From cf81c96be84307737a9debd70dcdb263eea55b13 Mon Sep 17 00:00:00 2001
From: Junji Hashimoto <junji.hashimoto@gmail.com>
Date: Thu, 22 Jul 2021 16:07:25 +0900
Subject: [PATCH 01/14] Update GHC-api's paths

---
 src/TypeLevel/Rewrite.hs                       | 18 +++++++++---------
 src/TypeLevel/Rewrite/Internal/ApplyRules.hs   |  2 +-
 .../Rewrite/Internal/DecomposedConstraint.hs   |  4 ++--
 src/TypeLevel/Rewrite/Internal/Lookup.hs       | 12 ++++++------
 src/TypeLevel/Rewrite/Internal/PrettyPrint.hs  |  6 +++---
 src/TypeLevel/Rewrite/Internal/TypeEq.hs       |  2 +-
 src/TypeLevel/Rewrite/Internal/TypeNode.hs     |  4 ++--
 src/TypeLevel/Rewrite/Internal/TypeRule.hs     |  6 +++---
 src/TypeLevel/Rewrite/Internal/TypeTemplate.hs |  2 +-
 src/TypeLevel/Rewrite/Internal/TypeTerm.hs     |  2 +-
 typelevel-rewrite-rules.cabal                  |  2 +-
 11 files changed, 30 insertions(+), 30 deletions(-)

diff --git a/src/TypeLevel/Rewrite.hs b/src/TypeLevel/Rewrite.hs
index 0738291..88875b2 100644
--- a/src/TypeLevel/Rewrite.hs
+++ b/src/TypeLevel/Rewrite.hs
@@ -8,15 +8,15 @@ import Data.Foldable
 import Data.Traversable
 
 -- GHC API
-import Coercion (Role(Representational), mkUnivCo)
-import Constraint (CtEvidence(ctev_loc), Ct, ctEvExpr, ctLoc, mkNonCanonical)
-import GhcPlugins (PredType, SDoc, eqType, fsep, ppr)
-import Plugins (Plugin(pluginRecompile, tcPlugin), CommandLineOption, defaultPlugin, purePlugin)
-import TcEvidence (EvExpr, EvTerm, evCast)
-import TcPluginM (newWanted)
-import TcRnTypes
-import TyCoRep (UnivCoProvenance(PluginProv))
-import TyCon (synTyConDefn_maybe)
+import GHC.Core.Coercion (Role(Representational), mkUnivCo)
+import GHC.Tc.Types.Constraint (CtEvidence(ctev_loc), Ct, ctEvExpr, ctLoc, mkNonCanonical)
+import GHC.Plugins (PredType, SDoc, eqType, fsep, ppr)
+import GHC.Plugins (Plugin(pluginRecompile, tcPlugin), CommandLineOption, defaultPlugin, purePlugin)
+import GHC.Tc.Types.Evidence (EvExpr, EvTerm, evCast)
+import GHC.Tc.Plugin (newWanted)
+import GHC.Core.TyCo.Rep (UnivCoProvenance(PluginProv))
+import GHC.Plugins (synTyConDefn_maybe)
+import GHC.Tc.Types (TcPluginResult(..), TcPluginM, ErrCtxt, pushErrCtxtSameOrigin, TcPlugin(..))
 
 import TypeLevel.Rewrite.Internal.ApplyRules
 import TypeLevel.Rewrite.Internal.DecomposedConstraint
diff --git a/src/TypeLevel/Rewrite/Internal/ApplyRules.hs b/src/TypeLevel/Rewrite/Internal/ApplyRules.hs
index 3587918..8c40150 100644
--- a/src/TypeLevel/Rewrite/Internal/ApplyRules.hs
+++ b/src/TypeLevel/Rewrite/Internal/ApplyRules.hs
@@ -13,7 +13,7 @@ import Data.Traversable
 import qualified Data.Map as Map
 
 -- GHC API
-import Type (TyVar)
+import GHC.Plugins (TyVar)
 
 -- term-rewriting API
 import Data.Rewriting.Rule (Rule(..))
diff --git a/src/TypeLevel/Rewrite/Internal/DecomposedConstraint.hs b/src/TypeLevel/Rewrite/Internal/DecomposedConstraint.hs
index 87d47af..1b9c66e 100644
--- a/src/TypeLevel/Rewrite/Internal/DecomposedConstraint.hs
+++ b/src/TypeLevel/Rewrite/Internal/DecomposedConstraint.hs
@@ -5,8 +5,8 @@ import Control.Applicative
 
 -- GHC API
 import GHC (Class, Type)
-import Constraint (Ct, ctEvPred, ctEvidence)
-import Predicate (EqRel(NomEq), Pred(ClassPred, EqPred), classifyPredType, mkClassPred, mkPrimEqPred)
+import GHC.Tc.Types.Constraint (Ct, ctEvPred, ctEvidence)
+import GHC.Core.Predicate (EqRel(NomEq), Pred(ClassPred, EqPred), classifyPredType, mkClassPred, mkPrimEqPred)
 
 
 data DecomposedConstraint a
diff --git a/src/TypeLevel/Rewrite/Internal/Lookup.hs b/src/TypeLevel/Rewrite/Internal/Lookup.hs
index dbb8323..758efbf 100644
--- a/src/TypeLevel/Rewrite/Internal/Lookup.hs
+++ b/src/TypeLevel/Rewrite/Internal/Lookup.hs
@@ -5,16 +5,16 @@ import Control.Arrow ((***), first)
 import Data.Tuple (swap)
 
 -- GHC API
-import Finder (cannotFindModule)
+import GHC.Driver.Finder (cannotFindModule)
 import GHC (DataCon, TyCon, dataConTyCon)
-import Module (Module, ModuleName, mkModuleName)
-import OccName (mkDataOcc, mkTcOcc)
-import Panic (panicDoc)
-import TcPluginM
+import GHC (Module, ModuleName, mkModuleName)
+import GHC.Plugins (mkDataOcc, mkTcOcc)
+import GHC.Utils.Panic (panicDoc)
+import GHC.Tc.Plugin
   ( FindResult(Found), TcPluginM, findImportedModule, lookupOrig, tcLookupDataCon, tcLookupTyCon
   , unsafeTcPluginTcM
   )
-import TcSMonad (getDynFlags)
+import GHC.Tc.Solver.Monad (getDynFlags)
 
 
 lookupModule
diff --git a/src/TypeLevel/Rewrite/Internal/PrettyPrint.hs b/src/TypeLevel/Rewrite/Internal/PrettyPrint.hs
index afc19ed..787e025 100644
--- a/src/TypeLevel/Rewrite/Internal/PrettyPrint.hs
+++ b/src/TypeLevel/Rewrite/Internal/PrettyPrint.hs
@@ -4,9 +4,9 @@ module TypeLevel.Rewrite.Internal.PrettyPrint where
 import Data.List (intercalate)
 
 -- GHC API
-import Outputable (ppr, showSDocUnsafe)
-import TyCon (TyCon)
-import Type (TyVar, Type)
+import GHC.Utils.Outputable (ppr, showSDocUnsafe)
+import GHC.Plugins (TyCon)
+import GHC.Plugins (TyVar, Type)
 
 -- term-rewriting API
 import Data.Rewriting.Rule (Rule(..))
diff --git a/src/TypeLevel/Rewrite/Internal/TypeEq.hs b/src/TypeLevel/Rewrite/Internal/TypeEq.hs
index 30272a6..2af9472 100644
--- a/src/TypeLevel/Rewrite/Internal/TypeEq.hs
+++ b/src/TypeLevel/Rewrite/Internal/TypeEq.hs
@@ -2,7 +2,7 @@ module TypeLevel.Rewrite.Internal.TypeEq where
 
 import Data.Function
 
-import GhcPlugins (Type, eqType)
+import GHC.Plugins (Type, eqType)
 
 
 -- | A newtype around 'Type' which has an 'Eq' instance.
diff --git a/src/TypeLevel/Rewrite/Internal/TypeNode.hs b/src/TypeLevel/Rewrite/Internal/TypeNode.hs
index 97e14ae..53c1c60 100644
--- a/src/TypeLevel/Rewrite/Internal/TypeNode.hs
+++ b/src/TypeLevel/Rewrite/Internal/TypeNode.hs
@@ -2,8 +2,8 @@
 module TypeLevel.Rewrite.Internal.TypeNode where
 
 -- GHC API
-import TyCon (TyCon)
-import Type (Type, isNumLitTy, isStrLitTy, mkTyConApp, splitTyConApp_maybe)
+import GHC (TyCon)
+import GHC.Plugins (Type, isNumLitTy, isStrLitTy, mkTyConApp, splitTyConApp_maybe)
 
 import TypeLevel.Rewrite.Internal.TypeEq
 
diff --git a/src/TypeLevel/Rewrite/Internal/TypeRule.hs b/src/TypeLevel/Rewrite/Internal/TypeRule.hs
index c44b46d..7021d42 100644
--- a/src/TypeLevel/Rewrite/Internal/TypeRule.hs
+++ b/src/TypeLevel/Rewrite/Internal/TypeRule.hs
@@ -3,9 +3,9 @@
 module TypeLevel.Rewrite.Internal.TypeRule where
 
 -- GHC API
-import Name (getOccString)
-import Predicate (mkPrimEqPred)
-import Type (TyVar, Type, mkTyVarTy)
+import GHC.Plugins (getOccString)
+import GHC.Core.Predicate (mkPrimEqPred)
+import GHC.Plugins (TyVar, Type, mkTyVarTy)
 
 -- term-rewriting API
 import Data.Rewriting.Rule (Rule(..))
diff --git a/src/TypeLevel/Rewrite/Internal/TypeTemplate.hs b/src/TypeLevel/Rewrite/Internal/TypeTemplate.hs
index bd870f2..831f8bb 100644
--- a/src/TypeLevel/Rewrite/Internal/TypeTemplate.hs
+++ b/src/TypeLevel/Rewrite/Internal/TypeTemplate.hs
@@ -2,7 +2,7 @@
 module TypeLevel.Rewrite.Internal.TypeTemplate where
 
 -- GHC API
-import Type (TyVar, Type, getTyVar_maybe)
+import GHC.Plugins (TyVar, Type, getTyVar_maybe)
 
 -- term-rewriting API
 import Data.Rewriting.Term (Term(Fun, Var))
diff --git a/src/TypeLevel/Rewrite/Internal/TypeTerm.hs b/src/TypeLevel/Rewrite/Internal/TypeTerm.hs
index 28ef65a..68309bc 100644
--- a/src/TypeLevel/Rewrite/Internal/TypeTerm.hs
+++ b/src/TypeLevel/Rewrite/Internal/TypeTerm.hs
@@ -2,7 +2,7 @@
 module TypeLevel.Rewrite.Internal.TypeTerm where
 
 -- GHC API
-import Type (Type, mkTyConApp)
+import GHC.Plugins (Type, mkTyConApp)
 
 -- term-rewriting API
 import Data.Rewriting.Term (Term(Fun, Var))
diff --git a/typelevel-rewrite-rules.cabal b/typelevel-rewrite-rules.cabal
index c33115e..df8a73d 100644
--- a/typelevel-rewrite-rules.cabal
+++ b/typelevel-rewrite-rules.cabal
@@ -48,7 +48,7 @@ library
   build-depends:
       base >=4.12 && <5
     , containers >=0.6.2.1
-    , ghc >=8.10.2 && <9.0
+    , ghc >=8.10.2 && <= 9.1
     , ghc-prim >=0.5.3
     , term-rewriting >=0.3.0.1
     , transformers >=0.5.6.2

From 26f8fd156f1d4f5bf22c0ef03ad904e01be98b55 Mon Sep 17 00:00:00 2001
From: Junji Hashimoto <junji.hashimoto@gmail.com>
Date: Thu, 22 Jul 2021 16:12:30 +0900
Subject: [PATCH 02/14] Add AllowAmbiguousTypes for test

---
 test/should-compile/GHC/TypeLits/Test.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/should-compile/GHC/TypeLits/Test.hs b/test/should-compile/GHC/TypeLits/Test.hs
index a228cce..da3aa55 100644
--- a/test/should-compile/GHC/TypeLits/Test.hs
+++ b/test/should-compile/GHC/TypeLits/Test.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE DataKinds, RankNTypes, TypeFamilies, TypeOperators #-}
+{-# LANGUAGE DataKinds, RankNTypes, TypeFamilies, TypeOperators, AllowAmbiguousTypes #-}
 {-# OPTIONS_GHC -fplugin TypeLevel.Rewrite
                 -fplugin-opt=TypeLevel.Rewrite:GHC.TypeLits.RewriteRules.NatRule
                 -fplugin-opt=TypeLevel.Rewrite:GHC.TypeLits.RewriteRules.SymbolRule #-}

From f3282bd37b30fd32b85ab4a2f6bc7d89b666a006 Mon Sep 17 00:00:00 2001
From: Junji Hashimoto <junji.hashimoto@gmail.com>
Date: Fri, 23 Jul 2021 02:33:50 +0900
Subject: [PATCH 03/14] Add CPP to support both ghc-8.10 and ghc-9

---
 package.yaml                                         |  3 ++-
 src/TypeLevel/Rewrite.hs                             | 12 ++++++++++++
 src/TypeLevel/Rewrite/Internal/ApplyRules.hs         |  4 ++++
 .../Rewrite/Internal/DecomposedConstraint.hs         |  5 +++++
 src/TypeLevel/Rewrite/Internal/Lookup.hs             | 12 ++++++++++--
 src/TypeLevel/Rewrite/Internal/PrettyPrint.hs        |  6 ++++++
 src/TypeLevel/Rewrite/Internal/TypeEq.hs             |  4 ++++
 src/TypeLevel/Rewrite/Internal/TypeNode.hs           |  5 +++++
 src/TypeLevel/Rewrite/Internal/TypeRule.hs           |  6 ++++++
 src/TypeLevel/Rewrite/Internal/TypeTemplate.hs       |  4 ++++
 src/TypeLevel/Rewrite/Internal/TypeTerm.hs           |  4 ++++
 typelevel-rewrite-rules.cabal                        |  1 +
 12 files changed, 63 insertions(+), 3 deletions(-)

diff --git a/package.yaml b/package.yaml
index 9f05ea6..8a36653 100644
--- a/package.yaml
+++ b/package.yaml
@@ -25,10 +25,11 @@ dependencies:
 library:
   source-dirs:      src
   dependencies:
-    - ghc >= 8.10.2 && < 9.0
+    - ghc >= 8.10.2 && <= 9.1
     - containers >= 0.6.2.1
     - term-rewriting >= 0.3.0.1
     - transformers >= 0.5.6.2
+  default-extensions:  CPP
 
 tests:
   should-compile:
diff --git a/src/TypeLevel/Rewrite.hs b/src/TypeLevel/Rewrite.hs
index 88875b2..5d1ef6a 100644
--- a/src/TypeLevel/Rewrite.hs
+++ b/src/TypeLevel/Rewrite.hs
@@ -8,6 +8,7 @@ import Data.Foldable
 import Data.Traversable
 
 -- GHC API
+#if MIN_VERSION_ghc(9,0,0)
 import GHC.Core.Coercion (Role(Representational), mkUnivCo)
 import GHC.Tc.Types.Constraint (CtEvidence(ctev_loc), Ct, ctEvExpr, ctLoc, mkNonCanonical)
 import GHC.Plugins (PredType, SDoc, eqType, fsep, ppr)
@@ -17,6 +18,17 @@ import GHC.Tc.Plugin (newWanted)
 import GHC.Core.TyCo.Rep (UnivCoProvenance(PluginProv))
 import GHC.Plugins (synTyConDefn_maybe)
 import GHC.Tc.Types (TcPluginResult(..), TcPluginM, ErrCtxt, pushErrCtxtSameOrigin, TcPlugin(..))
+#else
+import Coercion (Role(Representational), mkUnivCo)
+import Constraint (CtEvidence(ctev_loc), Ct, ctEvExpr, ctLoc, mkNonCanonical)
+import GhcPlugins (PredType, SDoc, eqType, fsep, ppr)
+import Plugins (Plugin(pluginRecompile, tcPlugin), CommandLineOption, defaultPlugin, purePlugin)
+import TcEvidence (EvExpr, EvTerm, evCast)
+import TcPluginM (newWanted)
+import TcRnTypes
+import TyCoRep (UnivCoProvenance(PluginProv))
+import TyCon (synTyConDefn_maybe)
+#endif
 
 import TypeLevel.Rewrite.Internal.ApplyRules
 import TypeLevel.Rewrite.Internal.DecomposedConstraint
diff --git a/src/TypeLevel/Rewrite/Internal/ApplyRules.hs b/src/TypeLevel/Rewrite/Internal/ApplyRules.hs
index 8c40150..1fbbfca 100644
--- a/src/TypeLevel/Rewrite/Internal/ApplyRules.hs
+++ b/src/TypeLevel/Rewrite/Internal/ApplyRules.hs
@@ -13,7 +13,11 @@ import Data.Traversable
 import qualified Data.Map as Map
 
 -- GHC API
+#if MIN_VERSION_ghc(9,0,0)
 import GHC.Plugins (TyVar)
+#else
+import Type (TyVar)
+#endif
 
 -- term-rewriting API
 import Data.Rewriting.Rule (Rule(..))
diff --git a/src/TypeLevel/Rewrite/Internal/DecomposedConstraint.hs b/src/TypeLevel/Rewrite/Internal/DecomposedConstraint.hs
index 1b9c66e..8226dbb 100644
--- a/src/TypeLevel/Rewrite/Internal/DecomposedConstraint.hs
+++ b/src/TypeLevel/Rewrite/Internal/DecomposedConstraint.hs
@@ -5,8 +5,13 @@ import Control.Applicative
 
 -- GHC API
 import GHC (Class, Type)
+#if MIN_VERSION_ghc(9,0,0)
 import GHC.Tc.Types.Constraint (Ct, ctEvPred, ctEvidence)
 import GHC.Core.Predicate (EqRel(NomEq), Pred(ClassPred, EqPred), classifyPredType, mkClassPred, mkPrimEqPred)
+#else
+import Constraint (Ct, ctEvPred, ctEvidence)
+import Predicate (EqRel(NomEq), Pred(ClassPred, EqPred), classifyPredType, mkClassPred, mkPrimEqPred)
+#endif
 
 
 data DecomposedConstraint a
diff --git a/src/TypeLevel/Rewrite/Internal/Lookup.hs b/src/TypeLevel/Rewrite/Internal/Lookup.hs
index 758efbf..62a1d32 100644
--- a/src/TypeLevel/Rewrite/Internal/Lookup.hs
+++ b/src/TypeLevel/Rewrite/Internal/Lookup.hs
@@ -5,8 +5,9 @@ import Control.Arrow ((***), first)
 import Data.Tuple (swap)
 
 -- GHC API
-import GHC.Driver.Finder (cannotFindModule)
 import GHC (DataCon, TyCon, dataConTyCon)
+#if MIN_VERSION_ghc(9,0,0)
+import GHC.Driver.Finder (cannotFindModule)
 import GHC (Module, ModuleName, mkModuleName)
 import GHC.Plugins (mkDataOcc, mkTcOcc)
 import GHC.Utils.Panic (panicDoc)
@@ -15,7 +16,14 @@ import GHC.Tc.Plugin
   , unsafeTcPluginTcM
   )
 import GHC.Tc.Solver.Monad (getDynFlags)
-
+#else
+import Finder (cannotFindModule)
+import Module (Module, ModuleName, mkModuleName)
+import OccName (mkDataOcc, mkTcOcc)
+import Panic (panicDoc)
+import TcPluginM
+import TcSMonad (getDynFlags)
+#endif
 
 lookupModule
   :: String  -- ^ module name
diff --git a/src/TypeLevel/Rewrite/Internal/PrettyPrint.hs b/src/TypeLevel/Rewrite/Internal/PrettyPrint.hs
index 787e025..4af808e 100644
--- a/src/TypeLevel/Rewrite/Internal/PrettyPrint.hs
+++ b/src/TypeLevel/Rewrite/Internal/PrettyPrint.hs
@@ -4,9 +4,15 @@ module TypeLevel.Rewrite.Internal.PrettyPrint where
 import Data.List (intercalate)
 
 -- GHC API
+#if MIN_VERSION_ghc(9,0,0)
 import GHC.Utils.Outputable (ppr, showSDocUnsafe)
 import GHC.Plugins (TyCon)
 import GHC.Plugins (TyVar, Type)
+#else
+import Outputable (ppr, showSDocUnsafe)
+import TyCon (TyCon)
+import Type (TyVar, Type)
+#endif
 
 -- term-rewriting API
 import Data.Rewriting.Rule (Rule(..))
diff --git a/src/TypeLevel/Rewrite/Internal/TypeEq.hs b/src/TypeLevel/Rewrite/Internal/TypeEq.hs
index 2af9472..53d2df5 100644
--- a/src/TypeLevel/Rewrite/Internal/TypeEq.hs
+++ b/src/TypeLevel/Rewrite/Internal/TypeEq.hs
@@ -2,7 +2,11 @@ module TypeLevel.Rewrite.Internal.TypeEq where
 
 import Data.Function
 
+#if MIN_VERSION_ghc(9,0,0)
 import GHC.Plugins (Type, eqType)
+#else
+import GhcPlugins (Type, eqType)
+#endif
 
 
 -- | A newtype around 'Type' which has an 'Eq' instance.
diff --git a/src/TypeLevel/Rewrite/Internal/TypeNode.hs b/src/TypeLevel/Rewrite/Internal/TypeNode.hs
index 53c1c60..31f32e6 100644
--- a/src/TypeLevel/Rewrite/Internal/TypeNode.hs
+++ b/src/TypeLevel/Rewrite/Internal/TypeNode.hs
@@ -2,8 +2,13 @@
 module TypeLevel.Rewrite.Internal.TypeNode where
 
 -- GHC API
+#if MIN_VERSION_ghc(9,0,0)
 import GHC (TyCon)
 import GHC.Plugins (Type, isNumLitTy, isStrLitTy, mkTyConApp, splitTyConApp_maybe)
+#else
+import TyCon (TyCon)
+import Type (Type, isNumLitTy, isStrLitTy, mkTyConApp, splitTyConApp_maybe)
+#endif
 
 import TypeLevel.Rewrite.Internal.TypeEq
 
diff --git a/src/TypeLevel/Rewrite/Internal/TypeRule.hs b/src/TypeLevel/Rewrite/Internal/TypeRule.hs
index 7021d42..9aeb5dd 100644
--- a/src/TypeLevel/Rewrite/Internal/TypeRule.hs
+++ b/src/TypeLevel/Rewrite/Internal/TypeRule.hs
@@ -3,9 +3,15 @@
 module TypeLevel.Rewrite.Internal.TypeRule where
 
 -- GHC API
+#if MIN_VERSION_ghc(9,0,0)
 import GHC.Plugins (getOccString)
 import GHC.Core.Predicate (mkPrimEqPred)
 import GHC.Plugins (TyVar, Type, mkTyVarTy)
+#else
+import Name (getOccString)
+import Predicate (mkPrimEqPred)
+import Type (TyVar, Type, mkTyVarTy)
+#endif
 
 -- term-rewriting API
 import Data.Rewriting.Rule (Rule(..))
diff --git a/src/TypeLevel/Rewrite/Internal/TypeTemplate.hs b/src/TypeLevel/Rewrite/Internal/TypeTemplate.hs
index 831f8bb..12dbe38 100644
--- a/src/TypeLevel/Rewrite/Internal/TypeTemplate.hs
+++ b/src/TypeLevel/Rewrite/Internal/TypeTemplate.hs
@@ -2,7 +2,11 @@
 module TypeLevel.Rewrite.Internal.TypeTemplate where
 
 -- GHC API
+#if MIN_VERSION_ghc(9,0,0)
 import GHC.Plugins (TyVar, Type, getTyVar_maybe)
+#else
+import Type (TyVar, Type, getTyVar_maybe)
+#endif
 
 -- term-rewriting API
 import Data.Rewriting.Term (Term(Fun, Var))
diff --git a/src/TypeLevel/Rewrite/Internal/TypeTerm.hs b/src/TypeLevel/Rewrite/Internal/TypeTerm.hs
index 68309bc..80fb411 100644
--- a/src/TypeLevel/Rewrite/Internal/TypeTerm.hs
+++ b/src/TypeLevel/Rewrite/Internal/TypeTerm.hs
@@ -2,7 +2,11 @@
 module TypeLevel.Rewrite.Internal.TypeTerm where
 
 -- GHC API
+#if MIN_VERSION_ghc(9,0,0)
 import GHC.Plugins (Type, mkTyConApp)
+#else
+import Type (Type, mkTyConApp)
+#endif
 
 -- term-rewriting API
 import Data.Rewriting.Term (Term(Fun, Var))
diff --git a/typelevel-rewrite-rules.cabal b/typelevel-rewrite-rules.cabal
index df8a73d..437b328 100644
--- a/typelevel-rewrite-rules.cabal
+++ b/typelevel-rewrite-rules.cabal
@@ -53,6 +53,7 @@ library
     , term-rewriting >=0.3.0.1
     , transformers >=0.5.6.2
   default-language: Haskell2010
+  default-extensions:  CPP
 
 test-suite should-compile
   type: exitcode-stdio-1.0

From 8b7955c794d5ce97b57b53f7ab113e3e9389f415 Mon Sep 17 00:00:00 2001
From: Junji Hashimoto <junji.hashimoto@gmail.com>
Date: Fri, 23 Jul 2021 02:41:32 +0900
Subject: [PATCH 04/14] Update CI-settings to support for ghc-9

---
 .github/workflows/ci.yml  | 7 ++++++-
 oldest-supported-lts.yaml | 2 +-
 stack.yaml                | 4 ++--
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b246375..2229d74 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -70,9 +70,12 @@ jobs:
           # versions of our dependencies allowed by our upper bounds.
           #
           # TODO: switch back to "ghc: latest" once we support ghc-9.0
-          - name: newest
+          - name: oldest
             ghc: "8.10"
             os: ubuntu-latest
+          - name: newest
+            ghc: "9.0"
+            os: ubuntu-latest
 
     steps:
     - uses: actions/checkout@v2
@@ -120,6 +123,8 @@ jobs:
         include:
           - ghc: "8.10"
             os: ubuntu-latest
+          - ghc: "9.0"
+            os: ubuntu-latest
 
     steps:
     - uses: actions/checkout@v2
diff --git a/oldest-supported-lts.yaml b/oldest-supported-lts.yaml
index bae91e3..04c2037 100644
--- a/oldest-supported-lts.yaml
+++ b/oldest-supported-lts.yaml
@@ -1,7 +1,7 @@
 # if this build fails and you need to bump the lts, remember
 # to also bump the lower bounds in package.yaml to match the
 # versions provided by that new lts!
-resolver: nightly-2020-12-10
+resolver: lts-18.3
 packages:
 - '.'
 
diff --git a/stack.yaml b/stack.yaml
index 7e0065b..8f2fd20 100644
--- a/stack.yaml
+++ b/stack.yaml
@@ -1,7 +1,7 @@
-resolver: nightly-2020-12-10
+resolver: nightly-2021-07-22
 packages:
 - '.'
 
 extra-deps:
 - term-rewriting-0.4.0.2
-- union-find-array-0.1.0.2
+- union-find-array-0.1.0.3

From 1c3ee60f4de5ee7cd5ee40adbc178c45e8507913 Mon Sep 17 00:00:00 2001
From: Junji Hashimoto <junji.hashimoto@gmail.com>
Date: Fri, 23 Jul 2021 02:54:16 +0900
Subject: [PATCH 05/14] Revert oldest-supported-lts.yaml

---
 oldest-supported-lts.yaml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/oldest-supported-lts.yaml b/oldest-supported-lts.yaml
index 04c2037..bae91e3 100644
--- a/oldest-supported-lts.yaml
+++ b/oldest-supported-lts.yaml
@@ -1,7 +1,7 @@
 # if this build fails and you need to bump the lts, remember
 # to also bump the lower bounds in package.yaml to match the
 # versions provided by that new lts!
-resolver: lts-18.3
+resolver: nightly-2020-12-10
 packages:
 - '.'
 

From cf23a3ccd4f9271b5cc4279da7a9e759a4a5b96f Mon Sep 17 00:00:00 2001
From: Junji Hashimoto <junji.hashimoto@gmail.com>
Date: Fri, 6 Aug 2021 18:24:33 +0900
Subject: [PATCH 06/14] Remove ghc-8.0 of error-messages test

---
 .github/workflows/ci.yml      | 2 --
 package.yaml                  | 2 +-
 typelevel-rewrite-rules.cabal | 2 +-
 3 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2229d74..4437222 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -121,8 +121,6 @@ jobs:
     strategy:
       matrix:
         include:
-          - ghc: "8.10"
-            os: ubuntu-latest
           - ghc: "9.0"
             os: ubuntu-latest
 
diff --git a/package.yaml b/package.yaml
index 8a36653..1450ec8 100644
--- a/package.yaml
+++ b/package.yaml
@@ -25,7 +25,7 @@ dependencies:
 library:
   source-dirs:      src
   dependencies:
-    - ghc >= 8.10.2 && <= 9.1
+    - ghc >= 8.10.2 && <9.1
     - containers >= 0.6.2.1
     - term-rewriting >= 0.3.0.1
     - transformers >= 0.5.6.2
diff --git a/typelevel-rewrite-rules.cabal b/typelevel-rewrite-rules.cabal
index 437b328..b13df50 100644
--- a/typelevel-rewrite-rules.cabal
+++ b/typelevel-rewrite-rules.cabal
@@ -48,7 +48,7 @@ library
   build-depends:
       base >=4.12 && <5
     , containers >=0.6.2.1
-    , ghc >=8.10.2 && <= 9.1
+    , ghc >=8.10.2 && <9.1
     , ghc-prim >=0.5.3
     , term-rewriting >=0.3.0.1
     , transformers >=0.5.6.2

From f3f810f2be9a8cc31c4e4aeb6578bbd8a7d203b2 Mon Sep 17 00:00:00 2001
From: Junji Hashimoto <junji.hashimoto@gmail.com>
Date: Fri, 6 Aug 2021 19:16:31 +0900
Subject: [PATCH 07/14] Update error messages for ghc-9

---
 test/error-messages-cases/no-plugin/expected | 27 +++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/test/error-messages-cases/no-plugin/expected b/test/error-messages-cases/no-plugin/expected
index 430509e..ec5caf3 100644
--- a/test/error-messages-cases/no-plugin/expected
+++ b/test/error-messages-cases/no-plugin/expected
@@ -1 +1,26 @@
-    • Couldn't match type ‘as ++ (bs ++ cs)’ with ‘(as ++ bs) ++ cs’
+configure (lib)
+Configuring no-plugin-0.0.0...
+build (lib)
+Preprocessing library for no-plugin-0.0.0..
+Building library for no-plugin-0.0.0..
+[1 of 2] Compiling NoPlugin.Test
+
+<path>/error-messages-cases/no-plugin/src/NoPlugin/Test.hs:15:16: error:
+    • Couldn't match type: as ++ (bs ++ cs)
+                     with: (as ++ bs) ++ cs
+      Expected: proxy ((as ++ bs) ++ cs)
+        Actual: proxy (as ++ (bs ++ cs))
+      NB: ‘++’ is a non-injective type family
+    • In the expression: r
+      In an equation for ‘ex2e’: ex2e _ _ _ r = r
+    • Relevant bindings include
+        r :: proxy (as ++ (bs ++ cs)) (bound at src/NoPlugin/Test.hs:15:12)
+        ex2e :: proxy as
+                -> proxy bs
+                -> proxy cs
+                -> proxy (as ++ (bs ++ cs))
+                -> proxy ((as ++ bs) ++ cs)
+          (bound at src/NoPlugin/Test.hs:15:1)
+   |
+15 | ex2e _ _ _ r = r
+   |                ^

From 1262d69e7e16705c1a85832125ce0b5b82a41278 Mon Sep 17 00:00:00 2001
From: Junji Hashimoto <junji.hashimoto@gmail.com>
Date: Thu, 12 Aug 2021 14:30:52 +0900
Subject: [PATCH 08/14] Bump hash of cabal-file

---
 typelevel-rewrite-rules.cabal | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/typelevel-rewrite-rules.cabal b/typelevel-rewrite-rules.cabal
index b13df50..bd2c839 100644
--- a/typelevel-rewrite-rules.cabal
+++ b/typelevel-rewrite-rules.cabal
@@ -1,10 +1,10 @@
 cabal-version: 1.12
 
--- This file has been generated from package.yaml by hpack version 0.33.0.
+-- This file has been generated from package.yaml by hpack version 0.34.4.
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 2673197ba6a9e92128e851017519e221b95a23ca70b1f7b84158feae74eba11b
+-- hash: 201dd297be3e249f9d5773e714652b18086e8f3160a1bdca783242cb52598513
 
 name:           typelevel-rewrite-rules
 version:        1.0
@@ -53,7 +53,8 @@ library
     , term-rewriting >=0.3.0.1
     , transformers >=0.5.6.2
   default-language: Haskell2010
-  default-extensions:  CPP
+  default-extensions:
+      CPP
 
 test-suite should-compile
   type: exitcode-stdio-1.0

From d4b6b514c3784814f74b1453544349bf7812f3eb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Samuel=20G=C3=A9lineau?= <gelisam+github@gmail.com>
Date: Wed, 15 Mar 2023 21:02:28 -0400
Subject: [PATCH 09/14] rename CI config file

According to my experiments in #36, renaming the CI config file
mysteriously allows CI to start running again!
---
 .github/workflows/{ci.yml => haskell.yml} | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 rename .github/workflows/{ci.yml => haskell.yml} (100%)

diff --git a/.github/workflows/ci.yml b/.github/workflows/haskell.yml
similarity index 100%
rename from .github/workflows/ci.yml
rename to .github/workflows/haskell.yml

From 9385576a99642cb60e445451e9ef152110a80a24 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Samuel=20G=C3=A9lineau?= <gelisam+github@gmail.com>
Date: Wed, 15 Mar 2023 21:26:31 -0400
Subject: [PATCH 10/14] test all the supported GHC versions

and list them in the "tested-with" section of the cabal file
---
 .github/workflows/haskell.yml | 22 ++++++++++++++--------
 package.yaml                  |  4 ++++
 2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/.github/workflows/haskell.yml b/.github/workflows/haskell.yml
index 4437222..48f97a6 100644
--- a/.github/workflows/haskell.yml
+++ b/.github/workflows/haskell.yml
@@ -65,16 +65,22 @@ jobs:
     strategy:
       matrix:
         include:
-          # Check that our upper bounds are correct by building with the latest
-          # version of everything. We use cabal because it uses the latest
-          # versions of our dependencies allowed by our upper bounds.
+          # The purpose of that section is two-fold. First, because we are
+          # using cabal and not stack, cabal will pick the most recent version
+          # of our dependencies which has been released. This way, if a
+          # dependency releases a breaking change, the next monthly CI will
+          # pick that version and notify us if we are affected by the change.
           #
-          # TODO: switch back to "ghc: latest" once we support ghc-9.0
-          - name: oldest
-            ghc: "8.10"
+          # Second, since this project is a ghc plugin, we rely on details of
+          # the GHC library which change between versions. It is thus quite
+          # easy to accidentally make a change which works for the latest
+          # version of GHC but not with older versions. CI should thus test all
+          # the supported GHC versions.
+          - name: ghc-8.10
+            ghc: "8.10.7"
             os: ubuntu-latest
-          - name: newest
-            ghc: "9.0"
+          - name: ghc-9.0
+            ghc: "9.0.2"
             os: ubuntu-latest
 
     steps:
diff --git a/package.yaml b/package.yaml
index 1450ec8..4e1e046 100644
--- a/package.yaml
+++ b/package.yaml
@@ -18,6 +18,10 @@ extra-source-files:
 # for release
 ghc-options: -W -Wall
 
+tested-with:
+  - GHC == 9.0.2
+  - GHC == 8.10.7
+
 dependencies:
   - base >= 4.12 && < 5
   - ghc-prim >= 0.5.3

From f5254d30f0f599aac4ebad49a06cbc062db22d45 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Samuel=20G=C3=A9lineau?= <gelisam+github@gmail.com>
Date: Wed, 15 Mar 2023 21:35:09 -0400
Subject: [PATCH 11/14] move CPP from the .cabal file to each .hs file

This makes it easier for some tools to determine all the language
extensions which apply.
---
 package.yaml                                           | 1 -
 src/TypeLevel/Rewrite.hs                               | 2 +-
 src/TypeLevel/Rewrite/Internal/ApplyRules.hs           | 2 +-
 src/TypeLevel/Rewrite/Internal/DecomposedConstraint.hs | 2 +-
 src/TypeLevel/Rewrite/Internal/Lookup.hs               | 2 +-
 src/TypeLevel/Rewrite/Internal/PrettyPrint.hs          | 2 +-
 src/TypeLevel/Rewrite/Internal/TypeEq.hs               | 1 +
 src/TypeLevel/Rewrite/Internal/TypeNode.hs             | 2 +-
 src/TypeLevel/Rewrite/Internal/TypeRule.hs             | 2 +-
 src/TypeLevel/Rewrite/Internal/TypeTemplate.hs         | 2 +-
 src/TypeLevel/Rewrite/Internal/TypeTerm.hs             | 2 +-
 typelevel-rewrite-rules.cabal                          | 9 +++++----
 12 files changed, 15 insertions(+), 14 deletions(-)

diff --git a/package.yaml b/package.yaml
index 4e1e046..87e2716 100644
--- a/package.yaml
+++ b/package.yaml
@@ -33,7 +33,6 @@ library:
     - containers >= 0.6.2.1
     - term-rewriting >= 0.3.0.1
     - transformers >= 0.5.6.2
-  default-extensions:  CPP
 
 tests:
   should-compile:
diff --git a/src/TypeLevel/Rewrite.hs b/src/TypeLevel/Rewrite.hs
index 5d1ef6a..27759f6 100644
--- a/src/TypeLevel/Rewrite.hs
+++ b/src/TypeLevel/Rewrite.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE LambdaCase, OverloadedStrings, RecordWildCards, ViewPatterns #-}
+{-# LANGUAGE CPP, LambdaCase, OverloadedStrings, RecordWildCards, ViewPatterns #-}
 module TypeLevel.Rewrite (plugin) where
 
 import Control.Monad
diff --git a/src/TypeLevel/Rewrite/Internal/ApplyRules.hs b/src/TypeLevel/Rewrite/Internal/ApplyRules.hs
index 1fbbfca..e6e7cfa 100644
--- a/src/TypeLevel/Rewrite/Internal/ApplyRules.hs
+++ b/src/TypeLevel/Rewrite/Internal/ApplyRules.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE LambdaCase, TupleSections, ViewPatterns #-}
+{-# LANGUAGE CPP, LambdaCase, TupleSections, ViewPatterns #-}
 {-# OPTIONS -Wno-name-shadowing #-}
 module TypeLevel.Rewrite.Internal.ApplyRules where
 
diff --git a/src/TypeLevel/Rewrite/Internal/DecomposedConstraint.hs b/src/TypeLevel/Rewrite/Internal/DecomposedConstraint.hs
index 8226dbb..e121dbd 100644
--- a/src/TypeLevel/Rewrite/Internal/DecomposedConstraint.hs
+++ b/src/TypeLevel/Rewrite/Internal/DecomposedConstraint.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE DeriveFunctor, DeriveFoldable, DeriveTraversable, LambdaCase, RecordWildCards, ViewPatterns #-}
+{-# LANGUAGE CPP, DeriveFunctor, DeriveFoldable, DeriveTraversable, LambdaCase, RecordWildCards, ViewPatterns #-}
 module TypeLevel.Rewrite.Internal.DecomposedConstraint where
 
 import Control.Applicative
diff --git a/src/TypeLevel/Rewrite/Internal/Lookup.hs b/src/TypeLevel/Rewrite/Internal/Lookup.hs
index 62a1d32..c390638 100644
--- a/src/TypeLevel/Rewrite/Internal/Lookup.hs
+++ b/src/TypeLevel/Rewrite/Internal/Lookup.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE LambdaCase, ViewPatterns #-}
+{-# LANGUAGE CPP, LambdaCase, ViewPatterns #-}
 module TypeLevel.Rewrite.Internal.Lookup where
 
 import Control.Arrow ((***), first)
diff --git a/src/TypeLevel/Rewrite/Internal/PrettyPrint.hs b/src/TypeLevel/Rewrite/Internal/PrettyPrint.hs
index 4af808e..efad118 100644
--- a/src/TypeLevel/Rewrite/Internal/PrettyPrint.hs
+++ b/src/TypeLevel/Rewrite/Internal/PrettyPrint.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE LambdaCase, RecordWildCards #-}
+{-# LANGUAGE CPP, LambdaCase, RecordWildCards #-}
 module TypeLevel.Rewrite.Internal.PrettyPrint where
 
 import Data.List (intercalate)
diff --git a/src/TypeLevel/Rewrite/Internal/TypeEq.hs b/src/TypeLevel/Rewrite/Internal/TypeEq.hs
index 53d2df5..acda114 100644
--- a/src/TypeLevel/Rewrite/Internal/TypeEq.hs
+++ b/src/TypeLevel/Rewrite/Internal/TypeEq.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 module TypeLevel.Rewrite.Internal.TypeEq where
 
 import Data.Function
diff --git a/src/TypeLevel/Rewrite/Internal/TypeNode.hs b/src/TypeLevel/Rewrite/Internal/TypeNode.hs
index 31f32e6..ca320d5 100644
--- a/src/TypeLevel/Rewrite/Internal/TypeNode.hs
+++ b/src/TypeLevel/Rewrite/Internal/TypeNode.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE ViewPatterns #-}
+{-# LANGUAGE CPP, ViewPatterns #-}
 module TypeLevel.Rewrite.Internal.TypeNode where
 
 -- GHC API
diff --git a/src/TypeLevel/Rewrite/Internal/TypeRule.hs b/src/TypeLevel/Rewrite/Internal/TypeRule.hs
index 9aeb5dd..0c1fab3 100644
--- a/src/TypeLevel/Rewrite/Internal/TypeRule.hs
+++ b/src/TypeLevel/Rewrite/Internal/TypeRule.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE LambdaCase, ViewPatterns #-}
+{-# LANGUAGE CPP, LambdaCase, ViewPatterns #-}
 {-# OPTIONS -Wno-name-shadowing #-}
 module TypeLevel.Rewrite.Internal.TypeRule where
 
diff --git a/src/TypeLevel/Rewrite/Internal/TypeTemplate.hs b/src/TypeLevel/Rewrite/Internal/TypeTemplate.hs
index 12dbe38..b2fa608 100644
--- a/src/TypeLevel/Rewrite/Internal/TypeTemplate.hs
+++ b/src/TypeLevel/Rewrite/Internal/TypeTemplate.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE LambdaCase, ViewPatterns #-}
+{-# LANGUAGE CPP, LambdaCase, ViewPatterns #-}
 module TypeLevel.Rewrite.Internal.TypeTemplate where
 
 -- GHC API
diff --git a/src/TypeLevel/Rewrite/Internal/TypeTerm.hs b/src/TypeLevel/Rewrite/Internal/TypeTerm.hs
index 80fb411..5e06acd 100644
--- a/src/TypeLevel/Rewrite/Internal/TypeTerm.hs
+++ b/src/TypeLevel/Rewrite/Internal/TypeTerm.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE LambdaCase, ViewPatterns #-}
+{-# LANGUAGE CPP, LambdaCase, ViewPatterns #-}
 module TypeLevel.Rewrite.Internal.TypeTerm where
 
 -- GHC API
diff --git a/typelevel-rewrite-rules.cabal b/typelevel-rewrite-rules.cabal
index bd2c839..26a9688 100644
--- a/typelevel-rewrite-rules.cabal
+++ b/typelevel-rewrite-rules.cabal
@@ -1,10 +1,10 @@
 cabal-version: 1.12
 
--- This file has been generated from package.yaml by hpack version 0.34.4.
+-- This file has been generated from package.yaml by hpack version 0.35.2.
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 201dd297be3e249f9d5773e714652b18086e8f3160a1bdca783242cb52598513
+-- hash: cac2a8aec9cc51f367be3e13c24e6efa7d62ba4ec28e8368137d8292de814188
 
 name:           typelevel-rewrite-rules
 version:        1.0
@@ -17,6 +17,9 @@ author:         Samuel Gélineau
 maintainer:     gelisam+github@gmail.com
 license:        PublicDomain
 build-type:     Simple
+tested-with:
+    GHC == 9.0.2
+  , GHC == 8.10.7
 extra-source-files:
     README.md
     CHANGELOG.md
@@ -53,8 +56,6 @@ library
     , term-rewriting >=0.3.0.1
     , transformers >=0.5.6.2
   default-language: Haskell2010
-  default-extensions:
-      CPP
 
 test-suite should-compile
   type: exitcode-stdio-1.0

From 2aa4ed22034d3e72cde2199dea3f9c08d56f13ff Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Samuel=20G=C3=A9lineau?= <gelisam+github@gmail.com>
Date: Wed, 15 Mar 2023 21:49:51 -0400
Subject: [PATCH 12/14] bump the recommended stackage snapshot

---
 stack.yaml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/stack.yaml b/stack.yaml
index 8f2fd20..1db2e48 100644
--- a/stack.yaml
+++ b/stack.yaml
@@ -1,4 +1,4 @@
-resolver: nightly-2021-07-22
+resolver: lts-19.33
 packages:
 - '.'
 

From 62c540baa0953154cffbe3dff30f7553f86e23da Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Samuel=20G=C3=A9lineau?= <gelisam+github@gmail.com>
Date: Wed, 15 Mar 2023 21:57:46 -0400
Subject: [PATCH 13/14] focus on the important part of the expected error

this way the test is less likely to break when the surrounding text
changes.
---
 test/error-messages-cases/no-plugin/expected | 24 --------------------
 1 file changed, 24 deletions(-)

diff --git a/test/error-messages-cases/no-plugin/expected b/test/error-messages-cases/no-plugin/expected
index ec5caf3..b2ac572 100644
--- a/test/error-messages-cases/no-plugin/expected
+++ b/test/error-messages-cases/no-plugin/expected
@@ -1,26 +1,2 @@
-configure (lib)
-Configuring no-plugin-0.0.0...
-build (lib)
-Preprocessing library for no-plugin-0.0.0..
-Building library for no-plugin-0.0.0..
-[1 of 2] Compiling NoPlugin.Test
-
-<path>/error-messages-cases/no-plugin/src/NoPlugin/Test.hs:15:16: error:
     • Couldn't match type: as ++ (bs ++ cs)
                      with: (as ++ bs) ++ cs
-      Expected: proxy ((as ++ bs) ++ cs)
-        Actual: proxy (as ++ (bs ++ cs))
-      NB: ‘++’ is a non-injective type family
-    • In the expression: r
-      In an equation for ‘ex2e’: ex2e _ _ _ r = r
-    • Relevant bindings include
-        r :: proxy (as ++ (bs ++ cs)) (bound at src/NoPlugin/Test.hs:15:12)
-        ex2e :: proxy as
-                -> proxy bs
-                -> proxy cs
-                -> proxy (as ++ (bs ++ cs))
-                -> proxy ((as ++ bs) ++ cs)
-          (bound at src/NoPlugin/Test.hs:15:1)
-   |
-15 | ex2e _ _ _ r = r
-   |                ^

From 6501dee5e59a9741346b12b89a66bc3b33caebce Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Samuel=20G=C3=A9lineau?= <gelisam+github@gmail.com>
Date: Wed, 15 Mar 2023 22:05:26 -0400
Subject: [PATCH 14/14] use the right proxy arguments

the purpose of the proxy argument was to make the type variables
unambiguous, but it was naming the wrong type variables.
---
 test/should-compile/GHC/TypeLits/Test.hs | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/test/should-compile/GHC/TypeLits/Test.hs b/test/should-compile/GHC/TypeLits/Test.hs
index da3aa55..ffc8fdd 100644
--- a/test/should-compile/GHC/TypeLits/Test.hs
+++ b/test/should-compile/GHC/TypeLits/Test.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE DataKinds, RankNTypes, TypeFamilies, TypeOperators, AllowAmbiguousTypes #-}
+{-# LANGUAGE DataKinds, RankNTypes, TypeFamilies, TypeOperators #-}
 {-# OPTIONS_GHC -fplugin TypeLevel.Rewrite
                 -fplugin-opt=TypeLevel.Rewrite:GHC.TypeLits.RewriteRules.NatRule
                 -fplugin-opt=TypeLevel.Rewrite:GHC.TypeLits.RewriteRules.SymbolRule #-}
@@ -17,6 +17,7 @@ ex2 :: ( ((s1 `AppendSymbol` "foo") `AppendSymbol` s2)
        ~ (s1 `AppendSymbol` ("foo" `AppendSymbol` s2))
       => r
        )
-    -> proxy s
+    -> proxy s1
+    -> proxy s2
     -> r
-ex2 r _ = r
+ex2 r _ _ = r