2026-06-15 — Last Week in Carbon

[josh11b]

Updates on leads issues

• Decisions
  • (none)
• New issues
  • (none)
• Active discussions
  • #7138 How to treat ambiguous .Self?
    • Extensive discussion in #generics-and-templates (see below)

Updates on proposals

• Decisions
  • #7314 CharLiteral difference should be an IntLiteral
    • Approved
• New RFC proposals
  • (none)
• Active discussions
  • (none)

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

• Conduct team updates:
  • none
• Moderation interventions last week:
  • none
• Activity in the past week:
  • BLOCKED: new landing page mockup that would incorporate self-learning quizzes in #7237
  • BLOCKED: discussing creating self-learning quizzes around the language, alongside more community culture-oriented ones.
  • WIP: TypeScript community interview summary for the moderation team
  • 1 new contributor! 🎉
  • 10 authors have pushed 29 commits to trunk.
  • On trunk, 844 files have changed and there have been 35,314 additions and 19,241 deletions
  • We merged 29 PRs, opened 13 additional PRs, closed 1 issue, and opened no new issue.

Activity on toolchain

• #toolchain 06-08 How to more easily view diagnostic changes in testdata?
  • #infra The scripts from the meeting notes might not work.
• 06-09 How to preserve location information through constant evaluation?
• #toolchain Base classes will use a pointer value representation by default. We have the option to allow them to use another representation, but then require virtual methods to take self by ref.
• #toolchain Diagnostic when there is a problem creating a thunk
• #generics-and-templates Rust only bounds: New ideas on Rust traits that are included by default (traits that are excluded/negative traits) like Sized.
• #generics-and-templates Why Lex knows an expected parse tree size: to correctly allocate the buffer for the parse nodes up front.
• PRs:
  • carbon build subcommand in #7239 #7321
  • derived classes in #7322
  • #toolchain debug dumping in #7328 #7333
  • adapters destroyability in #7271
  • 06-08 #toolchain toolchain build efficiency in #7325 #7339
  • 06-09 Move self to the explicit () parameter list (proposal #7016) in #7272
  • Core.CharLiteral in #7316
  • C++ operator in #7345
  • error recovery in #7341 #7342
  • thunking in #7332
  • 06-09 dev infrastructure in #7337 #7343 #7344 #7358 #7331 #7338
  • others in #7326 #7327 #7329 #7330 #7335 #7353
• New contributors:
  • @mstr-six made their first contribution in #7341

Activity about .Self in facet types

• #generics-and-templates What does a rewrite constraint do inside a disconnected facet type, such as one written inside a rewrite constraint?
• #generics-and-templates Attempting to treat .Self in a nested/disconnected facet type as a greater distance along a separate axis compared to .Self in a connected nested facet type (such as on the RHS of an impls constraint, or on the LHS of a where).
• #generics-and-templates Using a separate axis leads to type equality issues
• #generics-and-templates Example of an eval fn returning a facet type that makes it seemingly impossible to know what the .Self it’s returning should be referring to
• #generics-and-templates More discussion of using a separate distance axis for nested/disconnected facet types inside a facet type.
• #generics-and-templates Need to increment .Self distance in nested/disconnected facet types, then do the same increment when substing .Self.
• #generics-and-templates Challenging to only add distance to .Self in a nested disconnected facet type, going to try doing it for all nested facet types.
• #generics-and-templates Example of a named constraint passing through .Self, which means its distance is not increased.
• #generics-and-templates A positive relative distance on an outer .Self is a problem because you can always use interface calls to increment the distance of your current .Self and create a collision: Z(Z(Z(.Self))) adds distance 3.
• #generics-and-templates A nested/disconnected facet type introduces a new value for .Self at its where. This is an example of what could be considered an ambiguous .Self, since it introduces a second .Self value into the type.
• #generics-and-templates Attempted reduction of the .Self numbering problem, which constructs a type with two different .Self inside. One use of the outer .Self needs to be incremented, the other use not.
• #generics-and-templates Multiple values of .Self in a type essentially leads to us having to solve lambda calculus (where .Self is a free variable). Should we get rid of .Self?
• #generics-and-templates Are designators something we could get rid of? If we restrict the use of designators instead, can that solve our issues? No, we still get conflicting values of .Self.
• #generics-and-templates We need to rigorously enforce the .Self ambiguity rule. Any way to introduce a second value of .Self leads to complexity that is too expensive/difficult to resolve, and thus ends up in crashes or coherence issues. This includes preventing ambiguity through internally representing rewrite designators with .Self.

Activity on memory safety

• #safety Polling for best time for a talk on the memory safety design
• #safety Safety unit 49 with some realistic C++ callbacks with mutations
• #safety Discussion on the behaviour of owned place sets, invalidation, and aliases of place sets
• #safety memory safety design talk will be Jul 7 or 9, poll remains open a bit longer

Other active discussions

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

• #strategy Blog post about deprecations and removals in the C++ stdlib.
• #infra Can't submit due to prek failures.
  • Looks like non-hermetic behavior in ty. #7326 and #7331 may help.
• #infra Did something change to cause local workflows to run in forks?
  • Unclear, but there's a setting to disable them.
• #syntax Does Carbon have default parameters?
  • Not designed yet, but we expect to add them at some point.
• #build-integrations 06-11 How should building Core and the prelude work? How about libraries in general? Should the prelude be a separate package from the rest of Core?
• #infra How to access the files generated when Clang crashes?
• 06-08 AI generated changes policy ideas

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