Fix renaming after instance signature specializing (#660)

* rework rename

* Add regression test for Bug 613

* update tests

* update changelog

1 files changed, 16 insertions, 0 deletions

diff --git a/html-test/src/Bug613.hs b/html-test/src/Bug613.hs
new file mode 100644
index 00000000..effef695
--- /dev/null
+++ b/html-test/src/Bug613.hs
@@ -0,0 +1,16 @@
+module Bug613  where
+
+import Prelude (Either(Left, Right))
+
+class Functor f where
+  fmap :: (a -> b) -> f a -> f b
+
+instance Functor (Either a) where
+  fmap _ (Left x) = Left x
+  fmap f (Right y) = Right (f y)
+
+-- | Phantom type a0 is added to block the first renaming from a to a0. This ensures that the renamer doesn't create a new conflict
+data ThreeVars a0 a b = ThreeVars a b
+
+instance Functor (ThreeVars a0 a) where
+  fmap f (ThreeVars a b) = ThreeVars a (f b)