[GHC] #8944: Warn instead of stopping on misplaced Haddock comments

[GHC]

#8944: Warn instead of stopping on misplaced Haddock comments
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              Reporter:  Fuuzetsu    |            Owner:
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.9
             Component:  Compiler    |         Keywords:
  (Parser)                           |     Architecture:  Unknown/Multiple
            Resolution:              |       Difficulty:  Unknown
      Operating System:              |       Blocked By:
  Unknown/Multiple                   |  Related Tickets:
       Type of failure:              |
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by rodlogic):

 The following break GHC's validate (see
 https://phabricator.haskell.org/harbormaster/build/1562/)
 {{{

 -- * base
 import Control.Monad    ( unless, liftM )
 import GHC.Exts
 import Data.Char
 import Control.Monad    ( mplus )

 -- * compiler/hsSyn
 import HsSyn
 }}}

 I ended up having to remove '*' from the comment for it to work:
 {{{
 -- base
 import Control.Monad    ( unless, liftM )
 import GHC.Exts
 import Data.Char
 import Control.Monad    ( mplus )

 -- compiler/hsSyn
 import HsSyn
 }}}

 This seems to be the relevant part in Lexer.x:
 {{{
 "-- " ~[$docsym \#] .* { lineCommentToken }
 "--" [^$symbol \ ] .* { lineCommentToken }

 -- Next, match Haddock comments if no -haddock flag

 "-- " [$docsym \#] .* / { ifExtension (not . haddockEnabled) } {
 lineCommentToken }

 -- Now, when we've matched comments that begin with 2 dashes and continue
 -- with a different character, we need to match comments that begin with
 three
 -- or more dashes (which clearly can't be Haddock comments). We only need
 to
 -- make sure that the first non-dash character isn't a symbol, and munch
 the
 -- rest of the line.

 "---"\-* ~$symbol .* { lineCommentToken }

 -- Since the previous rules all match dashes followed by at least one
 -- character, we also need to match a whole line filled with just dashes.

 "--"\-* / { atEOL } { lineCommentToken }

 -- We need this rule since none of the other single line comment rules
 -- actually match this case.

 "-- " / { atEOL } { lineCommentToken }
 }}}

 And it seems that there is no case for when {{{haddockEnabled}}} is true.
 What should be the action for such rule?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8944#comment:1>
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