>The prefix keyword allows to change the list of namespaces in the SearchContext.
>If the list of searched namespaces could be fixed from the beginning this would greatly simplify the refactoring started in T185108.
>I propose to change how prefix works by moving the namespace filter inside the query it builds.
>While building the query if the prefix detects some incompatible settings, e.g. the namespace requested are set to `NS_MAIN` but the query asks for `prefix:Help:Page` I suggest that we emit a deprecation warning asking the user to change their query by prefixing it with `all:`.
UPDATE: this change caused many search forms to stop working properly. The warning message was not an appropriate solution. We will figure out another solution to move this forward.
~~The patch to revert this change will be deployed to production wikis on Monday May 14 at 15:00 CEST.~~
~~Deployment of this patch currently blocked by T194632.~~
The patch to revert has finally been deployed by @Reedy (thanks!!)