Pandoc and haddock-library gets rebuilt upon every "stack build" invocation

[k-bx]

General summary/comments (optional)

I've made a simple program which parses a bit of text via Pandoc. It recompiles pandoc and haddock-library upon every stack build invocation. I've made a small repo which shows this behavior.

Steps to reproduce

For example:

git clone https://github.com/k-bx/pandoc-rebuild.git
cd pandoc-rebuild
stack build
stack build

Expected

Immediately exit upon second step.

Actual

I see something like:

cd /home/kb/workspace/pandoc-rebuild-ghc84/ && stack build                                                                                                                                                                                                                                                           
haddock-library-1.5.0.1: unregistering                                                                                                                                                                                                                                                                               
haddock-library-1.5.0.1: configure                                                                                                                                                                                                                                                                                   
haddock-library-1.5.0.1: build                                                                                                                                                                                                                                                                                       
haddock-library-1.5.0.1: copy/register                                                                                                                                                                                                                                                                               
pandoc-2.1.3: configure                                                                                                                                                                                                                                                                                              
pandoc-2.1.3: build                                                                                                                                                                                                                                                                                                  

and the usual rebuild happening, which takes a long time for Pandoc. Here's a gist where I ran second stack build with a -v flag: https://gist.github.com/k-bx/2a5296f2d92b903cf8b2dfb4a2deca9c Stack is not latest there but I'm currently reproducing via 1.6.5 and it seems the effect is the same.

Stack version

$ stack --version
Version 1.6.5, Git revision 24ab0d6ff07f28276e082c3ce74dfdeb1a2ca9e9 (5514 commits) x86_64 hpack-0.20.0

Method of installation

• I had Ubuntu package for 1.6.3 but did a stack upgrade to get 1.6.5 and it reproduced the problem.

Thank you for looking into this!

[mgsloan]

Thanks for the report! I believe this is a duplicate of #3899 . Please reopen if not. Looks like the issue is that recent versions of haddock-library has an internal sub library that shadows attoparsec. One way or another this is causing rebuilds.

Digging into why this is happening and possibly fixing it with a PR would be greatly appreciated!