REST API: Guard against a non-array return from the rest_endpoints filter

[i-am-chitti]

Ticket

Trac ticket: https://core.trac.wordpress.org/ticket/65953

Description

WP_REST_Server::get_routes() documents an array return, but does not validate what the rest_endpoints filter gives back. A callback that forgets to return $endpoints makes it return null, which reaches array_merge( ...$with_namespace ) in match_request_to_handler() and throws a fatal TypeError on PHP 8. On PHP 7.4 it only warned, so it looks like an upgrade regression.

The fix validates the filtered value in get_routes(), where the bad value originates, so every caller is covered. A non-array falls back to an empty array and calls _doing_it_wrong() to surface the offending callback. Dispatch then returns a normal rest_no_route 404.

Unit tests are included.

Testing instructions

1. Add a broken filter, e.g. add_filter( 'rest_endpoints', function ( $endpoints ) { unset( $endpoints['/wp/v2/users'] ); } );
2. Request any REST route on trunk and observe the fatal TypeError.
3. With the patch, the request returns a rest_no_route 404 plus a _doing_it_wrong() notice for WP_REST_Server::get_routes.

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 5
Used for: drafting the fix and unit tests

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