[Haskell-cafe] how do cabal internal libraries work?

[Ben Kolera]

Do you get the same error if you give each library a different
hs-source-dir ?

I don't know the actual reason, but I would guess that maybe something
funny is happening with all of the modules being in the same folder.

Just a guess which is probably wrong! Hope it helps! :)

On Thu, 24 May 2018, 08:10 Evan Laforge, <qdunkan at gmail.com> wrote:

> The example at
> https://www.haskell.org/cabal/users-guide/developing-packages.html#library
> doesn't seem to work as I expect.  The doc for the library field is out of
> date, but if you scroll down it mentions "internal libraries".  But
> depending on the internal library doesn't seem to have any effect, in that
> cabal still complains I didn't mention Foo.Internal, and doesn't see the
> build-depends from it.  Am I misinterpreting how the feature is supposed to
> work?
>
> This is with Cabal 2.2.0.1 and cabal-install 2.2.0.0, ghc 8.4.1:
>
> % cat testing.cabal
> name:           foo
> version:        1.0
> license:        BSD3
> cabal-version:  >= 1.23
> build-type:     Simple
>
> library foo-internal
>     exposed-modules: Foo.Internal
>     build-depends: base, text
>
> library
>     exposed-modules: Foo.Public
>     build-depends: foo-internal, base
>
> % cat Foo/Internal.hs
> module Foo.Internal where
> import Data.Text
>
> % cat Foo/Public.hs
> module Foo.Public where
> import Foo.Internal
>
> % cabal build
> Resolving dependencies...
> Configuring foo-1.0...
> Warning: Packages using 'cabal-version: >= 1.10' must specify the
> 'default-language' field for each component (e.g. Haskell98 or
> Haskell2010).
> If a component uses different languages in different modules then list the
> other ones in the 'other-languages' field.
> Preprocessing library 'foo-internal' for foo-1.0..
> Building library 'foo-internal' for foo-1.0..
> [1 of 1] Compiling Foo.Internal     ( Foo/Internal.hs,
> dist/build/foo-internal/Foo/Internal.o )
> [1 of 1] Compiling Foo.Internal     ( Foo/Internal.hs,
> dist/build/foo-internal/Foo/Internal.p_o )
> Preprocessing library for foo-1.0..
> Building library for foo-1.0..
>
> <no location info>: warning: [-Wmissing-home-modules]
>     These modules are needed for compilation but not listed in your .cabal
> file's other-modules: Foo.Internal
> [1 of 2] Compiling Foo.Internal     ( Foo/Internal.hs,
> dist/build/Foo/Internal.o )
>
> Foo/Internal.hs:2:1: error:
>     Could not find module ‘Data.Text’
>     Use -v to see a list of the files searched for.
>   |
> 2 | import Data.Text
>   | ^^^^^^^^^^^^^^^^
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