Cabal ignores `hs-source-dirs:` if `main-is:` is a C source file

[mpilgrem]

Describe the bug

After GHC 9.8.2/Cabal-3.10.2.0, and by GHC 9.10.1/Cabal-3.12.0.0, Cabal (the library) ignores hs-source-dirs if main-is is a C source file. Previously, Cabal respected hs-source-dirs.

To Reproduce
Imagine a small package. In directory app it has Main.hs with contents:

module Main ( main ) where

import Lib ( myMax )

main :: IO ()
main = print $ myMax 10 100

In directory src it has Lib.hs with contents:

module Lib ( myMax ) where

myMax :: Int -> Int -> Int
myMax x1 x2 = if x1 > x2 then x1 else x2

foreign export ccall myMax :: Int -> Int -> Int

In directory c-app it has main.c with contents:

#include <stdio.h>
#include <HsFFI.h>
#ifdef __GLASGOW_HASKELL__
#include "Lib_stub.h"
#endif

int main(int argc, char *argv[]) {
  hs_init(&argc, &argv);
  printf("%lld\n", myMax(10,100));
  hs_exit();
  return 0;
}

It has the usual Setup.hs:

import Distribution.Simple
main = defaultMain

and it has a Cabal file:

cabal-version: 1.12

name:           haskell-c-tests
version:        0.1.0.0
build-type:     Simple

library
  exposed-modules: Lib
  hs-source-dirs: src
  ghc-options: -stubdir autogen-stubs
  build-depends: base
  default-language: Haskell2010

executable c-exe
  main-is: main.c
  hs-source-dirs: c-app
  ghc-options: -no-hs-main
  include-dirs: autogen-stubs
  build-depends: base, haskell-c-tests
  default-language: Haskell2010

executable haskell-exe
  main-is: Main.hs
  hs-source-dirs: app
  ghc-options: -threaded -rtsopts -with-rtsopts=-N
  build-depends: base, haskell-c-tests
  default-language: Haskell2010

With GHC 9.8.2/Cabal-3.10.2.0 all is fine (extracts only):

❯ stack --stack-yaml stack-ghc-9.8.2.yaml runghc --no-ghc-package-path -- Setup.hs configure
Configuring haskell-c-tests-0.1.0.0...

❯ stack --stack-yaml stack-ghc-9.8.2.yaml runghc --no-ghc-package-path -- Setup.hs build -v
...
Preprocessing executable 'c-exe' for haskell-c-tests-0.1.0.0..
Building executable 'c-exe' for haskell-c-tests-0.1.0.0..
creating dist\build\c-exe
creating dist\build\c-exe\c-exe-tmp
Building C Sources...
creating dist\build\c-exe\c-exe-tmp
Running: "C:\Users\mike\AppData\Local\Programs\stack\x86_64-windows\ghc-9.8.2\bin\ghc.exe" "-c" "-odir" "dist\build\c-exe\c-exe-tmp" "-Idist\build\c-exe\autogen" "-Idist\build\global-autogen" "-Idist\build\c-exe\c-exe-tmp" "-Iautogen-stubs" "-Idist\build\autogen-stubs" "-optc-O2" "-pgmc" "C:\Users\mike\AppData\Local\Programs\stack\x86_64-windows\ghc-9.8.2\lib\../mingw/bin\clang.exe" "-hide-all-packages" "-no-user-package-db" "-package-db" "dist\package.conf.inplace" "-package-id" "base-4.19.1.0-6554" "-package-id" "haskell-c-tests-0.1.0.0-2Qfk7puHfWxBnTSX2kZfQz" "c-app\main.c" "-no-hs-main"
Linking...

Note that Cabal has passed "c-app\main.c" to GHC 9.8.2 (the second from last argument).

However, with GHC 9.10.1/Cabal-3.12.0.0, Cabal passes only "main.c" to GHC 9.10.1 and, consequently, fails to find main.c:

❯ stack --stack-yaml stack-ghc-9.10.1.yaml runghc --no-ghc-package-path -- Setup.hs configure
Configuring haskell-c-tests-0.1.0.0...

❯ stack --stack-yaml stack-ghc-9.10.1.yaml runghc --no-ghc-package-path -- Setup.hs build -v
...
Preprocessing executable 'c-exe' for haskell-c-tests-0.1.0.0...
Building executable 'c-exe' for haskell-c-tests-0.1.0.0...
creating dist\build\c-exe
creating dist\build\c-exe\c-exe-tmp
Wanted build ways: [StaticWay]
Building C Sources...
creating dist\build\c-exe\c-exe-tmp
Running: "C:\Users\mike\AppData\Local\Programs\stack\x86_64-windows\ghc-9.10.1\bin\ghc.exe" "-c" "-odir" "dist\build\c-exe\c-exe-tmp" "-Idist\build\c-exe\autogen" "-Idist\build\global-autogen" "-Idist\build\c-exe\c-exe-tmp" "-Iautogen-stubs" "-Idist\build\autogen-stubs" "-optc-O2" "-pgmc" "C:\Users\mike\AppData\Local\Programs\stack\x86_64-windows\ghc-9.10.1\lib/../mingw//bin\clang.exe" "-hide-all-packages" "-no-user-package-db" "-package-db" "dist\package.conf.inplace" "-package-id" "base-4.20.0.0-30dc" "-package-id" "haskell-c-tests-0.1.0.0-BiMnNkNFjFZ2oxYL44TYmr" "main.c" "-no-hs-main"
<command line>: does not exist: main.c

(stack --stack-yaml stack-ghc-9.10.1.yaml runghc --no-ghc-package-path -- etc runs runghc in the correct environment - that is, one that provides the relevant version of GHC and its Cabal boot package. The --no-ghc-package-path is because GHC_PACKAGE_PATH and Cabal are incompatible.)

[ulysses4ever]

Have you checked GHC 9.10/Cabal-3.10? That may be helpful.

[mouse07410]

Have you checked GHC 9.10/Cabal-3.10?

With Cabal-3.10.3.0, Stack-2.15.7, and GHC-9.10.1 the build seems to succeed.

With Cabal-3.12.1.0 and GHC-9.6.5 the build fails (Cabal cannot find the .c file).

[mpilgrem]

Have you checked GHC 9.10/Cabal-3.10?

As the problem is what different versions of Cabal (the library) are, or are not, passing to GHC, I reason that changing GHC version for a given Cabal version has no effect. But I've not tested that empircially.

[mouse07410]

But I've not tested that empiricially

I have. The problem is with Cabal. :-(

[mpilgrem]

I agree with @mouse07410. I was able to try the GHC 9.10.1/Cabal 3.10.2.0 combination by adding to the Cabal file:

build-type:     Custom

custom-setup
  setup-depends: base, Cabal ==3.10.2.0

and to stack-ghc-9.10.1.yaml:

snapshot: nightly-2024-04-04 # GHC 9.8.2
compiler: ghc-9.10.1
extra-deps:
- Cabal-3.10.2.0
- Cabal-syntax-3.10.2.0
# Specifying a boot package as an extra-dep requires its boot package dependencies to be
# specified also
- Win32-2.13.4.0@sha256:6a1299d051c514aa5ac7b77ef5f86be6c0aa6940b00302c6dc246192c7a97d99,5769
- binary-0.8.9.2@sha256:03381e511429c44d13990c6d76281c4fc2468371cede4fe684b0c98d9b7d5f5a,6611
- containers-0.6.8@sha256:bb2bec1bbc6b39a7c97cd95e056a5698ec45beb5d8feb6caae12af64e4bd823c,2670
- directory-1.3.8.5@sha256:fbeec9ec346e5272167f63dcb86af513b457a7b9fc36dc818e4c7b81608d612b,3166
- filepath-1.4.300.2@sha256:345cbb1afe414a09e47737e4d14cbd51891a734e67c0ef3d77a1439518bb81e8,5900
- parsec-3.1.17.0@sha256:8407cbd428d7f640a0fff8891bd2f7aca13cebe70a5e654856f8abec9a648b56,5149
- process-1.6.20.0@sha256:2a9393de33f18415fb8f4826957a87a94ffe8840ca8472a9b69dca6de45aca03,2790
- text-2.1.1@sha256:78c3fb91055d0607a80453327f087b9dc82168d41d0dca3ff410d21033b5e87d,10653
- time-1.12.2@sha256:88e8493d9130038d3b9968a2530a0900141cd3d938483c83dde56e12b875ebc8,6510

[mouse07410]

Actually, things are even more interesting. Below is a proof that the regression is in Cabal 3.12.0.0 library, with which Stack-2.15.7 is built.

• With Cabal-3.12.1.0, both cabal build and stack build commands fail.
• With Cabal-3.10.3.0, cabal build (which uses cabal 3.10 library) works, but stack build (which uses cabal 3.12 library) fails:

$ cabal build
Resolving dependencies...
Build profile: -w ghc-9.10.1 -O2
In order, the following will be built (use -v for more details):
 - h-tst5-0.1.1.1 (lib) (configuration changed)
 - h-tst5-0.1.1.1 (exe:h-tst5-exe) (configuration changed)
 - h-tst5-0.1.1.1 (exe:h-tst5-c-exe) (configuration changed)
Configuring library for h-tst5-0.1.1.1..
Preprocessing library for h-tst5-0.1.1.1..
Building library for h-tst5-0.1.1.1..
Configuring executable 'h-tst5-exe' for h-tst5-0.1.1.1..
Configuring executable 'h-tst5-c-exe' for h-tst5-0.1.1.1..
Preprocessing executable 'h-tst5-c-exe' for h-tst5-0.1.1.1..
Building executable 'h-tst5-c-exe' for h-tst5-0.1.1.1..
Preprocessing executable 'h-tst5-exe' for h-tst5-0.1.1.1..
Building executable 'h-tst5-exe' for h-tst5-0.1.1.1..
[3 of 3] Linking /Users/ur20980/src/h-tst5/dist-newstyle/build/x86_64-osx/ghc-9.10.1/h-tst5-0.1.1.1/x/h-tst5-exe/opt/build/h-tst5-exe/h-tst5-exe [Library changed]
$ stack build

Warning: Stack has not been tested with GHC versions 9.10 and above, and using 9.10.1, this may fail.

Warning: Stack has not been tested with Cabal versions 3.12 and above, but version 3.12.0.0 was found, this may fail.
h-tst5> build (lib + exe) with ghc-9.10.1
Preprocessing library for h-tst5-0.1.1.1...
Building library for h-tst5-0.1.1.1...
Preprocessing executable 'h-tst5-c-exe' for h-tst5-0.1.1.1...
Building executable 'h-tst5-c-exe' for h-tst5-0.1.1.1...
<command line>: does not exist: test.c

Error: [S-7282]
       Stack failed to execute the build plan.
       
       While executing the build plan, Stack encountered the error:
       
       [S-7011]
       While building package h-tst5-0.1.1.1 (scroll up to its section to see the error) using:
       /Users/ur20980/.stack/setup-exe-cache/x86_64-osx/Cabal-simple_HwdwpEmb_3.12.0.0_ghc-9.10.1 --verbose=1 --builddir=.stack-work/dist/x86_64-osx/ghc-9.10.1 build lib:h-tst5 exe:h-tst5-c-exe exe:h-tst5-exe --ghc-options " -fdiagnostics-color=always"
       Process exited with code: ExitFailure 1 
$

[mpilgrem]

@mouse07410, the official release of Stack 2.15.7 has a dependency on Cabal=3.10.3.0, but Stack does not use that dependency to build. For Simple it uses the boot package of the specified GHC. That can be overriden using a Custom build.

[mouse07410]

@mouse07410, the official release of Stack 2.15.7 has a dependency on Cabal=3.10.3.0, but Stack does not use that dependency to build. For Simple it uses the boot package of the specified GHC. That can be overriden using a Custom build.

Ok, in that case why does "cabal-install"-v3.10.3.0 build succeeds when "stack" build fails? Does GHC-9.10.1 use boot package with cabal-3.12?

[ulysses4ever]

Thanks everyone for helping to isolate the problem to Cabal-3.12. Next step would be bisect it, perhaps.

[mpilgrem]

@mouse07410, yes GHC 9.10.1 comes with Cabal-3.12.0.0. This is a handy source: https://gitlab.haskell.org/ghc/ghc/-/wikis/commentary/libraries/version-history. This is another: https://www.snoyman.com/base/.