Do not quantify over the function itself in a RULE

We were erroneously quantifying over the function when it
had a dictionary type. A bit pathological, but possible.

This fixes Trac #10251

2 files changed, 42 insertions, 0 deletions

diff --git a/testsuite/tests/deSugar/should_compile/T10251.hs b/testsuite/tests/deSugar/should_compile/T10251.hs
new file mode 100644
index 0000000000..afca7fb9c7
--- /dev/null
+++ b/testsuite/tests/deSugar/should_compile/T10251.hs
@@ -0,0 +1,41 @@
+{-# LANGUAGE NoImplicitPrelude #-}
+{-# OPTIONS_GHC -O #-}
+module T10251 where
+
+data D = D
+data E = E
+
+class Storable a where
+    poke2 :: a -> E
+instance Storable D where
+    poke2 = poke2 -- undefined
+
+class Foo a where
+instance Foo D where
+
+class (Foo t, Storable t) => FooStorable t where
+
+instance FooStorable D where
+    {-# SPECIALIZE instance FooStorable D #-}
+
+{-# SPECIALIZE bug :: D -> E #-}
+
+bug
+  :: FooStorable t
+  => t
+  -> E
+bug = poke2
+{-
+sf 9160 # ghc -c -fforce-recomp -Wall B.hs
+
+ghc: panic! (the 'impossible' happened)
+  (GHC version 7.10.1 for x86_64-unknown-linux):
+        Template variable unbound in rewrite rule
+  $fFooStorableD_XU
+  [$fFooStorableD_XU]
+  [$fFooStorableD_XU]
+  []
+  []
+
+Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
+-}
diff --git a/testsuite/tests/deSugar/should_compile/all.T b/testsuite/tests/deSugar/should_compile/all.T
index ac8f95c0c2..956f951151 100644
--- a/testsuite/tests/deSugar/should_compile/all.T
+++ b/testsuite/tests/deSugar/should_compile/all.T
@@ -103,3 +103,4 @@ test('T5252Take2',
 test('T2431', normal, compile, ['-ddump-simpl -dsuppress-uniques'])
 test('T7669', normal, compile, [''])
 test('T8470', normal, compile, [''])
+test('T10251', normal, compile, [''])