Detached HEADs are normal with submodules. (I suppose sentences like that would have gotten me executed several centuries ago...)

When I look at https://github.com/mynguyenbmc/ghc/compare/93a3f9070d5d69ad6a28fe94ccccd20c54609698...wip/kind-app, which is, I believe, the difference between GHC HEAD and your branch, I see that the Cabal submodule has changed. I imagine you didn't mean to do this. (This has happened to me with an ill-timed `git add -u` while rebasing. Perhaps that's what caused the trouble for you, too.)

To fix, you can manually `git checkout abcdefabcdef` each erroneously changed submodule to point to the right commit from HEAD. Then, `git add` each submodule in the ghc repo (i.e. not inside any submodule) and try again.

I hope this helps!
Richard

On Dec 3, 2018, at 6:27 PM, My Nguyen <mnguyen1@brynmawr.edu> wrote:

I did not touch Cabal at all, but somehow `git status` in libraries/Cabal is telling me there’s a detached HEAD?

I built GHC with a fresh checkout from github, and it worked. But after applying my patch, it doesn’t work anymore. 
From: Richard Eisenberg <rae@cs.brynmawr.edu>
Sent: Monday, December 3, 2018 8:26 PM
To: My Nguyen
Cc: Krzysztof Gogolewski; ghc-devs@haskell.org
Subject: Re: Cabal not updated after rebase?
 
Did you change the Cabal submodule at all in your work? Maybe it's out of sync somehow...

What happens if you build GHC without including your changes? Does it work?

On Dec 3, 2018, at 12:13 PM, My Nguyen <mnguyen1@brynmawr.edu> wrote:

Hello,

Thanks for the suggestion. Unfortunately, the problem persists :(! 

My 
 
From: Krzysztof Gogolewski <krz.gogolewski@gmail.com>
Sent: Monday, December 3, 2018 2:46 PM
To: My Nguyen
Cc: ghc-devs@haskell.org
Subject: Re: Cabal not updated after rebase?
 
Hi,

Does `git clean -fdx .` in libraries/Cabal help? git clean doesn't go into submodules.

-Krzysztof

On Mon, Dec 3, 2018 at 6:09 PM My Nguyen <mnguyen1@brynmawr.edu> wrote:
Hi all,

I've finished quite a big rebase and was trying to rebuild, but it failed with:

ghc-cabal: Encountered missing dependencies:
Cabal ==2.5.*
I then tried applying my patch on a fresh checkout of GHC and found the reason:


libraries/Cabal/Cabal/Distribution/Compat/Prelude.hs:119:1:error:
   Bad interface file: libraries/Cabal/Cabal/dist-boot/build/Distribution/Compat/Binary.hi
       Something is amiss; requested module  Cabal-2.4.0.1:Distribution.Compat.Binary differs from name found in the interface file Cabal-2.5.0.0:Distribution.Compat.Binary (if these names look the same, try again with -dppr-debug)
   |
119 |import Distribution.Compat.Binary   (Binary (..))
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

libraries/Cabal/Cabal/Distribution/Compat/Prelude.hs:120:1:error:
   Bad interface file: libraries/Cabal/Cabal/dist-boot/build/Distribution/Compat/Semigroup.hi
       Something is amiss; requested module  Cabal-2.4.0.1:Distribution.Compat.Semigroup differs from name found in the interface file Cabal-2.5.0.0:Distribution.Compat.Semigroup (if these names look the same, try again with -dppr-debug)
   |
120 |import Distribution.Compat.Semigroup (Semigroup (..), gmappend, gmempty)
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

libraries/Cabal/Cabal/Distribution/Compat/Prelude.hs:141:1:error:
   Bad interface file: libraries/Cabal/Cabal/dist-boot/build/Distribution/Compat/Stack.hi
       Something is amiss; requested module  Cabal-2.4.0.1:Distribution.Compat.Stack differs from name found in the interface file Cabal-2.5.0.0:Distribution.Compat.Stack (if these names look the same, try again with -dppr-debug)
   |
141 |import Distribution.Compat.Stack
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


I'm sure I did `git module update`; I even `git clean` everything and  `make` from fresh but somehow the cabal still isn't updated. Can anyone help me on why this is happening and how to fix it?

Thanks so much,
My
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