Tracking Issue for Rust 2024: Rescope temporary lifetimes with respect to else

[traviscross]

This is a tracking issue for shortening the scope of temporary lifetimes in if-let blocks to end before else. E.g.:

if let Some(x) = ref_cell.write().some_method_that_returns_option() {
} else {
    // question is whether the `ref_cell` is still write-locked here;
    // currently, it is, but it wouldn't be under this change
}

About tracking issues

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.

Steps

• Implement with a feature gate.
  • Rescope temp lifetime in if-let into IfElse with migration lint #107251
• Do a crater run to analyze impact.
  • [Crater run experiment] let-chain rescoping #125151
  • [CRATER RUN DO NOT MERGE] Let chain lint crater run #129466
    • [DO NOT MERGE] Force edition 2024 lint into action on crater cargo#14447
• Implement in nightly Rust 2024.
• Implement migration lints.
• Add documentation to the dev guide.
  • See the instructions.
• Add documentation to the reference.
  • See the instructions.
• Add documentation to the edition guide.
  • Edition 2024 guide for temporary lifetime changes edition-guide#318
• Add formatting for new syntax to the style guide.
  • See the nightly style procedure.
• Ensure ready for Rust 2024 stabilization.

Unresolved Questions

TODO.

Related

• Drop order twist of && and || chains #103107
• if let should pre-drop wrt else #103108
• Let chain temporaries should drop before else #103248
• Remove drop order twist of && and || and make them associative #103293
• Broken MIR ICE with let chains #104843
• Rescope temp lifetime in if-let into IfElse with migration lint #107251

Implementation history

• Rescope temp lifetime in if-let into IfElse with migration lint #107251
• [Crater run experiment] let-chain rescoping #125151

[dingxiangfei2009]

@rustbot claim

[dingxiangfei2009]

Update: #107251 has been repurposed for this edition change.