Use cabal-doctest in polysemy, build on GHC 8.8.1

- Use @googleson78 's changes to build polysemy on GHC 8.8.1, with slight
  modifications. The source distribution is now found in "dist-newstyle/sdist",
  so we've updated the command to point at that folder. Additionally, cabal
  v2-install doesn't support installing .tar.gz files in the same way v1-install
  did, so updated the command to use "cabal v1-install".
- Modified polysemy to use "cabal-doctest" and so overcome issues with the
  doctest tests (see issue #258, PR #265).

.travis.yml

@@ -5,10 +5,11 @@ cache:
   directories:
     - $HOME/.cabal/store
 
-cabal: "2.4"
+cabal: "3.0"
 
 matrix:
   include:
+    - ghc: "8.8.1"
     - ghc: "8.6.5"
     - ghc: "8.4.4"
 
@@ -29,7 +30,8 @@ script:
 # If there are no other `.tar.gz` files in `dist`, this can be even simpler:
 # `cabal install --force-reinstalls dist/*-*.tar.gz`
  - SRC_TGZ=$(cabal info . | awk '{print $2;exit}').tar.gz &&
-   (cd dist && cabal install --force-reinstalls "$SRC_TGZ")
+   (cd dist-newstyle/sdist && cabal v1-install --force-reinstalls "$SRC_TGZ")
+
 
  - cabal v2-build polysemy-plugin
  - cabal v2-test --enable-test polysemy-plugin

Setup.hs

@@ -1,2 +1,3 @@
-import Distribution.Simple
-main = defaultMain
+import Distribution.Extra.Doctest (defaultMainWithDoctests)
+
+main = defaultMainWithDoctests "polysemy-test"

polysemy.cabal

@@ -18,11 +18,17 @@ maintainer:     sandy@sandymaguire.me
 copyright:      2019 Sandy Maguire
 license:        BSD3
 license-file:   LICENSE
-build-type:     Simple
+build-type:     Custom
 extra-source-files:
     README.md
     ChangeLog.md
 
+custom-setup
+    setup-depends:
+        base
+      , Cabal
+      , cabal-doctest >=1.0.6 && <1.1
+
 source-repository head
   type: git
   location: https://github.com/isovector/polysemy

stack.yaml

@@ -8,7 +8,7 @@ extra-deps:
 - aeson-1.4.3.0
 - bifunctors-5.5.4
 - dump-core-0.1.3.2
-- first-class-families-0.5.0.0
+- first-class-families-0.6.0.0
 - ghc-lib-0.20190204
 - inspection-testing-0.4.2
 - loopbreaker-0.1.1.1

test/DoctestSpec.hs

@@ -5,39 +5,41 @@ module DoctestSpec where
 import Test.Hspec
 import Test.DocTest
 
-spec :: Spec
-spec = parallel $ describe "Error messages" $ it "should pass the doctest" $ doctest
-  [ "-isrc/"
-  , "--fast"
-  , "-XDataKinds"
-  , "-XDeriveFunctor"
-  , "-XFlexibleContexts"
-  , "-XGADTs"
-  , "-XLambdaCase"
-  , "-XPolyKinds"
-  , "-XRankNTypes"
-  , "-XScopedTypeVariables"
-  , "-XStandaloneDeriving"
-  , "-XTypeApplications"
-  , "-XTypeFamilies"
-  , "-XTypeOperators"
-  , "-XUnicodeSyntax"
-
-  , "-package type-errors"
+import Build_doctests (flags, pkgs, module_sources)
 
+spec :: Spec
+spec = parallel $ describe "Error messages" $ it "should pass the doctest" $ doctest $
+  [ "--fast"
 #if __GLASGOW_HASKELL__ < 806
   , "-XMonadFailDesugaring"
   , "-XTypeInType"
 #endif
-
   , "test/TypeErrors.hs"
-
-  -- Modules that are explicitly imported for this test must be listed here
-  , "src/Polysemy.hs"
-  , "src/Polysemy/Error.hs"
-  , "src/Polysemy/Output.hs"
-  , "src/Polysemy/Reader.hs"
-  , "src/Polysemy/Resource.hs"
-  , "src/Polysemy/State.hs"
-  , "src/Polysemy/Trace.hs"
   ]
+  <> pkgs
+  <> removeFlagSearchPathSrc flags
+
+-- | Designed to remove flags that add the "polysemy-plugin/src" directory. For
+-- example, it will remove the following flag:
+-- "-i/Users/bob/code/polysemy/polysemy-plugin/src".
+--
+-- This was done because the presence of this flag causes the following error:
+--   test/TypeErrors.hs:9: failure in expression `:set -fplugin=Polysemy.Plugin'
+--   expected:   
+--    but got: attempting to use module ‘main:Polysemy.Plugin’
+--    (.../polysemy/polysemy-plugin/src/Polysemy/Plugin.hs) which is not loaded.
+--
+-- Without this flag, the tests pass as expected. My understanding of GHC isn't
+-- great, so feel free to remove this function if you know of some way of making
+-- this flag a non-issue.
+removeFlagSearchPathSrc :: [String] -> [String]
+removeFlagSearchPathSrc = filter (not . isSrcSearchPath)
+  where
+    isSrcSearchPath flag = isSearchPathFlag flag && isSrcDir flag
+
+    isSearchPathFlag ('-':'i':_) = True
+    isSearchPathFlag _           = False
+
+    isSrcDir ('s':'r':c':[]) = True
+    isSrcDir (x:xs)          = isSrcDir xs
+    isSrcDir []              = False