doctest: Ambiguous module name

[hololeap]

When compiling dhall-1.40.1 I hit this error when doctest is run:

 * >>> Test phase [cabal test]: dev-lang/dhall-1.40.1
./setup test --show-details=streaming
Running 2 test suites...
Test suite doctest: RUNNING...

/var/tmp/portage/dev-lang/dhall-1.40.1/work/dhall-1.40.1/ghc-src/Dhall/Crypto.hs:16:1: error:
    Ambiguous module name ‘Crypto.Hash’:
      it was found in multiple packages: cryptonite-0.28 hashing-0.1.0.1
   |
16 | import Crypto.Hash             (SHA256)
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

/var/tmp/portage/dev-lang/dhall-1.40.1/work/dhall-1.40.1/ghc-src/Dhall/Crypto.hs:22:1: error:
    Ambiguous module name ‘Crypto.Hash’:
      it was found in multiple packages: cryptonite-0.28 hashing-0.1.0.1
   |
22 | import qualified Crypto.Hash
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Test suite doctest: FAIL
Test suite logged to: dist/test/dhall-1.40.1-doctest.log

What is strange about this is that hashing is not mentioned anywhere in the package, but it is installed on my system. There are no such issues when the compile phase is run.

[hololeap]

$ cabal unpack dhall-1.40.1
$ cd dhall-1.40.1
$ cabal build
$ cabal test

I just tried this and got the same error, so it's probably a bug with doctest.

[hololeap]

This old doctest bug looks relevant.

[hololeap]

I discovered a much better solution to this problem: Patch the package to use cabal-doctest instead of using PackageImports.

cabal-doctest has some example packages in their repo. Here is a simple example of how to patch a package for gentoo-haskell:

diff -urN dhall-docs-1.0.8/Setup.hs dhall-docs-1.0.8-r1/Setup.hs
--- dhall-docs-1.0.8/Setup.hs	2001-09-08 19:46:40.000000000 -0600
+++ dhall-docs-1.0.8-r1/Setup.hs	2022-02-10 12:12:45.208325158 -0700
@@ -1,2 +1,6 @@
-import Distribution.Simple
-main = defaultMain
+module Main (main) where
+
+import Distribution.Extra.Doctest ( defaultMainWithDoctests )
+
+main :: IO ()
+main = defaultMainWithDoctests "doctest"
diff -urN dhall-docs-1.0.8/dhall-docs.cabal dhall-docs-1.0.8-r1/dhall-docs.cabal
--- dhall-docs-1.0.8/dhall-docs.cabal	2022-02-10 12:06:27.209021249 -0700
+++ dhall-docs-1.0.8-r1/dhall-docs.cabal	2022-02-10 12:12:29.418354235 -0700
@@ -2,7 +2,7 @@
 Version: 1.0.8
 x-revision: 2
 Cabal-Version: >=1.10
-Build-Type: Simple
+Build-Type: Custom
 License: BSD3
 License-File: LICENSE
 Copyright: 2020 Germán Robayo
@@ -59,6 +59,13 @@
   description: To enable use of data-files while running `stack ghci`
   default: False
 
+
+custom-setup
+  setup-depends:
+      base
+    , Cabal
+    , cabal-doctest
+
 Library
     Hs-Source-Dirs: src
     Build-Depends:
@@ -123,6 +130,8 @@
         base                           ,
         directory,
         filepath                 < 1.5 ,
+        base-compat,
+        cabal-doctest,
         doctest    >= 0.7.0
     Other-Extensions: OverloadedStrings RecordWildCards
     Default-Language: Haskell2010
diff -urN dhall-docs-1.0.8/doctest/Main.hs dhall-docs-1.0.8-r1/doctest/Main.hs
--- dhall-docs-1.0.8/doctest/Main.hs	2001-09-08 19:46:40.000000000 -0600
+++ dhall-docs-1.0.8-r1/doctest/Main.hs	2022-02-10 12:14:39.408114856 -0700
@@ -6,13 +6,24 @@
 import qualified System.Directory
 import qualified System.IO
 import qualified Test.DocTest
+import Build_doctests (pkgs)
 
 main :: IO ()
 main = do
     GHC.IO.Encoding.setLocaleEncoding System.IO.utf8
     pwd    <- System.Directory.getCurrentDirectory
     prefix <- System.Directory.makeAbsolute pwd
-    Test.DocTest.doctest
-        [ "--fast"
-        , prefix </> "src"
-        ]
+
+    let customFlags =
+            [ "-package-env=-"
+            , "-hide-all-packages"
+            , "-no-user-package-db"
+            , "-package-db=" ++ prefix </> "dist/package.conf.inplace"
+            ]
+
+    let origArgs = 
+            [ "--fast"
+            , prefix </> "src"
+            ]
+
+    Test.DocTest.doctest $ customFlags ++ pkgs ++ origArgs

[hololeap]

Related: #1270