Add test for dependency analysis in type checking

testsuite/tests/ghc-regress/typecheck/should_compile/all.T

@@ -216,6 +216,7 @@ test('tc203', normal, compile, [''])
 test('tc204', normal, compile, [''])
 test('tc205', normal, compile, [''])
 test('tc206', normal, compile, [''])
+test('tc207', normal, compile, [''])
 
 # Omitting temporarily
 # test('syn-perf', normal, compile, ['-fcontext-stack=30'])

testsuite/tests/ghc-regress/typecheck/should_compile/tc207.hs

+{-# OPTIONS -fglasgow-exts #-}
+
+-- Tests enhanced polymorphism
+
+module ShouldCompile where
+
+foo xs = let 
+	   f :: Eq a => [a] -> [a]
+	   f [] = []
+	   f xs | null (g [True]) = [] 
+		| otherwise       = tail (g xs) 
+
+	   g :: Eq b => [b] -> [b]
+	   g [] = []
+	   g xs | null (f "hello") = [] 
+		| otherwise       = tail (f xs) 
+ 	in f xs