From 6a3ca628536860542c8f5cfd4e28eafd4c9e6ea2 Mon Sep 17 00:00:00 2001
From: Matthew Pickering <matthewtpickering@gmail.com>
Date: Mon, 18 Jul 2022 11:47:52 +0100
Subject: Add tests that -XHaskell98 and -XHaskell2010 enable DeepSubsumption

(cherry picked from commit 5c4fbaf53f258d64aeb66a8172e13dc559eb8d8b)
---
 compiler/GHC/Driver/Session.hs                               |  4 +++-
 .../tests/typecheck/should_compile/DeepSubsumption06.hs      | 12 ++++++++++++
 .../tests/typecheck/should_compile/DeepSubsumption07.hs      | 12 ++++++++++++
 testsuite/tests/typecheck/should_compile/all.T               |  2 ++
 4 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 testsuite/tests/typecheck/should_compile/DeepSubsumption06.hs
 create mode 100644 testsuite/tests/typecheck/should_compile/DeepSubsumption07.hs

diff --git a/compiler/GHC/Driver/Session.hs b/compiler/GHC/Driver/Session.hs
index b3d53c4953..91f0ed92c0 100644
--- a/compiler/GHC/Driver/Session.hs
+++ b/compiler/GHC/Driver/Session.hs
@@ -1372,12 +1372,14 @@ languageExtensions (Just Haskell98)
        LangExt.DatatypeContexts,
        LangExt.TraditionalRecordSyntax,
        LangExt.FieldSelectors,
-       LangExt.NondecreasingIndentation
+       LangExt.NondecreasingIndentation,
            -- strictly speaking non-standard, but we always had this
            -- on implicitly before the option was added in 7.1, and
            -- turning it off breaks code, so we're keeping it on for
            -- backwards compatibility.  Cabal uses -XHaskell98 by
            -- default unless you specify another language.
+       LangExt.DeepSubsumption
+       -- Non-standard but enabled for backwards compatability (see GHC proposal #511)
       ]
 
 languageExtensions (Just Haskell2010)
diff --git a/testsuite/tests/typecheck/should_compile/DeepSubsumption06.hs b/testsuite/tests/typecheck/should_compile/DeepSubsumption06.hs
new file mode 100644
index 0000000000..6e8b64c2c2
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/DeepSubsumption06.hs
@@ -0,0 +1,12 @@
+{-# LANGUAGE NoPolyKinds #-}
+{-# LANGUAGE RankNTypes #-}
+module DeepSubsumption06 where
+
+class Profunctor p where
+  dimap :: (s -> a) -> (b -> t) -> p i a b -> p i s t
+
+type Iso s t a b = forall p i . Profunctor p => p i a b -> p i s t
+
+iso :: (s -> a) -> (b -> t) -> Iso s t a b
+-- iso f g = dimap f g
+iso = dimap
diff --git a/testsuite/tests/typecheck/should_compile/DeepSubsumption07.hs b/testsuite/tests/typecheck/should_compile/DeepSubsumption07.hs
new file mode 100644
index 0000000000..1c70025051
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/DeepSubsumption07.hs
@@ -0,0 +1,12 @@
+{-# LANGUAGE NoPolyKinds #-}
+{-# LANGUAGE RankNTypes #-}
+module DeepSubsumption07 where
+
+class Profunctor p where
+  dimap :: (s -> a) -> (b -> t) -> p i a b -> p i s t
+
+type Iso s t a b = forall p i . Profunctor p => p i a b -> p i s t
+
+iso :: (s -> a) -> (b -> t) -> Iso s t a b
+-- iso f g = dimap f g
+iso = dimap
diff --git a/testsuite/tests/typecheck/should_compile/all.T b/testsuite/tests/typecheck/should_compile/all.T
index 47ad8285c8..da674e0a2c 100644
--- a/testsuite/tests/typecheck/should_compile/all.T
+++ b/testsuite/tests/typecheck/should_compile/all.T
@@ -800,3 +800,5 @@ test('DeepSubsumption02', normal, compile, [''])
 test('DeepSubsumption03', normal, compile, [''])
 test('DeepSubsumption04', normal, compile, [''])
 test('DeepSubsumption05', normal, compile, [''])
+test('DeepSubsumption06', normal, compile, ['-XHaskell98'])
+test('DeepSubsumption07', normal, compile, ['-XHaskell2010'])
-- 
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