👓 Automatically add files to exposed-modules and other-modules.
https://hackage.haskell.org/package/velma
Although this package works, I wouldn't recommend using it. There are critical usability problems with both Cabal and Stack. (These problems also apply to autopack and cabal-auto-expose.)
The problem with Stack is straightforward: It shows a warning for modules that are automatically discovered by Velma. Everything continues to function correctly, but the warnings are annoying and can't be disabled. Here's the relevant issues: #1881 and #1705.
The problem with Cabal is more complicated.
Of course the core problem is that the *.cabal file format doesn't support globbing for module names (#5343).
Velma attempts to work around that by discovering modules as part of the custom setup.
Unfortunately sdist doesn't run the custom setup (#3424).
That alone wouldn't be the end of the world since Velma is meant more for applications than libraries.
But the show stopper is that Cabal won't rebuild when you change a module that was discovered by Velma.
This means that you need to reconfigure before rebuilding.
Taking all of the above into account, my suggestion is: Use something like hpack or cabal-fmt. If you're going to have to modify your build to run extra commands, you might as well explicitly generate the list of exposed modules.