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Showing content from https://github.com/rust-lang/rust/issues/84277 below:

Tracking Issue for `try_trait_v2`, A new design for the `?` desugaring (RFC#3058) · Issue #84277 · rust-lang/rust · GitHub

This is a tracking issue for the RFC "try_trait_v2: A new design for the ? desugaring" (rust-lang/rfcs#3058).
The feature gate for the issue is #![feature(try_trait_v2)].

This obviates rust-lang/rfcs#1859, tracked in #42327.

Tracking issues are used to record the overall progress of implementation.
They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions.
A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.

• Implement the RFC
  • Add the new traits and impls
  • Update the desugar in ast lowering
  • Fixup all the tests
  • Add nice error messages in inference
  • Improve perf with enough MIR optimizations
  • Delete the old way after a bootstrap update Remove the TryV2 alias #88223
• Not strictly needed, but a mir-opt to simplify the matches would really help: LLVM/MIR optimizations to simplify the new RFC3058 ? desugaring #85133
• Add more detailed documentation about how to implement and use the traits
• Decide whether to block return types that are FromResidual but not Try
• Fix rustdoc to show the default type parameter on FromResidual better (Issue rustdoc removes Try from <Self as Try>::Residual in std::ops::FromResidual #85454)
• Before stabilizing, ensure that all uses of Infallible are either fine that way or have been replaced by !
• Stabilizing this will allow people to implement Iterator::try_fold
  • As part of stabilizing, document implementing try_fold for iterators (perhaps reopen Document implementing try_fold for iterators for internal iteration #62606)
  • Ensure that the default implementations of other things have the desired long-term DAG, since changing them is essentially impossible later. (Specifically, it would be nice to have fold be implemented in terms of try_fold, so that both don't need to be overridden.)
• Adjust documentation (see instructions on rustc-dev-guide)
• Stabilization PR (see instructions on rustc-dev-guide)

From RFC:

• What vocabulary should Try use in the associated types/traits? Output+residual, continue+break, or something else entirely?
• Is it ok for the two traits to be tied together closely, as outlined here, or should they be split up further to allow types that can be only-created or only-destructured?

From experience in nightly:

• Should there be a trait requirement on residuals of any kind? It's currently possible to accidentally be FromResidual from a type that's never actually produced as a residual ( Fix the types in one of the FromResidual implementations rwf2/Rocket#1645). But that would add more friction for cases not using the Foo<!> pattern, so may not be worth it.
  • Given the trait in Make array::{try_from_fn, try_map} and Iterator::try_find generic over Try #91286, that might look like changing the associated type Residual; to type Residual: Residual<Self::Output>;.

• Basic traits and impls added, Add the try_trait_v2 library basics #84092
• Removing try_trait from stdarch, Remove #![feature(try_trait)] from a test stdarch#1142
• Implementing the desugaring, Implement the new desugaring from try_trait_v2 #84767

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