Make inert_cycle_breakers into a stack.

Close #20231.

2 files changed, 21 insertions, 0 deletions

diff --git a/testsuite/tests/typecheck/should_compile/T20231.hs b/testsuite/tests/typecheck/should_compile/T20231.hs
new file mode 100644
index 0000000000..f327f04217
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T20231.hs
@@ -0,0 +1,20 @@
+{-# LANGUAGE
+    DataKinds,
+    GADTs,
+    QuantifiedConstraints,
+    TypeFamilies
+  #-}
+
+module T20231 where
+
+type family Foo x where
+  Foo (Maybe a) = a
+
+data Bug1 a b c where
+  Bug1 :: (a ~ 'True => Show b, a ~ 'False => Show c) => Bug1 a b c
+
+data Bug2 f a b where
+  Bug2 :: (a ~ 'True => f b) => Bug2 f a b
+
+bug :: b ~ Maybe (Foo b) => Bug2 Show a (Foo b) -> Bug1 a (Foo b) Int
+bug Bug2 = Bug1
diff --git a/testsuite/tests/typecheck/should_compile/all.T b/testsuite/tests/typecheck/should_compile/all.T
index 1b1cb1ec5a..6d9ae4c566 100644
--- a/testsuite/tests/typecheck/should_compile/all.T
+++ b/testsuite/tests/typecheck/should_compile/all.T
@@ -570,6 +570,7 @@ test('T13490', normal, compile, [''])
 test('T13474', normal, compile, [''])
 test('T13524', normal, compile, [''])
 test('T20602', normal, compile, [''])
+test('T20231', normal, compile, [''])
 test('T20582', normal, compile, [''])
 test('T13509', normal, compile, [''])
 test('T13526', normal, compile, [''])