Add a test for the first part of #2806

testsuite/tests/ghc-regress/typecheck/should_fail/all.T

@@ -198,6 +198,9 @@ test('tcfail199', normal, compile_fail, [''])
 test('tcfail200', normal, compile_fail, [''])
 test('tcfail201', normal, compile_fail, [''])
 test('tcfail202', normal, compile_fail, [''])
+# -Werror is a temporary hack. Once GHC makes this an error, rather
+# than a warning, we won't need it.
+test('tcfail203', normal, compile_fail, ['-Werror'])
 
 test('T1899', normal, compile_fail, [''])
 test('T2126', normal, compile_fail, [''])

testsuite/tests/ghc-regress/typecheck/should_fail/tcfail203.hs

+-- trac #2806
+
+{-# LANGUAGE MagicHash, UnboxedTuples, BangPatterns #-}
+
+module Foo where
+
+import GHC.Base
+
+pass1 = 'a'
+    where !x = 5#
+
+pass2 = 'a'
+    where !(I# x) = 5
+
+pass3 = 'a'
+    where !(b, I# x) = (True, 5)
+
+pass4 = 'a'
+    where !(# b, I# x #) = (# True, 5 #)
+
+pass5 = 'a'
+    where !(# b, x #) = (# True, 5# #)
+
+fail1 = 'a'
+    where x = 5#
+
+fail2 = 'a'
+    where (I# x) = 5
+
+fail3 = 'a'
+    where (b, I# x) = (True, 5)
+
+fail4 = 'a'
+    where (# b, I# x #) = (# True, 5 #)
+
+fail5 = 'a'
+    where (# b, x #) = (# True, 5# #)
+
+fail6 = 'a'
+    where (I# !x) = 5
+
+fail7 = 'a'
+    where (b, !(I# x)) = (True, 5)
+
+fail8 = 'a'
+    where (# b, !(I# x) #) = (# True, 5 #)
+
+fail9 = 'a'
+    where (# b, !x #) = (# True, 5# #)
+

testsuite/tests/ghc-regress/typecheck/should_fail/tcfail203.stderr

+
+tcfail203.hs:25:10:
+    Warning: Bindings containing unlifted types must use an outermost bang pattern:
+                 { x = 5# }
+    In the definition of `fail1':
+        fail1 = 'a'
+              where
+                  x = 5#
+
+tcfail203.hs:28:10:
+    Warning: Bindings containing unlifted types must use an outermost bang pattern:
+                 { (I# x) = 5 }
+    In the definition of `fail2':
+        fail2 = 'a'
+              where
+                  (I# x) = 5
+
+tcfail203.hs:31:10:
+    Warning: Bindings containing unlifted types must use an outermost bang pattern:
+                 { (b, I# x) = (GHC.Bool.True, 5) }
+    In the definition of `fail3':
+        fail3 = 'a'
+              where
+                  (b, I# x) = (True, 5)
+
+tcfail203.hs:34:10:
+    Warning: Bindings containing unlifted types must use an outermost bang pattern:
+                 { (# b, I# x #) = (# GHC.Bool.True, 5 #) }
+    In the definition of `fail4':
+        fail4 = 'a'
+              where
+                  (# b, I# x #) = (# True, 5 #)
+
+tcfail203.hs:37:10:
+    Warning: Bindings containing unlifted types must use an outermost bang pattern:
+                 { (# b, x #) = (# GHC.Bool.True, 5# #) }
+    In the definition of `fail5':
+        fail5 = 'a'
+              where
+                  (# b, x #) = (# True, 5# #)
+
+tcfail203.hs:40:10:
+    Warning: Bindings containing unlifted types must use an outermost bang pattern:
+                 { (I# !x) = 5 }
+    In the definition of `fail6':
+        fail6 = 'a'
+              where
+                  (I# !x) = 5
+
+tcfail203.hs:43:10:
+    Warning: Bindings containing unlifted types must use an outermost bang pattern:
+                 { (b, !(I# x)) = (GHC.Bool.True, 5) }
+    In the definition of `fail7':
+        fail7 = 'a'
+              where
+                  (b, !(I# x)) = (True, 5)
+
+tcfail203.hs:46:10:
+    Warning: Bindings containing unlifted types must use an outermost bang pattern:
+                 { (# b, !(I# x) #) = (# GHC.Bool.True, 5 #) }
+    In the definition of `fail8':
+        fail8 = 'a'
+              where
+                  (# b, !(I# x) #) = (# True, 5 #)
+
+tcfail203.hs:49:10:
+    Warning: Bindings containing unlifted types must use an outermost bang pattern:
+                 { (# b, !x #) = (# GHC.Bool.True, 5# #) }
+    In the definition of `fail9':
+        fail9 = 'a'
+              where
+                  (# b, !x #) = (# True, 5# #)
+
+<no location info>: 
+Failing due to -Werror.
+