Consecutive named chunks in export list

[dmcclean]

When processing inclusion of named chunks in export lists, haddock 2.16.0 appears to only process the first in a consecutive series of named chunks, when an attempt is made to include multiple chunks without an intervening declaration.

To reproduce:

Place the following content in Foo.hs:

module Foo
(
  -- $chunk1
  -- $chunk2
  foo,
  -- $chunk3
  bar
)
where

{- $chunk1
This is chunk 1.
-}

{- $chunk2
This is chunk 2.
-}

{- $chunk3
This is chunk 3.
-}

foo = 3
bar = 7

Run haddock -o .\foodoc -h Foo.hs.

Observe that the result includes chunks 1 and 3, but not 2.

[Fuuzetsu]

I suspect this might have to go into GHC instead

[dmcclean]

Could you elaborate on why? It it's because multiple consecutive single-line comments are reported as one, I wouldn't have expected even chunk 1 to appear. But if that is the case, perhaps we could address it without waiting on ghc by allowing syntax like:

-- $chunk1, $chunk2

[Fuuzetsu]

Could you elaborate on why?

Haddock does not extract the comments itself. GHC lexer and parser are ran and we use the results. By the time we even get to the Haddock's comment parser, the information on what kind of comment we're processing ($, | etc.) is long lost. This way saves us the very hard job of trying to parse and make sense of Haskell files by letting GHC do that work but it means that if we want to somehow change or expand how something is processed or where it is allowed, that change needs to be made in GHC.

But if that is the case, perhaps we could address it without waiting on ghc by allowing syntax like …

It may be possible but it would not be sane. I suspect it would be more effort trying to put this in than to do it properly by changing GHC. Further, because the first $ would be expanded and the second $ would not, it would mean a change of behaviour for every $foo that appears in the comments. It's just not something I see as a viable solution.

[dmcclean]

OK, those are certainly good reasons. I'm not sure I can tackle making that change in GHC. Do you know how I should phrase my request if I make a GHC trac ticket?

[Fuuzetsu]

Something like “Support consecutive named Haddock comments” and a link to this ticket should work fine. Please post Trac number here when done.

EDIT: Also changing to enhancement, it's not really unexpected behaviour but it could be nicer.

[dmcclean]

See https://ghc.haskell.org/trac/ghc/ticket/10398.

Thanks.