2025-05-19 — Last Week in Carbon

[josh11b]

Updates on leads issues

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

Updates on proposals

• Decisions
  • (none)
• New RFC proposals
  • (none)
• Active discussions
  • #5337 Interface extension and final impl update
    • Thumbs up, with some concerns, from one lead

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: Talking community journey with Zig folks..
• Last week’s stats across our spaces:
  • A GitHub issue was closed due to its lack of constructive content. The account was reported to GitHub as well.
  • In the last 7 days in our repo: 8 authors pushed 33 commits to all branches, 32 of which to trunk, we changed 193 files with 8,705 additions and 13,628 deletions, with 32 merged PRs, 12 open PRs, 1 closed issue and 1 new one.

Activity on toolchain

• 05-12 05-15 Prioritizing work on generics
• 05-13 Changes to testing strategy now that we can get SemIR for a range of lines
• #generics-and-templates Bug in substitution
• #generics-and-templates #5485 Bug with types passed as runtime values
• #generics-and-templates Progress enforcing where rewrite constraints
• #toolchain Attached and unattached symbolic constants in import
• #toolchain Representation of symbolic names
• #toolchain Import resolution
• #toolchain Linkage of specific functions
• #toolchain Testing inst kinds in requires clauses
• #interop Planning support for int* interop
• #pattern-matching How to assign mangled name to a VarStorage.
• PRs:
  • test infrastructure in #5450 #5454 #5471
  • update dependencies in #5440 #5459 #5463 #5470 #5479 #5484 #5487
  • variant switch in #5433 #5437
  • formatting in #5458 #5460 #5474 (discussed) #5482
  • import final impl in #5461
  • linkstamp support in #5451 #5464
  • type iterator in #5453 #5480
  • tests in #5469 #5457 #5467 #5455 #5478 #5476
  • substitution in #5481 #5488
  • fuzzing in #5489
  • specific lowering in #5493
  • helper in #5490

Other active discussions

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

• 05-12 Links about Rust's issues with lifetimes and specialization: 1 2
• 05-12 Orphan rule for final impls is a bit awkward for T*; would need Rust's fundamental types to address. We'll see if it becomes a problem
• 05-12 #syntax 05-14 Function return forms
  • What forwarding can we do?
  • Interaction with returned var
  • Syntax for writing a return form
  • Will be incorporated into upcoming proposal #5434
• 05-14 #pointers-and-references More about forms
  • Decided no implicit conversion from types to forms
  • Separate types for parameter and return forms
  • Form literal syntax
• #generics-and-templates Type structure with members of a generic
• #generics-and-templates Conversions between facet types with where clauses
• #infra Clang updated to version 19
  • As a consequence, GitHub action runners are upgraded to Ubuntu 24.04
  • Discussion of whether to embed platform version numbers in action names
  • #infra This broke Carbon on Godbolt, because of glibc version mismatch. Fixed in #5479
  • Pending PRs will need to merge from trunk in order to pick up the GH action changes.
• #infra Carbon pre-commit sometimes uses the wrong version of prettier.
  • Hopefully fixed in #5463
• #pointers-and-references Will we need two kinds of references with different noalias/nocapture semantics?
  • Probably need multiple kinds of pointers, but the hope is that we can find a single set of ref semantics that covers the common cases, with pointers as a fallback.
• #infra How to avoid accidentally reviewing the wrong part of a stacked PR?
• #pointers-and-references Do we need to worry about self-assignment?
• #infra Discussion of build configuration for fuzzer, and to what extent Carbon tries to accommodate Google's internal build system
• #language-questions Is Carbon ready to compile C++17 code?
  • Carbon can compile any C++ code that Clang can.
• #strategy Link to blog post about the evolution of Rust compiler errors, with cool visualization tool.
• #llvm It would be nice to have an llvm::filter_map that combines map and filter

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