Why it highlights Data.MultiSet?

package.yaml:

name: anagram
version: 1.4.0.8

dependencies:
  - base
  - multiset
  - text
  - containers

library:
  exposed-modules: Anagram
  source-dirs: src
  ghc-options: -Wall

tests:
  test:
    main: Tests.hs
    source-dirs: test
    dependencies:
      - anagram
      - hspec

A program compiles fine and passes tests with stack test.

I tried to restart HLS in many ways. May be I don’t know the correct one.

Versions:

• stack 2.15.5
• stack resolver: lts-20.25
• ghc 9.8.2
• cabal 3.10.3.0
• HLS 2.7.0.0