Auto merge of #107251 - dingxiangfei2009:let-chain-rescope, r=jieyouxu

Rescope temp lifetime in if-let into IfElse with migration lint

Tracking issue #124085

This PR shortens the temporary lifetime to cover only the pattern matching and consequent branch of a `if let`.

At the expression location, means that the lifetime is shortened from previously the deepest enclosing block or statement in Edition 2021. This warrants an Edition change.

Coming with the Edition change, this patch also implements an edition lint to warn about the change and a safe rewrite suggestion to preserve the 2021 semantics in most cases.

Related to #103108.
Related crater runs: https://github.com/rust-lang/rust/pull/129466.
tree: 3dd45f08b8469ab0c17b9b0ec7c579371730edf7
  1. .github/
  2. compiler/
  3. library/
  4. LICENSES/
  5. src/
  6. tests/
  7. .clang-format
  8. .editorconfig
  9. .git-blame-ignore-revs
  10. .gitattributes
  11. .gitignore
  12. .gitmodules
  13. .ignore
  14. .mailmap
  15. Cargo.lock
  16. Cargo.toml
  17. CODE_OF_CONDUCT.md
  18. config.example.toml
  19. configure
  20. CONTRIBUTING.md
  21. COPYRIGHT
  22. INSTALL.md
  23. LICENSE-APACHE
  24. LICENSE-MIT
  25. README.md
  26. RELEASES.md
  27. REUSE.toml
  28. rust-bors.toml
  29. rustfmt.toml
  30. triagebot.toml
  31. x
  32. x.ps1
  33. x.py
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