Parse failure for 'if' with flags inside test-suite

[chshersh]

I'm following these suggestions from official documentation to use different main files for different flags:

• https://www.haskell.org/cabal/users-guide/developing-packages.html#meaning-of-field-values-when-using-conditionals

Real problem: I need to disable doctest tests for Windows because AppVeyor CI fails

But when I'm trying to use this approach for my test-suite I see parsing error when using cabal new-build command.

Expected behavior

Build without problems

Observed behavior

$ cabal new-build
Warning:
.../cabal-flag-example/cabal-flag-example.cabal:11:1:
The 'main-is' field is required for the exitcode-stdio-1.0 test suite type.
cabal: Failed parsing
".../cabal-flag-example/./cabal-flag-example.cabal".

I've tried to create minimal reproducible example. You can see it here:

• https://github.com/ChShersh/cabal-flag-example

$ cabal --version
cabal-install version 2.1.0.0
compiled using version 2.1.0.0 of the Cabal library 

[phadej]

So far I think this is a documentation bug

Trying with cabal-install-2.0 gives:

% /opt/cabal/2.0/bin/cabal check
cabal: ./cabal-flag-example.cabal:11: The 'main-is' field is required for the
exitcode-stdio-1.0 test suite type.

For now you can workaround this by writing (conditional statements are interpreted after "main" body):

test-suite flag-cabal-test
  type:                exitcode-stdio-1.0
  build-depends:       base >= 4.8 && < 5
  default-language:    Haskell2010

  main-is:             SecondMain.hs

  if os(windows)
    main-is:             FirstMain.hs

or having dummy Main.hs which includes module based on hs-source-dirs:

module Main (main) where
import Tests (main)

and

test-suite flag-cabal-test
  type:                exitcode-stdio-1.0
  build-depends:       base >= 4.8 && < 5
  default-language:    Haskell2010

  main-is: Main.hs

  hs-source-dirs: common
  other-modules: Tests

  if os(windows)
    hs-source-dirs: windows
  else 
    hs-source-dirs: unix

---

Currently we are conservative when checking that test-suite always have type, and if it's exitcode-stdio-1.0 then also main-is (for detailed-0.9 we required test-module). To fix this we need to verify that all possible "flattenings" have type, and then either main-is or test-module depending on the type. More concretely we need to generalise validateTestSuite check into validateCondTreeTestSuite.

Now as I look into the code, that check looks fishy anyway as

test-suite flag-cabal-test
  build-depends:       base >= 4.8 && < 5
  default-language:    Haskell2010

  if os(windows)
    type:                exitcode-stdio-1.0
    main-is:             FirstMain.hs
  else
    type:                exitcode-stdio-1.0
    main-is:             SecondMain.hs

works

AND with current-ish master also

test-suite flag-cabal-test
  build-depends:       base >= 4.8 && < 5
  default-language:    Haskell2010

  if os(windows)
    type:                exitcode-stdio-1.0
    main-is:             FirstMain.hs

which should fail and does fail with cabal-install-2.0:

cabal: ./cabal-flag-example.cabal:11: Test suite "flag-cabal-test" is missing
required field "type" or the field is not present in all conditional branches.
The available test types are: exitcode-stdio-1.0, detailed-0.9

---

that said, I think that fix won't be invasive. May need to change the public interface of
Distribution.PackageDescription.FieldGrammar. @23Skidoo is it ok to do the patch next week, to be still included in 2.2?

[chshersh]

@phadej Thanks a lot for your response! Your workarounds really help me 👍

[23Skidoo]

Fixed by #5076.