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For some upcoming improvements to FP Haskell Center, I recently added a new feature to Stackage: the ability to detect module name conflicts. This is where two different packages both export a module of the same name.

You can see the full module name conflict list for my most recent build. The file format is fairly dumb: one line lists all of the packages using a common module name, and the following line contains all of the module names shared. (JSON, YAML, or CSV would have been better file formats for this, but one of the goals of the Stackage codebase is to avoid extra package dependencies wherever possible.)

Most of these conflicts don't seem problematic at all. The fact that base, haskell98, haskell2010, and base-compat share a lot of the same module names, for example, should be expected, and users really do need to choose just one of those packages to depend on.

Some other cases, on the other hand, might cause issues. For example, both hashmap and unordered-containers export the Data.HashSet module. This can negatively affect users of GHCi who have both packages installed and try to import Data.HashSet. Also, if for some reason a cabal package depended on both, you'd need to use package imports to disambiguate. There can also be an issue of confusion: if I see Data.HashSet at the top of a module, it would be nice to know which package it comes from without having to check a cabal file or running ghc-pkg.

I'm mostly writing this blog post as I think it's the first time we've had any kind of collection of this information, and I don't think we've had a community discussion about conflicting module names. I don't know if the problem is significant enough to even warrant further analysis, or how have thoughts on how to proceed if we do want to try and disambiguate module names.

Here are some of the conflicting module names, and the packages using them: