Parse error when trying to use multiple public libraries within mixins

[chshersh]

Describe the bug

I have the following lines in my .cabal file:

  build-depends:       containers-backpack:{ int-strict, ordered-strict, unordered-strict, contrib }

  mixins:              containers-backpack:contrib (Map.Contrib.Group as Map.Contrib.Group.Int)
                                          requires (Map as Map.Int)

Here containes-backpack is a package with the public library contrib inside it. However, when trying to build this package with cabal-install I see the following error:

Errors encountered when parsing cabal file ./containers-backpack.cabal:

containers-backpack.cabal:142:43: error:
unexpected ':'
expecting "-", white space, "(", "hiding", "requires", comma or end of input

  140 |   build-depends:       containers-backpack:{ int-strict, ordered-strict, unordered-strict, contrib }
  141 | 
  142 |   mixins:              containers-backpack:contrib (Map.Contrib.Group as Map.Contrib.Group.Int)
      |                                           ^

To Reproduce

You can find full code here:

• [#45] Rewrite to Multiple Public Libraries kowainik/containers-backpack#46

Steps to reproduce the behavior:

1. Clone the repo.
2. Checkout to branch from linked PR.
3. Do cabal v2-build

Expected behavior

No parse error.

System informataion

• Ubuntu-18.04
• cabal-3.0.0.0
• ghc-8.6.5 or ghc-8.8.1

[fgaz]

Might be an instance of #5846.

[chshersh]

@fgaz Thanks for pointing to this issue! #5846 is another problem I have. For some reason the following doesn't parse:

build-depends: containers-backpack:sig
             , QuickCheck

But when I write dependencies in a single line, it parses:

build-depends: containers-backpack:sig, QuickCheck

Adding -any also parses

Which is for now only a minor UI inconvenience.

[fgaz]

Weird… I wonder what's wrong with the parsing code. I wasn't able to find the issue last time I tried to debug this. If you want to take a look at it yourself it's in Cabal/Distribution/Types/Dependency.hs

[phadej]

@fgaz this is missing functionality. Mixin (not Dependency) is atm defined as

data Mixin = Mixin { mixinPackageName :: PackageName
                   , mixinIncludeRenaming :: IncludeRenaming }

There are no sublibs.