Missing support for renaming Main module using main-is

[newton-migosi]

Building a project that defines an alternative name for the Main module fails. For example, I had defined a test suite whose main module was Spec.hs in the .cabal file

test tests
  import: shared
  type: exitcode-stdio-1.0
  hs-source-dirs: test
  main-is: Spec.hs
  other-modules: Spec.Endpoints

This worked just fine when doing cabal build.. but nix build failed with

<no location info>: error: output was redirected with -o, but no output will be generated because there is no Main module.
error: builder for '/nix/store/1rib7lymarlw3xcnlryqq89rdbnh4rk8-local-library-0.1.0.0.drv' failed with exit code 1
Error: Process completed with exit code 1.

Full logs at https://github.com/newton-migosi/mdn-local-library-tutorial/actions/runs/4868638253/jobs/8682285870

[newton-migosi]

Adding a Main.hs that executes Spec.hs fixes the problem