Manual:$wgExemptFromUserRobotsControl

Robot policies: $wgExemptFromUserRobotsControl
An array of namespace keys in which the __INDEX__/__NOINDEX__ magic words will not function.
Introduced in version:	1.14.0
Removed in version:	Still in use
Allowed values:	(array of integers)
Default value:	$wgContentNamespaces
Other settings: Alphabetical | By function

Details

An array of namespace keys in which the __INDEX__/__NOINDEX__ magic words will not function, so users can't decide whether pages in that namespace are indexed by search engines. If set to null, default to $wgContentNamespaces .

Example:

$wgExemptFromUserRobotsControl = [ NS_MAIN, NS_TALK, NS_PROJECT ];

Or, to switch it off entirely:

$wgExemptFromUserRobotsControl = [];