Last year was discussed the deprecation of GHCi’s tag generation feature, as it had become a liability with recent additions to the language, like Unboxed Sums. It was then decided to drop the integrated feature and rely on another piece of software that would prove more robust. This is why the ghc-tags tool was chosen.
The deprecation process starts with GHC 9.4, which adds warning messages in the console, and follows a three-releases cycle. GHC 9.6 will see another announcement, and GHC 9.8 will see the deletion of the code paths.
The migration is being documented in the “Tags” wiki page.
Concretely, here is how it is going to behave in GHC 9.4:
❯ ghci-9.4
GHCi, version 9.4.0.20220501: https://www.haskell.org/ghc/ :? for help
λ❯ :ctags!
Tags generation from GHCi will be deprecated in future releases
Use the method described in https://gitlab.haskell.org/ghc/ghc/-/wikis/commentary/GHCi/Tags
Cheers,
Hécate