Remove redundant-constraints from -Wall (#10635)

Removes -Wredundant-constraints from -Wall, as per the
discussion in #10635.

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2498

GHC Trac Issues: #10635

compiler/main/DynFlags.hs

@@ -3958,8 +3958,7 @@ minusWallOpts
         Opt_WarnUnusedDoBind,
         Opt_WarnTrustworthySafe,
         Opt_WarnUntickedPromotedConstructors,
-        Opt_WarnMissingPatternSynonymSignatures,
-        Opt_WarnRedundantConstraints
+        Opt_WarnMissingPatternSynonymSignatures
       ]
 
 -- | Things you get with -Weverything, i.e. *all* known warnings flags

testsuite/tests/typecheck/should_compile/T10632.hs

 {-# LANGUAGE ImplicitParams #-}
+{-# OPTIONS_GHC -Wredundant-constraints #-}
 
 f :: (?file1 :: String) => IO ()
 f = putStrLn $ "f2: "

testsuite/tests/typecheck/should_compile/T10632.stderr

 
-T10632.hs:3:1: warning: [-Wredundant-constraints (in -Wall)]
+T10632.hs:4:1: warning: [-Wredundant-constraints]
     • Redundant constraint: ?file1::String
     • In the type signature for:
            f :: (?file1::String) => IO ()

testsuite/tests/typecheck/should_compile/T10635.hs

+{-# LANGUAGE GADTs #-}
+
+module T9939 where
+
+f1 :: (Eq a, Ord a) => a -> a -> Bool
+-- Eq a redundant
+f1 x y = (x == y) && (x > y)
+
+f2 :: (Eq a, Ord a) => a -> a -> Bool
+-- Ord a redundant, but Eq a is reported
+f2 x y = (x == y)
+
+f3 :: (Eq a, a ~ b, Eq b) => a -> b -> Bool
+-- Eq b redundant
+f3 x y = x==y
+
+data Equal a b where
+  EQUAL :: Equal a a
+
+f4 :: (Eq a, Eq b) => a -> b -> Equal a b -> Bool
+-- Eq b redundant
+f4 x y EQUAL = y==y

testsuite/tests/typecheck/should_compile/T9939.hs

 {-# LANGUAGE GADTs #-}
+{-# OPTIONS_GHC -Wredundant-constraints #-}
 
 module T9939 where
 

testsuite/tests/typecheck/should_compile/T9939.stderr

 
-T9939.hs:5:1: warning: [-Wredundant-constraints (in -Wall)]
+T9939.hs:6:1: warning: [-Wredundant-constraints]
     • Redundant constraint: Eq a
     • In the type signature for:
            f1 :: (Eq a, Ord a) => a -> a -> Bool
 
-T9939.hs:9:1: warning: [-Wredundant-constraints (in -Wall)]
+T9939.hs:10:1: warning: [-Wredundant-constraints]
     • Redundant constraint: Eq a
     • In the type signature for:
            f2 :: (Eq a, Ord a) => a -> a -> Bool
 
-T9939.hs:13:1: warning: [-Wredundant-constraints (in -Wall)]
+T9939.hs:14:1: warning: [-Wredundant-constraints]
     • Redundant constraint: Eq b
     • In the type signature for:
            f3 :: (Eq a, a ~ b, Eq b) => a -> b -> Bool
 
-T9939.hs:20:1: warning: [-Wredundant-constraints (in -Wall)]
+T9939.hs:21:1: warning: [-Wredundant-constraints]
     • Redundant constraint: Eq a
     • In the type signature for:
            f4 :: (Eq a, Eq b) => a -> b -> Equal a b -> Bool

testsuite/tests/typecheck/should_compile/all.T

@@ -537,4 +537,5 @@ test('T12185', normal, compile, [''])
 test('T12133', normal, compile, [''])
 test('T12381', normal, compile, [''])
 test('T12082', normal, compile, [''])
+test('T10635', normal, compile, [''])
 test('T12170b', normal, compile, [''])

testsuite/tests/warnings/should_compile/PluralS.stderr

@@ -14,12 +14,12 @@ PluralS.hs:17:24: warning: [-Wtype-defaults (in -Wall)]
       In an equation for ‘defaultingNumAndShow’:
           defaultingNumAndShow = show 123
 
-PluralS.hs:23:1: warning: [-Wredundant-constraints (in -Wall)]
+PluralS.hs:23:1: warning: [-Wredundant-constraints]
     • Redundant constraint: Num a
     • In the type signature for:
            redundantNum :: (Num a, Num a) => a
 
-PluralS.hs:26:1: warning: [-Wredundant-constraints (in -Wall)]
+PluralS.hs:26:1: warning: [-Wredundant-constraints]
     • Redundant constraints: (Show a, Num a, Eq a, Eq a)
     • In the type signature for:
            redundantMultiple :: (Num a, Show a, Num a, Eq a, Eq a) => a