Does removing a Cabal flag constitute a breaking change?

[sjakobi]

This question came up in haskell/bytestring#371 (comment).

(CC @Bodigrim)

[phadej]

The flag in question is automatic, and doesn't affect public API (AFAIK). So removing it is not breaking change, I don't see how any consumer could break. (EDIT: compare to just adding/removing a dependency, those aren't breaking by themself)

[Bodigrim]

Yeah, since cabal does not mind passing non-existent package flags, I do not see this as a breaking change.

[sjakobi]

since cabal does not mind passing non-existent package flags

Ah, this is the bit that I was confused about. I thought that a user explicitly setting that flag might run into upgrade troubles.

If this question is something that should be documented on the website, I'd leave this issue open for now.