Test case for RULE map coerce = coerce

(This tests #2110.)

testsuite/tests/simplCore/should_run/T2110.hs

+{-# LANGUAGE MagicHash #-}
+
+import GHC.Exts
+import Unsafe.Coerce
+
+{-# RULES
+"map/coerce"  map coerce = coerce
+ #-}
+
+newtype Age = Age Int
+
+fooAge :: [Int] -> [Age]
+fooAge = map Age
+fooCoerce :: [Int] -> [Age]
+fooCoerce = map coerce
+fooUnsafeCoerce :: [Int] -> [Age]
+fooUnsafeCoerce = map unsafeCoerce
+
+same :: a -> b -> IO ()
+same x y = case reallyUnsafePtrEquality# (unsafeCoerce x) y of
+    1# -> putStrLn "yes"
+    _  -> putStrLn "no"
+
+main = do
+    let l = [1,2,3]
+    same (fooAge l) l
+    same (fooCoerce l) l
+    same (fooUnsafeCoerce l) l

testsuite/tests/simplCore/should_run/T2110.stdout

+yes
+yes
+yes

testsuite/tests/simplCore/should_run/all.T

@@ -51,6 +51,7 @@ test('T5453', normal, compile_and_run, [''])
 test('T5441', extra_clean(['T5441a.o','T5441a.hi']), 
               multimod_compile_and_run, ['T5441',''])
 test('T5603', normal, compile_and_run, [''])
+test('T2110', expect_broken(2110), compile_and_run, [''])
 
 # Run these tests *without* optimisation too
 test('T5625', [ only_ways(['normal','optasm']), exit_code(1) ], compile_and_run, [''])