Could cabal warn about unused package in dependencies?

Question

For given cabal project how could unused dependencies packages be retrieved?

Is there a way to get something like warning during cabal install process if there is a package mentioned in project dependency and there is no any usage of it, so it could be removed from dependencies?

I don't think `cabal` is prepared for that yet. It would certainly be a useful feature. — Daniel Fischer, May 06 '13 at 00:04
It'd be useful, but it's an engineering challenge right now. It straddles the line between what cabal knows (packages listed in the .cabal file) and what GHC knows (what packages are used). It might not be bad to add it as a standalone utility, but it's probably not practical to include it with by default with `cabal install`. — Carl, May 06 '13 at 05:53
If you had an answer to http://stackoverflow.com/q/15203191/812053 , the rest would be relatively straightforward... — Ben Millwood, May 16 '13 at 09:41

score 8 · Answer 1 · answered May 22 '13 at 18:04

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I think the program packunused is what you are looking for.

answered May 22 '13 at 18:04

LambdaStaal

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score 7 · Answer 2 · edited Apr 17 '23 at 13:09

There are some options:

For GHC 8.6 and earlier, Weeder version 1 by Neil Mitchell can find unused dependencies.
For GHC 8.10 and later, there is a warning GHC may emit (with the GHC option -Wunused-packages) when it sees unnecessary packages in the package database. Since Cabal prepares the package database, any unnecessary package is an unused dependency.

Unfortunately, GHC 8.8 is left out.

P. S. There was recently released a program called prune-juice that should work for GHC 8.8 too.

Gabriel Riba · Answer 3 · 2013-05-06T14:36:12.577

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cabal-progdeps lists dependencies once the cabal project has been built.

You can check if thay are all used by adding an unused one to your project.

It requires the same Cabal library version used in cabal-install, otherwise it gives errors parsing dist/setup-config.

edited May 06 '13 at 14:36

answered May 06 '13 at 14:30

Gabriel Riba

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I am sorry, I have checked cabal-progdeps and it lists all dependencies in the .cabal project file, wether used or not, so it is not a good tool to find out the unused ones. – Gabriel Riba May 07 '13 at 20:18
Yep, it doesn't help at all :[ – ДМИТРИЙ МАЛИКОВ May 08 '13 at 11:42
by the way, `cabal-progdeps` package is kinda outdated because of upper boundaries for `filepath` and `directory` – ДМИТРИЙ МАЛИКОВ May 08 '13 at 11:45
@ДМИТРИЙ МАЛИКОВ You can always do it manually. From a working project cabal file, comment out one suspected unused dependency and try to cabal configure and build it. – Gabriel Riba May 09 '13 at 09:29
Yep, question is about this process automation. – ДМИТРИЙ МАЛИКОВ May 09 '13 at 10:51

score 1 · Answer 4 · answered Dec 09 '17 at 21:59

1

There is yet another tool:

https://github.com/ndmitchell/weeder https://hackage.haskell.org/package/weeder

It's not yet on Stackage though

answered Dec 09 '17 at 21:59

nponeccop

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Could cabal warn about unused package in dependencies?

4 Answers4