internal error: extractDecl (ClsInstD)

[tmcdonell]

I encountered this error running haddock on accelerate-llvm-native (example travis log):

haddock: internal error: internal: extractDecl (ClsInstD)
CallStack (from HasCallStack):
  error, called at utils/haddock/haddock-api/src/Haddock/Interface/Create.hs:1067:16 in main:Haddock.Interface.Create

• ghc-8.4.1
• haddock-2.19.0 and 2.19.0.1
• ubuntu 14.04 and macOS 10.13

If you have some suggestions for how to trim this down to a smaller example I can try that. Otherwise this should reproduce it:

$ git clone https://github.com/AccelerateHS/accelerate-llvm.git
$ cd accelerate-llvm
$ stack haddock accelerate-llvm-native

[alexbiehl]

Trevor, thank you for your report. 'extractDecl' is called for exports that only export a small part of the whole declaration. In this case we are talking about a class instance which probably exports an associated data type or similar and we are only interested in that data type. Maybe that helps pinning down the offender.

I will investigate by myself later today.

[alexbiehl]

Trevor, I couldn't find anything suspicious from your source (I just had a look, couldn't build it for some reason). But I found missing cases in extractDecl (see 7b3f6f3).

These were strictly not possible with older versions of haddock. Could you give it a try?

[tmcdonell]

Hi @alexbiehl, thanks for the quick fix! haskell/haddock@ 7b3f6f3 seems to have done it! (:

[alexbiehl]

Good to know. Interestingly, AFAIK, this situation can only arise with the use of pattern exports like this:

module (pattern A) where

class T a where 
  data X a

instance T Bla where
  data X Blah = A | B

I couldn't find such a thing in your source code. Have you seen something like this?

[tmcdonell]

Interesting. I don't have any pattern synonyms at all. There are some associated data types (1, 2, 3, 4) which are all standard records, and a few non-associated data families (1, 2, 3), but I think that is it.

[alexbiehl]

Ok, could you upload the documentation somewhere?

[tmcdonell]

Uploaded here: https://tmcdonell.github.io/haddock-bug/accelerate-llvm-native-1.2.0.0/

Here is a slightly older version build with ghc-8.2 / haddock-2.18.1: http://tmcdonell-bot.github.io/accelerate-travis-buildbot/accelerate-llvm-native-1.2.0.0/index.html