Using requireExporting to select a module with a particular API
===============================================================

Note: This test case is due to Stephen Hicks, and I've just done a bit
of reformatting and making of examples.

This test demonstrates how you can use `requireModuleExporting` to ensure
that your code is linked with a module that exports a particular API.
We create two packages, `a` and `b`, each of which export the module
`Foo`, but with a subtly different API.

file: tests/testfind/a/Setup.hs
    import Distribution.Franchise
    main = build [] (version "1.0") (package "a" ["Foo"] [])

The first package, `a`, exports `Foo.foo` and `Foo.a`.

file: tests/testfind/a/Foo.hs
    module Foo ( foo, a ) where
    a :: Int
    a = 10
    foo :: String
    foo = "Foo a"

file: tests/testfind/b/Setup.hs
    import Distribution.Franchise
    main = build [] (version "2.0") (package "b" ["Foo"] [])

The second package, `b`, exports `Foo.foo` and `Foo.b`.

file: tests/testfind/b/Foo.hs
    module Foo ( foo, b ) where
    b :: Int
    b = 20
    foo :: String
    foo = "Foo b"

Finally, we introduce an executable called `c` that can be configured
to import either from package `a` or package `b` using
`requireModuleExporting`.

file: tests/testfind/c/Setup.hs
    import Distribution.Franchise
    req a = requireModuleExporting "Foo" a (a++" :: Int")
    options = [configureFlag "with-a" "" (req "a"),
               configureFlag "with-b" "" (req "b")]
    main = build options (version "1.0") (executable "c" "Main.hs" [])

file: tests/testfind/c/Main.hs
    import Foo ( foo )
    main = putStrLn foo

Now we demonstrate that franchise is able to select the desired
package.

file: tests/testfind/requireExporting.sh
....set -ev
    cd a
    runghc Setup.hs install --user
    cd ../b
    runghc Setup.hs install --user
    cd ../c
    
    runghc Setup.hs clean
    runghc Setup.hs configure --with-b
    runghc Setup.hs build
    ./c
    ./c | grep 'Foo b'
    
    runghc Setup.hs clean
    runghc Setup.hs configure --with-a
    runghc Setup.hs build
    ./c
    ./c | grep 'Foo a'

Did that work?