base: Remove `Monad(fail)` method and reexport `MonadFail(fail)` instead

As per https://prime.haskell.org/wiki/Libraries/Proposals/MonadFail

Coauthored-by: Ben Gamari <ben@well-typed.com>

1 files changed, 0 insertions, 43 deletions

diff --git a/compiler/rename/RnSource.hs b/compiler/rename/RnSource.hs
index 5181b7f2ed..e7ff909c02 100644
--- a/compiler/rename/RnSource.hs
+++ b/compiler/rename/RnSource.hs
@@ -43,7 +43,6 @@ import Module
 import HscTypes         ( Warnings(..), plusWarns )
 import PrelNames        ( applicativeClassName, pureAName, thenAName
                         , monadClassName, returnMName, thenMName
-                        , monadFailClassName, failMName, failMName_preMFP
                         , semigroupClassName, sappendName
                         , monoidClassName, mappendName
                         )
@@ -457,9 +456,6 @@ checkCanonicalInstances cls poly_ty mbinds = do
     whenWOptM Opt_WarnNonCanonicalMonadInstances
         checkCanonicalMonadInstances
 
-    whenWOptM Opt_WarnNonCanonicalMonadFailInstances
-        checkCanonicalMonadFailInstances
-
     whenWOptM Opt_WarnNonCanonicalMonoidInstances
         checkCanonicalMonoidInstances
 
@@ -510,45 +506,6 @@ checkCanonicalInstances cls poly_ty mbinds = do
 
       | otherwise = return ()
 
-    -- | Warn about unsound/non-canonical 'Monad'/'MonadFail' instance
-    -- declarations. Specifically, the following conditions are verified:
-    --
-    -- In 'Monad' instances declarations:
-    --
-    --  * If 'fail' is overridden it must be canonical
-    --    (i.e. @fail = Control.Monad.Fail.fail@)
-    --
-    -- In 'MonadFail' instance declarations:
-    --
-    --  * Warn if 'fail' is defined backwards
-    --    (i.e. @fail = Control.Monad.fail@).
-    --
-    checkCanonicalMonadFailInstances
-      | cls == monadFailClassName  = do
-          forM_ (bagToList mbinds) $ \(dL->L loc mbind) -> setSrcSpan loc $ do
-              case mbind of
-                  FunBind { fun_id = (dL->L _ name)
-                          , fun_matches = mg }
-                      | name == failMName, isAliasMG mg == Just failMName_preMFP
-                      -> addWarnNonCanonicalMethod1
-                            Opt_WarnNonCanonicalMonadFailInstances "fail"
-                            "Control.Monad.fail"
-
-                  _ -> return ()
-
-      | cls == monadClassName  = do
-          forM_ (bagToList mbinds) $ \(dL->L loc mbind) -> setSrcSpan loc $ do
-              case mbind of
-                  FunBind { fun_id      = (dL->L _ name)
-                          , fun_matches = mg }
-                      | name == failMName_preMFP, isAliasMG mg /= Just failMName
-                      -> addWarnNonCanonicalMethod2
-                            Opt_WarnNonCanonicalMonadFailInstances "fail"
-                            "Control.Monad.Fail.fail"
-                  _ -> return ()
-
-      | otherwise = return ()
-
     -- | Check whether Monoid(mappend) is defined in terms of
     -- Semigroup((<>)) (and not the other way round). Specifically,
     -- the following conditions are verified: