`runghc Setup.hs haddock` does not allow for `--haddock-options=--prologue=my-prologue`

[mpilgrem]

Haddock only allows --prologue to be specified once, ending in failure if the option is specified more than once.

runghc Setup.hs haddock makes use of the --prologue option itself, setting it to the content of the Cabal file's description field.

However, as a consequence, a user then has no mechanism to specify his or her own Haddock prologue.

A possible solution:

Cabal (the library) provides a --haddock-prologue= option that, if specified, prevails over Cabal's default use of --prologue.

Related Stack issue:

• stack haddock: How to correctly use --prologue? commercialhaskell/stack#6718