Constants are defined in CategoryTree.php, but they aren't available in LocalSettings.php, even using them after wfLoadExtension( 'CategoryTree' );

This looks like a limitation in extension registration system. Or at least I wasn't able to find how to do this in the schema documentation (thus adding MediaWiki-Configuration project)

In ExtensionRegistry.php I see there's this code:

		foreach ( $info['defines'] as $name => $val ) {
			define( $name, $val );
		}

Maybe defining them in extension.json inside a "defines" section may work, but it's undocumented at best

This is a core issue - constants aren't supported yet, see T141223: Support autoconfirmed constants in extension registration

It looks like they're not going to support constants at all, and this configuration should be changed to use string keys like $wgCategoryTreeMaxDepth = [ 'pages' => 2, 'all' => 2, 'categories' => 3 ];

@freephile: Which most recent version did you test, as you edited the summary to state that it's 1.28+?

I've observed this in 1.28 (I think 1.29) 1.30 1.31.

In T152294#3536413, @Ciencia_Al_Poder wrote:

In ExtensionRegistry.php I see there's this code:

		foreach ( $info['defines'] as $name => $val ) {
			define( $name, $val );
		}

Maybe defining them in extension.json inside a "defines" section may work, but it's undocumented at best

I tried this approach in 1.31 and it didn't appear to change the result (still getting warnings). I believe somebody else said that it's because the code is evaluated too late to be available in LocalSettings.php

In T152294#3536841, @Ciencia_Al_Poder wrote:

It looks like they're not going to support constants at all, and this configuration should be changed to use string keys like $wgCategoryTreeMaxDepth = [ 'pages' => 2, 'all' => 2, 'categories' => 3 ];

This is sort of correct. The documentation of the extension desperately needs updating to reflect this. The new values can be seen in https://gerrit.wikimedia.org/r/#/c/mediawiki/extensions/CategoryTree/+/268624/

$wgCategoryTreeMaxDepth = [ 10 => 2, 20 => 2, 0 => 3 ];

There is also discussion how these probably should be changed to strings instead of vague numbers: https://gerrit.wikimedia.org/r/#/c/mediawiki/extensions/CategoryTree/+/293318/

Was part of T87888: Convert CategoryTree to use extension registration

Change #1319143 had a related patch set uploaded (by TheDJ; author: TheDJ):

[mediawiki/extensions/CategoryTree@master] Log deprecation warnings for numeric CategoryTree constant values

https://gerrit.wikimedia.org/r/1319143

Change #293318 merged by jenkins-bot:

[mediawiki/extensions/CategoryTree@master] Use strings for constants values

https://gerrit.wikimedia.org/r/293318

Documentation needs updating
Config of wmf needs updating,
Deprecation warning patch can then be merged.

Change #1319945 had a related patch set uploaded (by TheDJ; author: TheDJ):

[operations/mediawiki-config@master] wgCategoryTreeCategoryPageMode: use the new values

https://gerrit.wikimedia.org/r/1319945