testsuite: Add test for #15316

This is the full testcase for T15316.

3 files changed, 28 insertions, 0 deletions

diff --git a/testsuite/tests/quantified-constraints/T15316A.hs b/testsuite/tests/quantified-constraints/T15316A.hs
new file mode 100644
index 0000000000..d48c46ed7d
--- /dev/null
+++ b/testsuite/tests/quantified-constraints/T15316A.hs
@@ -0,0 +1,16 @@
+{-# LANGUAGE RankNTypes, QuantifiedConstraints, ConstraintKinds, UndecidableInstances #-}
+
+-- Should produce a compile time "Reduction stack overflow" error
+module T15316A where
+
+import Data.Proxy
+
+class Class a where
+         method :: a
+
+subsume :: (Class a => Class b) => Proxy a -> Proxy b -> ((Class a => Class b) => r) -> r
+subsume _ _ x = x
+
+value :: Proxy a -> a
+value p = subsume p p method
+
diff --git a/testsuite/tests/quantified-constraints/T15316A.stderr b/testsuite/tests/quantified-constraints/T15316A.stderr
new file mode 100644
index 0000000000..7a4823caa0
--- /dev/null
+++ b/testsuite/tests/quantified-constraints/T15316A.stderr
@@ -0,0 +1,11 @@
+
+T15316A.hs:15:23:
+     Reduction stack overflow; size = 201
+      When simplifying the following type: Class a
+      Use -freduction-depth=0 to disable this check
+      (any upper bound you could choose might fail unpredictably with
+       minor updates to GHC, so disabling the check is recommended if
+       you're sure that type checking should terminate)
+     In the third argument of ‘subsume’, namely ‘method’
+      In the expression: subsume p p method
+      In an equation for ‘value’: value p = subsume p p method
diff --git a/testsuite/tests/quantified-constraints/all.T b/testsuite/tests/quantified-constraints/all.T
index ee32339dab..da3a6fecec 100644
--- a/testsuite/tests/quantified-constraints/all.T
+++ b/testsuite/tests/quantified-constraints/all.T
@@ -15,6 +15,7 @@ test('T15290', normal, compile, [''])
 test('T15290a', normal, compile_fail, [''])
 test('T15290b', normal, compile_fail, [''])
 test('T15316', normal, compile_fail, [''])
+test('T15316A', normal, compile_fail, [''])
 test('T15334', normal, compile_fail, [''])
 test('T15359', normal, compile, [''])
 test('T15359a', normal, compile, [''])