WASI Improvements for CPython Support#238
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malcolmstill merged 8 commits intomalcolmstill:masterfrom Dec 30, 2025
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December 29, 2025 17:18
- ArrayHashMap.put() now requires allocator as first parameter - ArrayList.append() now requires allocator as first parameter These changes are required for Zig 0.15.2 which changed the API for managed data structures to take the allocator explicitly.
- fd_tell: Get current file offset using cross-platform posix.lseek_CUR_get - fd_readdir: Read directory entries with WASI dirent format Platform support for fd_readdir: - Linux: Implemented using getdents64 syscall (no libc required) - macOS/iOS/tvOS/watchOS/visionOS: Implemented using getdirentries via libc - FreeBSD/OpenBSD/NetBSD/DragonFly: Implemented using getdents via libc - Windows: Compile-time error (TODO: implement with NtQueryDirectoryFile) - Other platforms: Compile-time error These are required for running CPython 3.13 WASM builds.
Changes: - Use @sizeof(wasi.dirent_t) instead of hardcoded 24 for WASI dirent header size - Add toWasiFiletype() helper to convert native DT_* values to wasi.filetype_t enum - Add writeWasiDirent() helper for spec-compliant WASI dirent structure writes - Implement Windows fd_readdir using NtQueryDirectoryFile API: - Uses FILE_BOTH_DIR_INFORMATION for directory enumeration - Converts UTF-16 filenames to UTF-8 - Maps FILE_ATTRIBUTE_* to wasi.filetype_t - Uses FileIndex as pseudo-inode (Windows has no true inodes) - Update doc comments to reference std.os.wasi type definitions Platform support: - Linux: getdents64 syscall (no libc) - macOS/iOS/tvOS/watchOS/visionOS: getdirentries via std.c - FreeBSD/OpenBSD/NetBSD/DragonFly: getdents via std.c - Windows: NtQueryDirectoryFile via std.os.windows - Other platforms: @CompileError
Add error mappings for: - Unseekable -> ESPIPE (illegal seek on pipes/sockets) - NotOpenForReading -> EBADF (bad file descriptor) - InvalidArgument -> EINVAL - PermissionDenied -> EPERM Note: The Windows fd_readdir implementation from the previous commit is untested - zware itself lacks Windows support in other areas (fd_t type handling, stat.inode types, posix.O flags, etc.)
WASI spec does not mandate filtering these entries, and major runtimes like wasmtime and wasmer include them. Removing the filter ensures compatibility with applications that may depend on seeing these entries.
- Remove verbose doc comments (code is self-documenting) - Remove Windows implementation (to be added in separate branch) - Simplify variable names and reduce code duplication - Keep Linux, macOS, and BSD implementations
Owner
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Thanks again @nbaertsch! I wonder if something like https://github.com/WebAssembly/wasi-testsuite might be nice to integrate (with tests running on all OSes, perhaps expanded to include FreeBSD and NetBSD...maybe even OpenBSD) to get this all sensibly tested. |
Owner
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Ah, I already mentioned the testsuite here: #15 (comment) |
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Added WASI P1:
This is enough for a cpython "Hello World" running in zware.
Disclaimer: LLM assisted code. Tested on Linux only. Includes the fixes for zig 0.15.2.