langserver won't work for some modules in the Nim compiler

[moigagoo]

Steps

1. git clone git@github.com:nim-lang/Nim.git
2. cd Nim
3. nimsuggest compiler/nim.nim
4. outline compiler/nim.nim
5. Run an editor with nimlangserver enabled. For example, Helix.
6. Open compiler/nim.nim.
7. Invoke documentSymbols LSP command (Space s in Helix).

Expectation

In the editor, langserver shows the same symbols as nimsuggest does.

Reality

nimsuggest works, the langserver doesn't.