Fix scoping of type variables in instances

This fixes Trac #12531:

   class Foo x where
     foo :: forall a . x a -> x a
     default foo :: forall b . x b -> x b
     foo x = go
       where go :: x b
             go = undefined

We want 'b' to scope over the code for 'foo', but we were
using 'a' instead.

1 files changed, 10 insertions, 0 deletions

diff --git a/testsuite/tests/rename/should_compile/T12533.hs b/testsuite/tests/rename/should_compile/T12533.hs
new file mode 100644
index 0000000000..a120babf3f
--- /dev/null
+++ b/testsuite/tests/rename/should_compile/T12533.hs
@@ -0,0 +1,10 @@
+{-# LANGUAGE ScopedTypeVariables, DefaultSignatures #-}
+
+module T12533 where
+
+class Foo x where
+  foo :: forall a . x a -> x a
+  default foo :: forall a . x a -> x a
+  foo x = go
+    where go :: x a
+          go = undefined