From e1c79038c3d0bc4cfca4413601217f365b60910d Mon Sep 17 00:00:00 2001
From: Leonid Vasilev <leonid.vasilev@serokell.io>
Date: Wed, 27 Apr 2022 14:51:05 +0300
Subject: [PATCH] [#208] `redundant constraint` test

Problem: in `ghc-8.6.3` your code can produce `redundant constraint` warning
if you derive `Container` for newtype, but in `ghc-9.0.2` and newer
no warnings would be produced.

Solution: added test, that should be compiled with `ghc-9.0.2` and newer
without warnings.
---
 test/Test/Universum/Issue208.hs | 23 +++++++++++++++++++++++
 universum.cabal                 |  4 +++-
 2 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 test/Test/Universum/Issue208.hs

diff --git a/test/Test/Universum/Issue208.hs b/test/Test/Universum/Issue208.hs
new file mode 100644
index 00000000..f5181183
--- /dev/null
+++ b/test/Test/Universum/Issue208.hs
@@ -0,0 +1,23 @@
+{-# LANGUAGE
+    GeneralizedNewtypeDeriving
+  , UndecidableInstances
+  , FlexibleContexts
+  , GADTs
+  , DerivingStrategies
+  , CPP
+#-}
+module Test.Universum.Issue208
+  () where
+
+#if __GLASGOW_HASKELL__ >= 900
+
+import Universum (Container)
+
+-- In ghc-8.6.3 this code will produce a @redundant constraint@ warning.
+-- In ghc-9.0.2 and newer no warnings would be produced.
+-- Issue #208: https://github.com/serokell/universum/issues/208
+
+newtype Test = Test [Int]
+    deriving newtype (Container)
+
+#endif
diff --git a/universum.cabal b/universum.cabal
index 81857333..1f04237b 100644
--- a/universum.cabal
+++ b/universum.cabal
@@ -121,7 +121,9 @@ test-suite universum-test
   hs-source-dirs:      test
   main-is:             Spec.hs
 
-  other-modules:       Test.Universum.Property
+  other-modules:
+                       Test.Universum.Issue208
+                       Test.Universum.Property
 
   build-depends:       universum
                      , bytestring