Tracking issue for pin-project 0.4

[taiki-e]

Current prerelease: 0.4.0-beta.1

The most important fix of this release is that pin projection has become a safe operation (#18, thanks @Aaron1011)

Changes

• #[unsafe_project] has been replaced with #[pin_project]. (Replace unsafe_project with safe pin_projectable attribute #18, Remove pin_project! macro and add #[pinned_drop] attribute #33)
• The Unpin argument has been removed - an Unpin impl is now generated by default. (Replace unsafe_project with safe pin_projectable attribute #18)
• Drop impls must be specified with #[pinned_drop] attribute instead of via a normal Drop impl. (Replace unsafe_project with safe pin_projectable attribute #18, Remove pin_project! macro and add #[pinned_drop] attribute #33, Change #[pinned_drop] to trait implementation #86)
• Unpin impls must be specified with an impl of UnsafeUnpin, instead of implementing the normal Unpin trait. (Replace unsafe_project with safe pin_projectable attribute #18)
• Changed project method generated by #[pin_project] attribute to take an &mut Pin<&mut Self> argument. (Make generated 'project' reference take an '&mut Pin<&mut Self>' #47) EDIT: reverted in Change the argument type of project method back to self: Pin<&mut Self> #90
• Removed "project_attr" feature and always enable #[project] attribute (Remove "project_attr" feature and always enable #[project] attribute #94)
• #[project] attribute can now be used for impl blocks. (Add impl block support to #[project] attribute #46)
• #[project] attribute can now be used for use statements. (Add use statements support to #[project] attribute #85)
• Made #[project] attribute disabled by default. (Should #[project] attribute be disabled by default? #36, Make #[project] attribute disabled by default #41) EDIT: replaced with Remove "project_attr" feature and always enable #[project] attribute #94
• Added project_ref method and #[project_ref] attribute. (Add project_ref method and #[project_ref] attribute #93)
• #[pin_project] attribute now determines the visibility of the projection type/method is based on the original type. (Determine the visibility based on the original type #96)

TODO

Some adjustments are needed.

• Make error message more obvious (Replace unsafe_project with safe pin_projectable attribute #18 (comment)); done in Cleanup #22
• unsafe_Unpin vs UnsafeUnpin vs unsafe_unpin (Replace unsafe_project with safe pin_projectable attribute #18 (comment)); done in Change 'unsafe_Unpin' to UpperCamelCase (UnsafeUnpin) #40 (Adopted UnsafeUnpin).
• Update proc-macro2, syn, and quote to 1.0; done in Update proc-macro2, syn, and quote to 1.0 #23
• Test code examples in README (Test code examples in README #19) EDIT: see Test code examples in README #19 (comment)
• Mention Can bypass repr(packed) checking by hiding it in a proc-macro-attribute #32 in the documents; done in Ensure that #[repr(packed)] cannot be used on #[pin_projectable] structs #34
• pin-project does not interoperate well with #[cfg()] (pin-project does not interoperate well with #[cfg()] #68)

Unresolved issues

• Different approach to Unpin vs Drop (Weirdly different approach to Unpin vs Drop #26); done in Change #[pinned_drop] to trait implementation #86
• Change the argument type of project method back to self: Pin<&mut Self> (Change the argument type of project method back to self: Pin<&mut Self> #89)

Blockers

• Whether or not self: &mut Pin<&mut Self> stabilizes in Rust 1.39 (Stabilize nested self receivers in 1.41.0 rust-lang/rust#64325) EDIT: replaced with Change the argument type of project method back to self: Pin<&mut Self> #89
• Rustdoc issues (will be fixed in Improve Rustdoc's handling of procedural macros rust-lang/rust#62855); see Properly inline documentation and use intra-crate lints #98
• 1.0 release of proc-macro2, syn, and quote

I plan to have a few alpha releases before the blockers are resolved.

[taiki-e]

I don't list it as a blocker, but rust-lang/rust#63281 is one of the issues to consider.

[Aaron1011]

Mention #32 in the documents can be checked off/removed, now that the issue is closed.

[taiki-e]

@Aaron1011 thanks 👍

[taiki-e]

Published 0.4.0-alpha.1 (crate.io, releases, docs)!