Add a missing guard in GHC.HsToCore.Utils.is_flat_prod_pat

This missing guard gave rise to #21519.

3 files changed, 35 insertions, 0 deletions

diff --git a/testsuite/tests/typecheck/should_compile/T21519.hs b/testsuite/tests/typecheck/should_compile/T21519.hs
new file mode 100644
index 0000000000..aa88fefb91
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T21519.hs
@@ -0,0 +1,18 @@
+{-# LANGUAGE MagicHash, UnboxedTuples #-}
+
+module T21519 where
+
+import GHC.Exts
+
+(# #) = (# #)
+
+g1 :: Bool -> (# Int #)
+g1 = g1
+
+f1 x =  let (# a #) = g1 True in a
+
+g2 :: Bool -> (#  #)
+g2 = g2
+
+f2 x =  let (#  #) = g2 True in True
+
diff --git a/testsuite/tests/typecheck/should_compile/T21519a.hs b/testsuite/tests/typecheck/should_compile/T21519a.hs
new file mode 100644
index 0000000000..04a1d629e0
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T21519a.hs
@@ -0,0 +1,15 @@
+{-# LANGUAGE UnliftedDatatypes, UnliftedNewtypes, MagicHash #-}
+module T21519a where
+
+import GHC.Exts
+
+type T :: UnliftedType
+data T = MkT Int
+MkT _ = MkT 10           -- (1)
+
+f x = let MkT _ = MkT 10 in True
+
+newtype T2 = MkT2 Int#
+MkT2 _ = MkT2 10#        -- (2)
+
+g x = let MkT2 _ = MkT2 10# in True
diff --git a/testsuite/tests/typecheck/should_compile/all.T b/testsuite/tests/typecheck/should_compile/all.T
index 1764ccb34b..4f546c0914 100644
--- a/testsuite/tests/typecheck/should_compile/all.T
+++ b/testsuite/tests/typecheck/should_compile/all.T
@@ -825,3 +825,5 @@ test('T21205', normal, compile, ['-O0'])
 test('T21323', normal, compile, [''])
 test('T21315', normal, compile, ['-Wredundant-constraints'])
 test('T21516', normal, compile, [''])
+test('T21519', normal, compile, [''])
+test('T21519a', normal, compile, [''])