pin-project 0.3.3 introduces breaking changes about "missing extern crate core" compared to 0.3.2

[shepmaster]

0.3.2

$ cargo update -p pin-project --precise 0.3.2
    Updating crates.io index
    Updating pin-project v0.3.3 -> v0.3.2

$ cargo test
    Finished dev [unoptimized + debuginfo] target(s) in 0.02s
     Running target/debug/deps/futures_compat-27fb39e639db3ee7

running 1 test
test implements_error ... ok

0.3.3

$ cargo update -p pin-project --precise 0.3.3
    Updating crates.io index
    Updating pin-project v0.3.2 -> v0.3.3

$ cargo test
   Compiling snafu v0.4.1 (/Users/shep/Projects/snafu)
error[E0433]: failed to resolve: maybe a missing `extern crate core;`?
   --> /Users/shep/Projects/snafu/src/futures/try_future.rs:127:18
    |
127 | #[unsafe_project(Unpin)]
    |                  ^^^^^ maybe a missing `extern crate core;`?

error[E0433]: failed to resolve: maybe a missing `extern crate core;`?
   --> /Users/shep/Projects/snafu/src/futures/try_future.rs:166:18
    |
166 | #[unsafe_project(Unpin)]
    |                  ^^^^^ maybe a missing `extern crate core;`?

error[E0433]: failed to resolve: maybe a missing `extern crate core;`?
   --> /Users/shep/Projects/snafu/src/futures/try_stream.rs:129:18
    |
129 | #[unsafe_project(Unpin)]
    |                  ^^^^^ maybe a missing `extern crate core;`?

error[E0433]: failed to resolve: maybe a missing `extern crate core;`?
   --> /Users/shep/Projects/snafu/src/futures/try_stream.rs:171:18
    |
171 | #[unsafe_project(Unpin)]
    |                  ^^^^^ maybe a missing `extern crate core;`?

error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0433`.
error: Could not compile `snafu`.

[taiki-e]

@shepmaster Thanks for the reporting!
I yanked 0.3.3.

I think that is related to 7efdfc6 or eee7fa9. I will investigate.

[taiki-e]

The cause is this code added in 7efdfc6:

pin-project/src/unsafe_project/mod.rs

Lines 65 to 67 in 7575fb9

	quote_spanned! { span =>
	impl #impl_generics ::core::marker::Unpin for #ident #ty_generics #where_clause {}
	}

Span contains information about the edition. So if pin-project is used in 2015 edition's crate, ::core::marker::Unpin is handled as code defined in the 2015 edition. Then 2015 edition's import rule is applied.

[taiki-e]

Published 0.3.4 which fixes this issue.