Test Trac #5287

testsuite/tests/deriving/should_fail/T5287.hs

+{-# LANGUAGE MultiParamTypeClasses, UndecidableInstances #-}
+module Bug where
+class A a oops
+data D d = D d
+instance A a oops => Read (D a)
+data E e = E (D e) deriving Read
+
+

testsuite/tests/deriving/should_fail/T5287.stderr

+ghc-stage2.exe: panic! (the 'impossible' happened)
+  (GHC version 7.3.20110721 for i386-unknown-mingw32):
+	solveDerivEqns: probable loop
+    (T5287.hs:6:29-32 main:Bug.$fReadE{v rhW} [e{tv aaR} [tv]] base:GHC.Read.Read{tc 2d} [main:Bug.E{tc raM}
+                                                                                            e{tv aaR} [tv]] = [base:GHC.Read.Read{tc 2d}
+                                                                                                                 (main:Bug.D{tc raO}
+                                                                                                                    e{tv aaR} [tv])])
+    [[main:Bug.A{tc raQ} e{tv aaR} [tv] oops{tv alO} [tcs]]]
+
+Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
+

testsuite/tests/deriving/should_fail/all.T

@@ -32,4 +32,5 @@ test('drvfail-foldable-traversable1', normal, compile_fail,
 test('T3833', normal, compile_fail, [''])
 test('T3834', normal, compile_fail, [''])
 test('T4528', normal, compile_fail, [''])
+test('T5287', normal, compile_fail, [''])