2026-03-16 — Last Week in Carbon

[josh11b]

Updates on leads issues

• Decisions
  • (none)
• New issues
  • (none)
• Active discussions
  • #6830 Should import Cpp inline be part of the declaration list rather than the preamble?
    • How does this affect name poisoning?

Updates on proposals

• Decisions
  • #6910 Support octal literals: Approved
• New RFC proposals
  • #6902 Identification of a named constraint during definition
• Active discussions
  • (none)

Updates on moderation across our community spaces (Discord and GitHub)

• Conduct team updates:
  • none
• Moderation interventions last week:
  • DONE: updated our community rules to make it more explicit that posting random job searches is not acceptable behavior in our spaces.
  • WIP: Outreach for new interview round of neighbor language community
• Activity in the past week:
  • 1 new contributor! 🎉
  • 10 authors have pushed 35 commits to trunk and 36 commits to all branches.
  • On trunk, 245 files have changed and there have been 12,774 additions and 9,264 deletions
  • We merged 35 PRs, opened 7 additional PRs, closed 7 issues, and opened 11 new issues.

Activity on toolchain

• 03-10 #generics-and-templates 03-12 Work out solution to cycles problem from doc Self Contradictions in Named Constraints
  • Will involve change to rules to forbid referencing the name of the constraint within its definition
• #toolchain 03-12 Trying to lower the SemIR for the dereference operator that is in the witness table
• 03-12 Prelude vs. builtins
• 03-12 require satisfying later requirements working in named constraints but not yet in interfaces
• #toolchain #infra Nightly builds have been broken for a few days.
  • Broken by #6855, fixed by #6866
  • Also seeing more timeouts due to the runtimes build. Fix for that is in progress.
• #toolchain Fix for #6793
• #toolchain Parameters and pattern matching
• #toolchain Getting a clang::FunctionDecl
• #toolchain Tests taking longer to run
• #toolchain Forwarding through thunks
• #generics-and-templates Why does deduction traverse into a ValueParamPattern?
  • Removed in #6869, but longer term we need bigger changes in that logic.
• PRs:
  • non-type template params in #6850
  • update deps in #6844 #6845 #6879 #6852 #6865 #6877
  • macro in #6843
  • build in #6859 #6863 #6872 #6851
  • ->? return forms in #6849
  • integer conversion in #6856
  • pattern match in #6870 #6869
  • character literal lexing in #6805
  • #interop Carbon value -> const C++ #6880
  • {} as Class in #6882
  • C++ && methods in #6881
  • constexpr functions in #6878
  • golden tests in #6894 #6897 #6899
  • C++ ranged for in #6890 #6900
  • named constraint in #6906
  • reverse interop in #6901
  • docs in #6853 #6889
  • others in #6896 #6904 #6866 #6903
• New contributors:
  • @primitive0 made their first contribution in #6805

Activity on memory safety

• #safety Updated Safety Unit No. 33: alias set parameter declarations to cover the big question about default returns.
• 03-10 thread safety
• #safety New: Safety Unit No. 39: ownership.
• #safety New: Safety Unit No. 40: catalog.
• 03-12 a b c #safety Default aliasing in returns, permissive mode, and where we mark "unsafe"
• #safety Split Safety Unit No. 33b: alias sets in returns out of unit 33.
• #safety Do we want to guarantee that correct C++ can be naively migrated to permissive Carbon?
• #safety The new indexing operator from #5389 raises questions much like the the puzzle from a couple weeks ago.

Other active discussions

These include Discord Chat, GitHub Discussions, or open discussion sessions.

• #typesystem Should as do the same thing as calling As.Op directly?
• 03-09 For thread-safety purposes, can we prevent reads by preventing value acquisition?
  • We don't say this yet, but probably atomics are the only things you can read without value acquisition.
• #typesystem How do you declare a local ref binding?
  • let ref.
• #infra New tool for generating compile_commands.json, please try it and give feedback:
  • bazel run //:generate_compile_commands.
• #contributing-help How to update a PR with a new trunk?
  • Prefer merge rather than rebase, and prefer not to do it until the end of the review.
  • Documentation updated in #6889.
• #pattern-matching Pattern-matching can't be purely top-down now that we have :?.
• #infra Do we provide builds for other architectures, like aarch64?
  • Looks like we'd just need to update the nightly build config.
• #pattern-matching Seeing a crash passing {} as X to a var parameter.
• #generics-and-templates Do we still want to disallow a constraint that require impls itself?
• #generics-and-templates Thoughts on another kind of cycle involving .Self?
• #infra clangd seems slower on toolchain codebase.
  • Probably a consequence of slower builds overall. Could probably fix with some forward-declarations to reduce use of Clang headers.
• #language-questions Seeing odd "would overwrite the output file" error when building a simple example.

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