Mixins: stack build error "Could not load module Relude.String, member of hidden package"

[ulidtko]

Hi @kowainik 🙏

Here I've minified a 4-file reproducer: relude-mixins.zip

On unpacking and stack build inside, this error appears:

foo> configure (lib)
Configuring foo-0.1.0.0...
foo> build (lib)
Preprocessing library for foo-0.1.0.0..
Building library for foo-0.1.0.0..
[1 of 2] Compiling Lib

/tmp/foo/src/Lib.hs:5:1: error:
    Could not load module ‘Relude.String’
    It is a member of the hidden package ‘relude-0.7.0.0’.
    Perhaps you need to add ‘relude’ to the build-depends in your .cabal file.
    Use -v (or `:set -v` in ghci) to see a list of the files searched for.
  |
5 | import Relude.String
  | ^^^^^^^^^^^^^^^^^^^^

And of course, build-depends in the cabal file contains exactly relude ==0.7.0.0.

Stack Version 2.7.3, Git revision 7927a3aec32e2b2e5e4fb5be76d0d50eddcc197f. Not sure if commercialhaskell/stack#5077 is related; perhaps it is. The --cabal-verbose commandline looks sane too; could be even bug in Cabal or further below 🤷‍♂️ Reporting to Relude for definiteness.

As a workaround, I'm switching to NoImplicitPrelude + import Relude. That way gives me the Text reexport, without further fiddling with dependencies.

HTH

[chshersh]

@ulidtko Yes, that mentioned Stack issue is the reason why stack doesn't work when the mixins approach is used. This is already documented in the README as per the relevant issue:

• Document that mixins doesn't work with stack repl #328
• https://github.com/kowainik/relude#mixins