Allow Schema elements as default values

[mabar]

• new feature?
• BC break? no

We have some composite extensions which simulates compiler passes. They can be disabled so configuration looks like this Expect::anyOf(false, SubExtension::createSchema()).

AnyOf does not match default value null (empty configuration) same way as if we directly use Expect::structure (no AnyOf) so that structure is not used.

Current workaround looks like this

	public function getConfigSchema(): Schema
	{
		$subExtensionSchema = SubExtension::createSchema();

		return Expect::structure([
			'subExtension' => Expect::anyOf(false, $subExtensionSchema)->default($subExtensionSchema->completeDefault(new Context())),
		]);
	}

With suggested change would be simplified call to default to default($subExtensionSchema) and it also allows any schemas used as default values.

Alternative solution would be match Structure with null value in AnyOf but I am not sure if it's a correct behavior as it would depend on order of structure and null if both used and maybe break also some other combinations.

[dg]

Great. Can you add test?

[mabar]

Done

[dg]

Thanks

[dg]

Wouldn't it be better to use this solution, ie method that sets the first item as the default?

   Expect::anyOf(
        $subExtensionSchema
        false, 
   )->firstAsDefault(),

[mabar]

Imho it's better to keep that behavior hidden. If I implemented this now, I would throw exception for any Schema element except Structure, because behavior of inheriting e.g. null from Expect::string() is mostly confusing and useless.

But yeah, may be a nice shortcut.