Move 'HsBangTy' out in constructor arguments

When run with -haddock, a constructor argument can have both a a
strictness/unpackedness annotation and a docstring. The parser binds
'HsBangTy' more tightly than 'HsDocTy', yet for constructor arguments we
really need the 'HsBangTy' on the outside.

This commit does this shuffling in the 'mkConDeclH98' and 'mkGadtDecl'
smart constructors.

Test Plan: haddockA038, haddockC038

Reviewers: bgamari, dfeuer

Reviewed By: bgamari

Subscribers: dfeuer, rwbarton, thomie, carter

Differential Revision: https://phabricator.haskell.org/D4727

6 files changed, 64 insertions, 2 deletions

diff --git a/compiler/parser/RdrHsSyn.hs b/compiler/parser/RdrHsSyn.hs
index dfcccd369e..35371af9c8 100644
--- a/compiler/parser/RdrHsSyn.hs
+++ b/compiler/parser/RdrHsSyn.hs
@@ -626,8 +626,10 @@ mkConDeclH98 name mb_forall mb_cxt args
                , con_forall = isJust mb_forall
                , con_ex_tvs = mb_forall `orElse` []
                , con_mb_cxt = mb_cxt
-               , con_args   = args
+               , con_args   = args'
                , con_doc    = Nothing }
+  where
+    args' = nudgeHsSrcBangs args
 
 mkGadtDecl :: [Located RdrName]
            -> LHsType GhcPs     -- Always a HsForAllTy
@@ -638,7 +640,7 @@ mkGadtDecl names ty
                 , con_forall = isLHsForAllTy ty
                 , con_qvars  = mkHsQTvs tvs
                 , con_mb_cxt = mcxt
-                , con_args   = args
+                , con_args   = args'
                 , con_res_ty = res_ty
                 , con_doc    = Nothing }
   where
@@ -651,6 +653,7 @@ mkGadtDecl names ty
     split_rho tau                  = (Nothing, tau)
 
     (args, res_ty) = split_tau tau
+    args' = nudgeHsSrcBangs args
 
     -- See Note [GADT abstract syntax] in HsDecls
     split_tau (L _ (HsFunTy _ (L loc (HsRecTy _ rf)) res_ty))
@@ -658,6 +661,28 @@ mkGadtDecl names ty
     split_tau (L _ (HsParTy _ ty)) = split_tau ty
     split_tau tau                  = (PrefixCon [], tau)
 
+nudgeHsSrcBangs :: HsConDeclDetails GhcPs -> HsConDeclDetails GhcPs
+-- ^ This function ensures that fields with strictness or packedness
+-- annotations put these annotations on an outer 'HsBangTy'.
+--
+-- The problem is that in the parser, strictness and packedness annotations
+-- bind more tightly that docstrings. However, the expectation downstream of
+-- the parser (by functions such as 'getBangType' and 'getBangStrictness')
+-- is that docstrings bind more tightly so that 'HsBangTy' may end up as the
+-- top-level type.
+--
+-- See #15206
+nudgeHsSrcBangs details
+  = case details of
+      PrefixCon as -> PrefixCon (map go as)
+      RecCon r -> RecCon r
+      InfixCon a1 a2 -> InfixCon (go a1) (go a2)
+  where
+    go (L l (HsDocTy _ (L _ (HsBangTy _ s lty)) lds)) =
+      L l (HsBangTy noExt s (addCLoc lty lds (HsDocTy noExt lty lds)))
+    go lty = lty
+
+
 setRdrNameSpace :: RdrName -> NameSpace -> RdrName
 -- ^ This rather gruesome function is used mainly by the parser.
 -- When parsing:
diff --git a/testsuite/tests/haddock/should_compile_flag_haddock/all.T b/testsuite/tests/haddock/should_compile_flag_haddock/all.T
index 90d4a55c3f..5450fcbe7f 100644
--- a/testsuite/tests/haddock/should_compile_flag_haddock/all.T
+++ b/testsuite/tests/haddock/should_compile_flag_haddock/all.T
@@ -42,6 +42,7 @@ test('haddockA032', normal, compile, ['-haddock -ddump-parsed'])
 test('haddockA035', normal, compile, ['-haddock -ddump-parsed'])
 test('haddockA036', normal, compile, ['-haddock -ddump-parsed'])
 test('haddockA037', normal, compile, ['-haddock -ddump-parsed'])
+test('haddockA038', normal, compile, ['-haddock -ddump-parsed'])
 
 # The tests below this line are not duplicated in
 # should_compile_noflag_haddock.
diff --git a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA038.hs b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA038.hs
new file mode 100644
index 0000000000..b839bdee22
--- /dev/null
+++ b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA038.hs
@@ -0,0 +1,14 @@
+module UnamedConstructorStrictFields where
+-- See #15206
+
+data A = A
+data B = B
+
+data Foo = MkFoo
+  {-# UNPACK #-} !A -- ^ Unpacked strict field
+                 B
+
+data Bar =
+  {-# UNPACK #-} !A -- ^ Unpacked strict field
+    :%%
+                 B
diff --git a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA038.stderr b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA038.stderr
new file mode 100644
index 0000000000..94318efe2b
--- /dev/null
+++ b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA038.stderr
@@ -0,0 +1,7 @@
+
+==================== Parser ====================
+module UnamedConstructorStrictFields where
+data A = A
+data B = B
+data Foo = MkFoo {-# UNPACK #-} !A  Unpacked strict field B
+data Bar = {-# UNPACK #-} !A  Unpacked strict field :%% B
diff --git a/testsuite/tests/haddock/should_compile_noflag_haddock/all.T b/testsuite/tests/haddock/should_compile_noflag_haddock/all.T
index edb2bd0e05..4e52c2d92c 100644
--- a/testsuite/tests/haddock/should_compile_noflag_haddock/all.T
+++ b/testsuite/tests/haddock/should_compile_noflag_haddock/all.T
@@ -42,6 +42,7 @@ test('haddockC032', normal, compile, [''])
 test('haddockC035', normal, compile, [''])
 test('haddockC036', normal, compile, [''])
 test('haddockC037', normal, compile, [''])
+test('haddockC038', normal, compile, [''])
 
 # The tests below this line are not duplicated in
 # should_compile_flag_haddock.
diff --git a/testsuite/tests/haddock/should_compile_noflag_haddock/haddockC038.hs b/testsuite/tests/haddock/should_compile_noflag_haddock/haddockC038.hs
new file mode 100644
index 0000000000..b839bdee22
--- /dev/null
+++ b/testsuite/tests/haddock/should_compile_noflag_haddock/haddockC038.hs
@@ -0,0 +1,14 @@
+module UnamedConstructorStrictFields where
+-- See #15206
+
+data A = A
+data B = B
+
+data Foo = MkFoo
+  {-# UNPACK #-} !A -- ^ Unpacked strict field
+                 B
+
+data Bar =
+  {-# UNPACK #-} !A -- ^ Unpacked strict field
+    :%%
+                 B