Inconsistent parsing of Haddocks in export lists

Summary

Originally reported in https://github.com/tweag/ormolu/issues/901. The issue is that given this input:

module Beckhoff.ADS
  ( -- $intro
    -- * Connections
    ConnectInfo(..)
  ) where

The comment ends up in two different places:

• As an annotation:

(L
 (Anchor
  { <input>:(2,5)-(3,20) }
  (UnchangedAnchor))
 (EpaComment
  (EpaDocCommentNamed
   "intro\n * Connections")
  { <input>:2:3 }))       

• As a Haddock (IEDocNamed):

(L
 (SrcSpanAnn (EpAnnNotUsed) { <input>:(2,5)-(3,20) })
 (IEDocNamed
  (NoExtField)
  "intro"))

However, the Haddock version is truncated and does not contain the -- * Connections part. This, one could argue, is misleading because the -- * construct (supposed to start a new section) is not recognized in this case, presumably because there is no empty line between the -- $ part and the -- * part?

Steps to reproduce

Run the parser on the snippet provided above.

Expected behavior

I think there are two ways to resole it:

• Make both the annotation and the Haddock form of the comment match. This is only logical and it would fix the problem in Ormolu.
• Change the parser to recognize -- * even when it follows -- $ without a newline between them. This seems to me preferable because it is what users would normally want.

Environment

• GHC version used: Seems to be reproducible with 9.0.2, 9.2.5, 9.4.4.

Optional:

• Operating System: NixOS 23.05 (Stoat)
• System Architecture: x86_64