    const std = @import("std.zig");
    const builtin = @import("builtin");
    const cstr = std.cstr;
    const unicode = std.unicode;
    const io = std.io;
    const fs = std.fs;
    const os = std.os;
    const process = std.process;
    const File = std.fs.File;
    const windows = os.windows;
    const linux = os.linux;
    const mem = std.mem;
    const math = std.math;
    const debug = std.debug;
    const EnvMap = process.EnvMap;
    const Os = std.builtin.Os;
    const TailQueue = std.TailQueue;
    const maxInt = std.math.maxInt;
    const assert = std.debug.assert;

    pub const ChildProcess = struct {
        pid: if (builtin.os.tag == .windows) void else i32,
        handle: if (builtin.os.tag == .windows) windows.HANDLE else void,
        thread_handle: if (builtin.os.tag == .windows) windows.HANDLE else void,

        allocator: mem.Allocator,

        stdin: ?File,
        stdout: ?File,
        stderr: ?File,

        term: ?(SpawnError!Term),

        argv: []const []const u8,

        /// Leave as null to use the current env map using the supplied allocator.
        env_map: ?*const EnvMap,

        stdin_behavior: StdIo,
        stdout_behavior: StdIo,
        stderr_behavior: StdIo,

        /// Set to change the user id when spawning the child process.
        uid: if (builtin.os.tag == .windows or builtin.os.tag == .wasi) void else ?os.uid_t,

        /// Set to change the group id when spawning the child process.
        gid: if (builtin.os.tag == .windows or builtin.os.tag == .wasi) void else ?os.gid_t,

        /// Set to change the current working directory when spawning the child process.
        cwd: ?[]const u8,
        /// Set to change the current working directory when spawning the child process.
        /// This is not yet implemented for Windows. See https://github.com/ziglang/zig/issues/5190
        /// Once that is done, `cwd` will be deprecated in favor of this field.
        cwd_dir: ?fs.Dir = null,

        err_pipe: ?if (builtin.os.tag == .windows) void else [2]os.fd_t,

        expand_arg0: Arg0Expand,

        /// Darwin-only. Disable ASLR for the child process.
        disable_aslr: bool = false,

        pub const Arg0Expand = os.Arg0Expand;

        pub const SpawnError = error{
            OutOfMemory,

            /// POSIX-only. `StdIo.Ignore` was selected and opening `/dev/null` returned ENODEV.
            NoDevice,

            /// Windows-only. One of:
            /// * `cwd` was provided and it could not be re-encoded into UTF16LE, or
            /// * The `PATH` or `PATHEXT` environment variable contained invalid UTF-8.
            InvalidUtf8,

            /// Windows-only. `cwd` was provided, but the path did not exist when spawning the child process.
            CurrentWorkingDirectoryUnlinked,
        } ||
            os.ExecveError ||
            os.SetIdError ||
            os.ChangeCurDirError ||
            windows.CreateProcessError ||
            windows.WaitForSingleObjectError ||
            os.posix_spawn.Error;

        pub const Term = union(enum) {
            Exited: u8,
            Signal: u32,
            Stopped: u32,
            Unknown: u32,
        };

        pub const StdIo = enum {
            Inherit,
            Ignore,
            Pipe,
            Close,
        };

        /// First argument in argv is the executable.
        pub fn init(argv: []const []const u8, allocator: mem.Allocator) ChildProcess {
            return .{
                .allocator = allocator,
                .argv = argv,
                .pid = undefined,
                .handle = undefined,
                .thread_handle = undefined,
                .err_pipe = null,
                .term = null,
                .env_map = null,
                .cwd = null,
                .uid = if (builtin.os.tag == .windows or builtin.os.tag == .wasi) {} else null,
                .gid = if (builtin.os.tag == .windows or builtin.os.tag == .wasi) {} else null,
                .stdin = null,
                .stdout = null,
                .stderr = null,
                .stdin_behavior = StdIo.Inherit,
                .stdout_behavior = StdIo.Inherit,
                .stderr_behavior = StdIo.Inherit,
                .expand_arg0 = .no_expand,
            };
        }

        pub fn setUserName(self: *ChildProcess, name: []const u8) !void {
            const user_info = try std.process.getUserInfo(name);
            self.uid = user_info.uid;
            self.gid = user_info.gid;
        }

        /// On success must call `kill` or `wait`.
        pub fn spawn(self: *ChildProcess) SpawnError!void {
            if (!std.process.can_spawn) {
                @compileError("the target operating system cannot spawn processes");
            }

            if (comptime builtin.target.isDarwin()) {
                return self.spawnMacos();
            }

            if (builtin.os.tag == .windows) {
                return self.spawnWindows();
            } else {
                return self.spawnPosix();
            }
        }

        pub fn spawnAndWait(self: *ChildProcess) SpawnError!Term {
            try self.spawn();
            return self.wait();
        }

        /// Forcibly terminates child process and then cleans up all resources.
        pub fn kill(self: *ChildProcess) !Term {
            if (builtin.os.tag == .windows) {
                return self.killWindows(1);
            } else {
                return self.killPosix();
            }
        }

        pub fn killWindows(self: *ChildProcess, exit_code: windows.UINT) !Term {
            if (self.term) |term| {
                self.cleanupStreams();
                return term;
            }

            try windows.TerminateProcess(self.handle, exit_code);
            try self.waitUnwrappedWindows();
            return self.term.?;
        }

        pub fn killPosix(self: *ChildProcess) !Term {
            if (self.term) |term| {
                self.cleanupStreams();
                return term;
            }
            try os.kill(self.pid, os.SIG.TERM);
            try self.waitUnwrapped();
            return self.term.?;
        }

        /// Blocks until child process terminates and then cleans up all resources.
        pub fn wait(self: *ChildProcess) !Term {
            if (builtin.os.tag == .windows) {
                return self.waitWindows();
            } else {
                return self.waitPosix();
            }
        }

        pub const ExecResult = struct {
            term: Term,
            stdout: []u8,
            stderr: []u8,
        };

        fn collectOutputPosix(
            child: ChildProcess,
            stdout: *std.ArrayList(u8),
            stderr: *std.ArrayList(u8),
            max_output_bytes: usize,
        ) !void {
            var poll_fds = [_]os.pollfd{
                .{ .fd = child.stdout.?.handle, .events = os.POLL.IN, .revents = undefined },
                .{ .fd = child.stderr.?.handle, .events = os.POLL.IN, .revents = undefined },
            };

            var dead_fds: usize = 0;
            // We ask for ensureTotalCapacity with this much extra space. This has more of an

            // effect on small reads because once the reads start to get larger the amount

            // of space an ArrayList will allocate grows exponentially.

            const bump_amt = 512;

            const err_mask = os.POLL.ERR | os.POLL.NVAL | os.POLL.HUP;

            while (dead_fds < poll_fds.len) {
                const events = try os.poll(&poll_fds, std.math.maxInt(i32));
                if (events == 0) continue;

                var remove_stdout = false;
                var remove_stderr = false;
                // Try reading whatever is available before checking the error

                // conditions.

                // It's still possible to read after a POLL.HUP is received, always

                // check if there's some data waiting to be read first.

                if (poll_fds[0].revents & os.POLL.IN != 0) {
                    // stdout is ready.

                    const new_capacity = std.math.min(stdout.items.len + bump_amt, max_output_bytes);
                    try stdout.ensureTotalCapacity(new_capacity);
                    const buf = stdout.unusedCapacitySlice();
                    if (buf.len == 0) return error.StdoutStreamTooLong;
                    const nread = try os.read(poll_fds[0].fd, buf);
                    stdout.items.len += nread;

                    // Remove the fd when the EOF condition is met.

                    remove_stdout = nread == 0;
                } else {
                    remove_stdout = poll_fds[0].revents & err_mask != 0;
                }

                if (poll_fds[1].revents & os.POLL.IN != 0) {
                    // stderr is ready.

                    const new_capacity = std.math.min(stderr.items.len + bump_amt, max_output_bytes);
                    try stderr.ensureTotalCapacity(new_capacity);
                    const buf = stderr.unusedCapacitySlice();
                    if (buf.len == 0) return error.StderrStreamTooLong;
                    const nread = try os.read(poll_fds[1].fd, buf);
                    stderr.items.len += nread;

                    // Remove the fd when the EOF condition is met.

                    remove_stderr = nread == 0;
                } else {
                    remove_stderr = poll_fds[1].revents & err_mask != 0;
                }

                // Exclude the fds that signaled an error.

                if (remove_stdout) {
                    poll_fds[0].fd = -1;
                    dead_fds += 1;
                }
                if (remove_stderr) {
                    poll_fds[1].fd = -1;
                    dead_fds += 1;
                }
            }
        }

        const WindowsAsyncReadResult = enum {
            pending,
            closed,
            full,
        };

        fn windowsAsyncRead(
            handle: windows.HANDLE,
            overlapped: *windows.OVERLAPPED,
            buf: *std.ArrayList(u8),
            bump_amt: usize,
            max_output_bytes: usize,
        ) !WindowsAsyncReadResult {
            while (true) {
                const new_capacity = std.math.min(buf.items.len + bump_amt, max_output_bytes);
                try buf.ensureTotalCapacity(new_capacity);
                const next_buf = buf.unusedCapacitySlice();
                if (next_buf.len == 0) return .full;
                var read_bytes: u32 = undefined;
                const read_result = windows.kernel32.ReadFile(handle, next_buf.ptr, math.cast(u32, next_buf.len) orelse maxInt(u32), &read_bytes, overlapped);
                if (read_result == 0) return switch (windows.kernel32.GetLastError()) {
                    .IO_PENDING => .pending,
                    .BROKEN_PIPE => .closed,
                    else => |err| windows.unexpectedError(err),
                };
                buf.items.len += read_bytes;
            }
        }

        fn collectOutputWindows(child: ChildProcess, outs: [2]*std.ArrayList(u8), max_output_bytes: usize) !void {
            const bump_amt = 512;
            const handles = [_]windows.HANDLE{
                child.stdout.?.handle,
                child.stderr.?.handle,
            };

            var overlapped = [_]windows.OVERLAPPED{
                mem.zeroes(windows.OVERLAPPED),
                mem.zeroes(windows.OVERLAPPED),
            };

            var wait_objects: [2]windows.HANDLE = undefined;
            var wait_object_count: u2 = 0;

            // we need to cancel all pending IO before returning so our OVERLAPPED values don't go out of scope

            defer for (wait_objects[0..wait_object_count]) |o| {
                _ = windows.kernel32.CancelIo(o);
            };

            // Windows Async IO requires an initial call to ReadFile before waiting on the handle

            for ([_]u1{ 0, 1 }) |i| {
                switch (try windowsAsyncRead(handles[i], &overlapped[i], outs[i], bump_amt, max_output_bytes)) {
                    .pending => {
                        wait_objects[wait_object_count] = handles[i];
                        wait_object_count += 1;
                    },
                    .closed => {}, // don't add to the wait_objects list

                    .full => return if (i == 0) error.StdoutStreamTooLong else error.StderrStreamTooLong,
                }
            }

            while (wait_object_count > 0) {
                const status = windows.kernel32.WaitForMultipleObjects(wait_object_count, &wait_objects, 0, windows.INFINITE);
                if (status == windows.WAIT_FAILED) {
                    switch (windows.kernel32.GetLastError()) {
                        else => |err| return windows.unexpectedError(err),
                    }
                }
                if (status < windows.WAIT_OBJECT_0 or status > windows.WAIT_OBJECT_0 + wait_object_count - 1)
                    unreachable;

                const wait_idx = status - windows.WAIT_OBJECT_0;

                // this extra `i` index is needed to map the wait handle back to the stdout or stderr

                // values since the wait_idx can change which handle it corresponds with

                const i: u1 = if (wait_objects[wait_idx] == handles[0]) 0 else 1;

                // remove completed event from the wait list

                wait_object_count -= 1;
                if (wait_idx == 0)
                    wait_objects[0] = wait_objects[1];

                var read_bytes: u32 = undefined;
                if (windows.kernel32.GetOverlappedResult(handles[i], &overlapped[i], &read_bytes, 0) == 0) {
                    switch (windows.kernel32.GetLastError()) {
                        .BROKEN_PIPE => continue,
                        else => |err| return windows.unexpectedError(err),
                    }
                }

                outs[i].items.len += read_bytes;

                switch (try windowsAsyncRead(handles[i], &overlapped[i], outs[i], bump_amt, max_output_bytes)) {
                    .pending => {
                        wait_objects[wait_object_count] = handles[i];
                        wait_object_count += 1;
                    },
                    .closed => {}, // don't add to the wait_objects list

                    .full => return if (i == 0) error.StdoutStreamTooLong else error.StderrStreamTooLong,
                }
            }
        }

        /// Spawns a child process, waits for it, collecting stdout and stderr, and then returns.
        /// If it succeeds, the caller owns result.stdout and result.stderr memory.
        pub fn exec(args: struct {
            allocator: mem.Allocator,
            argv: []const []const u8,
            cwd: ?[]const u8 = null,
            cwd_dir: ?fs.Dir = null,
            env_map: ?*const EnvMap = null,
            max_output_bytes: usize = 50 * 1024,
            expand_arg0: Arg0Expand = .no_expand,
        }) !ExecResult {
            var child = ChildProcess.init(args.argv, args.allocator);
            child.stdin_behavior = .Ignore;
            child.stdout_behavior = .Pipe;
            child.stderr_behavior = .Pipe;
            child.cwd = args.cwd;
            child.cwd_dir = args.cwd_dir;
            child.env_map = args.env_map;
            child.expand_arg0 = args.expand_arg0;

            try child.spawn();

            if (builtin.os.tag == .haiku) {
                const stdout_in = child.stdout.?.reader();
                const stderr_in = child.stderr.?.reader();

                const stdout = try stdout_in.readAllAlloc(args.allocator, args.max_output_bytes);
                errdefer args.allocator.free(stdout);
                const stderr = try stderr_in.readAllAlloc(args.allocator, args.max_output_bytes);
                errdefer args.allocator.free(stderr);

                return ExecResult{
                    .term = try child.wait(),
                    .stdout = stdout,
                    .stderr = stderr,
                };
            }

            var stdout = std.ArrayList(u8).init(args.allocator);
            var stderr = std.ArrayList(u8).init(args.allocator);
            errdefer {
                stdout.deinit();
                stderr.deinit();
            }

            if (builtin.os.tag == .windows) {
                try collectOutputWindows(child, [_]*std.ArrayList(u8){ &stdout, &stderr }, args.max_output_bytes);
            } else {
                try collectOutputPosix(child, &stdout, &stderr, args.max_output_bytes);
            }

            return ExecResult{
                .term = try child.wait(),
                .stdout = stdout.toOwnedSlice(),
                .stderr = stderr.toOwnedSlice(),
            };
        }

        fn waitWindows(self: *ChildProcess) !Term {
            if (self.term) |term| {
                self.cleanupStreams();
                return term;
            }

            try self.waitUnwrappedWindows();
            return self.term.?;
        }

        fn waitPosix(self: *ChildProcess) !Term {
            if (self.term) |term| {
                self.cleanupStreams();
                return term;
            }

            try self.waitUnwrapped();
            return self.term.?;
        }

        fn waitUnwrappedWindows(self: *ChildProcess) !void {
            const result = windows.WaitForSingleObjectEx(self.handle, windows.INFINITE, false);

            self.term = @as(SpawnError!Term, x: {
                var exit_code: windows.DWORD = undefined;
                if (windows.kernel32.GetExitCodeProcess(self.handle, &exit_code) == 0) {
                    break :x Term{ .Unknown = 0 };
                } else {
                    break :x Term{ .Exited = @truncate(u8, exit_code) };
                }
            });

            os.close(self.handle);
            os.close(self.thread_handle);
            self.cleanupStreams();
            return result;
        }

        fn waitUnwrapped(self: *ChildProcess) !void {
            const res: os.WaitPidResult = if (comptime builtin.target.isDarwin())
                try os.posix_spawn.waitpid(self.pid, 0)
            else
                os.waitpid(self.pid, 0);
            const status = res.status;
            self.cleanupStreams();
            self.handleWaitResult(status);
        }

        fn handleWaitResult(self: *ChildProcess, status: u32) void {
            self.term = self.cleanupAfterWait(status);
        }

        fn cleanupStreams(self: *ChildProcess) void {
            if (self.stdin) |*stdin| {
                stdin.close();
                self.stdin = null;
            }
            if (self.stdout) |*stdout| {
                stdout.close();
                self.stdout = null;
            }
            if (self.stderr) |*stderr| {
                stderr.close();
                self.stderr = null;
            }
        }

        fn cleanupAfterWait(self: *ChildProcess, status: u32) !Term {
            if (self.err_pipe) |err_pipe| {
                defer destroyPipe(err_pipe);

                if (builtin.os.tag == .linux) {
                    var fd = [1]std.os.pollfd{std.os.pollfd{
                        .fd = err_pipe[0],
                        .events = std.os.POLL.IN,
                        .revents = undefined,
                    }};

                    // Check if the eventfd buffer stores a non-zero value by polling

                    // it, that's the error code returned by the child process.

                    _ = std.os.poll(&fd, 0) catch unreachable;

                    // According to eventfd(2) the descriptor is readable if the counter

                    // has a value greater than 0

                    if ((fd[0].revents & std.os.POLL.IN) != 0) {
                        const err_int = try readIntFd(err_pipe[0]);
                        return @errSetCast(SpawnError, @intToError(err_int));
                    }
                } else {
                    // Write maxInt(ErrInt) to the write end of the err_pipe. This is after

                    // waitpid, so this write is guaranteed to be after the child

                    // pid potentially wrote an error. This way we can do a blocking

                    // read on the error pipe and either get maxInt(ErrInt) (no error) or

                    // an error code.

                    try writeIntFd(err_pipe[1], maxInt(ErrInt));
                    const err_int = try readIntFd(err_pipe[0]);
                    // Here we potentially return the fork child's error from the parent

                    // pid.

                    if (err_int != maxInt(ErrInt)) {
                        return @errSetCast(SpawnError, @intToError(err_int));
                    }
                }
            }

            return statusToTerm(status);
        }

        fn statusToTerm(status: u32) Term {
            return if (os.W.IFEXITED(status))
                Term{ .Exited = os.W.EXITSTATUS(status) }
            else if (os.W.IFSIGNALED(status))
                Term{ .Signal = os.W.TERMSIG(status) }
            else if (os.W.IFSTOPPED(status))
                Term{ .Stopped = os.W.STOPSIG(status) }
            else
                Term{ .Unknown = status };
        }

        fn spawnMacos(self: *ChildProcess) SpawnError!void {
            const pipe_flags = if (io.is_async) os.O.NONBLOCK else 0;
            const stdin_pipe = if (self.stdin_behavior == StdIo.Pipe) try os.pipe2(pipe_flags) else undefined;
            errdefer if (self.stdin_behavior == StdIo.Pipe) destroyPipe(stdin_pipe);

            const stdout_pipe = if (self.stdout_behavior == StdIo.Pipe) try os.pipe2(pipe_flags) else undefined;
            errdefer if (self.stdout_behavior == StdIo.Pipe) destroyPipe(stdout_pipe);

            const stderr_pipe = if (self.stderr_behavior == StdIo.Pipe) try os.pipe2(pipe_flags) else undefined;
            errdefer if (self.stderr_behavior == StdIo.Pipe) destroyPipe(stderr_pipe);

            const any_ignore = (self.stdin_behavior == StdIo.Ignore or self.stdout_behavior == StdIo.Ignore or self.stderr_behavior == StdIo.Ignore);
            const dev_null_fd = if (any_ignore)
                os.openZ("/dev/null", os.O.RDWR, 0) catch |err| switch (err) {
                    error.PathAlreadyExists => unreachable,
                    error.NoSpaceLeft => unreachable,
                    error.FileTooBig => unreachable,
                    error.DeviceBusy => unreachable,
                    error.FileLocksNotSupported => unreachable,
                    error.BadPathName => unreachable, // Windows-only

                    error.InvalidHandle => unreachable, // WASI-only

                    error.WouldBlock => unreachable,
                    else => |e| return e,
                }
            else
                undefined;
            defer if (any_ignore) os.close(dev_null_fd);

            var attr = try os.posix_spawn.Attr.init();
            defer attr.deinit();
            var flags: u16 = os.darwin.POSIX_SPAWN_SETSIGDEF | os.darwin.POSIX_SPAWN_SETSIGMASK;
            if (self.disable_aslr) {
                flags |= os.darwin._POSIX_SPAWN_DISABLE_ASLR;
            }
            try attr.set(flags);

            var actions = try os.posix_spawn.Actions.init();
            defer actions.deinit();

            try setUpChildIoPosixSpawn(self.stdin_behavior, &actions, stdin_pipe, os.STDIN_FILENO, dev_null_fd);
            try setUpChildIoPosixSpawn(self.stdout_behavior, &actions, stdout_pipe, os.STDOUT_FILENO, dev_null_fd);
            try setUpChildIoPosixSpawn(self.stderr_behavior, &actions, stderr_pipe, os.STDERR_FILENO, dev_null_fd);

            if (self.cwd_dir) |cwd| {
                try actions.fchdir(cwd.fd);
            } else if (self.cwd) |cwd| {
                try actions.chdir(cwd);
            }

            var arena_allocator = std.heap.ArenaAllocator.init(self.allocator);
            defer arena_allocator.deinit();
            const arena = arena_allocator.allocator();

            const argv_buf = try arena.allocSentinel(?[*:0]u8, self.argv.len, null);
            for (self.argv) |arg, i| argv_buf[i] = (try arena.dupeZ(u8, arg)).ptr;

            const envp = if (self.env_map) |env_map| m: {
                const envp_buf = try createNullDelimitedEnvMap(arena, env_map);
                break :m envp_buf.ptr;
            } else std.c.environ;

            const pid = try os.posix_spawn.spawnp(self.argv[0], actions, attr, argv_buf, envp);

            if (self.stdin_behavior == StdIo.Pipe) {
                self.stdin = File{ .handle = stdin_pipe[1] };
            } else {
                self.stdin = null;
            }
            if (self.stdout_behavior == StdIo.Pipe) {
                self.stdout = File{ .handle = stdout_pipe[0] };
            } else {
                self.stdout = null;
            }
            if (self.stderr_behavior == StdIo.Pipe) {
                self.stderr = File{ .handle = stderr_pipe[0] };
            } else {
                self.stderr = null;
            }

            self.pid = pid;
            self.term = null;

            if (self.stdin_behavior == StdIo.Pipe) {
                os.close(stdin_pipe[0]);
            }
            if (self.stdout_behavior == StdIo.Pipe) {
                os.close(stdout_pipe[1]);
            }
            if (self.stderr_behavior == StdIo.Pipe) {
                os.close(stderr_pipe[1]);
            }
        }

        fn setUpChildIoPosixSpawn(
            stdio: StdIo,
            actions: *os.posix_spawn.Actions,
            pipe_fd: [2]i32,
            std_fileno: i32,
            dev_null_fd: i32,
        ) !void {
            switch (stdio) {
                .Pipe => {
                    const idx: usize = if (std_fileno == 0) 0 else 1;
                    try actions.dup2(pipe_fd[idx], std_fileno);
                    try actions.close(pipe_fd[1 - idx]);
                },
                .Close => try actions.close(std_fileno),
                .Inherit => {},
                .Ignore => try actions.dup2(dev_null_fd, std_fileno),
            }
        }

        fn spawnPosix(self: *ChildProcess) SpawnError!void {
            const pipe_flags = if (io.is_async) os.O.NONBLOCK else 0;
            const stdin_pipe = if (self.stdin_behavior == StdIo.Pipe) try os.pipe2(pipe_flags) else undefined;
            errdefer if (self.stdin_behavior == StdIo.Pipe) {
                destroyPipe(stdin_pipe);
            };

            const stdout_pipe = if (self.stdout_behavior == StdIo.Pipe) try os.pipe2(pipe_flags) else undefined;
            errdefer if (self.stdout_behavior == StdIo.Pipe) {
                destroyPipe(stdout_pipe);
            };

            const stderr_pipe = if (self.stderr_behavior == StdIo.Pipe) try os.pipe2(pipe_flags) else undefined;
            errdefer if (self.stderr_behavior == StdIo.Pipe) {
                destroyPipe(stderr_pipe);
            };

            const any_ignore = (self.stdin_behavior == StdIo.Ignore or self.stdout_behavior == StdIo.Ignore or self.stderr_behavior == StdIo.Ignore);
            const dev_null_fd = if (any_ignore)
                os.openZ("/dev/null", os.O.RDWR, 0) catch |err| switch (err) {
                    error.PathAlreadyExists => unreachable,
                    error.NoSpaceLeft => unreachable,
                    error.FileTooBig => unreachable,
                    error.DeviceBusy => unreachable,
                    error.FileLocksNotSupported => unreachable,
                    error.BadPathName => unreachable, // Windows-only

                    error.InvalidHandle => unreachable, // WASI-only

                    error.WouldBlock => unreachable,
                    else => |e| return e,
                }
            else
                undefined;
            defer {
                if (any_ignore) os.close(dev_null_fd);
            }

            var arena_allocator = std.heap.ArenaAllocator.init(self.allocator);
            defer arena_allocator.deinit();
            const arena = arena_allocator.allocator();

            // The POSIX standard does not allow malloc() between fork() and execve(),

            // and `self.allocator` may be a libc allocator.

            // I have personally observed the child process deadlocking when it tries

            // to call malloc() due to a heap allocation between fork() and execve(),

            // in musl v1.1.24.

            // Additionally, we want to reduce the number of possible ways things

            // can fail between fork() and execve().

            // Therefore, we do all the allocation for the execve() before the fork().

            // This means we must do the null-termination of argv and env vars here.

            const argv_buf = try arena.allocSentinel(?[*:0]u8, self.argv.len, null);
            for (self.argv) |arg, i| argv_buf[i] = (try arena.dupeZ(u8, arg)).ptr;

            const envp = m: {
                if (self.env_map) |env_map| {
                    const envp_buf = try createNullDelimitedEnvMap(arena, env_map);
                    break :m envp_buf.ptr;
                } else if (builtin.link_libc) {
                    break :m std.c.environ;
                } else if (builtin.output_mode == .Exe) {
                    // Then we have Zig start code and this works.

                    // TODO type-safety for null-termination of `os.environ`.

                    break :m @ptrCast([*:null]?[*:0]u8, os.environ.ptr);
                } else {
                    // TODO come up with a solution for this.

                    @compileError("missing std lib enhancement: ChildProcess implementation has no way to collect the environment variables to forward to the child process");
                }
            };

            // This pipe is used to communicate errors between the time of fork

            // and execve from the child process to the parent process.

            const err_pipe = blk: {
                if (builtin.os.tag == .linux) {
                    const fd = try os.eventfd(0, linux.EFD.CLOEXEC);
                    // There's no distinction between the readable and the writeable

                    // end with eventfd

                    break :blk [2]os.fd_t{ fd, fd };
                } else {
                    break :blk try os.pipe2(os.O.CLOEXEC);
                }
            };
            errdefer destroyPipe(err_pipe);

            const pid_result = try os.fork();
            if (pid_result == 0) {
                // we are the child

                setUpChildIo(self.stdin_behavior, stdin_pipe[0], os.STDIN_FILENO, dev_null_fd) catch |err| forkChildErrReport(err_pipe[1], err);
                setUpChildIo(self.stdout_behavior, stdout_pipe[1], os.STDOUT_FILENO, dev_null_fd) catch |err| forkChildErrReport(err_pipe[1], err);
                setUpChildIo(self.stderr_behavior, stderr_pipe[1], os.STDERR_FILENO, dev_null_fd) catch |err| forkChildErrReport(err_pipe[1], err);

                if (self.stdin_behavior == .Pipe) {
                    os.close(stdin_pipe[0]);
                    os.close(stdin_pipe[1]);
                }
                if (self.stdout_behavior == .Pipe) {
                    os.close(stdout_pipe[0]);
                    os.close(stdout_pipe[1]);
                }
                if (self.stderr_behavior == .Pipe) {
                    os.close(stderr_pipe[0]);
                    os.close(stderr_pipe[1]);
                }

                if (self.cwd_dir) |cwd| {
                    os.fchdir(cwd.fd) catch |err| forkChildErrReport(err_pipe[1], err);
                } else if (self.cwd) |cwd| {
                    os.chdir(cwd) catch |err| forkChildErrReport(err_pipe[1], err);
                }

                if (self.gid) |gid| {
                    os.setregid(gid, gid) catch |err| forkChildErrReport(err_pipe[1], err);
                }

                if (self.uid) |uid| {
                    os.setreuid(uid, uid) catch |err| forkChildErrReport(err_pipe[1], err);
                }

                const err = switch (self.expand_arg0) {
                    .expand => os.execvpeZ_expandArg0(.expand, argv_buf.ptr[0].?, argv_buf.ptr, envp),
                    .no_expand => os.execvpeZ_expandArg0(.no_expand, argv_buf.ptr[0].?, argv_buf.ptr, envp),
                };
                forkChildErrReport(err_pipe[1], err);
            }

            // we are the parent

            const pid = @intCast(i32, pid_result);
            if (self.stdin_behavior == StdIo.Pipe) {
                self.stdin = File{ .handle = stdin_pipe[1] };
            } else {
                self.stdin = null;
            }
            if (self.stdout_behavior == StdIo.Pipe) {
                self.stdout = File{ .handle = stdout_pipe[0] };
            } else {
                self.stdout = null;
            }
            if (self.stderr_behavior == StdIo.Pipe) {
                self.stderr = File{ .handle = stderr_pipe[0] };
            } else {
                self.stderr = null;
            }

            self.pid = pid;
            self.err_pipe = err_pipe;
            self.term = null;

            if (self.stdin_behavior == StdIo.Pipe) {
                os.close(stdin_pipe[0]);
            }
            if (self.stdout_behavior == StdIo.Pipe) {
                os.close(stdout_pipe[1]);
            }
            if (self.stderr_behavior == StdIo.Pipe) {
                os.close(stderr_pipe[1]);
            }
        }

        fn spawnWindows(self: *ChildProcess) SpawnError!void {
            const saAttr = windows.SECURITY_ATTRIBUTES{
                .nLength = @sizeOf(windows.SECURITY_ATTRIBUTES),
                .bInheritHandle = windows.TRUE,
                .lpSecurityDescriptor = null,
            };

            const any_ignore = (self.stdin_behavior == StdIo.Ignore or self.stdout_behavior == StdIo.Ignore or self.stderr_behavior == StdIo.Ignore);

            const nul_handle = if (any_ignore)
                // "\Device\Null" or "\??\NUL"

                windows.OpenFile(&[_]u16{ '\\', 'D', 'e', 'v', 'i', 'c', 'e', '\\', 'N', 'u', 'l', 'l' }, .{
                    .access_mask = windows.GENERIC_READ | windows.SYNCHRONIZE,
                    .share_access = windows.FILE_SHARE_READ,
                    .creation = windows.OPEN_EXISTING,
                    .io_mode = .blocking,
                }) catch |err| switch (err) {
                    error.PathAlreadyExists => unreachable, // not possible for "NUL"

                    error.PipeBusy => unreachable, // not possible for "NUL"

                    error.FileNotFound => unreachable, // not possible for "NUL"

                    error.AccessDenied => unreachable, // not possible for "NUL"

                    error.NameTooLong => unreachable, // not possible for "NUL"

                    error.WouldBlock => unreachable, // not possible for "NUL"

                    else => |e| return e,
                }
            else
                undefined;
            defer {
                if (any_ignore) os.close(nul_handle);
            }
            if (any_ignore) {
                try windows.SetHandleInformation(nul_handle, windows.HANDLE_FLAG_INHERIT, 0);
            }

            var g_hChildStd_IN_Rd: ?windows.HANDLE = null;
            var g_hChildStd_IN_Wr: ?windows.HANDLE = null;
            switch (self.stdin_behavior) {
                StdIo.Pipe => {
                    try windowsMakePipeIn(&g_hChildStd_IN_Rd, &g_hChildStd_IN_Wr, &saAttr);
                },
                StdIo.Ignore => {
                    g_hChildStd_IN_Rd = nul_handle;
                },
                StdIo.Inherit => {
                    g_hChildStd_IN_Rd = windows.GetStdHandle(windows.STD_INPUT_HANDLE) catch null;
                },
                StdIo.Close => {
                    g_hChildStd_IN_Rd = null;
                },
            }
            errdefer if (self.stdin_behavior == StdIo.Pipe) {
                windowsDestroyPipe(g_hChildStd_IN_Rd, g_hChildStd_IN_Wr);
            };

            var g_hChildStd_OUT_Rd: ?windows.HANDLE = null;
            var g_hChildStd_OUT_Wr: ?windows.HANDLE = null;
            switch (self.stdout_behavior) {
                StdIo.Pipe => {
                    try windowsMakeAsyncPipe(&g_hChildStd_OUT_Rd, &g_hChildStd_OUT_Wr, &saAttr);
                },
                StdIo.Ignore => {
                    g_hChildStd_OUT_Wr = nul_handle;
                },
                StdIo.Inherit => {
                    g_hChildStd_OUT_Wr = windows.GetStdHandle(windows.STD_OUTPUT_HANDLE) catch null;
                },
                StdIo.Close => {
                    g_hChildStd_OUT_Wr = null;
                },
            }
            errdefer if (self.stdin_behavior == StdIo.Pipe) {
                windowsDestroyPipe(g_hChildStd_OUT_Rd, g_hChildStd_OUT_Wr);
            };

            var g_hChildStd_ERR_Rd: ?windows.HANDLE = null;
            var g_hChildStd_ERR_Wr: ?windows.HANDLE = null;
            switch (self.stderr_behavior) {
                StdIo.Pipe => {
                    try windowsMakeAsyncPipe(&g_hChildStd_ERR_Rd, &g_hChildStd_ERR_Wr, &saAttr);
                },
                StdIo.Ignore => {
                    g_hChildStd_ERR_Wr = nul_handle;
                },
                StdIo.Inherit => {
                    g_hChildStd_ERR_Wr = windows.GetStdHandle(windows.STD_ERROR_HANDLE) catch null;
                },
                StdIo.Close => {
                    g_hChildStd_ERR_Wr = null;
                },
            }
            errdefer if (self.stdin_behavior == StdIo.Pipe) {
                windowsDestroyPipe(g_hChildStd_ERR_Rd, g_hChildStd_ERR_Wr);
            };

            const cmd_line = try windowsCreateCommandLine(self.allocator, self.argv);
            defer self.allocator.free(cmd_line);

            var siStartInfo = windows.STARTUPINFOW{
                .cb = @sizeOf(windows.STARTUPINFOW),
                .hStdError = g_hChildStd_ERR_Wr,
                .hStdOutput = g_hChildStd_OUT_Wr,
                .hStdInput = g_hChildStd_IN_Rd,
                .dwFlags = windows.STARTF_USESTDHANDLES,

                .lpReserved = null,
                .lpDesktop = null,
                .lpTitle = null,
                .dwX = 0,
                .dwY = 0,
                .dwXSize = 0,
                .dwYSize = 0,
                .dwXCountChars = 0,
                .dwYCountChars = 0,
                .dwFillAttribute = 0,
                .wShowWindow = 0,
                .cbReserved2 = 0,
                .lpReserved2 = null,
            };
            var piProcInfo: windows.PROCESS_INFORMATION = undefined;

            const cwd_w = if (self.cwd) |cwd| try unicode.utf8ToUtf16LeWithNull(self.allocator, cwd) else null;
            defer if (cwd_w) |cwd| self.allocator.free(cwd);
            const cwd_w_ptr = if (cwd_w) |cwd| cwd.ptr else null;

            const maybe_envp_buf = if (self.env_map) |env_map| try createWindowsEnvBlock(self.allocator, env_map) else null;
            defer if (maybe_envp_buf) |envp_buf| self.allocator.free(envp_buf);
            const envp_ptr = if (maybe_envp_buf) |envp_buf| envp_buf.ptr else null;

            // the cwd set in ChildProcess is in effect when choosing the executable path

            // to match posix semantics

            const app_path = x: {
                if (self.cwd) |cwd| {
                    const resolved = try fs.path.resolve(self.allocator, &[_][]const u8{ cwd, self.argv[0] });
                    defer self.allocator.free(resolved);
                    break :x try cstr.addNullByte(self.allocator, resolved);
                } else {
                    break :x try cstr.addNullByte(self.allocator, self.argv[0]);
                }
            };
            defer self.allocator.free(app_path);

            const app_path_w = try unicode.utf8ToUtf16LeWithNull(self.allocator, app_path);
            defer self.allocator.free(app_path_w);

            const cmd_line_w = try unicode.utf8ToUtf16LeWithNull(self.allocator, cmd_line);
            defer self.allocator.free(cmd_line_w);

            windowsCreateProcess(app_path_w.ptr, cmd_line_w.ptr, envp_ptr, cwd_w_ptr, &siStartInfo, &piProcInfo) catch |no_path_err| {
                if (no_path_err != error.FileNotFound) return no_path_err;

                var free_path = true;
                const PATH = process.getEnvVarOwned(self.allocator, "PATH") catch |err| switch (err) {
                    error.EnvironmentVariableNotFound => blk: {
                        free_path = false;
                        break :blk "";
                    },
                    else => |e| return e,
                };
                defer if (free_path) self.allocator.free(PATH);

                var free_path_ext = true;
                const PATHEXT = process.getEnvVarOwned(self.allocator, "PATHEXT") catch |err| switch (err) {
                    error.EnvironmentVariableNotFound => blk: {
                        free_path_ext = false;
                        break :blk "";
                    },
                    else => |e| return e,
                };
                defer if (free_path_ext) self.allocator.free(PATHEXT);

                const app_name = self.argv[0];

                var it = mem.tokenize(u8, PATH, ";");
                retry: while (it.next()) |search_path| {
                    const path_no_ext = try fs.path.join(self.allocator, &[_][]const u8{ search_path, app_name });
                    defer self.allocator.free(path_no_ext);

                    var ext_it = mem.tokenize(u8, PATHEXT, ";");
                    while (ext_it.next()) |app_ext| {
                        const joined_path = try mem.concat(self.allocator, u8, &[_][]const u8{ path_no_ext, app_ext });
                        defer self.allocator.free(joined_path);

                        const joined_path_w = try unicode.utf8ToUtf16LeWithNull(self.allocator, joined_path);
                        defer self.allocator.free(joined_path_w);

                        if (windowsCreateProcess(joined_path_w.ptr, cmd_line_w.ptr, envp_ptr, cwd_w_ptr, &siStartInfo, &piProcInfo)) |_| {
                            break :retry;
                        } else |err| switch (err) {
                            error.FileNotFound => continue,
                            error.AccessDenied => continue,
                            else => return err,
                        }
                    }
                } else {
                    return no_path_err; // return the original error

                }
            };

            if (g_hChildStd_IN_Wr) |h| {
                self.stdin = File{ .handle = h };
            } else {
                self.stdin = null;
            }
            if (g_hChildStd_OUT_Rd) |h| {
                self.stdout = File{ .handle = h };
            } else {
                self.stdout = null;
            }
            if (g_hChildStd_ERR_Rd) |h| {
                self.stderr = File{ .handle = h };
            } else {
                self.stderr = null;
            }

            self.handle = piProcInfo.hProcess;
            self.thread_handle = piProcInfo.hThread;
            self.term = null;

            if (self.stdin_behavior == StdIo.Pipe) {
                os.close(g_hChildStd_IN_Rd.?);
            }
            if (self.stderr_behavior == StdIo.Pipe) {
                os.close(g_hChildStd_ERR_Wr.?);
            }
            if (self.stdout_behavior == StdIo.Pipe) {
                os.close(g_hChildStd_OUT_Wr.?);
            }
        }

        fn setUpChildIo(stdio: StdIo, pipe_fd: i32, std_fileno: i32, dev_null_fd: i32) !void {
            switch (stdio) {
                .Pipe => try os.dup2(pipe_fd, std_fileno),
                .Close => os.close(std_fileno),
                .Inherit => {},
                .Ignore => try os.dup2(dev_null_fd, std_fileno),
            }
        }
    };

    fn windowsCreateProcess(app_name: [*:0]u16, cmd_line: [*:0]u16, envp_ptr: ?[*]u16, cwd_ptr: ?[*:0]u16, lpStartupInfo: *windows.STARTUPINFOW, lpProcessInformation: *windows.PROCESS_INFORMATION) !void {
        // TODO the docs for environment pointer say:

        // > A pointer to the environment block for the new process. If this parameter

        // > is NULL, the new process uses the environment of the calling process.

        // > ...

        // > An environment block can contain either Unicode or ANSI characters. If

        // > the environment block pointed to by lpEnvironment contains Unicode

        // > characters, be sure that dwCreationFlags includes CREATE_UNICODE_ENVIRONMENT.

        // > If this parameter is NULL and the environment block of the parent process

        // > contains Unicode characters, you must also ensure that dwCreationFlags

        // > includes CREATE_UNICODE_ENVIRONMENT.

        // This seems to imply that we have to somehow know whether our process parent passed

        // CREATE_UNICODE_ENVIRONMENT if we want to pass NULL for the environment parameter.

        // Since we do not know this information that would imply that we must not pass NULL

        // for the parameter.

        // However this would imply that programs compiled with -DUNICODE could not pass

        // environment variables to programs that were not, which seems unlikely.

        // More investigation is needed.

        return windows.CreateProcessW(
            app_name,
            cmd_line,
            null,
            null,
            windows.TRUE,
            windows.CREATE_UNICODE_ENVIRONMENT,
            @ptrCast(?*anyopaque, envp_ptr),
            cwd_ptr,
            lpStartupInfo,
            lpProcessInformation,
        );
    }

    /// Caller must dealloc.
    fn windowsCreateCommandLine(allocator: mem.Allocator, argv: []const []const u8) ![:0]u8 {
        var buf = std.ArrayList(u8).init(allocator);
        defer buf.deinit();

        for (argv) |arg, arg_i| {
            if (arg_i != 0) try buf.append(' ');
            if (mem.indexOfAny(u8, arg, " \t\n\"") == null) {
                try buf.appendSlice(arg);
                continue;
            }
            try buf.append('"');
            var backslash_count: usize = 0;
            for (arg) |byte| {
                switch (byte) {
                    '\\' => backslash_count += 1,
                    '"' => {
                        try buf.appendNTimes('\\', backslash_count * 2 + 1);
                        try buf.append('"');
                        backslash_count = 0;
                    },
                    else => {
                        try buf.appendNTimes('\\', backslash_count);
                        try buf.append(byte);
                        backslash_count = 0;
                    },
                }
            }
            try buf.appendNTimes('\\', backslash_count * 2);
            try buf.append('"');
        }

        return buf.toOwnedSliceSentinel(0);
    }

    fn windowsDestroyPipe(rd: ?windows.HANDLE, wr: ?windows.HANDLE) void {
        if (rd) |h| os.close(h);
        if (wr) |h| os.close(h);
    }

    fn windowsMakePipeIn(rd: *?windows.HANDLE, wr: *?windows.HANDLE, sattr: *const windows.SECURITY_ATTRIBUTES) !void {
        var rd_h: windows.HANDLE = undefined;
        var wr_h: windows.HANDLE = undefined;
        try windows.CreatePipe(&rd_h, &wr_h, sattr);
        errdefer windowsDestroyPipe(rd_h, wr_h);
        try windows.SetHandleInformation(wr_h, windows.HANDLE_FLAG_INHERIT, 0);
        rd.* = rd_h;
        wr.* = wr_h;
    }

    var pipe_name_counter = std.atomic.Atomic(u32).init(1);

    fn windowsMakeAsyncPipe(rd: *?windows.HANDLE, wr: *?windows.HANDLE, sattr: *const windows.SECURITY_ATTRIBUTES) !void {
        var tmp_bufw: [128]u16 = undefined;

        // Anonymous pipes are built upon Named pipes.

        // https://docs.microsoft.com/en-us/windows/win32/api/namedpipeapi/nf-namedpipeapi-createpipe

        // Asynchronous (overlapped) read and write operations are not supported by anonymous pipes.

        // https://docs.microsoft.com/en-us/windows/win32/ipc/anonymous-pipe-operations

        const pipe_path = blk: {
            var tmp_buf: [128]u8 = undefined;
            // Forge a random path for the pipe.

            const pipe_path = std.fmt.bufPrintZ(
                &tmp_buf,
                "\\\\.\\pipe\\zig-childprocess-{d}-{d}",
                .{ windows.kernel32.GetCurrentProcessId(), pipe_name_counter.fetchAdd(1, .Monotonic) },
            ) catch unreachable;
            const len = std.unicode.utf8ToUtf16Le(&tmp_bufw, pipe_path) catch unreachable;
            tmp_bufw[len] = 0;
            break :blk tmp_bufw[0..len :0];
        };

        // Create the read handle that can be used with overlapped IO ops.

        const read_handle = windows.kernel32.CreateNamedPipeW(
            pipe_path.ptr,
            windows.PIPE_ACCESS_INBOUND | windows.FILE_FLAG_OVERLAPPED,
            windows.PIPE_TYPE_BYTE,
            1,
            4096,
            4096,
            0,
            sattr,
        );
        if (read_handle == windows.INVALID_HANDLE_VALUE) {
            switch (windows.kernel32.GetLastError()) {
                else => |err| return windows.unexpectedError(err),
            }
        }
        errdefer os.close(read_handle);

        var sattr_copy = sattr.*;
        const write_handle = windows.kernel32.CreateFileW(
            pipe_path.ptr,
            windows.GENERIC_WRITE,
            0,
            &sattr_copy,
            windows.OPEN_EXISTING,
            windows.FILE_ATTRIBUTE_NORMAL,
            null,
        );
        if (write_handle == windows.INVALID_HANDLE_VALUE) {
            switch (windows.kernel32.GetLastError()) {
                else => |err| return windows.unexpectedError(err),
            }
        }
        errdefer os.close(write_handle);

        try windows.SetHandleInformation(read_handle, windows.HANDLE_FLAG_INHERIT, 0);

        rd.* = read_handle;
        wr.* = write_handle;
    }

    fn destroyPipe(pipe: [2]os.fd_t) void {
        os.close(pipe[0]);
        if (pipe[0] != pipe[1]) os.close(pipe[1]);
    }

    // Child of fork calls this to report an error to the fork parent.

    // Then the child exits.

    fn forkChildErrReport(fd: i32, err: ChildProcess.SpawnError) noreturn {
        writeIntFd(fd, @as(ErrInt, @errorToInt(err))) catch {};
        // If we're linking libc, some naughty applications may have registered atexit handlers

        // which we really do not want to run in the fork child. I caught LLVM doing this and

        // it caused a deadlock instead of doing an exit syscall. In the words of Avril Lavigne,

        // "Why'd you have to go and make things so complicated?"

        if (builtin.link_libc) {
            // The _exit(2) function does nothing but make the exit syscall, unlike exit(3)

            std.c._exit(1);
        }
        os.exit(1);
    }

    const ErrInt = std.meta.Int(.unsigned, @sizeOf(anyerror) * 8);

    fn writeIntFd(fd: i32, value: ErrInt) !void {
        const file = File{
            .handle = fd,
            .capable_io_mode = .blocking,
            .intended_io_mode = .blocking,
        };
        file.writer().writeIntNative(u64, @intCast(u64, value)) catch return error.SystemResources;
    }

    fn readIntFd(fd: i32) !ErrInt {
        const file = File{
            .handle = fd,
            .capable_io_mode = .blocking,
            .intended_io_mode = .blocking,
        };
        return @intCast(ErrInt, file.reader().readIntNative(u64) catch return error.SystemResources);
    }

    /// Caller must free result.
    pub fn createWindowsEnvBlock(allocator: mem.Allocator, env_map: *const EnvMap) ![]u16 {
        // count bytes needed

        const max_chars_needed = x: {
            var max_chars_needed: usize = 4; // 4 for the final 4 null bytes

            var it = env_map.iterator();
            while (it.next()) |pair| {
                // +1 for '='

                // +1 for null byte

                max_chars_needed += pair.key_ptr.len + pair.value_ptr.len + 2;
            }
            break :x max_chars_needed;
        };
        const result = try allocator.alloc(u16, max_chars_needed);
        errdefer allocator.free(result);

        var it = env_map.iterator();
        var i: usize = 0;
        while (it.next()) |pair| {
            i += try unicode.utf8ToUtf16Le(result[i..], pair.key_ptr.*);
            result[i] = '=';
            i += 1;
            i += try unicode.utf8ToUtf16Le(result[i..], pair.value_ptr.*);
            result[i] = 0;
            i += 1;
        }
        result[i] = 0;
        i += 1;
        result[i] = 0;
        i += 1;
        result[i] = 0;
        i += 1;
        result[i] = 0;
        i += 1;
        return allocator.shrink(result, i);
    }

    pub fn createNullDelimitedEnvMap(arena: mem.Allocator, env_map: *const EnvMap) ![:null]?[*:0]u8 {
        const envp_count = env_map.count();
        const envp_buf = try arena.allocSentinel(?[*:0]u8, envp_count, null);
        {
            var it = env_map.iterator();
            var i: usize = 0;
            while (it.next()) |pair| : (i += 1) {
                const env_buf = try arena.allocSentinel(u8, pair.key_ptr.len + pair.value_ptr.len + 1, 0);
                mem.copy(u8, env_buf, pair.key_ptr.*);
                env_buf[pair.key_ptr.len] = '=';
                mem.copy(u8, env_buf[pair.key_ptr.len + 1 ..], pair.value_ptr.*);
                envp_buf[i] = env_buf.ptr;
            }
            assert(i == envp_count);
        }
        return envp_buf;
    }

    test "createNullDelimitedEnvMap" {
        const testing = std.testing;
        const allocator = testing.allocator;
        var envmap = EnvMap.init(allocator);
        defer envmap.deinit();

        try envmap.put("HOME", "/home/ifreund");
        try envmap.put("WAYLAND_DISPLAY", "wayland-1");
        try envmap.put("DISPLAY", ":1");
        try envmap.put("DEBUGINFOD_URLS", " ");
        try envmap.put("XCURSOR_SIZE", "24");

        var arena = std.heap.ArenaAllocator.init(allocator);
        defer arena.deinit();
        const environ = try createNullDelimitedEnvMap(arena.allocator(), &envmap);

        try testing.expectEqual(@as(usize, 5), environ.len);

        inline for (.{
            "HOME=/home/ifreund",
            "WAYLAND_DISPLAY=wayland-1",
            "DISPLAY=:1",
            "DEBUGINFOD_URLS= ",
            "XCURSOR_SIZE=24",
        }) |target| {
            for (environ) |variable| {
                if (mem.eql(u8, mem.span(variable orelse continue), target)) break;
            } else {
                try testing.expect(false); // Environment variable not found

            }
        }
    }