Generated code (the kind that you generate in
build.rs) is in an interesting spot in terms of edition changes. Obviously, if the generated code uses features like async blocks, it’ll have to require the new edition, as those are (unfortunately) impossible to express in the 2015 edition.
But for smaller quality-of-life changes in behavior, such as the path changes, generated code is in the unenviable spot of wanting to generate code that works in either edition. (For current stable compilers, the same applies to procedural macro-generated code with
Would it make sense to add a
#[edition = "2018"] attribute such that modules can specify a different edition from the crate default? This would allow generated modules at least to start with
#![edition = "2018"] and not worry about the edition of the crate they’re generating code for.
This would also help large crates where
rustfix doesn’t quite cover everything to do a slower more piecewise conversion. Or is this too much risk? Either way we should probably record somewhere best practices for code generating into an unknown edition, and keep that use case in mind for future edition changes.