#15138: Unable to instantiate data members of kind Nat in backpack signatures. -------------------------------------+------------------------------------- Reporter: ppk | Owner: (none) Type: bug | Status: patch Priority: normal | Milestone: 8.8.1 Component: Compiler | Version: 8.4.1 Resolution: | Keywords: backpack Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D4951 Wiki Page: | -------------------------------------+------------------------------------- Comment (by ppk): Replying to [comment:4 bgamari]:
Unfortunately it doesn't look like this will quite make it. Sorry ppk!
That is okey. Thanks for all the effort you and the ghc team makes. But here are some of the things about the failing test cases. I am documenting it here so that it can be useful for diagnosing them if this patch has to eventually land. 1. The failing tests are all in the backpack tests should_fail section namely bkpfail23,25,26,27 and 46 2. Of these all except `bkpfail46` is still giving compilation error which but the stderr are not matching. As a result the most interesting test is `bkpfail46` as that is a case that was rejected before the patch which is getting accepted now. So we should really understand bkpfail46 to make sense whether it is i. Making backpack more general (a good thing). This just means that the test case is no more relevant and could just be removed or ignored. ii. Or this could be a break in typesafety and hence bad. I do not think I understand the issues there fully to make a comment on it one way or the other. 3. The next critical test is the bkpfail25 as it gives an error message of the form {{{ bkpfail25.bkp:7:18: error: _ The type synonym _T_ should have 1 argument, but has been given none _ In the instance declaration for _Functor T_ }}} There is a comment `bkpfail25.bkp` that precisely says that such an error message is "too late". So this too looks like a test case that needs some analysis. 4. The other tests that fails, I do not have much to say. I wanted to say that I also have a dependent phab which builds on this to fix #15379 where I did document this. These tests were failing on my machine and I was thinking that it could be some change that I introduced in that patch which made the difference. Now it looks like this is a problem even here. In summary, this looks like a test that requires some serious thought from someone who understands the backpack system much more than me. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15138#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler