2025-12-22— Last Week in Carbon

[josh11b]

News

• Posted Carbon Copy #10: Generics Part II

Updates on leads issues

• Decisions
  • (none)
• New issues
  • (none)
• Active discussions
  • (none)

Updates on proposals

• Decisions
  • (none)
• New RFC proposals
  • (none)
• Active discussions
  • #5990: Principle: The signature is the contract
    • What should this principle be named?

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

• Moderation and conduct teams are still the same size, available in theory from UTC-7 until UTC-5.5: 10 trained members altogether + community lead (hands-off trainer, coach, guide)
  • WIP: Prepare more resources to help close our skill gaps as identified by the team itself
  • WIP: Discussing holiday period coverage
  • Several moderation interventions last week:
    2 Discord server members were told that personal job search messages are off-topic in our spaces, and
    1 link to a non-Carbon server was deleted from our GitHub repo.
• Activity in the past week:
  • One new contributor! 🎉
  • In the last 7 days in our repo: 7 authors pushed 24 commits to trunk, we changed 668 files with 37,626 additions and 36,133 deletions, which means we merged 24 PRs, opened 8 PRs, we closed 7 issues.

Activity on toolchain

• #functions How to generalize textual SemIR format to support non-initializing returns?
• #llvm Does the sret parameter need to be listed first?
• #toolchain Workaround for missing .Self functionality
• #toolchain Terminology for "custom" witnesses; possibly "synthetic" or "synthesized" instead?
• #toolchain Debugging As poisoning errors
• #toolchain Update #6498 with plan for name mangling?
• #toolchain #6514 Splitting up long function EvalLookupSingleImplWitness.
• #toolchain Lowering incomplete types, has an interaction with building vtables
• #toolchain Unused variable checking dataflow analysis
• #toolchain GetTransitiveAdaptedType -> GetObjectRepr
• #toolchain Out parameters maybe would have different calling convention than returns
• #toolchain Why does GetCallee takes an optional SpecificId?
• #toolchain Removing a field from OutParamPattern
• #toolchain Diagnosing invalid declarations in parse vs. check
• #toolchain Fingerprinting
• 12-16 Behavior of CheckFunctionReturnType if the type isn't concrete is different depending on whether it was initially incomplete
• 12-18 Could we get rid of the style rule that captured parameters have to be passed by pointer?
• PRs:
  • C++ templates in #6474 #6475
  • custom witness (for Destroy and those from C++) in #6491 #6515 #6520 #6512
  • abstract types in #6499 #6513
  • packages in #6495 #6497
  • unused pattern bindings in #6460 #6479
  • private base members in #6521
  • lldb debugging in #6524 #6526 #6527
  • documentation in #6496 #6528 (see #toolchain)
  • others in #6484 #6485 #6517 #6516 #6519 #6525
• New contributors:
  • @ozguronsoy made their first contribution in #6499

Activity on memory safety

• 12-15 #safety Different approach for dealing with flow-sensitivity in overload resolution:
  • If the state is flow-sensitive at the point of impl lookup, assume it always matches for impl selection purposes, then error if it doesn't.
  • If you get such an error, the fix is to embed the state into a type, so that it's visible to impl selection.
  • Written up as Safety Unit No. 29: Flow sensitivity and impl selection
• 12-17 A ref parameter can affect flow-sensitive state, and that change needs to occur before the function call and affect earlier parameters.
• #safety Cancelling Jan 1 safety meeting due to holidays.

Other active discussions

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

• #generics-and-templates 12-16 Should we treat impls as effectively final if they can't be further specialized?
• #getting-started Is it possible to import and use <cassert> in Carbon?
  • You can import the header, but you can't actually use assert() because it's a macro.
  • Unclear whether/how we'll support it.
  • You can wrap it in a C++ function and call that from Carbon, but diagnostics will point to the C++ function.
• #proposals-prs-and-process Draft proposal for char redesign.
• #infra Reminder for the holidays: if you mark yourself "busy" in GitHub, you won't get auto-assigned PR reviews, and if you say /fizz away in Discord you won't get review pings.
• #strategy Interesting talk on syntax design. Also cites interesting paper.
  • The paper references the Quorum language, which has a page summarizing human factors PL research.
• #error-handling Interesting post on sum types.

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