Tracking issue for `#![register_attr]`

[petrochenkov]

This is a direct replacement for now removed #![feature(custom_attribute)] (#29642), except it doesn't rely on implicit fallback from unresolved attributes to custom attributes (which was always hacky and is the primary reason for the removal of custom_attribute) and requires registering the attribute explicitly.

#![register_attr(my_attr)]

#[my_attr] // OK
fn main() {}

It's not yet clear whether this should go through stabilization or not.
It's quite possible that all the uses should migrate to #![register_tool] (#66079) instead.

[joshtriplett]

It's quite possible that all the uses should migrate to #![register_tool] (#66079) instead.

We discussed this in today's @rust-lang/lang meeting, and we agreed: anything new should be scoped, and anything existing we need to support for backwards compatibility shouldn't require calling register_tool first, so we can just keep the hardcoding of the handful of exceptions in the compiler.

@rfcbot close

[rfcbot]

Team member @joshtriplett has proposed to close this. The next step is review by the rest of the tagged team members:

• @cramertj
• @joshtriplett
• @nikomatsakis
• @pnkfelix
• @scottmcm

No concerns currently listed.

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