8c6794b6.github.io

For self reminder. When we're creating cabal package, sometime we want to call itself as a depdency, for instance when making a package with library and bundled executable, using cabal's test-suite feature.

For quite a while I didn't realise that we can call itself as dependency and suppress compiling the whole library modules used in exectuables and tests. The trick was, separating the directory containing library source and executable source in single package.

Sample cabal config:

name:          selfdep
build-type:    Simple
cabal-version: >=1.8

library
  exposed-modules:
    Self.Dep
    Self.Dep.Foo
    Self.Dep.Bar
  build-depends:
    base       >= 4.4 && < 5,
    containers >= 0.4 && < 1.0

test-suite tests
  type: exitcode-stdio-1.0
  hs-source-dirs: tests
  main-is: test.hs
  build-depends:
    base       >= 4.4 && < 5,
    QuickCheck >= 2.4 && < 3,
    selfdep -any

executable foo
  hs-source-dirs: run
  main-is: foo.hs
  build-depends:
    base    >= 4.4 && < 5,
    selfdep -any

In file foo.hs, module Self.Dep.Foo is imported:

$ cat run/foo.hs
module Main where

import qualified Self.Dep.Foo

main :: IO ()
main = print Self.Dep.Foo.foo

Building the package:

$ cabal configure && cabal build
Resolving dependencies...
Configuring selfdep-0.1.0.0...
Building selfdep-0.1.0.0...
Preprocessing library selfdep-0.1.0.0...
[1 of 3] Compiling Self.Dep.Bar     ( Self/Dep/Bar.hs, dist/build/Self/Dep/Bar.o )
[2 of 3] Compiling Self.Dep.Foo     ( Self/Dep/Foo.hs, dist/build/Self/Dep/Foo.o )
[3 of 3] Compiling Self.Dep         ( Self/Dep.hs, dist/build/Self/Dep.o )
Registering selfdep-0.1.0.0...
Preprocessing executable 'foo' for selfdep-0.1.0.0...
[1 of 1] Compiling Main             ( run/foo.hs, dist/build/foo/foo-tmp/Main.o )
Linking dist/build/foo/foo ...

During the compilation of executable foo, modules under Self.* were not recompiled. This separation of the directory works also for tests.