Upgrade to zig 0.16.0

.github/workflows/ci_cross_compile.yml

@@ -29,7 +29,7 @@ jobs:
 
       - uses: mlugg/setup-zig@8d6198c65fb0feaa111df26e6b467fea8345e46f # 2.0.5
         with:
-          version: 0.15.2
+          version: 0.15.2 # TODO ZIG 16: update to 0.16.x
           use-cache: false
 
       - name: Setup MSVC (Windows)

.github/workflows/ci_zig.yml

@@ -16,7 +16,7 @@ jobs:
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # ratchet:actions/checkout@v4
       - uses: mlugg/setup-zig@8d6198c65fb0feaa111df26e6b467fea8345e46f # ratchet:mlugg/setup-zig@v2.0.5
         with:
-          version: 0.15.2
+          version: 0.16.0
           use-cache: true
 
       - name: zig lints
@@ -89,35 +89,35 @@ jobs:
         include:
           - os: macos-15-intel
             cpu_flag: -Dcpu=x86_64_v3
-            target_flag: ''
+            target_flag: ""
           - os: macos-15
-            cpu_flag: ''
-            target_flag: ''
+            cpu_flag: ""
+            target_flag: ""
           - os: ubuntu-22.04
             cpu_flag: -Dcpu=x86_64_v3
             target_flag: -Dtarget=x86_64-linux-musl
           - os: ubuntu-24.04
-            cpu_flag: ''
+            cpu_flag: ""
             target_flag: -Dtarget=x86_64-linux-musl
           - os: ubuntu-24.04-arm
-            cpu_flag: ''
-            target_flag: ''  # Native build for kcov (Zig 0.15.2 x86_64 has DWARF bug)
+            cpu_flag: ""
+            target_flag: "" # Native build for kcov (Zig 0.15.2 x86_64 has DWARF bug) # TODO ZIG 16: re-check if DWARF bug is fixed in 0.16
           - os: windows-2022
             cpu_flag: -Dcpu=x86_64_v3
-            target_flag: ''
+            target_flag: ""
           - os: windows-2025
             cpu_flag: -Dcpu=x86_64_v3
-            target_flag: ''
+            target_flag: ""
           - os: windows-11-arm
-            cpu_flag: ''
-            target_flag: ''
+            cpu_flag: ""
+            target_flag: ""
 
     steps:
       - name: Checkout
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # ratchet:actions/checkout@v4
       - uses: mlugg/setup-zig@8d6198c65fb0feaa111df26e6b467fea8345e46f # ratchet:mlugg/setup-zig@v2.0.5
         with:
-          version: 0.15.2
+          version: 0.15.2 # TODO ZIG 16: update to 0.16.x
           use-cache: true
       # temp fix, see https://roc.zulipchat.com/#narrow/channel/395097-compiler-development/topic/CI/near/542085291
       - name: delete llvm-config
@@ -152,7 +152,7 @@ jobs:
 
       - name: Setup MSVC (Windows)
         if: runner.os == 'Windows'
-        uses: ilammy/msvc-dev-cmd@0b201ec74fa43914dc39ae48a89fd1d8cb592756  # ratchet:ilammy/msvc-dev-cmd@v1.13.0
+        uses: ilammy/msvc-dev-cmd@0b201ec74fa43914dc39ae48a89fd1d8cb592756 # ratchet:ilammy/msvc-dev-cmd@v1.13.0
         with:
           arch: ${{ matrix.os == 'windows-11-arm' && 'arm64' || 'x64' }}
 
@@ -241,6 +241,7 @@ jobs:
           }
 
       # Parser code coverage - run on ARM64 Linux (native build)
+      # TODO ZIG 16: re-check if DWARF bug is fixed in 0.16 — may be able to enable x86_64 coverage
       # Note: Zig 0.15.2 on x86_64 generates invalid DWARF .debug_line sections,
       # causing libdw to fail parsing user source files. ARM64 works correctly.
       - name: Install kcov dependencies
@@ -301,7 +302,7 @@ jobs:
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # ratchet:actions/checkout@v4
       - uses: mlugg/setup-zig@8d6198c65fb0feaa111df26e6b467fea8345e46f # ratchet:mlugg/setup-zig@v2.0.5
         with:
-          version: 0.15.2
+          version: 0.15.2 # TODO ZIG 16: update to 0.16.x
           use-cache: true
 
       - name: cross compile with llvm

.gitignore

@@ -27,6 +27,7 @@ target
 generated-docs
 
 zig-out
+zig-pkg
 .zig-cache
 .direnv
 .envrc

BUILDING_FROM_SOURCE.md

@@ -6,6 +6,7 @@ If you run into any problems getting Roc built from source, please ask for help
 
 ## Recommended way
 
+<!-- TODO ZIG 16: update version to 0.16.x -->
 [Download zig 0.15.2](https://ziglang.org/download/) and add it to your PATH.
 [Search "Setting up PATH"](https://ziglang.org/learn/getting-started/) for more details.
 

REMAINING_ISSUES.md

@@ -0,0 +1,146 @@
+# Zig 0.16 Migration — Remaining Issues
+
+## TL;DR
+
+`zig build minici` is mostly green — `fmt`, `zig lints`, `tidy`, `check-test-wiring`,
+`zig build`, Builtin.roc formatting, `snapshot`, checkfx, and the core module-test
+pipeline all compile. The remaining blocker is a single **architectural regression**
+introduced by the 0.16 migration:
+
+> The shims (`libroc_interpreter_shim.a`, `libroc_dev_shim.a`) transitively link
+> libc and reference compiler_rt symbols. That breaks Roc's promise that user
+> programs are libc- and compiler_rt-independent.
+
+Symptom when linking a user Roc app against `test/fx/platform` or `test/int/platform`:
+
+```
+ld.lld: error: undefined symbol: statx
+  >>> referenced by std/Io/Threaded.zig:3893  (Io.Threaded.fileStatLinux)
+  >>>              main.o in libroc_shim.a
+
+ld.lld: error: undefined symbol: __modti3
+  >>> referenced by std/Io/Threaded.zig:14253 (Io.Threaded.timestampToPosix)
+  >>>              roc_builtins.o / host.o
+```
+
+The bundled platform `libc.a` is intentionally minimal and doesn't ship `statx`,
+and user programs should never need compiler_rt's 128-bit math helpers.
+
+---
+
+## Root Cause
+
+Commit `df29a20f08` ("WIP: Zig 0.16 migration - rename Io to RocIo and thread
+std.Io through codebase") introduced into each shim main.zig:
+
+```zig
+// src/interpreter_shim/main.zig:58
+// src/dev_shim/main.zig:34
+var app_std_io: std.Io = std.Io.Threaded.global_single_threaded.io();
+```
+
+`app_std_io` is passed to `std.Thread.Mutex.lockUncancelable`/`unlock` and
+`SharedMemoryAllocator.fromCoordination` — both of which gained a mandatory
+`std.Io` parameter in 0.16.
+
+Referencing `std.Io.Threaded.global_single_threaded.io()` instantiates the full
+`std.Io.Threaded` vtable, which pulls the entire file/network/timestamp/stat
+implementation into the compile graph. On Linux-musl:
+
+- `fileStatLinux` / `dirStatFileLinux` → `std.c.statx` (because `statx_use_c`
+  returns `true` on musl) → `U statx`
+- `timestampToPosix` → 128-bit `@mod`/`@divTrunc` → `__modti3`, `__divti3`
+
+Before 0.16 the shim used `std.Thread.Mutex.lock()` and `SharedMemoryAllocator
+.fromCoordination(allocator, page_size)` — neither took an `Io`, neither pulled
+in `std.Io.Threaded`.
+
+## Fix Direction
+
+Need a minimal `std.Io` for the shim that only implements what mutex/futex and
+mmap-style shared memory actually use. Options, roughly in increasing invasiveness:
+
+1. **Thin wrapper Io.** Audit what methods `std.Thread.Mutex.lockUncancelable`,
+   `std.Thread.Mutex.unlock`, and `ipc.SharedMemoryAllocator.fromCoordination`
+   call on the Io vtable. Likely just `futexWait`/`futexWake` for mutex, and
+   a couple of mmap-adjacent calls for shm. Implement a custom `std.Io` whose
+   other vtable entries `@panic`/`unreachable`. This keeps `std.Io.Threaded`
+   out of the shim's compile graph entirely.
+2. **Drop the Io parameter at our boundary.** Rework `ipc.SharedMemoryAllocator
+   .fromCoordination` so it doesn't take an `Io` — it can call `std.os.linux`
+   syscalls directly for shared memory. Similarly, replace `std.Thread.Mutex`
+   with a direct futex wrapper for the shim's single PlatformMutex.
+3. **Two compile modes.** Move the `app_std_io` line behind a `comptime` flag
+   and provide a syscall-direct mutex implementation when building the shim.
+   Everything else (roc exe, tests) keeps using `std.Io.Threaded`.
+
+(1) is probably the cleanest. (2) is less code but pushes into the ipc module.
+
+Do **not**:
+- Stub `statx` into `libhost.a` of each platform (I prototyped this — it works
+  mechanically but hides the real regression and the stub misses callers that
+  link against other platforms).
+- Flip `createTestPlatformHostLib`'s `bundle_compiler_rt` on for musl targets
+  (same objection: paper-over).
+- Regenerate the bundled `libc.a` files with a newer musl. The bundled libc is
+  a platform-provided contract; expanding it to satisfy compiler-side additions
+  is the wrong direction.
+
+See also: `~/.claude/projects/-home-lbw-Documents-Github-roc/memory/feedback_roc_libc_independence.md`.
+
+---
+
+## What's Already Fixed on This Branch (uncommitted)
+
+| Area | Change | File |
+|---|---|---|
+| std.posix removals | `std.posix.close`/`inotify_init1`/`inotify_add_watch` → `std.os.linux.*` with manual errno handling. `std.Io.Dir.openDirAbsolute`/`dir.close`/iterator `next` gained required `io` parameter (currently supplied via `std.Io.Threaded.global_single_threaded.io()` locally — TODO: thread io through the Watcher struct). | `src/watch/watch.zig` |
+| Darwin `std.c._NSGetExecutablePath` | Wrapped in `switch (comptime builtin.os.tag)` with Linux (`readLinkAbsolute /proc/self/exe`) and Windows (`peb.ImagePathName`) branches. 0.16's comptime assertion on `std.c.darwin` now passes on non-Darwin hosts. | `src/cli/linker.zig` |
+| Test-level libc linkage | Expanded `createModuleTests` link_libc to `true` for all module tests (was just `ipc`, `bundle`, `eval`, `repl`, `sljmp`). Any module whose source touches `std.c` or transitively imports one that does now compiles its tests. | `src/build/modules.zig` |
+| Exe-level libc linkage | Added `.link_libc = true` explicitly to `builtin_compiler_exe` (via `ctx.CoreCtx`), `test_runner_exe` (direct `std.c` use), `roc_subcommands_test`, `glue_test`, `fx_platform_test`. | `build.zig` |
+
+## Reverted (attempted workarounds — do not re-apply)
+
+- `.link_libc = false` on shim_lib root module (doesn't override transitive
+  `.link_libc = true` from `bundle → zstd` import chain, and breaks other
+  modules that legitimately need libc on shim's compile graph).
+- `@export(&statxCompat, ...)` from `test/fx/platform/host.zig` forwarding to
+  the `SYS_statx` syscall with manual errno.
+- `lib.bundle_compiler_rt = … or is_linux_musl` in `createTestPlatformHostLib`
+  to drag `__modti3`/`__divti3` into each musl `libhost.a`.
+
+---
+
+## Other Follow-Ups Spotted (not blockers for `minici`)
+
+- **ci_zig.yml still pins zig 0.15.2** for the matrix jobs and the
+  `check-once` nix/benchmark jobs are on 0.16.0. Once the shim fix lands and CI
+  is green on 0.16, flip the remaining `version: 0.15.2 # TODO ZIG 16` pins in
+  `.github/workflows/ci_zig.yml`.
+- **watch.zig io threading.** The `std.Io.Threaded.global_single_threaded.io()`
+  call sites the sub-agent added as part of the posix-removal fix violate the
+  spirit of `ci/tidy.zig`'s ban (the ban is scoped to core modules, so tidy
+  passes today). Thread a real `std.Io` through the `Watcher` struct later.
+- **DWARF bug re-check.** `ci_zig.yml` has `TODO ZIG 16: re-check if DWARF bug
+  is fixed in 0.16` around the ARM64-only kcov coverage job. Should retest.
+
+---
+
+## How to Reproduce Today
+
+From repo root:
+
+```bash
+rm -rf .zig-cache src/cli/libroc_*.a
+zig build                        # should succeed
+zig build test-cli 2>&1 | tail   # fails with statx / __modti3 symbols
+```
+
+Or the full pipeline:
+
+```bash
+zig build minici                 # fails at the `zig build test-cli` sub-step
+```
+
+The earlier sub-steps (`fmt`, `zig lints`, `tidy`, snapshot, module tests) all
+pass.