[commit: ghc] master: Fix #14888 by adding more special cases for ArrowT (6ee831f)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/6ee831f279c91888ee5815f8eee473bcd6fd25c6/ghc

>---------------------------------------------------------------

commit 6ee831f279c91888ee5815f8eee473bcd6fd25c6
Author: Ryan Scott <ryan.gl.scott at gmail.com>
Date:   Mon Mar 5 08:57:04 2018 -0500

    Fix #14888 by adding more special cases for ArrowT
    
    Summary:
    There were previously some situations where `(->)` would
    not be desugared or reified as `ArrowT`, leading to various oddities
    such as those observed in #14888. We now uniformly treat `(->)` as
    `ArrowT` in Template Haskell–world by checking for any tycon that
    has the same name as `(->)`, and converting that to `ArrowT`.
    
    Test Plan: make test TEST=T14888
    
    Reviewers: goldfire, bgamari, simonpj
    
    Reviewed By: goldfire, simonpj
    
    Subscribers: simonpj, rwbarton, thomie, carter
    
    GHC Trac Issues: #14888
    
    Differential Revision: https://phabricator.haskell.org/D4466


>---------------------------------------------------------------

6ee831f279c91888ee5815f8eee473bcd6fd25c6
 compiler/deSugar/DsMeta.hs       |  1 +
 compiler/typecheck/TcSplice.hs   |  1 +
 testsuite/tests/th/T14888.hs     | 18 ++++++++++++++++++
 testsuite/tests/th/T14888.stderr | 11 +++++++++++
 testsuite/tests/th/all.T         |  2 ++
 5 files changed, 33 insertions(+)

diff --git a/compiler/deSugar/DsMeta.hs b/compiler/deSugar/DsMeta.hs
index db25c55..5029f9d 100644
--- a/compiler/deSugar/DsMeta.hs
+++ b/compiler/deSugar/DsMeta.hs
@@ -994,6 +994,7 @@ repTy ty@(HsQualTy {})   = repForall ty
 repTy (HsTyVar _ (L _ n))
   | isLiftedTypeKindTyConName n       = repTStar
   | n `hasKey` constraintKindTyConKey = repTConstraint
+  | n `hasKey` funTyConKey            = repArrowTyCon
   | isTvOcc occ   = do tv1 <- lookupOcc n
                        repTvar tv1
   | isDataOcc occ = do tc1 <- lookupOcc n
diff --git a/compiler/typecheck/TcSplice.hs b/compiler/typecheck/TcSplice.hs
index 45e18e6..00591d1 100644
--- a/compiler/typecheck/TcSplice.hs
+++ b/compiler/typecheck/TcSplice.hs
@@ -1881,6 +1881,7 @@ reify_tc_app tc tys
          | isTupleTyCon tc                = if isPromotedDataCon tc
                                             then TH.PromotedTupleT arity
                                             else TH.TupleT arity
+         | tc `hasKey` funTyConKey        = TH.ArrowT
          | tc `hasKey` listTyConKey       = TH.ListT
          | tc `hasKey` nilDataConKey      = TH.PromotedNilT
          | tc `hasKey` consDataConKey     = TH.PromotedConsT
diff --git a/testsuite/tests/th/T14888.hs b/testsuite/tests/th/T14888.hs
new file mode 100644
index 0000000..e2bcec6
--- /dev/null
+++ b/testsuite/tests/th/T14888.hs
@@ -0,0 +1,18 @@
+{-# LANGUAGE TemplateHaskell #-}
+module T14888 where
+
+import Language.Haskell.TH
+
+foo :: $([t| (->) Bool Bool |])
+foo x = x
+
+class Functor' f where
+  fmap' :: (a -> b) -> f a -> f b
+
+instance Functor' ((->) r) where
+  fmap' = (.)
+
+$(return [])
+
+functor'Instances :: String
+functor'Instances = $(reify ''Functor' >>= stringE . pprint)
diff --git a/testsuite/tests/th/T14888.stderr b/testsuite/tests/th/T14888.stderr
new file mode 100644
index 0000000..963937f
--- /dev/null
+++ b/testsuite/tests/th/T14888.stderr
@@ -0,0 +1,11 @@
+T14888.hs:6:10-30: Splicing type
+    [t| (->) Bool Bool |] ======> Bool -> Bool
+T14888.hs:15:3-11: Splicing declarations return [] ======>
+T14888.hs:18:23-59: Splicing expression
+    reify ''Functor' >>= stringE . pprint
+  ======>
+    "class T14888.Functor' (f_0 :: * -> *)
+    where T14888.fmap' :: forall (f_0 :: * ->
+                                         *) . T14888.Functor' f_0 =>
+                          forall (a_1 :: *) (b_2 :: *) . (a_1 -> b_2) -> f_0 a_1 -> f_0 b_2
+instance T14888.Functor' ((->) r_3 :: * -> *)"
diff --git a/testsuite/tests/th/all.T b/testsuite/tests/th/all.T
index 47e8a9c..e9f2838 100644
--- a/testsuite/tests/th/all.T
+++ b/testsuite/tests/th/all.T
@@ -403,3 +403,5 @@ test('T14838', [], multimod_compile,
      ['T14838.hs', '-v0 -Wincomplete-patterns ' + config.ghc_th_way_flags])
 test('T14817', normal, compile, ['-v0 -ddump-splices -dsuppress-uniques'])
 test('T14843', normal, compile, ['-v0'])
+test('T14888', normal, compile,
+    ['-v0 -ddump-splices -dsuppress-uniques ' + config.ghc_th_way_flags])