Add another test for #17267

This one came in a comment from James Payor

3 files changed, 41 insertions, 0 deletions

diff --git a/testsuite/tests/quantified-constraints/T17267e.hs b/testsuite/tests/quantified-constraints/T17267e.hs
new file mode 100644
index 0000000000..0b00995ab2
--- /dev/null
+++ b/testsuite/tests/quantified-constraints/T17267e.hs
@@ -0,0 +1,27 @@
+{-# LANGUAGE QuantifiedConstraints #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE MonoLocalBinds #-}
+
+module Main where
+
+class Show a => Thing a b
+instance Show a => Thing a b
+
+class (Show a => Thing a ()) => PseudoShow a b
+instance PseudoShow a b
+
+pseudoShow :: PseudoShow a () => a -> String
+pseudoShow = show
+
+
+{-
+    [G] PseudoShow a ()
+(and hence by SC)
+    [G] Show a => Thing a ()
+(and hence by SC)
+    [G] Show a => Show a
+The latter loops
+-}
+
diff --git a/testsuite/tests/quantified-constraints/T17267e.stderr b/testsuite/tests/quantified-constraints/T17267e.stderr
new file mode 100644
index 0000000000..b497fa1009
--- /dev/null
+++ b/testsuite/tests/quantified-constraints/T17267e.stderr
@@ -0,0 +1,13 @@
+
+T17267e.hs:1:1: error:
+    The IO action ‘main’ is not defined in module ‘Main’
+
+T17267e.hs:16:14: error:
+    • Reduction stack overflow; size = 201
+      When simplifying the following type: Show 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 expression: show
+      In an equation for ‘pseudoShow’: pseudoShow = show
diff --git a/testsuite/tests/quantified-constraints/all.T b/testsuite/tests/quantified-constraints/all.T
index 7fb728654a..6a1d41eeee 100644
--- a/testsuite/tests/quantified-constraints/all.T
+++ b/testsuite/tests/quantified-constraints/all.T
@@ -26,3 +26,4 @@ test('T17267a', normal, compile_fail, [''])
 test('T17267b', normal, compile_fail, [''])
 test('T17267c', normal, compile_fail, [''])
 test('T17267d', normal, compile_and_run, [''])
+test('T17267e', normal, compile_fail, [''])