Assertion failure on FD3 test in TcErrors
typecheck/should_compile/FD3 leads to an
ghc-stage2: panic! (the 'impossible' happened) (GHC version 7.11.20150605 for x86_64-apple-darwin): ASSERT failed! file compiler/typecheck/TcErrors.hs line 321 [[D] _ :: a_amP[sk] ~ (String, a_amP[sk]) (CNonCanonical)] Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
FD3.log (attached) shows the error happening.
(When originally posting this ticket, I was very confused. The first several comments, through ticket:10533#comment:101025, are now bogus. Please ignore.)