mkDataConRep: fix bug in strictness signature (#14290)

The strictness signature for a data con wrapper wasn't including any
dictionary arguments, which meant that bangs on the fields of a
constructor with an existential context would be moved to the wrong
fields.  See T14290 for an example.

Test Plan:
* New test T14290
* validate

Reviewers: simonpj, niteria, austin, bgamari, erikd

Reviewed By: simonpj, bgamari

Subscribers: rwbarton, thomie

GHC Trac Issues: #14290

Differential Revision: https://phabricator.haskell.org/D4040

(cherry picked from commit 5935acdb)

compiler/basicTypes/MkId.hs

@@ -528,7 +528,11 @@ mkDataConRep dflags fam_envs wrap_name mb_bangs data_con
 
              wrap_sig = mkClosedStrictSig wrap_arg_dmds (dataConCPR data_con)
 
-             wrap_arg_dmds = map mk_dmd arg_ibangs
+             wrap_arg_dmds =
+               replicate (length theta) topDmd ++ map mk_dmd arg_ibangs
+               -- Don't forget the dictionary arguments when building
+               -- the strictness signature (#14290).
+
              mk_dmd str | isBanged str = evalDmd
                         | otherwise           = topDmd
 

testsuite/tests/stranal/should_run/T14290.hs

+{-# LANGUAGE ExistentialQuantification #-}
+module Main (main) where
+
+main :: IO ()
+main = r `seq` return ()
+
+r :: Rec
+r = Rec{ a = error "xxx", b = 3, c = True }
+
+class C t
+instance C Bool
+
+data Rec = forall t. C t => Rec
+  { a :: ()
+  , b :: !Int
+  , c :: t
+  }

testsuite/tests/stranal/should_run/all.T

@@ -15,3 +15,4 @@ test('T11555a', normal, compile_and_run, [''])
 test('T12368', exit_code(1), compile_and_run, [''])
 test('T12368a', exit_code(1), compile_and_run, [''])
 test('T13380', [expect_broken(13380), exit_code(1)], compile_and_run, [''])
+test('T14290', normal, compile_and_run, [''])