Export (~) from Data.Type.Equality (#18862)wip/eqtycon-rn

* Users can define their own (~) type operator
* Haddock can display documentation for the built-in (~)
* New transitional warnings implemented:
    -Wtype-equality-out-of-scope
    -Wtype-equality-requires-operators

Updates the haddock submodule.

43 files changed, 91 insertions, 26 deletions

diff --git a/testsuite/tests/backpack/should_fail/bkpfail23.bkp b/testsuite/tests/backpack/should_fail/bkpfail23.bkp
index 831ce42c72..55e533390c 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail23.bkp
+++ b/testsuite/tests/backpack/should_fail/bkpfail23.bkp
@@ -1,5 +1,5 @@
 {-# LANGUAGE Haskell2010 #-}
-{-# LANGUAGE GADTs, RoleAnnotations #-}
+{-# LANGUAGE GADTs, TypeOperators, RoleAnnotations #-}
 unit p where
     signature H where
         type role F phantom
diff --git a/testsuite/tests/deriving/should_compile/T14933.hs b/testsuite/tests/deriving/should_compile/T14933.hs
index 5ab808365f..854f5f717a 100644
--- a/testsuite/tests/deriving/should_compile/T14933.hs
+++ b/testsuite/tests/deriving/should_compile/T14933.hs
@@ -2,9 +2,12 @@
 {-# LANGUAGE DefaultSignatures #-}
 {-# LANGUAGE DeriveAnyClass    #-}
 {-# LANGUAGE TypeFamilies      #-}
+{-# LANGUAGE TypeOperators     #-}
+
 module T14933 where
 
 import Data.Kind (Type)
+import Data.Type.Equality (type (~))
 
 class Wrapped s where
   type Unwrapped s :: Type
diff --git a/testsuite/tests/ghci/scripts/T12447.script b/testsuite/tests/ghci/scripts/T12447.script
index 826dec0b63..3a30c65905 100644
--- a/testsuite/tests/ghci/scripts/T12447.script
+++ b/testsuite/tests/ghci/scripts/T12447.script
@@ -1,5 +1,5 @@
 :set -XHaskell2010
-:set -XRankNTypes -XConstraintKinds -XTypeApplications
+:set -XRankNTypes -XConstraintKinds -XTypeApplications -XTypeOperators
 
 import Data.Typeable
 
diff --git a/testsuite/tests/ghci/scripts/ghci024.stdout b/testsuite/tests/ghci/scripts/ghci024.stdout
index 20750f5817..db6a7b955e 100644
--- a/testsuite/tests/ghci/scripts/ghci024.stdout
+++ b/testsuite/tests/ghci/scripts/ghci024.stdout
@@ -16,6 +16,7 @@ warning settings:
   -Wsemigroup
   -Wstar-is-type
   -Wcompat-unqualified-imports
+  -Wtype-equality-out-of-scope
 ~~~~~~~~~~ Testing :set -a
 options currently set: none.
 base language is: GHC2021
diff --git a/testsuite/tests/ghci/scripts/ghci024.stdout-mingw32 b/testsuite/tests/ghci/scripts/ghci024.stdout-mingw32
index 1c03e5fab8..a693b73aaf 100644
--- a/testsuite/tests/ghci/scripts/ghci024.stdout-mingw32
+++ b/testsuite/tests/ghci/scripts/ghci024.stdout-mingw32
@@ -15,6 +15,7 @@ warning settings:
   -Wsemigroup
   -Wstar-is-type
   -Wcompat-unqualified-imports
+  -Wtype-equality-out-of-scope
 ~~~~~~~~~~ Testing :set -a
 options currently set: none.
 base language is: GHC2021
diff --git a/testsuite/tests/indexed-types/should_compile/InstEqContext2.hs b/testsuite/tests/indexed-types/should_compile/InstEqContext2.hs
index ea356a44ad..f693837354 100644
--- a/testsuite/tests/indexed-types/should_compile/InstEqContext2.hs
+++ b/testsuite/tests/indexed-types/should_compile/InstEqContext2.hs
@@ -1,6 +1,6 @@
 {-# LANGUAGE Haskell2010 #-}
 {-# OPTIONS_GHC -fno-warn-redundant-constraints #-}
-{-# LANGUAGE TypeFamilies, EmptyDataDecls #-}
+{-# LANGUAGE TypeFamilies, TypeOperators, EmptyDataDecls #-}
 
 module InstEqContext2  where 
 
diff --git a/testsuite/tests/indexed-types/should_compile/T11361.hs b/testsuite/tests/indexed-types/should_compile/T11361.hs
index 7534734790..d2dc75fe8f 100644
--- a/testsuite/tests/indexed-types/should_compile/T11361.hs
+++ b/testsuite/tests/indexed-types/should_compile/T11361.hs
@@ -1,5 +1,6 @@
 {-# LANGUAGE Haskell2010 #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE UndecidableInstances #-}
   -- this is needed because |FamHelper a x| /< |Fam a x|
   -- This file compiled with -dunique-increment=-1 made GHC crash before
diff --git a/testsuite/tests/indexed-types/should_compile/T15122.hs b/testsuite/tests/indexed-types/should_compile/T15122.hs
index 49a3de642d..1730f3a826 100644
--- a/testsuite/tests/indexed-types/should_compile/T15122.hs
+++ b/testsuite/tests/indexed-types/should_compile/T15122.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE Haskell2010 #-}
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE TypeInType #-}
 module T15122 where
 
diff --git a/testsuite/tests/indexed-types/should_compile/T15352.hs b/testsuite/tests/indexed-types/should_compile/T15352.hs
index 25c4640809..0bb4a2bc63 100644
--- a/testsuite/tests/indexed-types/should_compile/T15352.hs
+++ b/testsuite/tests/indexed-types/should_compile/T15352.hs
@@ -2,6 +2,7 @@
 {-# LANGUAGE TypeInType #-} -- or PolyKinds
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
 
 module T15352 where
 
diff --git a/testsuite/tests/parser/should_fail/T12811.stderr b/testsuite/tests/parser/should_fail/T12811.stderr
index 3dbf6bc342..ec4c79bef9 100644
--- a/testsuite/tests/parser/should_fail/T12811.stderr
+++ b/testsuite/tests/parser/should_fail/T12811.stderr
@@ -1,6 +1,6 @@
 
 T12811.hs:5:15: error:
     Illegal operator ‘.’ in type ‘foral a . a’
-      Use TypeOperators to allow operators in types
+    Suggested fix: Perhaps you intended to use TypeOperators
 
 T12811.hs:5:15: error: Not in scope: type constructor or class ‘.’
diff --git a/testsuite/tests/parser/should_fail/T15209.stderr b/testsuite/tests/parser/should_fail/T15209.stderr
index 9d1e151cf2..fe1666c37e 100644
--- a/testsuite/tests/parser/should_fail/T15209.stderr
+++ b/testsuite/tests/parser/should_fail/T15209.stderr
@@ -1,2 +1,4 @@
 
-T15209.hs:6:10: error: Not in scope: type constructor or class ‘~#’
+T15209.hs:6:10: error:
+    Not in scope: type constructor or class ‘~#’
+    Suggested fix: Perhaps use ‘~’ (imported from Prelude)
diff --git a/testsuite/tests/partial-sigs/should_fail/T14584.hs b/testsuite/tests/partial-sigs/should_fail/T14584.hs
index 1615b26205..077c80c490 100644
--- a/testsuite/tests/partial-sigs/should_fail/T14584.hs
+++ b/testsuite/tests/partial-sigs/should_fail/T14584.hs
@@ -25,6 +25,7 @@ module T14584 where
 
 import Data.Monoid
 import Data.Kind
+import Data.Type.Equality
 
 data family Sing (a::k)
 
diff --git a/testsuite/tests/partial-sigs/should_fail/T14584.stderr b/testsuite/tests/partial-sigs/should_fail/T14584.stderr
index 7a47f25967..2cc457e635 100644
--- a/testsuite/tests/partial-sigs/should_fail/T14584.stderr
+++ b/testsuite/tests/partial-sigs/should_fail/T14584.stderr
@@ -1,25 +1,25 @@
 
-T14584.hs:56:50: warning: [-Wdeferred-type-errors (in -Wdefault)]
+T14584.hs:57:50: warning: [-Wdeferred-type-errors (in -Wdefault)]
     • Could not deduce (m1 ~ *)
       from the context: (Action act, Monoid a, Good m1)
-        bound by the instance declaration at T14584.hs:54:10-89
+        bound by the instance declaration at T14584.hs:55:10-89
       ‘m1’ is a rigid type variable bound by
         the instance declaration
-        at T14584.hs:54:10-89
+        at T14584.hs:55:10-89
     • In the type ‘a’
       In the second argument of ‘fromSing’, namely
         ‘(sing @m @a :: Sing _)’
       In the fourth argument of ‘act’, namely
         ‘(fromSing @m (sing @m @a :: Sing _))’
 
-T14584.hs:56:60: warning: [-Wpartial-type-signatures (in -Wdefault)]
+T14584.hs:57:60: warning: [-Wpartial-type-signatures (in -Wdefault)]
     • Found type wildcard ‘_’ standing for ‘a0 :: m’
       Where: ‘a0’ is an ambiguous type variable
              ‘m’ is a rigid type variable bound by
                the instance declaration
-               at T14584.hs:54:10-89
+               at T14584.hs:55:10-89
     • In the first argument of ‘Sing’, namely ‘_’
       In the type ‘Sing _’
       In an expression type signature: Sing _
     • Relevant bindings include
-        monHom :: a -> a (bound at T14584.hs:56:3)
+        monHom :: a -> a (bound at T14584.hs:57:3)
diff --git a/testsuite/tests/perf/compiler/T3064.hs b/testsuite/tests/perf/compiler/T3064.hs
index af3dc2cde7..b0eba0bad2 100644
--- a/testsuite/tests/perf/compiler/T3064.hs
+++ b/testsuite/tests/perf/compiler/T3064.hs
@@ -2,6 +2,7 @@
 {-# OPTIONS_GHC -fno-warn-redundant-constraints #-}
 {-# LANGUAGE Rank2Types, TypeSynonymInstances, FlexibleInstances #-}
 {-# LANGUAGE TypeFamilies, GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE TypeOperators #-}
 
 module T3064 where
 import Control.Applicative
diff --git a/testsuite/tests/polykinds/T11523.hs b/testsuite/tests/polykinds/T11523.hs
index 97551b2208..679d1d13d5 100644
--- a/testsuite/tests/polykinds/T11523.hs
+++ b/testsuite/tests/polykinds/T11523.hs
@@ -19,7 +19,8 @@
 
 module T11523 where
 
-import GHC.Types (Constraint, Type)
+import Data.Kind (Constraint, Type)
+import Data.Type.Equality (type (~))
 import qualified Prelude
 
 type Cat i = i -> i -> Type
diff --git a/testsuite/tests/polykinds/T12055.hs b/testsuite/tests/polykinds/T12055.hs
index de3ad455ea..72c208d77d 100644
--- a/testsuite/tests/polykinds/T12055.hs
+++ b/testsuite/tests/polykinds/T12055.hs
@@ -17,8 +17,8 @@
 
 module T12055 where
 
-import GHC.Base ( Constraint, Type )
-import GHC.Exts ( type (~~) )
+import Data.Kind (Constraint, Type)
+import Data.Type.Equality (type (~), type (~~))
 
 type Cat k = k -> k -> Type
 
diff --git a/testsuite/tests/quantified-constraints/T15359.hs b/testsuite/tests/quantified-constraints/T15359.hs
index 2a58d89c05..ca84c0e8be 100644
--- a/testsuite/tests/quantified-constraints/T15359.hs
+++ b/testsuite/tests/quantified-constraints/T15359.hs
@@ -1,6 +1,6 @@
 {-# LANGUAGE Haskell2010 #-}
 {-# LANGUAGE MultiParamTypeClasses, GADTs, RankNTypes,
-             ConstraintKinds, QuantifiedConstraints #-}
+             ConstraintKinds, QuantifiedConstraints, TypeOperators #-}
 
 module T15359 where
 
diff --git a/testsuite/tests/quantified-constraints/T15359a.hs b/testsuite/tests/quantified-constraints/T15359a.hs
index a5b16acf75..277793b81c 100644
--- a/testsuite/tests/quantified-constraints/T15359a.hs
+++ b/testsuite/tests/quantified-constraints/T15359a.hs
@@ -1,6 +1,6 @@
 {-# LANGUAGE Haskell2010 #-}
 {-# LANGUAGE MultiParamTypeClasses, GADTs, RankNTypes,
-             ConstraintKinds, QuantifiedConstraints,
+             ConstraintKinds, QuantifiedConstraints, TypeOperators,
              UndecidableInstances #-}
 
 module T15359a where
diff --git a/testsuite/tests/rebindable/T19167.hs b/testsuite/tests/rebindable/T19167.hs
index 6f7ebff33d..4e98e815ea 100644
--- a/testsuite/tests/rebindable/T19167.hs
+++ b/testsuite/tests/rebindable/T19167.hs
@@ -6,6 +6,7 @@ module Bug where
 import qualified Prelude as P
 import qualified GHC.Exts as P
 import Data.List.NonEmpty ( NonEmpty )
+import Data.Type.Equality ( type (~) )
 
 fromInteger :: P.Integer -> forall a. P.Num a => a
 fromInteger n = P.fromInteger n
diff --git a/testsuite/tests/rename/should_fail/T15214.hs b/testsuite/tests/rename/should_compile/T15214.hs
index 55f15593be..55f15593be 100644
--- a/testsuite/tests/rename/should_fail/T15214.hs
+++ b/testsuite/tests/rename/should_compile/T15214.hs
diff --git a/testsuite/tests/rename/should_compile/T18862.hs b/testsuite/tests/rename/should_compile/T18862.hs
new file mode 100644
index 0000000000..7356a27ad8
--- /dev/null
+++ b/testsuite/tests/rename/should_compile/T18862.hs
@@ -0,0 +1,12 @@
+{-# LANGUAGE PolyKinds, DataKinds, TypeOperators, TypeFamilies #-}
+
+module T18862 where
+
+import Prelude (Bool)
+import Data.Kind (Constraint)
+import qualified Data.Type.Equality as E
+
+type family (a :: k) ~ (b :: k) :: result_kind
+
+type instance a ~ b = (a E.~ b :: Constraint)
+type instance a ~ b = (a E.== b :: Bool)
diff --git a/testsuite/tests/rename/should_compile/all.T b/testsuite/tests/rename/should_compile/all.T
index 536c5b9013..3a6fdceac3 100644
--- a/testsuite/tests/rename/should_compile/all.T
+++ b/testsuite/tests/rename/should_compile/all.T
@@ -161,6 +161,7 @@ test('T14881', [], multimod_compile, ['T14881', '-W'])
 test('T14487', [], multimod_compile, ['T14487', '-v0'])
 test('T14747', [], multimod_compile, ['T14747', '-v0'])
 test('T15149', [], multimod_compile, ['T15149', '-v0'])
+test('T15214', normal, compile, [''])
 test('T13064', normal, compile, [''])
 test('T15994', [], makefile_test, ['T15994'])
 test('T15798a', normal, compile, [''])
@@ -184,3 +185,4 @@ test('T20609a', normal, compile, [''])
 test('T20609b', normal, compile, [''])
 test('T20609c', normal, compile, [''])
 test('T20609d', normal, compile, [''])
+test('T18862', normal, compile, [''])
diff --git a/testsuite/tests/rename/should_fail/T15214.stderr b/testsuite/tests/rename/should_fail/T15214.stderr
deleted file mode 100644
index 399438adb5..0000000000
--- a/testsuite/tests/rename/should_fail/T15214.stderr
+++ /dev/null
@@ -1,2 +0,0 @@
-
-T15214.hs:4:1: error: Illegal binding of built-in syntax: ~
diff --git a/testsuite/tests/rename/should_fail/all.T b/testsuite/tests/rename/should_fail/all.T
index 4ce00de399..5e62e28847 100644
--- a/testsuite/tests/rename/should_fail/all.T
+++ b/testsuite/tests/rename/should_fail/all.T
@@ -137,7 +137,6 @@ test('T14307', normal, compile_fail, [''])
 test('T14591', normal, compile_fail, [''])
 test('T14907a', normal, compile_fail, [''])
 test('T14907b', normal, compile_fail, [''])
-test('T15214', normal, compile_fail, [''])
 test('T15539', normal, compile_fail, [''])
 test('T15487', normal, multimod_compile_fail, ['T15487','-v0'])
 test('T15659', normal, compile_fail, [''])
diff --git a/testsuite/tests/roles/should_compile/Roles3.hs b/testsuite/tests/roles/should_compile/Roles3.hs
index b71d9cf2ec..b79129162e 100644
--- a/testsuite/tests/roles/should_compile/Roles3.hs
+++ b/testsuite/tests/roles/should_compile/Roles3.hs
@@ -1,5 +1,6 @@
 {-# LANGUAGE Haskell2010 #-}
 {-# LANGUAGE TypeFamilies, MultiParamTypeClasses #-}
+{-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE AllowAmbiguousTypes #-}  -- meth3, meth4 are ambiguous
 
 module Roles3 where
@@ -20,4 +21,4 @@ class C4 a b where
   meth4 :: a -> F4 b -> F4 b
 
 type Syn1 a = F4 a
-type Syn2 a = [a]
\ No newline at end of file
+type Syn2 a = [a]
diff --git a/testsuite/tests/tcplugins/TcPlugin_Rewrite.hs b/testsuite/tests/tcplugins/TcPlugin_Rewrite.hs
index 6df19b7b62..5cacd28618 100644
--- a/testsuite/tests/tcplugins/TcPlugin_Rewrite.hs
+++ b/testsuite/tests/tcplugins/TcPlugin_Rewrite.hs
@@ -2,13 +2,16 @@
 {-# OPTIONS_GHC -fplugin RewritePlugin #-}
 
 {-# LANGUAGE Haskell2010 #-}
-{-# LANGUAGE DataKinds, ScopedTypeVariables, TypeFamilies #-}
+{-# LANGUAGE DataKinds, ScopedTypeVariables, TypeFamilies, TypeOperators #-}
 
 module TcPlugin_Rewrite where
 
 import Data.Kind
   ( Type )
 
+import Data.Type.Equality
+  ( type (~) )
+
 import Definitions
   ( Add, Nat(..) )
 
diff --git a/testsuite/tests/typecheck/should_compile/LocalGivenEqs.hs b/testsuite/tests/typecheck/should_compile/LocalGivenEqs.hs
index fd37ede0db..43063d20aa 100644
--- a/testsuite/tests/typecheck/should_compile/LocalGivenEqs.hs
+++ b/testsuite/tests/typecheck/should_compile/LocalGivenEqs.hs
@@ -1,5 +1,5 @@
 {-# LANGUAGE Haskell2010 #-}
-{-# LANGUAGE RankNTypes, TypeFamilies, FlexibleInstances #-}
+{-# LANGUAGE RankNTypes, TypeFamilies, TypeOperators, FlexibleInstances #-}
 {-# OPTIONS_GHC -Wno-missing-methods -Wno-unused-matches #-}
 
 module LocalGivenEqs where
diff --git a/testsuite/tests/typecheck/should_compile/T11524.hs b/testsuite/tests/typecheck/should_compile/T11524.hs
index 0856afe50b..a8c40c88c6 100644
--- a/testsuite/tests/typecheck/should_compile/T11524.hs
+++ b/testsuite/tests/typecheck/should_compile/T11524.hs
@@ -3,6 +3,7 @@
 {-# LANGUAGE PolyKinds #-}
 {-# LANGUAGE ExplicitForAll #-}
 {-# LANGUAGE PatternSynonyms #-}
+{-# LANGUAGE TypeOperators #-}
 
 module T11524 where
 
diff --git a/testsuite/tests/typecheck/should_compile/T12919.hs b/testsuite/tests/typecheck/should_compile/T12919.hs
index 29eb9dc469..825b7f65c1 100644
--- a/testsuite/tests/typecheck/should_compile/T12919.hs
+++ b/testsuite/tests/typecheck/should_compile/T12919.hs
@@ -1,5 +1,5 @@
 {-# LANGUAGE Haskell2010 #-}
-{-# LANGUAGE DataKinds, PolyKinds, TypeFamilies, GADTs, ConstraintKinds #-}
+{-# LANGUAGE DataKinds, PolyKinds, TypeFamilies, GADTs, ConstraintKinds, TypeOperators #-}
 
 module T12919 where
 
diff --git a/testsuite/tests/typecheck/should_compile/T13651a.hs b/testsuite/tests/typecheck/should_compile/T13651a.hs
index f08407b738..80cda684e1 100644
--- a/testsuite/tests/typecheck/should_compile/T13651a.hs
+++ b/testsuite/tests/typecheck/should_compile/T13651a.hs
@@ -1,5 +1,5 @@
 {-# LANGUAGE Haskell2010 #-}
-{-# LANGUAGE TypeFamilies, TypeFamilyDependencies #-}
+{-# LANGUAGE TypeFamilies, TypeFamilyDependencies, TypeOperators #-}
 module T13651 where
 
 type family F r s = f | f -> r s
diff --git a/testsuite/tests/typecheck/should_compile/T17202.hs b/testsuite/tests/typecheck/should_compile/T17202.hs
index cda5783ec9..ee639b9cc0 100644
--- a/testsuite/tests/typecheck/should_compile/T17202.hs
+++ b/testsuite/tests/typecheck/should_compile/T17202.hs
@@ -2,6 +2,7 @@
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE QuantifiedConstraints #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE ConstraintKinds #-}
 
 module T17202 where
diff --git a/testsuite/tests/typecheck/should_compile/T17562b.hs b/testsuite/tests/typecheck/should_compile/T17562b.hs
index b73e6b1bc7..44eb03ce97 100644
--- a/testsuite/tests/typecheck/should_compile/T17562b.hs
+++ b/testsuite/tests/typecheck/should_compile/T17562b.hs
@@ -1,5 +1,5 @@
 {-# LANGUAGE Haskell2010 #-}
-{-# LANGUAGE QuantifiedConstraints, MultiParamTypeClasses, TypeFamilies #-}
+{-# LANGUAGE QuantifiedConstraints, MultiParamTypeClasses, TypeFamilies, TypeOperators #-}
 -- NB: No PolyKinds
 
 module T17562b where
diff --git a/testsuite/tests/typecheck/should_compile/T17567StupidThetaB.hs b/testsuite/tests/typecheck/should_compile/T17567StupidThetaB.hs
index d555511004..1d397f9861 100644
--- a/testsuite/tests/typecheck/should_compile/T17567StupidThetaB.hs
+++ b/testsuite/tests/typecheck/should_compile/T17567StupidThetaB.hs
@@ -1,5 +1,5 @@
 {-# LANGUAGE Haskell2010 #-}
-{-# LANGUAGE QuantifiedConstraints, DatatypeContexts, TypeFamilies #-}
+{-# LANGUAGE QuantifiedConstraints, DatatypeContexts, TypeFamilies, TypeOperators #-}
 -- NB: -XNoPolyKinds, to get defaulting.
 
 module T17567StupidThetaB where
diff --git a/testsuite/tests/typecheck/should_compile/T21010A.hs b/testsuite/tests/typecheck/should_compile/T21010A.hs
index 234e1c72d7..5e8ef6fe96 100644
--- a/testsuite/tests/typecheck/should_compile/T21010A.hs
+++ b/testsuite/tests/typecheck/should_compile/T21010A.hs
@@ -2,6 +2,7 @@
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE KindSignatures #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
 
 module T21010A ( WrapMono, Constrained(..), withMonoCoercible ) where
 import T21010B ( WrapMono(..), withMonoCoercible )
diff --git a/testsuite/tests/typecheck/should_compile/tc250.hs b/testsuite/tests/typecheck/should_compile/tc250.hs
index 445d702b69..1076fc5f49 100644
--- a/testsuite/tests/typecheck/should_compile/tc250.hs
+++ b/testsuite/tests/typecheck/should_compile/tc250.hs
@@ -1,5 +1,6 @@
 {-# LANGUAGE Haskell2010 #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
 module ShouldCompile where
 
 import Data.Kind (Type)
diff --git a/testsuite/tests/typecheck/should_compile/tc251.hs b/testsuite/tests/typecheck/should_compile/tc251.hs
index e9315263af..1c69c1d9ac 100644
--- a/testsuite/tests/typecheck/should_compile/tc251.hs
+++ b/testsuite/tests/typecheck/should_compile/tc251.hs
@@ -1,5 +1,6 @@
 {-# LANGUAGE Haskell2010 #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
 module ShouldCompile where
 
 import Tc251_Help
diff --git a/testsuite/tests/typecheck/should_compile/tc252.hs b/testsuite/tests/typecheck/should_compile/tc252.hs
index 1ad9c7c514..6ff23e75e4 100644
--- a/testsuite/tests/typecheck/should_compile/tc252.hs
+++ b/testsuite/tests/typecheck/should_compile/tc252.hs
@@ -1,5 +1,6 @@
 {-# LANGUAGE Haskell2010 #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
 module ShouldCompile where
 
 import Data.Kind (Type)
diff --git a/testsuite/tests/typecheck/should_compile/tc253.hs b/testsuite/tests/typecheck/should_compile/tc253.hs
index 7553b756a8..5c032daa01 100644
--- a/testsuite/tests/typecheck/should_compile/tc253.hs
+++ b/testsuite/tests/typecheck/should_compile/tc253.hs
@@ -1,5 +1,6 @@
 {-# LANGUAGE Haskell2010 #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE UndecidableInstances #-}
   -- this is needed because |FamHelper a x| /< |Fam a x|
 module ShouldCompile where
diff --git a/testsuite/tests/warnings/should_compile/T18862a.hs b/testsuite/tests/warnings/should_compile/T18862a.hs
new file mode 100644
index 0000000000..532cd83e83
--- /dev/null
+++ b/testsuite/tests/warnings/should_compile/T18862a.hs
@@ -0,0 +1,6 @@
+{-# LANGUAGE NoTypeOperators #-}
+
+module T18862a where
+
+f :: (a ~ b) => a -> b
+f = id
diff --git a/testsuite/tests/warnings/should_compile/T18862a.stderr b/testsuite/tests/warnings/should_compile/T18862a.stderr
new file mode 100644
index 0000000000..e2a6fe3f3c
--- /dev/null
+++ b/testsuite/tests/warnings/should_compile/T18862a.stderr
@@ -0,0 +1,5 @@
+
+T18862a.hs:5:9: warning: [-Wtype-equality-requires-operators (in -Wdefault)]
+    The use of ‘~’ without TypeOperators
+    will become an error in a future GHC release.
+    Suggested fix: Perhaps you intended to use TypeOperators
diff --git a/testsuite/tests/warnings/should_compile/T18862b.hs b/testsuite/tests/warnings/should_compile/T18862b.hs
new file mode 100644
index 0000000000..7259547b7c
--- /dev/null
+++ b/testsuite/tests/warnings/should_compile/T18862b.hs
@@ -0,0 +1,8 @@
+{-# OPTIONS -Wcompat -Wno-error=type-equality-out-of-scope #-}
+
+module T18862b where
+
+import Prelude (id)
+
+f :: (a ~ b) => a -> b
+f = id
diff --git a/testsuite/tests/warnings/should_compile/T18862b.stderr b/testsuite/tests/warnings/should_compile/T18862b.stderr
new file mode 100644
index 0000000000..ac959be7d8
--- /dev/null
+++ b/testsuite/tests/warnings/should_compile/T18862b.stderr
@@ -0,0 +1,8 @@
+
+T18862b.hs:7:9: warning: [-Wtype-equality-out-of-scope (in -Wcompat)]
+    • The ‘~’ operator is out of scope.
+      Assuming it to stand for an equality constraint.
+    • NB: ‘~’ used to be built-in syntax but now is a regular type operator
+          exported from Data.Type.Equality and Prelude.
+      If you are using a custom Prelude, consider re-exporting it.
+    • This will become an error in a future GHC release.
diff --git a/testsuite/tests/warnings/should_compile/all.T b/testsuite/tests/warnings/should_compile/all.T
index 2934db7ad4..3c514245fe 100644
--- a/testsuite/tests/warnings/should_compile/all.T
+++ b/testsuite/tests/warnings/should_compile/all.T
@@ -47,3 +47,5 @@ test('T19564d', normal, compile, [''])
 test('T19296', normal, compile, ['-fdiagnostics-show-caret -Wredundant-constraints -dsuppress-uniques'])
 test('DodgyExports01', normal, compile, ['-Wdodgy-exports'])
 test('DerivingTypeable', normal, compile, ['-Wderiving-typeable'])
+test('T18862a', normal, compile, [''])
+test('T18862b', normal, compile, [''])