Haskell Cabal项目似乎正在导入Cabal Library breaking Setup.hs的多个版本

简称：

我有一个阴谋集团项目，它依赖于使用阴谋集团沙盒添加源代码构建的库。此库导出预处理器函数BuildInfo->LocalBuildInfo->preprocessor。当我尝试在Setup.hs中为我的主要cabal项目使用该预处理器时，我得到错误：

Couldn't match type ‘Cabal-1.18.1.3:Distribution.PackageDescription.BuildInfo’
              with ‘BuildInfo’
NB: ‘Cabal-1.18.1.3:Distribution.PackageDescription.BuildInfo’
      is defined in ‘Distribution.PackageDescription’
          in package ‘Cabal-1.18.1.3’
    ‘BuildInfo’
      is defined in ‘Distribution.PackageDescription’
          in package ‘Cabal-1.20.0.1’

Couldn't match type ‘Cabal-1.18.1.3:Distribution.PackageDescription.BuildInfo’
              with ‘BuildInfo’
NB: ‘Cabal-1.18.1.3:Distribution.PackageDescription.BuildInfo’
      is defined in ‘Distribution.PackageDescription’
          in package ‘Cabal-1.18.1.3’
    ‘BuildInfo’
      is defined in ‘Distribution.PackageDescription’
          in package ‘Cabal-1.20.0.1’

不那么短：

我目前在我的阴谋集团沙箱中有以下目录结构：

├── main.cabal
├── Setup.hs
├── Main.hs
├── lib
│   ├── myPP.cabal
│   ├── MyPP.hs
│   └── myPP
│       ├── MyPP.hs
│       ├── myPP.cabal

我的主程序包有一个myPP，它有一个构建。myPP是一个库，myPP作为公开模块，Cabal和ghc作为依赖项。MyPP模块导出一个函数

myPP :: BuildInfo -> LocalBuildInfo -> PreProcessor

然后我就跑

cabal sandbox add-source ./lib/*
cabal install myPP

在my Setup.hs中，我有：

module Main (main) where
import Distribution.Simple
import Distribution.Simple.PreProcess
import Distribution.Simple.Utils
import Distribution.PackageDescription
import Distribution.Simple.LocalBuildInfo
import MyPP(myPP)
main :: IO ()
main = let hooks = simpleUserHooks
           pp = ("pp",myPP)
       in defaultMainWithHooks hooks {hookedPreProcessors = pp:knownSuffixHandlers}

然后，我尝试实际构建阴谋集团，只是为了得到错误：

Couldn't match type ‘Cabal-1.18.1.3:Distribution.PackageDescription.BuildInfo’
              with ‘BuildInfo’
NB: ‘Cabal-1.18.1.3:Distribution.PackageDescription.BuildInfo’
      is defined in ‘Distribution.PackageDescription’
          in package ‘Cabal-1.18.1.3’
    ‘BuildInfo’
      is defined in ‘Distribution.PackageDescription’
          in package ‘Cabal-1.20.0.1’

Couldn't match type ‘Cabal-1.18.1.3:Distribution.PackageDescription.BuildInfo’
              with ‘BuildInfo’
NB: ‘Cabal-1.18.1.3:Distribution.PackageDescription.BuildInfo’
      is defined in ‘Distribution.PackageDescription’
          in package ‘Cabal-1.18.1.3’
    ‘BuildInfo’
      is defined in ‘Distribution.PackageDescription’
          in package ‘Cabal-1.20.0.1’

尝试诊断错误：

Couldn't match type ‘Cabal-1.18.1.3:Distribution.PackageDescription.BuildInfo’
              with ‘BuildInfo’
NB: ‘Cabal-1.18.1.3:Distribution.PackageDescription.BuildInfo’
      is defined in ‘Distribution.PackageDescription’
          in package ‘Cabal-1.18.1.3’
    ‘BuildInfo’
      is defined in ‘Distribution.PackageDescription’
          in package ‘Cabal-1.20.0.1’

Couldn't match type ‘Cabal-1.18.1.3:Distribution.PackageDescription.BuildInfo’
              with ‘BuildInfo’
NB: ‘Cabal-1.18.1.3:Distribution.PackageDescription.BuildInfo’
      is defined in ‘Distribution.PackageDescription’
          in package ‘Cabal-1.18.1.3’
    ‘BuildInfo’
      is defined in ‘Distribution.PackageDescription’
          in package ‘Cabal-1.20.0.1’

---

我的理解是，当你有一个同时依赖于ghc和Cabal的包时，你就得到了Cabal的版本，这个版本与ghc建立的时间有关。因此，myPP包是使用旧版本的cabal构建的。当custom Setup.hs由cabal运行时，它会导入我安装的cabal版本。这将导致错误。然而，我希望有一个更好的解决方案，而不仅仅是降级我的阴谋集团版本……

你不会喜欢另一个解决方案：从当前头部构建ghc，以获得1.21.1.0版本的新阴谋集团。不幸的是，无法使一个包的两个不同版本在一个构建中共存。降低阴谋集团的级别可能是最不痛苦的选择