3 files changed, 36 insertions, 1 deletions
diff --git a/testsuite/tests/simplCore/should_compile/T22715_2.hs b/testsuite/tests/simplCore/should_compile/T22715_2.hs
new file mode 100644
index 0000000000..4001f92c30
--- /dev/null
+++ b/testsuite/tests/simplCore/should_compile/T22715_2.hs
@@ -0,0 +1,6 @@
+module T22715_2 where
+
+import T22715_2a
+
+debugTerminalKeys :: (forall m. CommandMonad m => m Char) -> Input IO Char
+debugTerminalKeys eval = runIdT eval
diff --git a/testsuite/tests/simplCore/should_compile/T22715_2a.hs b/testsuite/tests/simplCore/should_compile/T22715_2a.hs
new file mode 100644
index 0000000000..d53cccd7aa
--- /dev/null
+++ b/testsuite/tests/simplCore/should_compile/T22715_2a.hs
@@ -0,0 +1,29 @@
+{-# OPTIONS_GHC -Wno-missing-methods #-}
+
+module T22715_2a where
+
+newtype IdentityT m a = IdentityT (m a) deriving Functor
+newtype IdT m a = IdT {runIdT :: m a} deriving Functor
+
+class Functor m => SillyA m where
+  unused :: m a -> m a
+
+class SillyA m => SillyB m where
+  unused2 :: m a -> m a
+
+instance SillyA m => SillyA (IdentityT m) where
+instance SillyB m => SillyB (IdentityT m) where
+
+instance SillyA m => SillyA (IdT m) where
+instance SillyB m => SillyB (IdT m) where
+
+instance SillyA IO where
+instance SillyB IO where
+
+class Functor m => Special m
+instance Functor m => Special (IdT m)
+
+type Input m = IdentityT (IdentityT m)
+
+class (Special m, SillyB m) => CommandMonad m
+instance SillyB m => CommandMonad (IdT (Input m))
diff --git a/testsuite/tests/simplCore/should_compile/all.T b/testsuite/tests/simplCore/should_compile/all.T
index 068b830a51..a07aba3940 100644
--- a/testsuite/tests/simplCore/should_compile/all.T
+++ b/testsuite/tests/simplCore/should_compile/all.T
@@ -469,4 +469,4 @@ test('T22662', normal, compile, [''])
 test('T22725', normal, compile, ['-O'])
 test('T22502', normal, compile, ['-O'])
 test('T22611', [when(wordsize(32), skip), grep_errmsg(r'\$salterF') ], compile, ['-O -ddump-simpl -dsuppress-uniques -dsuppress-all'])
-
+test('T22715_2', normal, multimod_compile, ['T22715_2', '-v0 -O -fspecialise-aggressively'])