Dhall-lang: Prelude: Remove files without .dhall extension?!

[sjakobi]

https://github.com/dhall-lang/dhall-lang/pull/1076#discussion_r498206835 indicates that there's some confusion about the purpose of the Prelude files without the .dhall extension.

When can we remove these files?

[Gabriel439]

@sjakobi: I think one way we can ease the migration is for dhall lint to fix old Prelude imports to use the .dhall extension. Then after a grace period we can remove the extension-free imports.

[SiriusStarr]

That'd be great. I've been trying to go through and update stuff where I see it, but I have so many prelude imports scattered through so many projects, haha.

[Gabriel439]

dhall lint change is up here: https://github.com/dhall-lang/dhall-haskell/pull/2061

[german1608]

I don't know if this is only relevant for dhall-haskell, but wouldn't be great to have a mechanism to let users mark a dhall file as deprecated? That way implementations could show a warning when the user imports those files

[german1608]

That way we could mark these old files without the extension as deprecated and the user would notice it