Yeah it's indeed the 2015 edition because while compiletest watches for // edition:something comments [0] (like this [1]), it doesn't pass any edition flag to t

Yeah it's indeed the 2015 edition because while compiletest watches for // edition:something comments [0] (like this [1]), it doesn't pass any edition flag to the compiler if no such comment is present, and the rust compiler defaults to the 2015 edition if none was specified. [0]: https://github.com/rust-lang/rust/blob/69b352ef7749825abde2d8f8e31c05f681e61a10/src/tools/compiletest/src/header.rs#L439 https://github.com/rust-lang/rust/blob/69b352ef7749825abde2d... [1]: https://github.com/rust-lang/rust/blob/69b352ef7749825abde2d8f8e31c05f681e61a10/src/test/ui/editions/edition-imports-2018.rs https://github.com/rust-lang/rust/blob/69b352ef7749825abde2d...