From 704b66a03c7b139f7945a934f60a7b0c95f2b520 Mon Sep 17 00:00:00 2001
From: nikivazou <nikivazou@gmail.com>
Date: Mon, 24 Feb 2020 11:31:19 +0100
Subject: [PATCH] make functor a generic class for #1619

---
 .../Haskell/Liquid/Constraint/Generate.hs     |  5 ++--
 tests/pos/T1619.hs                            | 30 +++++++++++++++++++
 2 files changed, 32 insertions(+), 3 deletions(-)
 create mode 100644 tests/pos/T1619.hs

diff --git a/src/Language/Haskell/Liquid/Constraint/Generate.hs b/src/Language/Haskell/Liquid/Constraint/Generate.hs
index aeeefbbad2..2b716ee205 100644
--- a/src/Language/Haskell/Liquid/Constraint/Generate.hs
+++ b/src/Language/Haskell/Liquid/Constraint/Generate.hs
@@ -1458,14 +1458,13 @@ isPLETerm γ
 
 -- | @isGenericVar@ determines whether the @RTyVar@ has no class constraints
 isGenericVar :: RTyVar -> SpecType -> Bool
-isGenericVar α t =  all (\(c, α') -> (α'/=α) || isOrd c || isEq c ) (classConstrs t)
+isGenericVar α t =  all (\(c, α') -> (α'/=α) || isGenericClass c ) (classConstrs t)
   where 
     classConstrs t = [(c, ty_var_value α')
                         | (c, ts) <- tyClasses t
                         , t'      <- ts
                         , α'      <- freeTyVars t']
-    isOrd          = (ordClassName ==) . className
-    isEq           = (eqClassName ==) . className
+    isGenericClass c = className c `elem` [ordClassName, eqClassName, functorClassName]
 
 -- instance MonadFail CG where 
 --  fail msg = panic Nothing msg
diff --git a/tests/pos/T1619.hs b/tests/pos/T1619.hs
new file mode 100644
index 0000000000..966a0a3f59
--- /dev/null
+++ b/tests/pos/T1619.hs
@@ -0,0 +1,30 @@
+{-# LANGUAGE Rank2Types #-}
+
+{-@ data Label<label :: User -> Bool> where @-}
+data Label
+data User
+data Tagged l a = Tag a
+data MyFunctor f = MyFunctor { myFmap :: forall a b. (a -> b) -> f a -> f b }
+
+instance Functor (Tagged l) where
+  fmap = fmapTagged
+
+taggedFunctor :: MyFunctor (Tagged l)
+taggedFunctor = MyFunctor fmapTagged
+
+fmapTagged :: (a -> b) -> Tagged l a -> Tagged l b
+fmapTagged f (Tag x) = Tag (f x)
+
+{-@
+myFmapPreservesLabel :: forall <label :: User -> Bool>.
+(a -> b) -> Tagged (Label<label>) a -> Tagged (Label<label>) b
+@-}
+myFmapPreservesLabel :: (a -> b) -> Tagged Label a -> Tagged Label b
+myFmapPreservesLabel = myFmap taggedFunctor
+
+{-@
+fmapPreservesLabel :: forall <label :: User -> Bool>.
+(a -> b) -> Tagged (Label<label>) a -> Tagged (Label<label>) b
+@-}
+fmapPreservesLabel :: (a -> b) -> Tagged Label a -> Tagged Label b
+fmapPreservesLabel = fmap
\ No newline at end of file