Binding things matched by an unboxed pattern synonym should require a bang

testsuite/tests/patsyn/should_compile/all.T

@@ -10,3 +10,4 @@ test('incomplete', normal, compile, [''])
 test('export', normal, compile, [''])
 test('T8966', normal, compile, [''])
 test('T9023', normal, compile, [''])
+test('unboxed-bind-bang', normal, compile, [''])

testsuite/tests/patsyn/should_compile/unboxed-bind-bang.hs

+{-# LANGUAGE PatternSynonyms, MagicHash, BangPatterns #-}
+module ShouldCompile where
+
+import GHC.Base
+
+data Foo = MkFoo Int# Int#
+
+pattern P x = MkFoo 0# x
+
+f x = let !(P arg) = x in arg

testsuite/tests/patsyn/should_fail/all.T

-
 test('mono', normal, compile_fail, [''])
 test('unidir', normal, compile_fail, [''])
 test('local', normal, compile_fail, [''])
@@ -8,3 +7,4 @@ test('T9161-1', normal, compile_fail, [''])
 test('T9161-2', normal, compile_fail, [''])
 test('T9705-1', normal, compile_fail, [''])
 test('T9705-2', normal, compile_fail, [''])
+test('unboxed-bind', normal, compile_fail, [''])

testsuite/tests/patsyn/should_fail/unboxed-bind.hs

+{-# LANGUAGE PatternSynonyms, MagicHash #-}
+module ShouldFail where
+
+import GHC.Base
+
+data Foo = MkFoo Int# Int#
+
+pattern P x = MkFoo 0# x
+
+f x = let P arg = x in arg

testsuite/tests/patsyn/should_fail/unboxed-bind.stderr

+
+unboxed-bind.hs:10:11:
+    Pattern bindings containing unlifted types should use an outermost bang pattern:
+      P arg = x
+    In the expression: let P arg = x in arg
+    In an equation for ‘f’: f x = let P arg = x in arg