testsuite: Add test for #16509

testsuite/tests/patsyn/should_compile/T16509.hs

+{-# LANGUAGE PatternSynonyms #-}
+{-# LANGUAGE ViewPatterns #-}
+
+module PatternPanic where
+
+pattern TestPat :: (Int, Int)
+pattern TestPat <- (isSameRef -> True, 0)
+
+isSameRef :: Int -> Bool
+isSameRef e | 0 <- e = True
+isSameRef _ = False
+

testsuite/tests/patsyn/should_compile/T16509.script

+:load T16509.hs

testsuite/tests/patsyn/should_compile/all.T

@@ -77,5 +77,6 @@ test('T14326', normal, compile, [''])
 test('T14394', normal, ghci_script, ['T14394.script'])
 test('T14552', normal, compile, [''])
 test('T14498', normal, compile, [''])
+test('T16509', expect_broken(16509), ghci_script, ['T16509.script'])
 test('T16682', [extra_files(['T16682.hs', 'T16682a.hs'])],
                multimod_compile, ['T16682', '-v0 -fwarn-incomplete-patterns -fno-code'])