Haskell - Packaging cabal package with custom preprocessors

Question

I've implemented a custom preprocessor which creates *.hs files form *.tpl files. It is specified in Setup.hs by using a Build-Type: Custom. Everything works fine, but I can't create tar.gz package from it (using cabal sdist).

Cabal complains, that it can not find the exposed modules which are generated by the preprocessor. The error message is

cabal: Error: Could not find module with any
suffix: ["gc","chs","hsc","x","y","ly","cpphs","hs","lhs"]

How can I make Cabal aware of the fact that the module is not missing, or maybe add tpl to the known file extensions, or something?

Corn

Can you show us your .cabal file? – Origen

What I think you need is to write a custom sdist hook and then build the tarball with Setup sdist (because of github.com/haskell/cabal/issues/403). – Origen

Actually, I think this'll work just by running Setup sdist. – Origen

Answer 1

This is a known issue with cabal sdist. Use ./dist/setup/setup sdist instead.

Here's an example:

$ cat preprocessor-test.cabal 
name:                preprocessor-test
version:             0.1.0.0
build-type:          Custom
cabal-version:       >=1.10
extra-source-files:  PreprocessorTest/*.prepro

library
  exposed-modules:     PreprocessorTest.PreprocessorTest
  build-depends:       base ==4.5.*
  -- hs-source-dirs:
  default-language:    Haskell2010

$ cat Setup.hs 
#!/usr/bin/env runhaskell

import Distribution.Simple
import Distribution.Simple.PreProcess
import Distribution.Simple.Utils
import Distribution.PackageDescription
import Distribution.Simple.LocalBuildInfo
import System.Cmd (rawSystem)
import System.FilePath ((</>))

main = let hooks = simpleUserHooks
           dummy = ("prepro", dummyPreprocessor)
       in defaultMainWithHooks hooks
          { hookedPreProcessors = dummy:knownSuffixHandlers  }

dummyPreprocessor :: BuildInfo -> LocalBuildInfo -> PreProcessor
dummyPreprocessor build local = PreProcessor {
  platformIndependent = True,
  runPreProcessor =
    mkSimplePreProcessor $ \inFile outFile verbosity -> do
      notice verbosity (inFile ++ " is being preprocessed to " ++ outFile)
      rawSystem "cp" [inFile, outFile]
      return ()
  }
$ cat PreprocessorTest/PreprocessorTest.prepro 
module PreprocessorTest.PreprocessorTest
       where

preprocessorTest :: Int
preprocessorTest = 1

$ cabal configure
Resolving dependencies...
[1 of 1] Compiling Main             ( Setup.hs, dist/setup/Main.o )
Linking ./dist/setup/setup ...
Configuring preprocessor-test-0.1.0.0...

$ cabal build    
Building preprocessor-test-0.1.0.0...
Preprocessing library preprocessor-test-0.1.0.0...
PreprocessorTest/PreprocessorTest.prepro is being preprocessed to
dist/build/PreprocessorTest/PreprocessorTest.hs
[1 of 1] Compiling PreprocessorTest.PreprocessorTest ( dist/build/PreprocessorTest/PreprocessorTest.hs, dist/build/PreprocessorTest/PreprocessorTest.o )
Registering preprocessor-test-0.1.0.0...

$ ./dist/setup/setup sdist
Distribution quality errors:
No 'synopsis' or 'description' field.
The 'license' field is missing or specified as AllRightsReserved.
Distribution quality warnings:
No 'category' field.
No 'maintainer' field.
Note: the public hackage server would reject this package.
Building source dist for preprocessor-test-0.1.0.0...
Preprocessing library preprocessor-test-0.1.0.0...
PreprocessorTest/PreprocessorTest.prepro is being preprocessed to
dist/src/sdist.-6767/preprocessor-test-0.1.0.0/dist/build/PreprocessorTest/PreprocessorTest.hs
Source tarball created: dist/preprocessor-test-0.1.0.0.tar.gz

$ tar tzf dist/preprocessor-test-0.1.0.0.tar.gz
preprocessor-test-0.1.0.0/
preprocessor-test-0.1.0.0/dist/
preprocessor-test-0.1.0.0/dist/build/
preprocessor-test-0.1.0.0/dist/build/PreprocessorTest/
preprocessor-test-0.1.0.0/dist/build/PreprocessorTest/PreprocessorTest.hs
preprocessor-test-0.1.0.0/Setup.hs
preprocessor-test-0.1.0.0/PreprocessorTest/
preprocessor-test-0.1.0.0/PreprocessorTest/PreprocessorTest.prepro
preprocessor-test-0.1.0.0/preprocessor-test.cabal

Origen