False positive

[bhoudebert]

I am facing an issue with weeder, it literally says that all of my functions are unused.

Version used:

• weeder 2.2.0
• ghc 8.10.7
• linux + nix

It was working fine a couple of weeks ago and I just discover this weird behavior during:

• ghc upgrade (8.10.3)
• migration a simple nix project to haskell.nix
• moving back from stack to cabal

The hie files are well generated, HLS is able to use them correctly in my editor (so they should be fine).

I end up trying differents configs in the dhall without any success, from my old configuration to the default one propose in this repo.

By chance do you have any tips or hint about this weird situation?

[ocharles]

Can you share you weeder Dhall config, along with sample weeds and why you think they are false positives?

[bhoudebert]

First, thanks for helping me.

I used several different dhall file without any different behavior, last/current one is:

{ roots =
    [ "^Main.main$" ],
    type-class-roots = True
}

It really list every functions of the whole program. As the program is somehow small (just a couple of files), it is easy for me to verify that weeder is wrong. For example, -Wunused-top-binds does not see anything. Most important, like I said in the beginning,weeder before migrations was fine with the code.

Here is also some extra informations.

What is weird is the output of weeder:

src/Business.hs:82: logUserMonthSimulation
src/Business.hs:63: processMonth
src/Business.hs:29: processingBalances
src/Business.hs:56: processingConduit
src/Business.hs:95: updateUserForMonth

and it stops there, without any detail or number of weeds but the program exit with a 1 (echo $?)

If I compare with another project (different version of everything, weeder, stack, ghc)

(...)
src/Commons/Model/User/Permission.hs:16:1: error: allWritePermissions is unused

      14 ┃ 
      15 ┃ allWritePermissions :: [PowerUser] -> [Permission]
      16 ┃ allWritePermissions = fmap Write

    Delete this definition or add ‘Commons.Model.User.Permission.allWritePermissions’ as a root to fix this error.
Weeds detected: 8

If there is not dead code on the second project obvioulsy the output of weeder is Weeds detected: 0

NB: note that for some reason I had to position export LC_ALL=C.UTF-8 in order to run correctly weeder (on the second project) otherwise it fails on parsing file. On the first project doing that will not produce anything.

The difference of weeder behavior on the first project is very weird and as I do not get the number of weeds maybe it could tell us that it crash?

[shapr]

I'm also getting some definite false positives with ghc 8.10.7 and weeder 2.1.3 , but in a proprietary codebase.
I'll check some of our public repos and see if I can reproduce it there.

[bhoudebert]

Any news over here?

[ocharles]

Sorry, I haven't had a chance to look.