Plan: libc17-704 — port libzigc onto Zig 0.17.0-dev.704 and release 0.17.0-dev.704.libc.1

[cataggar]

Plan: libc17-704 branch — port libzigc onto Zig 0.17.0-dev.704, release 0.17.0-dev.704.libc.1

Create branch libc17-704 that starts at Zig 0.17.0-dev.704 and incrementally ports all of the
musl-libc-in-Zig (libzigc) work from
ctaggart/zig@libc/0.16.x, so we can tag
0.17.0-dev.704.libc.1 and publish a release like
ctaggart/zig 0.16.0-libc.5 — but without the .sha256 sidecars.

Background: ctaggart/zig#10. Reference release: 0.16.0-libc.5.

Prerequisite (blocking)

• Build llvm-zig for LLVM 22 (llvmorg-22.1.2) — prerequisite for cataggar/zig libc 0.17 llvm-project#4 — an llvm-zig LLVM 22 build (llvmorg-22.1.2). Zig 0.17.0-dev.704's
  CMakeLists.txt pins find_package(llvm 22) (0.16.0 pinned llvm 21), so the existing 21.1.8 LLVM
  cannot be used.

Verified topology

• Base: b8cb780230197ce7e7e3059c7e37e1a40d9dcfc2 = Zig 0.17.0-dev.704 = exactly 704 commits past 24fdd5b7a ("Release 0.16.0").
• ctaggart/zig@libc/0.16.x = 444 commits on top of that same 24fdd5b7a (0.16.0) base.
• ⇒ Conceptually git rebase --onto b8cb78023 24fdd5b7a libc/0.16.x: replay 444 commits across 704 commits of upstream drift. Do it incrementally and CI-gated, not as one giant rebase.
• Upstream already ships lib/c/ + lib/c.zig at both commits and added/changed files by 0.17 (e.g. new lib/c/pthread.zig), so expect real 3-way conflicts in exactly the files the fork edits.

Scope of the fork delta (444 commits, ~1000 files)

• lib/libc/** (~921) — musl sources; many become commented-out manifest entries, not hand-ported code.
• lib/c/*.zig (~52) + lib/c.zig — the hand-written Zig implementations (the real work).
• src/libs/musl.zig — the migration manifest (comments out migrated .c/.s entries). Also src/libs/mingw.zig, src/libs/wasi_libc.zig, src/codegen/llvm/FuncGen.zig.
• lib/std/* touch-ups (c.zig, builtin.zig, math*, os/linux.zig), test/libc.zig, test/behavior/var_args.zig.
• Infra: .github/workflows/{build-release,test-libc,lint-libc-migration,...}.yml, scripts/sign-asset.exp, doc/libc-release-notes.md, copilot instructions, .gitattributes/.gitignore.
• ⚠️ Do not port the accidentally committed build artifacts libc.a and c.o (add to .gitignore).

Release pipeline (what "tag → release" requires)

Mirror build-release.yml (currently only on ctaggart/zig; missing from cataggar/zig along with scripts/sign-asset.exp). Per-target it: downloads the host-zig mirror v$ZIG_VERSION + the prebuilt llvm-zig, runs
zig build -Denable-llvm -Dstatic-llvm -Doptimize=Debug -Dno-langref -Duse-zig-libcxx -Dversion-string=$TAG --search-prefix $LLVM_PREFIX,
packages, minisign-signs, then gh release upload.

Adaptations for 0.17:

• ZIG_VERSION = 0.17.0-dev.704+b8cb78023 — host mirror already exists in cataggar/zig (v0.17.0-dev.704+b8cb78023, assets zig-<arch>-<os>-0.17.0-dev.704+b8cb78023.{tar.xz,zip}).
• LLVM_VERSION = 22.1.2; download llvm-zig-22.1.2-<target> from cataggar/llvm-project (Build llvm-zig for LLVM 22 (llvmorg-22.1.2) — prerequisite for cataggar/zig libc 0.17 llvm-project#4).
• Tag + -Dversion-string = 0.17.0-dev.704.libc.1 ⇒ assets zig-<target>-0.17.0-dev.704.libc.1.{tar.xz,zip}.
• Remove .sha256 generation (shasum/Get-FileHash steps) and drop .sha256 from artifact + gh release upload globs. Keep the minisign step → .minisig sidecars only.
• Repo secrets required: MINISIGN_SECRET_KEY, MINISIGN_PASSWORD (ghr public key RWSuACSgOY8bwS0fMGytTyBlrVQsUtK/6ydxuOT/OjzlnFx2go0w1DX5).
• Build matrix: x86_64-linux, aarch64-macos, x86_64-windows-msvc (x86_64-macos excluded, as upstream).

Phased work

• Phase 0 — branch + infra. Create libc17-704 from b8cb78023. Port test-libc.yml, lint-libc-migration.yml, build-release.yml (0.17 / LLVM 22 / no-sha256 / cataggar URLs), scripts/sign-asset.exp, copilot instructions, doc/libc-release-notes.md. Add libc.a/c.o to .gitignore. Confirm test-libc.yml runs green on the clean 0.17 base.
• Phase 1 — foundation. lib/c.zig wiring + src/libs/musl.zig manifest plumbing + core helpers (lib/c/internal.zig, errno.zig, ctype.zig, string.zig, stdlib.zig), resolving against upstream's evolved lib/c/*.
• Phases 2…N — migration categories (mirror the #305–#361 tiers; one PR per category, each = the relevant lib/c/*.zig + the matching "migrated" comment-outs in src/libs/musl.zig, gated by test-libc.yml across all 10 targets):
  mman / sched / misc / conf → stdio → math → time → process → signal → network (lib/std + lib/c) → env/__init_tls → fenv (all arches) → thread / ldso / setjmp → legacy / exit.
• Phase final — Windows + cross libc. lib/c/win32/* (#248 phases 0/1/2/4/6/7/8), src/libs/mingw.zig, src/libs/wasi_libc.zig, lib/c/wasi_*.
• Release. Tag 0.17.0-dev.704.libc.1; run build-release.yml; verify the release has only *.tar.xz / *.zip + *.minisig (no *.sha256); confirm ghr install cataggar/zig@0.17.0-dev.704.libc.1 RWSuACSgOY8bwS0fMGytTyBlrVQsUtK/6ydxuOT/OjzlnFx2go0w1DX5 works.

Definition of done

• libc17-704 builds and passes test-libc.yml on all targets at parity with libc/0.16.x (only the 2 intentionally-retained setjmp-tail .c files remain).
• Release 0.17.0-dev.704.libc.1 published with signed (.minisig) archives and no .sha256 sidecars.