The HSC.hsc file does not get reprocessed when the CPP definitions
change, only when the HSC.hsc file itself is changed. On the other
hand, the regular Haskell HS.hs file does get reprocessed when the CPP
definitions change.
$ cabal --version
cabal-install version 1.22.6.0
using version 1.22.2.0 of the Cabal library
$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.10.2
$ cabal sandbox init
$ cat bug/Main.hs
module Main where
import HS
import HSC
main = do
putStrLn $ "hsTest = " ++ show hsTest
putStrLn $ "hscTest = " ++ show hscTest
$ cat src/HS.hs
{-# LANGUAGE CPP #-}
module HS where
hsTest :: Bool
#ifdef CPP_FLAG
hsTest = True
#else
hsTest = False
#endif
$ cat src/HSC.hsc
{-# LANGUAGE CPP #-}
module HSC where
hscTest :: Bool
#ifdef CPP_FLAG
hscTest = True
#else
hscTest = False
#endif
$ cat cabal-hsc2hs-bug.cabal
name: cabal-hsc2hs-bug
version: 0.1.0.0
license: BSD3
license-file: LICENSE
author: Nathan Collins
maintainer: [email protected]
build-type: Simple
cabal-version: >=1.10
flag cabal_flag
description: a Cabal flag
default: True
manual: True
library
exposed-modules: HS, HSC
other-extensions: CPP
build-depends: base
hs-source-dirs: src
build-tools: hsc2hs
default-language: Haskell2010
if flag(cabal_flag)
cpp-options: -DCPP_FLAG
cc-options: -DCPP_FLAG
executable bug
main-is: Main.hs
hs-source-dirs: bug
build-depends: base, cabal-hsc2hs-bug
default-language: Haskell2010
$ for prefix in "+" "-"; do \
cabal configure --flags="${prefix}cabal_flag" && \
cabal build -j1 && \
cabal copy \
&& .cabal-sandbox/bin/bug; \
done
[...]
hsTest = True
hscTest = True
[...]
hsTest = False
hscTest = True
Notice that hscTest is always True. If you instead configure with
the flag disabled the first time, then hscTest is always False.
By touching the HSC.hsc file first, we can force a regeneration of
the HSC.hs file:
$ for prefix in "+" "-"; do \
touch src/HSC.hsc && \
cabal configure --flags="${prefix}cabal_flag" && \
cabal build -j1 && \
cabal copy \
&& .cabal-sandbox/bin/bug; \
done
[...]
hsTest = True
hscTest = True
[...]
hsTest = False
hscTest = False
See file FULL_OUTPUT.md if interested in full output.
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