support for multiline text doctest properties

[thielema]

Doctest supports multiline syntax :{ .. :} for doctest unit tests, e.g.

>>> :{ runMyTest
   longArgumentA
   longArgumentB
   longArgumentC
:}
expected output

but it does not support that syntax for doctest properties, that is

prop> :{ runMyTest
   longArgumentA
   longArgumentB
   longArgumentC
:}

We would like to support multiline syntax for properties in doctest-extract, though, which is currently blocked by missing support in Haddock. We have factored out the doctest parser to https://hackage.haskell.org/package/doctest-lib, thus haddock and doctest-extract and doctest could use the same parser.

See also: sol/doctest#131

[Kleidukos]

Hi, thank you for this ticket, but Haddock now lives full-time in the GHC repository!
Read more at https://discourse.haskell.org/t/haddock-now-lives-in-the-ghc-repository/9576.

Let me know if you feel it is still needed, and I'll migrate it. :)