Fix the build with -contravariant

For the most part, this is a matter of guarding the relevant definitions behind
`defined(MIN_VERSION_contravariant)` CPP. I also altered some definitions to
avoid relying on the `contravariant` library where they didn't need to do so.

Fixes #136.

.github/workflows/haskell-ci.yml

@@ -8,9 +8,9 @@
 #
 # For more information, see https://github.com/haskell-CI/haskell-ci
 #
-# version: 0.15.20230312
+# version: 0.16.6
 #
-# REGENDATA ("0.15.20230312",["github","--config=cabal.haskell-ci","cabal.project"])
+# REGENDATA ("0.16.6",["github","--config=cabal.haskell-ci","cabal.project"])
 #
 name: Haskell-CI
 on:
@@ -86,7 +86,7 @@ jobs:
           apt-get install -y --no-install-recommends gnupg ca-certificates dirmngr curl git software-properties-common libtinfo5
           if [ "${{ matrix.setup-method }}" = ghcup ]; then
             mkdir -p "$HOME/.ghcup/bin"
-            curl -sL https://downloads.haskell.org/ghcup/0.1.18.0/x86_64-linux-ghcup-0.1.18.0 > "$HOME/.ghcup/bin/ghcup"
+            curl -sL https://downloads.haskell.org/ghcup/0.1.19.2/x86_64-linux-ghcup-0.1.19.2 > "$HOME/.ghcup/bin/ghcup"
             chmod a+x "$HOME/.ghcup/bin/ghcup"
             "$HOME/.ghcup/bin/ghcup" install ghc "$HCVER" || (cat "$HOME"/.ghcup/logs/*.* && false)
             "$HOME/.ghcup/bin/ghcup" install cabal 3.10.1.0 || (cat "$HOME"/.ghcup/logs/*.* && false)
@@ -95,7 +95,7 @@ jobs:
             apt-get update
             apt-get install -y "$HCNAME"
             mkdir -p "$HOME/.ghcup/bin"
-            curl -sL https://downloads.haskell.org/ghcup/0.1.18.0/x86_64-linux-ghcup-0.1.18.0 > "$HOME/.ghcup/bin/ghcup"
+            curl -sL https://downloads.haskell.org/ghcup/0.1.19.2/x86_64-linux-ghcup-0.1.19.2 > "$HOME/.ghcup/bin/ghcup"
             chmod a+x "$HOME/.ghcup/bin/ghcup"
             "$HOME/.ghcup/bin/ghcup" install cabal 3.10.1.0 || (cat "$HOME"/.ghcup/logs/*.* && false)
           fi
@@ -173,17 +173,17 @@ jobs:
       - name: install cabal-plan
         run: |
           mkdir -p $HOME/.cabal/bin
-          curl -sL https://github.com/haskell-hvr/cabal-plan/releases/download/v0.6.2.0/cabal-plan-0.6.2.0-x86_64-linux.xz > cabal-plan.xz
-          echo 'de73600b1836d3f55e32d80385acc055fd97f60eaa0ab68a755302685f5d81bc  cabal-plan.xz' | sha256sum -c -
+          curl -sL https://github.com/haskell-hvr/cabal-plan/releases/download/v0.7.3.0/cabal-plan-0.7.3.0-x86_64-linux.xz > cabal-plan.xz
+          echo 'f62ccb2971567a5f638f2005ad3173dba14693a45154c1508645c52289714cb2  cabal-plan.xz' | sha256sum -c -
           xz -d < cabal-plan.xz > $HOME/.cabal/bin/cabal-plan
           rm -f cabal-plan.xz
           chmod a+x $HOME/.cabal/bin/cabal-plan
           cabal-plan --version
       - name: install cabal-docspec
         run: |
           mkdir -p $HOME/.cabal/bin
-          curl -sL https://github.com/phadej/cabal-extras/releases/download/cabal-docspec-0.0.0.20211114/cabal-docspec-0.0.0.20211114.xz > cabal-docspec.xz
-          echo 'e224700d9e8c9ec7ec6bc3f542ba433cd9925a5d356676c62a9bd1f2c8be8f8a  cabal-docspec.xz' | sha256sum -c -
+          curl -sL https://github.com/phadej/cabal-extras/releases/download/cabal-docspec-0.0.0.20230517/cabal-docspec-0.0.0.20230517-x86_64-linux.xz > cabal-docspec.xz
+          echo '3b31bbe463ad4d671abbc103db49628562ec48a6604cab278207b5b6acd21ed7  cabal-docspec.xz' | sha256sum -c -
           xz -d < cabal-docspec.xz > $HOME/.cabal/bin/cabal-docspec
           rm -f cabal-docspec.xz
           chmod a+x $HOME/.cabal/bin/cabal-docspec
@@ -251,12 +251,22 @@ jobs:
       - name: prepare for constraint sets
         run: |
           rm -f cabal.project.local
+      - name: constraint set no-contravariant
+        run: |
+          $CABAL v2-build $ARG_COMPILER --disable-tests --disable-benchmarks --constraint='semigroupoids -contravariant' all --dry-run
+          cabal-plan topo | sort
+          $CABAL v2-build $ARG_COMPILER --disable-tests --disable-benchmarks --constraint='semigroupoids -contravariant' --dependencies-only -j2 all
+          $CABAL v2-build $ARG_COMPILER --disable-tests --disable-benchmarks --constraint='semigroupoids -contravariant' all
       - name: constraint set no-containers
         run: |
+          $CABAL v2-build $ARG_COMPILER --disable-tests --disable-benchmarks --constraint='semigroupoids -containers' all --dry-run
+          cabal-plan topo | sort
           $CABAL v2-build $ARG_COMPILER --disable-tests --disable-benchmarks --constraint='semigroupoids -containers' --dependencies-only -j2 all
           $CABAL v2-build $ARG_COMPILER --disable-tests --disable-benchmarks --constraint='semigroupoids -containers' all
       - name: constraint set no-comonad
         run: |
+          $CABAL v2-build $ARG_COMPILER --disable-tests --disable-benchmarks --constraint='semigroupoids -comonad' all --dry-run
+          cabal-plan topo | sort
           $CABAL v2-build $ARG_COMPILER --disable-tests --disable-benchmarks --constraint='semigroupoids -comonad' --dependencies-only -j2 all
           $CABAL v2-build $ARG_COMPILER --disable-tests --disable-benchmarks --constraint='semigroupoids -comonad' all
       - name: save cache

cabal.haskell-ci

@@ -10,3 +10,6 @@ constraint-set no-comonad
 
 constraint-set no-containers
   constraints: semigroupoids -containers
+
+constraint-set no-contravariant
+  constraints: semigroupoids -contravariant

semigroupoids.cabal

@@ -170,9 +170,6 @@ library
     Data.Functor.Bind
     Data.Functor.Bind.Class
     Data.Functor.Bind.Trans
-    Data.Functor.Contravariant.Conclude
-    Data.Functor.Contravariant.Decide
-    Data.Functor.Contravariant.Divise
     Data.Functor.Extend
     Data.Functor.Plus
     Data.Groupoid
@@ -193,6 +190,12 @@ library
   other-modules:
     Semigroupoids.Internal
 
+  if impl(ghc >= 8.6) || flag(contravariant)
+    exposed-modules:
+      Data.Functor.Contravariant.Conclude
+      Data.Functor.Contravariant.Decide
+      Data.Functor.Contravariant.Divise
+
   ghc-options: -Wall -Wno-warnings-deprecations -Wno-trustworthy-safe
 
   if impl(ghc >= 9.0)

src/Data/Functor/Contravariant/Conclude.hs

@@ -12,6 +12,8 @@
 -- Stability   :  provisional
 -- Portability :  portable
 --
+-- This module is only available if building with GHC 8.6 or later, or if the
+-- @+contravariant@ @cabal@ build flag is available.
 ----------------------------------------------------------------------------
 module Data.Functor.Contravariant.Conclude (
     Conclude(..)
@@ -22,7 +24,6 @@ module Data.Functor.Contravariant.Conclude (
 
 import Control.Applicative.Backwards
 import Control.Monad.Trans.Identity
-import Control.Monad.Trans.Maybe
 import qualified Control.Monad.Trans.RWS.Lazy as Lazy
 import qualified Control.Monad.Trans.RWS.Strict as Strict
 import Control.Monad.Trans.Reader
@@ -35,17 +36,20 @@ import Data.Functor.Apply
 import Data.Functor.Compose
 import Data.Functor.Contravariant
 import Data.Functor.Contravariant.Decide
-import Data.Functor.Contravariant.Divise
-import Data.Functor.Contravariant.Divisible
 import Data.Functor.Product
 import Data.Functor.Reverse
 import Data.Monoid (Alt(..))
 import Data.Proxy
 import Data.Void
 import GHC.Generics
 
-#if !(MIN_VERSION_transformers(0,6,0))
+#if defined(MIN_VERSION_contravariant)
+# if !(MIN_VERSION_transformers(0,6,0))
 import Control.Monad.Trans.List
+# endif
+import Control.Monad.Trans.Maybe
+import Data.Functor.Contravariant.Divise
+import Data.Functor.Contravariant.Divisible
 #endif
 
 #ifdef MIN_VERSION_StateVar
@@ -110,37 +114,48 @@ concluded = conclude id
 gconcluded :: (Generic1 f, Conclude (Rep1 f)) => f Void
 gconcluded = to1 concluded
 
--- | @since 5.3.6
+#if defined(MIN_VERSION_contravariant)
+-- | This instance is only available if the @+contravariant@ @cabal@ flag is
+-- enabled.
+--
+-- @since 5.3.6
 instance Decidable f => Conclude (WrappedDivisible f) where
     conclude f = WrapDivisible (lose f)
+#endif
 
 -- | @since 5.3.6
-instance Conclude Comparison where conclude = lose
+instance Conclude Comparison where
+  conclude f = Comparison $ \a _ -> absurd (f a)
 
 -- | @since 5.3.6
-instance Conclude Equivalence where conclude = lose
+instance Conclude Equivalence where
+  conclude f = Equivalence $ absurd . f
 
 -- | @since 5.3.6
-instance Conclude Predicate where conclude = lose
+instance Conclude Predicate where
+  conclude f = Predicate $ absurd . f
 
 -- | @since 5.3.6
 instance Conclude (Op r) where
   conclude f = Op $ absurd . f
 
 -- | @since 5.3.6
-instance Conclude Proxy where conclude = lose
+instance Conclude Proxy where
+  conclude _ = Proxy
 
 #ifdef MIN_VERSION_StateVar
 -- | @since 5.3.6
-instance Conclude SettableStateVar where conclude = lose
+instance Conclude SettableStateVar where
+  conclude k = SettableStateVar (absurd . k)
 #endif
 
 -- | @since 5.3.6
 instance Conclude f => Conclude (Alt f) where
   conclude = Alt . conclude
 
 -- | @since 5.3.6
-instance Conclude U1 where conclude = lose
+instance Conclude U1 where
+  conclude _ = U1
 
 -- | @since 5.3.6
 instance Conclude f => Conclude (Rec1 f) where
@@ -178,15 +193,23 @@ instance Conclude m => Conclude (Lazy.RWST r w s m) where
 instance Conclude m => Conclude (Strict.RWST r w s m) where
   conclude f = Strict.RWST $ \_ _ -> contramap (\(a, _, _) -> a) (conclude f)
 
-#if !(MIN_VERSION_transformers(0,6,0))
--- | @since 5.3.6
+#if defined(MIN_VERSION_contravariant)
+# if !(MIN_VERSION_transformers(0,6,0))
+-- | This instance is only available if the @+contravariant@ @cabal@ flag is
+-- enabled.
+--
+-- @since 5.3.6
 instance (Divisible m, Divise m) => Conclude (ListT m) where
   conclude _ = ListT conquer
-#endif
+# endif
 
--- | @since 5.3.6
+-- | This instance is only available if the @+contravariant@ @cabal@ flag is
+-- enabled.
+--
+-- @since 5.3.6
 instance (Divisible m, Divise m) => Conclude (MaybeT m) where
   conclude _ = MaybeT conquer
+#endif
 
 -- | @since 5.3.6
 instance Conclude m => Conclude (Lazy.StateT s m) where

src/Data/Functor/Contravariant/Decide.hs

@@ -14,6 +14,8 @@
 -- Stability   :  provisional
 -- Portability :  portable
 --
+-- This module is only available if building with GHC 8.6 or later, or if the
+-- @+contravariant@ @cabal@ build flag is available.
 ----------------------------------------------------------------------------
 module Data.Functor.Contravariant.Decide (
     Decide(..)
@@ -37,7 +39,6 @@ import Data.Functor.Apply
 import Data.Functor.Compose
 import Data.Functor.Contravariant
 import Data.Functor.Contravariant.Divise
-import Data.Functor.Contravariant.Divisible
 import Data.Functor.Product
 import Data.Functor.Reverse
 import Data.Monoid (Alt(..))
@@ -50,6 +51,10 @@ import Control.Monad.Trans.List
 import Data.Either
 #endif
 
+#if defined(MIN_VERSION_contravariant)
+import Data.Functor.Contravariant.Divisible
+#endif
+
 #ifdef MIN_VERSION_StateVar
 import Data.StateVar
 #endif
@@ -99,18 +104,38 @@ decided = decide id
 gdecided :: (Generic1 f, Decide (Rep1 f)) => f b -> f c -> f (Either b c)
 gdecided fb fc = gdecide id fb fc
 
--- | @since 5.3.6
+#if defined(MIN_VERSION_contravariant)
+-- | This instance is only available if the @+contravariant@ @cabal@ flag is
+-- enabled.
+--
+-- @since 5.3.6
 instance Decidable f => Decide (WrappedDivisible f) where
     decide f (WrapDivisible x) (WrapDivisible y) = WrapDivisible (choose f x y)
+#endif
 
 -- | @since 5.3.6
-instance Decide Comparison where decide = choose
+instance Decide Comparison where
+  decide f (Comparison g) (Comparison h) = Comparison $ \a b -> case f a of
+    Left c -> case f b of
+      Left d -> g c d
+      Right{} -> LT
+    Right c -> case f b of
+      Left{} -> GT
+      Right d -> h c d
 
 -- | @since 5.3.6
-instance Decide Equivalence where decide = choose
+instance Decide Equivalence where
+  decide f (Equivalence g) (Equivalence h) = Equivalence $ \a b -> case f a of
+    Left c -> case f b of
+      Left d -> g c d
+      Right{} -> False
+    Right c -> case f b of
+      Left{} -> False
+      Right d -> h c d
 
 -- | @since 5.3.6
-instance Decide Predicate where decide = choose
+instance Decide Predicate where
+  decide f (Predicate g) (Predicate h) = Predicate $ either g h . f
 
 -- | Unlike 'Decidable', requires no constraint on @r@.
 --
@@ -123,7 +148,8 @@ instance Decide f => Decide (Alt f) where
   decide f (Alt l) (Alt r) = Alt $ decide f l r
 
 -- | @since 5.3.6
-instance Decide U1 where decide = choose
+instance Decide U1 where
+  decide _ U1 U1 = U1
 
 -- | Has no 'Decidable' or 'Conclude' instance.
 --