wasi: fix wasm-wasi-musl constants

Zig's copy of the `SYMLINK_{NO,}FOLLOW` constants from wasi-musl was
wrong, as were the `IFIFO` and `IFSOCK` file type flags.  Fix these up, and
add comments pointing to exactly where they come from (as wasi-musl has
lots of unused, different definitions of these constants).

Add tests for the Zig convention that WASM preopen 3 is the current
working directory.   This is true for WASM with or without libc.

Enable several fs and posix tests that are now passing (not necessarily
because of this change) on wasm targets.

Fixes ziglang#20890.

lib/std/c.zig

@@ -691,6 +691,7 @@ pub const F = switch (native_os) {
     .linux => linux.F,
     .emscripten => emscripten.F,
     .wasi => struct {
+        // Match `F_*` constants from lib/libc/include/wasm-wasi-musl/__header_fcntl.h
         pub const GETFD = 1;
         pub const SETFD = 2;
         pub const GETFL = 3;
@@ -1722,17 +1723,50 @@ pub const S = switch (native_os) {
     .linux => linux.S,
     .emscripten => emscripten.S,
     .wasi => struct {
-        pub const IEXEC = @compileError("TODO audit this");
+        // Match `S_*` constants from lib/libc/include/wasm-wasi-musl/__mode_t.h
+        //
+        // Note, a bug in wasi-libc means both IFIFO and IFSOCK have the same value (0xc000).
+        // IFIFO should be 0x1000 (see https://github.com/WebAssembly/wasi-libc/pull/463), and
+        // 0x1000 is used by the wasi-libc bottom-half implementation.  So we use 0x1000 here.
+        // But the actual bit values we get back from a wasi-libc may get masked with the wrong
+        // values, or may get mistranslated.  So the FIFO and FSOCK file-type bits are not
+        // trustworthy.
         pub const IFBLK = 0x6000;
         pub const IFCHR = 0x2000;
         pub const IFDIR = 0x4000;
-        pub const IFIFO = 0xc000;
+        pub const IFIFO = 0x1000; // also IFSOCK
         pub const IFLNK = 0xa000;
         pub const IFMT = IFBLK | IFCHR | IFDIR | IFIFO | IFLNK | IFREG | IFSOCK;
         pub const IFREG = 0x8000;
-        /// There's no concept of UNIX domain socket but we define this value here
-        /// in order to line with other OSes.
-        pub const IFSOCK = 0x1;
+        pub const IFSOCK = 0xc000;
+
+        pub fn ISBLK(m: u32) bool {
+            return m & IFMT == IFBLK;
+        }
+
+        pub fn ISCHR(m: u32) bool {
+            return m & IFMT == IFCHR;
+        }
+
+        pub fn ISDIR(m: u32) bool {
+            return m & IFMT == IFDIR;
+        }
+
+        pub fn ISFIFO(m: u32) bool {
+            return m & IFMT == IFIFO;
+        }
+
+        pub fn ISLNK(m: u32) bool {
+            return m & IFMT == IFLNK;
+        }
+
+        pub fn ISREG(m: u32) bool {
+            return m & IFMT == IFREG;
+        }
+
+        pub fn ISSOCK(m: u32) bool {
+            return m & IFMT == IFSOCK;
+        }
     },
     .macos, .ios, .tvos, .watchos, .visionos => struct {
         pub const IFMT = 0o170000;
@@ -6768,6 +6802,7 @@ pub const Stat = switch (native_os) {
     },
     .emscripten => emscripten.Stat,
     .wasi => extern struct {
+        // Match wasi-libc's `struct stat` in lib/libc/include/wasm-wasi-musl/__struct_stat.h
         dev: dev_t,
         ino: ino_t,
         nlink: nlink_t,
@@ -7468,17 +7503,18 @@ pub const AT = switch (native_os) {
         pub const RECURSIVE = 0x8000;
     },
     .wasi => struct {
-        pub const SYMLINK_NOFOLLOW = 0x100;
-        pub const SYMLINK_FOLLOW = 0x400;
-        pub const REMOVEDIR: u32 = 0x4;
+        // Match `AT_*` constants in lib/libc/include/wasm-wasi-musl/__header_fcntl.h
+        pub const EACCESS = 0x0;
+        pub const SYMLINK_NOFOLLOW = 0x1;
+        pub const SYMLINK_FOLLOW = 0x2;
+        pub const REMOVEDIR = 0x4;
         /// When linking libc, we follow their convention and use -2 for current working directory.
         /// However, without libc, Zig does a different convention: it assumes the
         /// current working directory is the first preopen. This behavior can be
         /// overridden with a public function called `wasi_cwd` in the root source
         /// file.
         pub const FDCWD: fd_t = if (builtin.link_libc) -2 else 3;
     },
-
     else => void,
 };
 
@@ -7507,6 +7543,7 @@ pub const O = switch (native_os) {
         _: u9 = 0,
     },
     .wasi => packed struct(u32) {
+        // Match `O_*` bits from lib/libc/include/wasm-wasi-musl/__header_fcntl.h
         APPEND: bool = false,
         DSYNC: bool = false,
         NONBLOCK: bool = false,
@@ -7523,6 +7560,8 @@ pub const O = switch (native_os) {
         read: bool = false,
         SEARCH: bool = false,
         write: bool = false,
+        // O_CLOEXEC, O_TTY_ININT, O_NOCTTY are 0 in wasi-musl, so they're silently
+        // ignored in C code.  Thus no mapping in Zig.
         _: u3 = 0,
     },
     .solaris, .illumos => packed struct(u32) {

lib/std/fs/Dir.zig

@@ -1295,17 +1295,10 @@ pub fn realpathZ(self: Dir, pathname: [*:0]const u8, out_buffer: []u8) RealPathE
         return self.realpathW(pathname_w.span(), out_buffer);
     }
 
-    const flags: posix.O = switch (native_os) {
-        .linux => .{
-            .NONBLOCK = true,
-            .CLOEXEC = true,
-            .PATH = true,
-        },
-        else => .{
-            .NONBLOCK = true,
-            .CLOEXEC = true,
-        },
-    };
+    var flags: posix.O = .{};
+    if (@hasField(posix.O, "NONBLOCK")) flags.NONBLOCK = true;
+    if (@hasField(posix.O, "CLOEXEC")) flags.CLOEXEC = true;
+    if (@hasField(posix.O, "PATH")) flags.PATH = true;
 
     const fd = posix.openatZ(self.fd, pathname, flags, 0) catch |err| switch (err) {
         error.FileLocksNotSupported => return error.Unexpected,

lib/std/fs/test.zig

@@ -361,9 +361,12 @@ test "openDirAbsolute" {
 }
 
 test "openDir cwd parent '..'" {
-    if (native_os == .wasi) return error.SkipZigTest;
-
-    var dir = try fs.cwd().openDir("..", .{});
+    var dir = fs.cwd().openDir("..", .{}) catch |err| {
+        if (native_os == .wasi and err == error.AccessDenied) {
+            return; // This is okay. WASI disallows escaping from the fs sandbox
+        }
+        return err;
+    };
     defer dir.close();
 }
 
@@ -1678,8 +1681,6 @@ test "read from locked file" {
 }
 
 test "walker" {
-    if (native_os == .wasi and builtin.link_libc) return error.SkipZigTest;
-
     var tmp = tmpDir(.{ .iterate = true });
     defer tmp.cleanup();
 
@@ -1731,8 +1732,6 @@ test "walker" {
 }
 
 test "walker without fully iterating" {
-    if (native_os == .wasi and builtin.link_libc) return error.SkipZigTest;
-
     var tmp = tmpDir(.{ .iterate = true });
     defer tmp.cleanup();
 
@@ -1754,8 +1753,6 @@ test "walker without fully iterating" {
 }
 
 test "'.' and '..' in fs.Dir functions" {
-    if (native_os == .wasi and builtin.link_libc) return error.SkipZigTest;
-
     if (native_os == .windows and builtin.cpu.arch == .aarch64) {
         // https://github.com/ziglang/zig/issues/17134
         return error.SkipZigTest;

lib/std/os/wasi.zig

@@ -1,7 +1,7 @@
 //! wasi_snapshot_preview1 spec available (in witx format) here:
 //! * typenames -- https://github.com/WebAssembly/WASI/blob/main/legacy/preview1/witx/typenames.witx
 //! * module -- https://github.com/WebAssembly/WASI/blob/main/legacy/preview1/witx/wasi_snapshot_preview1.witx
-//! Note that libc API does *not* go in this file. wasi libc API goes into std/c/wasi.zig instead.
+//! Note that libc API does *not* go in this file. wasi libc API goes into std/c.zig instead.
 const builtin = @import("builtin");
 const std = @import("std");
 const assert = std.debug.assert;

lib/std/posix.zig

@@ -5107,10 +5107,10 @@ pub fn sysctl(
     newlen: usize,
 ) SysCtlError!void {
     if (native_os == .wasi) {
-        @panic("unsupported"); // TODO should be compile error, not panic
+        @compileError("sysctl not supported on WASI");
     }
     if (native_os == .haiku) {
-        @panic("unsupported"); // TODO should be compile error, not panic
+        @compileError("sysctl not supported on Haiku");
     }
 
     const name_len = cast(c_uint, name.len) orelse return error.NameTooLong;
@@ -5132,10 +5132,10 @@ pub fn sysctlbynameZ(
     newlen: usize,
 ) SysCtlError!void {
     if (native_os == .wasi) {
-        @panic("unsupported"); // TODO should be compile error, not panic
+        @compileError("sysctl not supported on WASI");
     }
     if (native_os == .haiku) {
-        @panic("unsupported"); // TODO should be compile error, not panic
+        @compileError("sysctl not supported on Haiku");
     }
 
     switch (errno(system.sysctlbyname(name, oldp, oldlenp, newp, newlen))) {

lib/std/posix/test.zig

@@ -31,6 +31,19 @@ test "WTF-8 to WTF-16 conversion buffer overflows" {
     try expectError(error.NameTooLong, posix.chdirZ(input_wtf8));
 }
 
+test "check WASI CWD" {
+    if (native_os == .wasi) {
+        if (std.options.wasiCwd() != 3) {
+            @panic("WASI code that uses cwd (like this test) needs a preopen for cwd (add '--dir=.' to wasmtime)");
+        }
+
+        if (!builtin.link_libc) {
+            // WASI without-libc hardcodes fd 3 as the FDCWD token so it can be passed directly to WASI calls
+            try expectEqual(3, posix.AT.FDCWD);
+        }
+    }
+}
+
 test "chdir smoke test" {
     if (native_os == .wasi) return error.SkipZigTest;
 
@@ -151,7 +164,6 @@ test "open smoke test" {
 }
 
 test "openat smoke test" {
-    if (native_os == .wasi and builtin.link_libc) return error.SkipZigTest;
     if (native_os == .windows) return error.SkipZigTest;
 
     // TODO verify file attributes using `fstatat`
@@ -200,10 +212,13 @@ test "openat smoke test" {
     }), mode);
     posix.close(fd);
 
-    // Try opening as file which should fail.
-    try expectError(error.IsDir, posix.openat(tmp.dir.fd, "some_dir", CommonOpenFlags.lower(.{
-        .ACCMODE = .RDWR,
-    }), mode));
+    // Try opening as file which should fail (skip on wasi+libc due to
+    // https://github.com/bytecodealliance/wasmtime/issues/9054)
+    if (native_os != .wasi or !builtin.link_libc) {
+        try expectError(error.IsDir, posix.openat(tmp.dir.fd, "some_dir", CommonOpenFlags.lower(.{
+            .ACCMODE = .RDWR,
+        }), mode));
+    }
 }
 
 test "symlink with relative paths" {
@@ -366,8 +381,7 @@ test "fstatat" {
     defer file.close();
 
     // now repeat but using `fstatat` instead
-    const flags = if (native_os == .wasi) 0x0 else posix.AT.SYMLINK_NOFOLLOW;
-    const statat = try posix.fstatat(tmp.dir.fd, "file.txt", flags);
+    const statat = try posix.fstatat(tmp.dir.fd, "file.txt", posix.AT.SYMLINK_NOFOLLOW);
 
     // s390x-linux does not have nanosecond precision for fstat(), but it does for fstatat(). As a
     // result, comparing the two structures is doomed to fail.
@@ -1308,22 +1322,17 @@ const CommonOpenFlags = packed struct {
     NONBLOCK: bool = false,
 
     pub fn lower(cof: CommonOpenFlags) posix.O {
-        if (native_os == .wasi) return .{
+        var result: posix.O = if (native_os == .wasi) .{
             .read = cof.ACCMODE != .WRONLY,
             .write = cof.ACCMODE != .RDONLY,
-            .CREAT = cof.CREAT,
-            .EXCL = cof.EXCL,
-            .DIRECTORY = cof.DIRECTORY,
-            .NONBLOCK = cof.NONBLOCK,
-        };
-        var result: posix.O = .{
+        } else .{
             .ACCMODE = cof.ACCMODE,
-            .CREAT = cof.CREAT,
-            .EXCL = cof.EXCL,
-            .DIRECTORY = cof.DIRECTORY,
-            .NONBLOCK = cof.NONBLOCK,
-            .CLOEXEC = cof.CLOEXEC,
         };
+        result.CREAT = cof.CREAT;
+        result.EXCL = cof.EXCL;
+        result.DIRECTORY = cof.DIRECTORY;
+        result.NONBLOCK = cof.NONBLOCK;
+        if (@hasField(posix.O, "CLOEXEC")) result.CLOEXEC = cof.CLOEXEC;
         if (@hasField(posix.O, "LARGEFILE")) result.LARGEFILE = cof.LARGEFILE;
         return result;
     }