AllowInCustomizations = Never, gives no compiler warning when field is still used about al HOT 4 OPEN

I've stumbled over this issue today, too.
To be honest - in my opinion the current behaviour is a bug.
We should be able to add a Field with the property to a page via a PageExtension, but still disallow to add the field via customization.

e.g. Imagine the following (very common) scenario.
A field is added to the SalesLine or the SalesHeader. The field has only a valid meaning in the conext of a Sales Invoice.
Therefore we add this field via PageExtension to those places.
Furthermore we don't want users to add those fields to any other page (e.g. Sales Order) via customization.
Then I would expect that I can sett the property AllowInCustomizations to Never and still see the field where it's added via a PageExtension.

Here is small exmaple of this scenario.
https://github.com/pri-kise/msdyn365bc-allowincustomizations-test

from al.

Agree with @pri-kise - the current behaviour makes no sense. If the property is used in the base app, partners won't be able to add the field to any page. Is this REALLY something Microsoft wants to enforce? Long term, this property should be used for most of the "background" fields if Microsoft wants to allow fields added through customizations to be editable. However, partners still need to be able to add such fields to page extensions as they may have specific use cases (and this may even be legal requirements - for partners' localizations - field may not be useful for W1, but some countries may need the field to be visible/exposed to users.

The current behaviour would add additional logic for partners and Microsoft when partners start asking for "make the field accessible from page extension", similar to what we have right now with events, local/internal procedures, onprem scope etc.

from al.

Agree that you can even call it a bug.
Other option could be to add a third option Between "Always" and "Never" something like "OnlyCode".
That enables that you can only add it in code (with page Extensions) but not with customizations in the client.
Then Never makes sure nobody even third party extensions can add it to a page with page extensions.

from al.

Agree that you can even call it a bug. Other option could be to add a third option Between "Always" and "Never" something like "OnlyCode". That enables that you can only add it in code (with page Extensions) but not with customizations in the client. Then Never makes sure nobody even third party extensions can add it to a page with page extensions.

I don't think this is needed/useful. If partners need such field to be available, they will still have options - you can use variable to show the page field and validate the field in the background. This would just add unnecessary complexity without any benefits. This should remain only for customization where we want to prevent users showing the field when they are not aware of the logic.

from al.