2026-06-29 — Last Week in Carbon

[josh11b]

News

• Memory safety presentation scheduled for July 6, 2026 at 12:00-2:00 PM Pacific time. See here for meeting info.

Updates on leads issues

• Decisions
  • (none)
• New issues
  • #7404 Should trailing commas be allowed in struct patterns.
• Active discussions
  • (none)

Updates on proposals

• Decisions
  • #5913 Reworking unformed state
    • Closed due to inactivity
• New RFC proposals
  • (none)
• Active discussions
  • #7381 Adopt `ref` in `Core.Iterate.Next`
    • Questions about how to structure the desugaring of for loops.
  • #7254 Replace `:!` and `:?` with keywords and contextual defaults
    • #naming How to name the syntax that follows -> in a function signature.

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

• Conduct team updates:
  • none
• Moderation interventions last week:
  • PENDING: blocking or warning a GitHub user posting generic comments with little to no added value, disregarding our contribution guidelines.
• Activity in the past week:
  • BLOCKED: new landing page mockup that would incorporate self-learning quizzes in #7237
  • WIP: discussing creating self-learning quizzes around the language, alongside more community culture-oriented ones.
  • WIP: finalizing specific guidelines around LLM-generated content and contributions.
  • 8 authors have pushed 27 commits to trunk.
  • On trunk, 221 files have changed and there have been 4,743 additions and 3,405 deletions
  • We merged 27 PRs, opened 4 additional PRs, closed 2 issues, and opened 4 new issues.

Activity on toolchain

• 06-23 Where do we build the C++ runtimes source file keys that are used when expanding the C++ template with bazel?
• 06-23 Tracking desugared locations
• 06-23 More efficient prelude processing
• #build-integrations 06-25 Building and using the runtimes cache for the prelude
• #toolchain Checklist for everything that should be done when adding a new ID or Store type
• #toolchain template for making specifics?
• #toolchain pattern insts in separate blocks from non-pattern insts
• #contributing-help How to make a DirRef from a std::filesystem::path.
• PRs:
  • debugging in #7398 #7429
  • MultiplexExternalSemaSource in #7405 #7416
  • forms/extended types in #7392 #7393
  • .Self in #7400
  • deps in #7413 #7409
  • conversions in #7415
  • member access in #7406
  • where inside a where in #7378 #7397
  • diagnostics in #7401
  • symbolic forms in #7408
  • category in #7426
  • language server in #7417 #7420
  • dev infra in #7423 #7407 #7419 #7418
  • syntax highlighting in #7395
  • others in #7410 #7411 #7422

Activity on memory safety

• #safety Continued discussion of more type-like syntax for place sets.

Other active discussions

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

• #pattern-matching Clarifying struct pattern syntax
  • Filed as leads issue #7404.
• #generics-and-templates 06-25 Found infinite cycle in generics when replacing a .Self and there’s a final impl that causes the same replacement to repeat.
• #infra Are we ready to automatically block dependent PR merges?
• #generics-and-templates Printing an error diagnostic with Stringify from inside FinishGeneric will crash if the decl instruction has not been fully set up (typically by ReplaceInstBeforeConstantUse).
• #infra "Fix missing deps" pre-commit seems slower.
• #syntax LuaJIT is considering using same symbol for bit-negate and bit-xor
• #generics-and-templates 06-25 We can prevent concrete queries from finding a witness in a symbolic facet’s facet type, as a way to stop the infinite cycles of .Self replacement with a final impl. Though we don’t want to limit the language in this way if we can help it.
• #infra Switching to new Markdown formatter rumdl in #7423.
  • #contributing-help VS Code has a good rumdl extension, but we still use prettier for other languages.
    • We've hit some bugs in rumdl, but they're getting fixed quickly.
• #strategy Have the recent NDC talks been posted yet?
  • No.
• #generics-and-templates We could stop final impl from providing concrete values in facet types but this restricts the language too much. We found a smaller change that does make some concrete queries fail against a symbolic facet type where a final impl is rewriting values in the facet type. We have some ideas about how to make those queries work again by finding a fixed point during .Self replacement, and will leave TODOs in the code.
• #editor-integrations It would be nice if Compiler Explorer mirrored its C++ libraries into Carbon (feature request).
• #llvm 06-25 LLVM dev conference registration opened

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