Change #1041184 had a related patch set uploaded (by Sbailey; author: Sbailey):

[mediawiki/extensions/Linter@master] Fix the Linter category subpage search when namespace field is blank

https://gerrit.wikimedia.org/r/1041184

As there is a desire to support both finding the exact page title as well as search for a range of page titles by prefix, I think the continued use of the current Linter search interface widgets is reasonable.
What was not reasonable is that when no namespace was specified, that the main (0) namespace was used silently instead of not filtering on namespace at all and returning all exact title matches or title prefix matches for all namespaces if namespace is not selected.
The namespace field allows multiple selections of specific namespaces to filter for a few desired namespaces out of all so this change should cover all possible use cases for namespaces and fixes the bug that a blank namespace was silently selecting main.

Linking bugs up: the original issue was T360865: Slow query in Special:LintErrors. Let's just make sure we're not regressing that bug.

There's also a NamespacesMultiSelectWidget in OOUI we could be using, even if we wanted to hand-roll the title prefix portion.

Change #1041184 merged by jenkins-bot:

[mediawiki/extensions/Linter@master] Fix the Linter category subpage search when namespace field is blank

https://gerrit.wikimedia.org/r/1041184