2025-05-12 — Last Week in Carbon

[josh11b]

Updates on leads issues

• Decisions
  • impl in class redeclaration syntax with parameterization #5367
    • Syntax will look like impl C.(forall [T:! type] as I(T));.
    • Decision will be captured in #5366.
• New issues
  • (none)
• Active discussions
  • (none)

Updates on proposals

• Decisions
  • #5366 The name of an impl in class scope
    • An impl of I in class C can be redeclared with impl C.(as I).
  • (none)
• New RFC proposals
  • (none)
• Active discussions
  • #5337 Interface extension and final impl update
    • #generics-and-templates (continued) 05-05 Resolved to only allow overlap between final impls in a single file within a final match_first block
    • 05-06 Resolved open question about using the value of an associated constant from an impl in a final match_first block
    • Multiple iterations of review, ready for leads

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

• 10 trained moderation & conduct team members + community lead, in theory available from UTC-7 to UTC+5.5.
  • WIP: Discussing ways to be more welcoming to newcomers in the future.
• Last week’s stats across our spaces:
  • Several spamming accounts were reported to GitHub, their comments were hidden, and GitHub seems to have banned them; so the comments have been fully deleted in the meanwhile.
  • In the last 7 days in our repo: 8 authors pushed 43 commits to all branches, 31 of which to trunk, we changed 144 files with 9,602 additions and 3,035 deletions, with 31 merged PRs, 12 open PRs, 2 closed issues and 3 new ones.
  • One new contributor!

Activity on toolchain

• #interop: How to get Clang to generate inline function bodies.
  • __attribute__((used)) will work to start with, but eventually we'll need to call Sema::MarkFunctionReferenced because it triggers template instantiation.
  • #5427 wound up doing the latter.
• #toolchain: Whether/when to add tests of missing features (spun off from #5406).
• #toolchain (continued): Should we try to consolidate the C++ file shards in interop tests?
  • Or maybe explicitly mark setup files vs. test files?
• #toolchain: Considering factoring out a type iterator from TypeStructure.
  • #toolchain: Seemed to work out well.
• #toolchain: Having difficulty merging #5400 because of conflict with #5313.
• #toolchain (continued): Clarifying the comments on SymbolicConstant.
• #interop: Any design docs or other starting points for pointer/reference support?
  • Might make sense to wait on that, because it will depend on things like Optional. Introducing references could also change the landscape here.
• 05-06, #toolchain: Can we have something like CARBON_KIND_SWITCH for situations where we currently use std::variant?
• #toolchain: Proposed direction for testing. See this commit in particular, and #5455 generally.
  • If we go ahead with this, it would be nice to share the work of updating the tests.
• #generics-and-templates (continued): Concrete types in type structure
• #generics-and-templates: Infrastructure for writing unit tests?
• 05-06: Asan currently enabled for fastbuild, not debug builds
• 05-08: Bumping Clang to version 19
• 05-08 #5438 #5456: Poisoning of value stores when they get invalidated. Looking for contributions of fixes.
• PRs:
  • impls in #5419 #5416 #5412 #5423 #5417
  • import in #5418 #5447
  • thunks in #5424 #5403 #5452 #generics-and-templates
  • debug in #5432 #5429
  • Remove needs_substitution logic in #5443
  • test infra in #5442
  • Update tool versions in #5445 #5446
  • C++ interop in #5392 #5393 #5406
  • type structure in #5430 #5431
  • others in #5421 #5425 #5428 #5444

Other active discussions

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

• #pointers-and-references: Will the references proposal cover things like lambda captures?
  • That can probably be a separate follow-up if the author prefers.
• #infra: Having trouble with "No install marker at path" errors
• #infra: Can we update to Clang 19?
  • Probably yes.
  • Need special branch access to test the upgrade.
• #getting-started: How to write unit tests in Carbon.
  • No unit test framework yet, and it's not in any of the currently-planned milestones.
• #5435: Does Carbon have an opportunity to be simpler than C++?
  • It depends, because "simple" can mean lots of different things.
  • We're planning to take a holistic look at Carbon's syntax closer to 1.0.
• #infra: Tip for setting up a Chrome shortcut to search the Carbon repo.
• 05-08, #pointers-and-references: Discussion of return calling conventions in the context of reference returns.
• #generics-and-templates: When to use values in type structure
• 05-06: It is an error to use an associated constant from a final impl that has been declared but not defined.
• 05-06: For returning a ref to a bound parameter, a bound pointer's lifetime is within the lifetime of what it points to
• 05-07: Marking ref non-self arguments at call sites
• 05-07, 05-08: Forms are the type system for expressions, not object types. We want to support being generic across forms, including allowing the Self parameter of an interface to be a form instead of a type. Will allow implied constraints on forms, and some conversions between types and forms.

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