这个存储库包含一个我doctest在测试套件中使用时遇到的恼人错误的复现。
cabal-installs 求解器无法build-depends使用 GHC 8.0.2 找到该字段的解决方案：
build-depends:
base >= 4.7 && < 5
, doctest == 0.11.4
, containers == 0.5.10.2
请注意，doctest依赖传递依赖于ghc-8.0.2，它本身依赖于containers-0.5.7.1，与我自己的约束相冲突。这基本上cabal install就是试图告诉我的：
Resolving dependencies...
cabal.exe: Could not resolve dependencies:
next goal: containers (dependency of repro-0.1.0.0)
rejecting: containers-0.5.7.1/installed-0.5... (conflict: repro =>
containers==0.5.10.2)
trying: containers-0.5.10.2
next goal: doctest (dependency of repro-0.1.0.0)
rejecting: doctest-0.13.0, doctest-0.12.0 (conflict: repro => doctest==0.11.4)
trying: doctest-0.11.4
next goal: ghc (dependency of doctest-0.11.4)
rejecting: ghc-8.0.2/installed-8.0... (conflict: containers==0.5.10.2, ghc =>
containers==0.5.7.1/installed-0.5...)
Dependency tree exhaustively searched.
现在，让我烦恼的是，使用and an for the containers versionstack install效果很好。所以理论上，也可以在这里做“正确的事”。我怎么能告诉它？lts-9extra-depscabal-install