] })

Yes, I know, I am using __unstableBase here which is a private API. But please still hear me out since the surfaced issue is a fundamental bug that probably can also occur in other situations. I just wasn't able to find another example quickly now.

---

I think this issue appeared when removing Lodash _.get() in https://github.com/WordPress/gutenberg/commit/4b12c75df261f62c7ca5312c900628920338b16b#diff-6fae435c7327c5edb1a67718054b7ee8513d4691a19b416e7d5f628aefc4459bR69-R72 of #48310.

The problem is that using the dot syntax to limit the retrieved data to a nested property tries to get a property of undefined here when first requesting the data:

https://github.com/WordPress/gutenberg/blob/a5a32c1da19589a60d48ae793a3d0a5a48223db6/packages/core-data/src/queried-data/selectors.js#L71

which fails with the Type Error mentioned above.

This is also confirmed by the fact that the following runs flawlessly:

wp.data.select('core').getEntityRecord('root', '__unstableBase', undefined, { _fields: [ 'routes' ] })

The old implementation with Lodash _.get()

https://github.com/WordPress/gutenberg/blob/e086b2b595618a5f4c9491119695be3e074d736b/packages/core-data/src/queried-data/selectors.js#L69

though would handle this edge case returning undefined instead of causing a Type Error in both cases.

---

So as a solution I'd assume an additional check for undefined would solve this issue. Something along the lines of

value = typeof value === 'undefined' ? undefined: value[fieldName];

Which a quick check altering WP 6.3 core confirmed.

Step-by-step reproduction instructions

1. Open the block editor

2. Run wp.data.select('core').getEntityRecord()'root', '__unstableBase', undefined, { _fields: [ 'routes./wp/v2/posts' ] }) in the console

3. See a "Uncaught TypeError: value is undefined".

4. Open the block editor (reload, doesn't work when the data has been requested before)

5. Run wp.data.select('core').getEntityRecord()'root', '__unstableBase', undefined, { _fields: [ 'routes' ] }) in the console

6. See no error but a value of undefined returned.

Screenshots, screen recording, code snippet

No response

Environment info

• WordPress 6.3
• no Gutenberg

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes

[Mamaduka]

@tyxla, do you have time to look into this?

[tyxla]

Thanks for the thorough report @kraftner and for the ping @Mamaduka.

I'm happy to take a look this week.

[tyxla]

Fix is in #54790.