Problems when a directory field contains a dot

[yamadapc]

When a field that takes a directory contains a dot, hpack's renderer will generate a line with nothing but a . in it. However, this is invalid in a cabal file, as dots on their single lines are meant to express empty-lines (I think, I can't find the documentation the source that does it is here).

A simple example of the bug is here: https://gist.github.com/0cc7f8f8e2cbc9ee7bbf82876a822e28

In there, source-dirs: . generates an invalid cabal file. Though this specific case isn't super common, without specifying source-dirs: ., hpack won't include the other-modules section for the modules in the current directory (I'd consider that another ticket).

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My idea for a fix would be to output:

field: .
  , other-value
  , other-value

Whenever . is a value.

[soenkehahn]

Another solution might be to replace . with ./..

[yamadapc]

Mm... Yeah, that could be a much cleaner solution.