Merge pull request #6250 from ziglang/stage2-zig-cc

move `zig cc`, `zig translate-c`, `zig libc`, main(), and linking from stage1 to stage2

1 files changed, 2345 insertions, 0 deletions

diff --git a/src/stage1/os.cpp b/src/stage1/os.cpp
new file mode 100644
index 0000000000..33d98fd416
--- /dev/null
+++ b/src/stage1/os.cpp
@@ -0,0 +1,2345 @@
+/*
+ * Copyright (c) 2015 Andrew Kelley
+ *
+ * This file is part of zig, which is MIT licensed.
+ * See http://opensource.org/licenses/MIT
+ */
+
+#include "os.hpp"
+#include "buffer.hpp"
+#include "heap.hpp"
+#include "util.hpp"
+#include "error.hpp"
+#include "util_base.hpp"
+#include <stdint.h>
+#include <stdio.h>
+
+#if defined(_WIN32)
+
+#if !defined(NOMINMAX)
+#define NOMINMAX
+#endif
+
+#if !defined(VC_EXTRALEAN)
+#define VC_EXTRALEAN
+#endif
+
+#if !defined(WIN32_LEAN_AND_MEAN)
+#define WIN32_LEAN_AND_MEAN
+#endif
+
+#if !defined(_WIN32_WINNT)
+#define _WIN32_WINNT 0x600
+#endif
+
+#if !defined(NTDDI_VERSION)
+#define NTDDI_VERSION 0x06000000
+#endif
+
+#include <windows.h>
+#include <shlobj.h>
+#include <io.h>
+#include <fcntl.h>
+#include <ntsecapi.h>
+
+#if defined(_MSC_VER)
+typedef SSIZE_T ssize_t;
+#endif
+#else
+#define ZIG_OS_POSIX
+
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <sys/resource.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <spawn.h>
+
+#endif
+
+#if defined(ZIG_OS_LINUX) || defined(ZIG_OS_FREEBSD) || defined(ZIG_OS_NETBSD) || defined(ZIG_OS_DRAGONFLY)
+#include <link.h>
+#endif
+
+#if defined(ZIG_OS_LINUX)
+#include <sys/auxv.h>
+#endif
+
+#if defined(ZIG_OS_FREEBSD) || defined(ZIG_OS_NETBSD) || defined(ZIG_OS_DRAGONFLY)
+#include <sys/sysctl.h>
+#endif
+
+#if defined(__MACH__)
+#include <mach/clock.h>
+#include <mach/mach.h>
+#include <mach-o/dyld.h>
+#endif
+
+#if defined(ZIG_OS_WINDOWS)
+static void utf16le_ptr_to_utf8(Buf *out, WCHAR *utf16le);
+static size_t utf8_to_utf16le(WCHAR *utf16_le, Slice<uint8_t> utf8);
+static uint64_t windows_perf_freq;
+#elif defined(__MACH__)
+static clock_serv_t macos_calendar_clock;
+static clock_serv_t macos_monotonic_clock;
+#endif
+
+#include <stdlib.h>
+#include <errno.h>
+#include <time.h>
+
+#if !defined(environ)
+extern char **environ;
+#endif
+
+#if defined(ZIG_OS_POSIX)
+static void populate_termination(Termination *term, int status) {
+    if (WIFEXITED(status)) {
+        term->how = TerminationIdClean;
+        term->code = WEXITSTATUS(status);
+    } else if (WIFSIGNALED(status)) {
+        term->how = TerminationIdSignaled;
+        term->code = WTERMSIG(status);
+    } else if (WIFSTOPPED(status)) {
+        term->how = TerminationIdStopped;
+        term->code = WSTOPSIG(status);
+    } else {
+        term->how = TerminationIdUnknown;
+        term->code = status;
+    }
+}
+
+static void os_spawn_process_posix(ZigList<const char *> &args, Termination *term) {
+    const char **argv = heap::c_allocator.allocate<const char *>(args.length + 1);
+    for (size_t i = 0; i < args.length; i += 1) {
+        argv[i] = args.at(i);
+    }
+    argv[args.length] = nullptr;
+
+    pid_t pid;
+    int rc = posix_spawnp(&pid, args.at(0), nullptr, nullptr, const_cast<char *const*>(argv), environ);
+    if (rc != 0) {
+        zig_panic("unable to spawn %s: %s", args.at(0), strerror(rc));
+    }
+
+    int status;
+    waitpid(pid, &status, 0);
+    populate_termination(term, status);
+}
+#endif
+
+#if defined(ZIG_OS_WINDOWS)
+
+static void os_windows_create_command_line(Buf *command_line, ZigList<const char *> &args) {
+    buf_resize(command_line, 0);
+    const char *prefix = "\"";
+    for (size_t arg_i = 0; arg_i < args.length; arg_i += 1) {
+        const char *arg = args.at(arg_i);
+        buf_append_str(command_line, prefix);
+        prefix = " \"";
+        size_t arg_len = strlen(arg);
+        for (size_t c_i = 0; c_i < arg_len; c_i += 1) {
+            if (arg[c_i] == '\"') {
+                zig_panic("TODO");
+            }
+            buf_append_char(command_line, arg[c_i]);
+        }
+        buf_append_char(command_line, '\"');
+    }
+}
+
+static void os_spawn_process_windows(ZigList<const char *> &args, Termination *term) {
+    Buf command_line = BUF_INIT;
+    os_windows_create_command_line(&command_line, args);
+
+    PROCESS_INFORMATION piProcInfo = {0};
+    STARTUPINFOW siStartInfo = {0};
+    siStartInfo.cb = sizeof(STARTUPINFOW);
+
+    Slice<uint8_t> exe_slice = str(args.at(0));
+    auto exe_utf16_slice = Slice<WCHAR>::alloc(exe_slice.len + 1);
+    exe_utf16_slice.ptr[utf8_to_utf16le(exe_utf16_slice.ptr, exe_slice)] = 0;
+
+    auto command_line_utf16 = Slice<WCHAR>::alloc(buf_len(&command_line) + 1);
+    command_line_utf16.ptr[utf8_to_utf16le(command_line_utf16.ptr, buf_to_slice(&command_line))] = 0;
+
+    BOOL success = CreateProcessW(exe_utf16_slice.ptr, command_line_utf16.ptr, nullptr, nullptr, TRUE, CREATE_UNICODE_ENVIRONMENT, nullptr, nullptr,
+            &siStartInfo, &piProcInfo);
+
+    if (!success) {
+        zig_panic("CreateProcess failed. exe: %s command_line: %s", args.at(0), buf_ptr(&command_line));
+    }
+
+    WaitForSingleObject(piProcInfo.hProcess, INFINITE);
+
+    DWORD exit_code;
+    if (!GetExitCodeProcess(piProcInfo.hProcess, &exit_code)) {
+        zig_panic("GetExitCodeProcess failed");
+    }
+    term->how = TerminationIdClean;
+    term->code = exit_code;
+}
+#endif
+
+void os_spawn_process(ZigList<const char *> &args, Termination *term) {
+#if defined(ZIG_OS_WINDOWS)
+    os_spawn_process_windows(args, term);
+#elif defined(ZIG_OS_POSIX)
+    os_spawn_process_posix(args, term);
+#else
+#error "missing os_spawn_process implementation"
+#endif
+}
+
+void os_path_dirname(Buf *full_path, Buf *out_dirname) {
+    return os_path_split(full_path, out_dirname, nullptr);
+}
+
+bool os_is_sep(uint8_t c) {
+#if defined(ZIG_OS_WINDOWS)
+    return c == '\\' || c == '/';
+#else
+    return c == '/';
+#endif
+}
+
+void os_path_split(Buf *full_path, Buf *out_dirname, Buf *out_basename) {
+    size_t len = buf_len(full_path);
+    if (len != 0) {
+        size_t last_index = len - 1;
+        char last_char = buf_ptr(full_path)[last_index];
+        if (os_is_sep(last_char)) {
+            if (last_index == 0) {
+                if (out_dirname) buf_init_from_mem(out_dirname, &last_char, 1);
+                if (out_basename) buf_init_from_str(out_basename, "");
+                return;
+            }
+            last_index -= 1;
+        }
+        for (size_t i = last_index;;) {
+            uint8_t c = buf_ptr(full_path)[i];
+            if (os_is_sep(c)) {
+                if (out_dirname) {
+                    buf_init_from_mem(out_dirname, buf_ptr(full_path), (i == 0) ? 1 : i);
+                }
+                if (out_basename) {
+                    buf_init_from_mem(out_basename, buf_ptr(full_path) + i + 1, buf_len(full_path) - (i + 1));
+                }
+                return;
+            }
+            if (i == 0) break;
+            i -= 1;
+        }
+    }
+    if (out_dirname) buf_init_from_mem(out_dirname, ".", 1);
+    if (out_basename) buf_init_from_buf(out_basename, full_path);
+}
+
+void os_path_extname(Buf *full_path, Buf *out_basename, Buf *out_extname) {
+    if (buf_len(full_path) == 0) {
+        if (out_basename) buf_init_from_str(out_basename, "");
+        if (out_extname) buf_init_from_str(out_extname, "");
+        return;
+    }
+    size_t i = buf_len(full_path) - 1;
+    while (true) {
+        if (buf_ptr(full_path)[i] == '.') {
+            if (out_basename) {
+                buf_resize(out_basename, 0);
+                buf_append_mem(out_basename, buf_ptr(full_path), i);
+            }
+
+            if (out_extname) {
+                buf_resize(out_extname, 0);
+                buf_append_mem(out_extname, buf_ptr(full_path) + i, buf_len(full_path) - i);
+            }
+            return;
+        }
+
+        if (i == 0) {
+            if (out_basename) buf_init_from_buf(out_basename, full_path);
+            if (out_extname) buf_init_from_str(out_extname, "");
+            return;
+        }
+        i -= 1;
+    }
+}
+
+void os_path_join(Buf *dirname, Buf *basename, Buf *out_full_path) {
+    if (buf_len(dirname) == 0) {
+        buf_init_from_buf(out_full_path, basename);
+        return;
+    }
+
+    buf_init_from_buf(out_full_path, dirname);
+    uint8_t c = *(buf_ptr(out_full_path) + buf_len(out_full_path) - 1);
+    if (!os_is_sep(c))
+        buf_append_char(out_full_path, ZIG_OS_SEP_CHAR);
+    buf_append_buf(out_full_path, basename);
+}
+
+Error os_path_real(Buf *rel_path, Buf *out_abs_path) {
+#if defined(ZIG_OS_WINDOWS)
+    PathSpace rel_path_space = slice_to_prefixed_file_w(buf_to_slice(rel_path));
+    PathSpace out_abs_path_space;
+
+    if (_wfullpath(&out_abs_path_space.data.items[0], &rel_path_space.data.items[0], PATH_MAX_WIDE) == nullptr) {
+        zig_panic("_wfullpath failed");
+    }
+    utf16le_ptr_to_utf8(out_abs_path, &out_abs_path_space.data.items[0]);
+    return ErrorNone;
+#elif defined(ZIG_OS_POSIX)
+    buf_resize(out_abs_path, PATH_MAX + 1);
+    char *result = realpath(buf_ptr(rel_path), buf_ptr(out_abs_path));
+    if (!result) {
+        int err = errno;
+        if (err == EACCES) {
+            return ErrorAccess;
+        } else if (err == ENOENT) {
+            return ErrorFileNotFound;
+        } else if (err == ENOMEM) {
+            return ErrorNoMem;
+        } else {
+            return ErrorFileSystem;
+        }
+    }
+    buf_resize(out_abs_path, strlen(buf_ptr(out_abs_path)));
+    return ErrorNone;
+#else
+#error "missing os_path_real implementation"
+#endif
+}
+
+#if defined(ZIG_OS_WINDOWS)
+// Ported from std/os/path.zig
+static bool isAbsoluteWindows(Slice<uint8_t> path) {
+    if (path.ptr[0] == '/')
+        return true;
+
+    if (path.ptr[0] == '\\') {
+        return true;
+    }
+    if (path.len < 3) {
+        return false;
+    }
+    if (path.ptr[1] == ':') {
+        if (path.ptr[2] == '/')
+            return true;
+        if (path.ptr[2] == '\\')
+            return true;
+    }
+    return false;
+}
+#endif
+
+bool os_path_is_absolute(Buf *path) {
+#if defined(ZIG_OS_WINDOWS)
+    return isAbsoluteWindows(buf_to_slice(path));
+#elif defined(ZIG_OS_POSIX)
+    return buf_ptr(path)[0] == '/';
+#else
+#error "missing os_path_is_absolute implementation"
+#endif
+}
+
+#if defined(ZIG_OS_WINDOWS)
+
+enum WindowsPathKind {
+    WindowsPathKindNone,
+    WindowsPathKindDrive,
+    WindowsPathKindNetworkShare,
+};
+
+struct WindowsPath {
+    Slice<uint8_t> disk_designator;
+    WindowsPathKind kind;
+    bool is_abs;
+};
+
+
+// Ported from std/os/path.zig
+static WindowsPath windowsParsePath(Slice<uint8_t> path) {
+    if (path.len >= 2 && path.ptr[1] == ':') {
+        return WindowsPath{
+            path.slice(0, 2),
+            WindowsPathKindDrive,
+            isAbsoluteWindows(path),
+        };
+    }
+    if (path.len >= 1 && (path.ptr[0] == '/' || path.ptr[0] == '\\') &&
+        (path.len == 1 || (path.ptr[1] != '/' && path.ptr[1] != '\\')))
+    {
+        return WindowsPath{
+            path.slice(0, 0),
+            WindowsPathKindNone,
+            true,
+        };
+    }
+    WindowsPath relative_path = {
+        str(""),
+        WindowsPathKindNone,
+        false,
+    };
+    if (path.len < strlen("//a/b")) {
+        return relative_path;
+    }
+
+    {
+        if (memStartsWith(path, str("//"))) {
+            if (path.ptr[2] == '/') {
+                return relative_path;
+            }
+
+            SplitIterator it = memSplit(path, str("/"));
+            {
+                Optional<Slice<uint8_t>> opt_component = SplitIterator_next(&it);
+                if (!opt_component.is_some) return relative_path;
+            }
+            {
+                Optional<Slice<uint8_t>> opt_component = SplitIterator_next(&it);
+                if (!opt_component.is_some) return relative_path;
+            }
+            return WindowsPath{
+                path.slice(0, it.index),
+                WindowsPathKindNetworkShare,
+                isAbsoluteWindows(path),
+            };
+        }
+    }
+    {
+        if (memStartsWith(path, str("\\\\"))) {
+            if (path.ptr[2] == '\\') {
+                return relative_path;
+            }
+
+            SplitIterator it = memSplit(path, str("\\"));
+            {
+                Optional<Slice<uint8_t>> opt_component = SplitIterator_next(&it);
+                if (!opt_component.is_some) return relative_path;
+            }
+            {
+                Optional<Slice<uint8_t>> opt_component = SplitIterator_next(&it);
+                if (!opt_component.is_some) return relative_path;
+            }
+            return WindowsPath{
+                path.slice(0, it.index),
+                WindowsPathKindNetworkShare,
+                isAbsoluteWindows(path),
+            };
+        }
+    }
+    return relative_path;
+}
+
+// Ported from std/os/path.zig
+static uint8_t asciiUpper(uint8_t byte) {
+    if (byte >= 'a' && byte <= 'z') {
+        return 'A' + (byte - 'a');
+    }
+    return byte;
+}
+
+// Ported from std/os/path.zig
+static bool asciiEqlIgnoreCase(Slice<uint8_t> s1, Slice<uint8_t> s2) {
+    if (s1.len != s2.len)
+        return false;
+    for (size_t i = 0; i < s1.len; i += 1) {
+        if (asciiUpper(s1.ptr[i]) != asciiUpper(s2.ptr[i]))
+            return false;
+    }
+    return true;
+}
+
+// Ported from std/os/path.zig
+static bool compareDiskDesignators(WindowsPathKind kind, Slice<uint8_t> p1, Slice<uint8_t> p2) {
+    switch (kind) {
+        case WindowsPathKindNone:
+            assert(p1.len == 0);
+            assert(p2.len == 0);
+            return true;
+        case WindowsPathKindDrive:
+            return asciiUpper(p1.ptr[0]) == asciiUpper(p2.ptr[0]);
+        case WindowsPathKindNetworkShare:
+            uint8_t sep1 = p1.ptr[0];
+            uint8_t sep2 = p2.ptr[0];
+
+            SplitIterator it1 = memSplit(p1, {&sep1, 1});
+            SplitIterator it2 = memSplit(p2, {&sep2, 1});
+
+            // TODO ASCII is wrong, we actually need full unicode support to compare paths.
+            return asciiEqlIgnoreCase(SplitIterator_next(&it1).value, SplitIterator_next(&it2).value) &&
+                asciiEqlIgnoreCase(SplitIterator_next(&it1).value, SplitIterator_next(&it2).value);
+    }
+    zig_unreachable();
+}
+
+// Ported from std/os/path.zig
+static Buf os_path_resolve_windows(Buf **paths_ptr, size_t paths_len) {
+    if (paths_len == 0) {
+        Buf cwd = BUF_INIT;
+        int err;
+        if ((err = os_get_cwd(&cwd))) {
+            zig_panic("get cwd failed");
+        }
+        return cwd;
+    }
+
+    // determine which disk designator we will result with, if any
+    char result_drive_buf[3] = {'_', ':', '\0'}; // 0 needed for strlen later
+    Slice<uint8_t> result_disk_designator = str("");
+    WindowsPathKind have_drive_kind = WindowsPathKindNone;
+    bool have_abs_path = false;
+    size_t first_index = 0;
+    size_t max_size = 0;
+    for (size_t i = 0; i < paths_len; i += 1) {
+        Slice<uint8_t> p = buf_to_slice(paths_ptr[i]);
+        WindowsPath parsed = windowsParsePath(p);
+        if (parsed.is_abs) {
+            have_abs_path = true;
+            first_index = i;
+            max_size = result_disk_designator.len;
+        }
+        switch (parsed.kind) {
+            case WindowsPathKindDrive:
+                result_drive_buf[0] = asciiUpper(parsed.disk_designator.ptr[0]);
+                result_disk_designator = str(result_drive_buf);
+                have_drive_kind = WindowsPathKindDrive;
+                break;
+            case WindowsPathKindNetworkShare:
+                result_disk_designator = parsed.disk_designator;
+                have_drive_kind = WindowsPathKindNetworkShare;
+                break;
+            case WindowsPathKindNone:
+                break;
+        }
+        max_size += p.len + 1;
+    }
+
+    // if we will result with a disk designator, loop again to determine
+    // which is the last time the disk designator is absolutely specified, if any
+    // and count up the max bytes for paths related to this disk designator
+    if (have_drive_kind != WindowsPathKindNone) {
+        have_abs_path = false;
+        first_index = 0;
+        max_size = result_disk_designator.len;
+        bool correct_disk_designator = false;
+
+        for (size_t i = 0; i < paths_len; i += 1) {
+            Slice<uint8_t> p = buf_to_slice(paths_ptr[i]);
+            WindowsPath parsed = windowsParsePath(p);
+            if (parsed.kind != WindowsPathKindNone) {
+                if (parsed.kind == have_drive_kind) {
+                    correct_disk_designator = compareDiskDesignators(have_drive_kind, result_disk_designator, parsed.disk_designator);
+                } else {
+                    continue;
+                }
+            }
+            if (!correct_disk_designator) {
+                continue;
+            }
+            if (parsed.is_abs) {
+                first_index = i;
+                max_size = result_disk_designator.len;
+                have_abs_path = true;
+            }
+            max_size += p.len + 1;
+        }
+    }
+
+    // Allocate result and fill in the disk designator, calling getCwd if we have to.
+    Slice<uint8_t> result;
+    size_t result_index = 0;
+
+    if (have_abs_path) {
+        switch (have_drive_kind) {
+            case WindowsPathKindDrive: {
+                result = Slice<uint8_t>::alloc(max_size);
+
+                memCopy(result, result_disk_designator);
+                result_index += result_disk_designator.len;
+                break;
+            }
+            case WindowsPathKindNetworkShare: {
+                result = Slice<uint8_t>::alloc(max_size);
+                SplitIterator it = memSplit(buf_to_slice(paths_ptr[first_index]), str("/\\"));
+                Slice<uint8_t> server_name = SplitIterator_next(&it).value;
+                Slice<uint8_t> other_name = SplitIterator_next(&it).value;
+
+                result.ptr[result_index] = '\\';
+                result_index += 1;
+                result.ptr[result_index] = '\\';
+                result_index += 1;
+                memCopy(result.sliceFrom(result_index), server_name);
+                result_index += server_name.len;
+                result.ptr[result_index] = '\\';
+                result_index += 1;
+                memCopy(result.sliceFrom(result_index), other_name);
+                result_index += other_name.len;
+
+                result_disk_designator = result.slice(0, result_index);
+                break;
+            }
+            case WindowsPathKindNone: {
+                Buf cwd = BUF_INIT;
+                int err;
+                if ((err = os_get_cwd(&cwd))) {
+                    zig_panic("get cwd failed");
+                }
+                WindowsPath parsed_cwd = windowsParsePath(buf_to_slice(&cwd));
+                result = Slice<uint8_t>::alloc(max_size + parsed_cwd.disk_designator.len + 1);
+                memCopy(result, parsed_cwd.disk_designator);
+                result_index += parsed_cwd.disk_designator.len;
+                result_disk_designator = result.slice(0, parsed_cwd.disk_designator.len);
+                if (parsed_cwd.kind == WindowsPathKindDrive) {
+                    result.ptr[0] = asciiUpper(result.ptr[0]);
+                }
+                have_drive_kind = parsed_cwd.kind;
+                break;
+            }
+        }
+    } else {
+        // TODO call get cwd for the result_disk_designator instead of the global one
+        Buf cwd = BUF_INIT;
+        int err;
+        if ((err = os_get_cwd(&cwd))) {
+            zig_panic("get cwd failed");
+        }
+        result = Slice<uint8_t>::alloc(max_size + buf_len(&cwd) + 1);
+
+        memCopy(result, buf_to_slice(&cwd));
+        result_index += buf_len(&cwd);
+        WindowsPath parsed_cwd = windowsParsePath(result.slice(0, result_index));
+        result_disk_designator = parsed_cwd.disk_designator;
+        if (parsed_cwd.kind == WindowsPathKindDrive) {
+            result.ptr[0] = asciiUpper(result.ptr[0]);
+        }
+        have_drive_kind = parsed_cwd.kind;
+    }
+
+    // Now we know the disk designator to use, if any, and what kind it is. And our result
+    // is big enough to append all the paths to.
+    bool correct_disk_designator = true;
+    for (size_t i = 0; i < paths_len; i += 1) {
+        Slice<uint8_t> p = buf_to_slice(paths_ptr[i]);
+        WindowsPath parsed = windowsParsePath(p);
+
+        if (parsed.kind != WindowsPathKindNone) {
+            if (parsed.kind == have_drive_kind) {
+                correct_disk_designator = compareDiskDesignators(have_drive_kind, result_disk_designator, parsed.disk_designator);
+            } else {
+                continue;
+            }
+        }
+        if (!correct_disk_designator) {
+            continue;
+        }
+        SplitIterator it = memSplit(p.sliceFrom(parsed.disk_designator.len), str("/\\"));
+        while (true) {
+            Optional<Slice<uint8_t>> opt_component = SplitIterator_next(&it);
+            if (!opt_component.is_some) break;
+            Slice<uint8_t> component = opt_component.value;
+            if (memEql(component, str("."))) {
+                continue;
+            } else if (memEql(component, str(".."))) {
+                while (true) {
+                    if (result_index == 0 || result_index == result_disk_designator.len)
+                        break;
+                    result_index -= 1;
+                    if (result.ptr[result_index] == '\\' || result.ptr[result_index] == '/')
+                        break;
+                }
+            } else {
+                result.ptr[result_index] = '\\';
+                result_index += 1;
+                memCopy(result.sliceFrom(result_index), component);
+                result_index += component.len;
+            }
+        }
+    }
+
+    if (result_index == result_disk_designator.len) {
+        result.ptr[result_index] = '\\';
+        result_index += 1;
+    }
+
+    Buf return_value = BUF_INIT;
+    buf_init_from_mem(&return_value, (char *)result.ptr, result_index);
+    return return_value;
+}
+#endif
+
+#if defined(ZIG_OS_POSIX)
+// Ported from std/os/path.zig
+static Buf os_path_resolve_posix(Buf **paths_ptr, size_t paths_len) {
+    if (paths_len == 0) {
+        Buf cwd = BUF_INIT;
+        int err;
+        if ((err = os_get_cwd(&cwd))) {
+            zig_panic("get cwd failed");
+        }
+        return cwd;
+    }
+
+    size_t first_index = 0;
+    bool have_abs = false;
+    size_t max_size = 0;
+    for (size_t i = 0; i < paths_len; i += 1) {
+        Buf *p = paths_ptr[i];
+        if (os_path_is_absolute(p)) {
+            first_index = i;
+            have_abs = true;
+            max_size = 0;
+        }
+        max_size += buf_len(p) + 1;
+    }
+
+    uint8_t *result_ptr;
+    size_t result_len;
+    size_t result_index = 0;
+
+    if (have_abs) {
+        result_len = max_size;
+        result_ptr = heap::c_allocator.allocate_nonzero<uint8_t>(result_len);
+    } else {
+        Buf cwd = BUF_INIT;
+        int err;
+        if ((err = os_get_cwd(&cwd))) {
+            zig_panic("get cwd failed");
+        }
+        result_len = max_size + buf_len(&cwd) + 1;
+        result_ptr = heap::c_allocator.allocate_nonzero<uint8_t>(result_len);
+        memcpy(result_ptr, buf_ptr(&cwd), buf_len(&cwd));
+        result_index += buf_len(&cwd);
+    }
+
+    for (size_t i = first_index; i < paths_len; i += 1) {
+        Buf *p = paths_ptr[i];
+        SplitIterator it = memSplit(buf_to_slice(p), str("/"));
+        while (true) {
+            Optional<Slice<uint8_t>> opt_component = SplitIterator_next(&it);
+            if (!opt_component.is_some) break;
+            Slice<uint8_t> component = opt_component.value;
+
+            if (memEql<uint8_t>(component, str("."))) {
+                continue;
+            } else if (memEql<uint8_t>(component, str(".."))) {
+                while (true) {
+                    if (result_index == 0)
+                        break;
+                    result_index -= 1;
+                    if (result_ptr[result_index] == '/')
+                        break;
+                }
+            } else {
+                result_ptr[result_index] = '/';
+                result_index += 1;
+                memcpy(result_ptr + result_index, component.ptr, component.len);
+                result_index += component.len;
+            }
+        }
+    }
+
+    if (result_index == 0) {
+        result_ptr[0] = '/';
+        result_index += 1;
+    }
+
+    Buf return_value = BUF_INIT;
+    buf_init_from_mem(&return_value, (char *)result_ptr, result_index);
+    return return_value;
+}
+#endif
+
+// Ported from std/os/path.zig
+Buf os_path_resolve(Buf **paths_ptr, size_t paths_len) {
+#if defined(ZIG_OS_WINDOWS)
+    return os_path_resolve_windows(paths_ptr, paths_len);
+#elif defined(ZIG_OS_POSIX)
+    return os_path_resolve_posix(paths_ptr, paths_len);
+#else
+#error "missing os_path_resolve implementation"
+#endif
+}
+
+Error os_fetch_file(FILE *f, Buf *out_buf) {
+    static const ssize_t buf_size = 0x2000;
+    buf_resize(out_buf, buf_size);
+    ssize_t actual_buf_len = 0;
+
+    for (;;) {
+        size_t amt_read = fread(buf_ptr(out_buf) + actual_buf_len, 1, buf_size, f);
+        actual_buf_len += amt_read;
+
+        if (amt_read != buf_size) {
+            if (feof(f)) {
+                buf_resize(out_buf, actual_buf_len);
+                return ErrorNone;
+            } else {
+                return ErrorFileSystem;
+            }
+        }
+
+        buf_resize(out_buf, actual_buf_len + buf_size);
+    }
+    zig_unreachable();
+}
+
+Error os_file_exists(Buf *full_path, bool *result) {
+#if defined(ZIG_OS_WINDOWS)
+    PathSpace path_space = slice_to_prefixed_file_w(buf_to_slice(full_path));
+    *result = GetFileAttributesW(&path_space.data.items[0]) != INVALID_FILE_ATTRIBUTES;
+    return ErrorNone;
+#else
+    *result = access(buf_ptr(full_path), F_OK) != -1;
+    return ErrorNone;
+#endif
+}
+
+#if defined(ZIG_OS_POSIX)
+static Error os_exec_process_posix(ZigList<const char *> &args,
+        Termination *term, Buf *out_stderr, Buf *out_stdout)
+{
+    int stdin_pipe[2];
+    int stdout_pipe[2];
+    int stderr_pipe[2];
+    int err_pipe[2];
+
+    int err;
+    if ((err = pipe(stdin_pipe)))
+        zig_panic("pipe failed");
+    if ((err = pipe(stdout_pipe)))
+        zig_panic("pipe failed");
+    if ((err = pipe(stderr_pipe)))
+        zig_panic("pipe failed");
+    if ((err = pipe(err_pipe)))
+        zig_panic("pipe failed");
+
+    pid_t pid = fork();
+    if (pid == -1)
+        zig_panic("fork failed: %s", strerror(errno));
+    if (pid == 0) {
+        // child
+        if (dup2(stdin_pipe[0], STDIN_FILENO) == -1)
+            zig_panic("dup2 failed");
+
+        if (dup2(stdout_pipe[1], STDOUT_FILENO) == -1)
+            zig_panic("dup2 failed");
+
+        if (dup2(stderr_pipe[1], STDERR_FILENO) == -1)
+            zig_panic("dup2 failed");
+
+        const char **argv = heap::c_allocator.allocate<const char *>(args.length + 1);
+        argv[args.length] = nullptr;
+        for (size_t i = 0; i < args.length; i += 1) {
+            argv[i] = args.at(i);
+        }
+        execvp(argv[0], const_cast<char * const *>(argv));
+        Error report_err = ErrorUnexpected;
+        if (errno == ENOENT) {
+            report_err = ErrorFileNotFound;
+        }
+        if (write(err_pipe[1], &report_err, sizeof(Error)) == -1) {
+            zig_panic("write failed");
+        }
+        exit(1);
+    } else {
+        // parent
+        close(stdin_pipe[0]);
+        close(stdin_pipe[1]);
+        close(stdout_pipe[1]);
+        close(stderr_pipe[1]);
+
+        int status;
+        waitpid(pid, &status, 0);
+        populate_termination(term, status);
+
+        FILE *stdout_f = fdopen(stdout_pipe[0], "rb");
+        FILE *stderr_f = fdopen(stderr_pipe[0], "rb");
+        Error err1 = os_fetch_file(stdout_f, out_stdout);
+        Error err2 = os_fetch_file(stderr_f, out_stderr);
+
+        fclose(stdout_f);
+        fclose(stderr_f);
+
+        if (err1) return err1;
+        if (err2) return err2;
+
+        Error child_err = ErrorNone;
+        if (write(err_pipe[1], &child_err, sizeof(Error)) == -1) {
+            zig_panic("write failed");
+        }
+        close(err_pipe[1]);
+        if (read(err_pipe[0], &child_err, sizeof(Error)) == -1) {
+            zig_panic("write failed");
+        }
+        close(err_pipe[0]);
+        return child_err;
+    }
+}
+#endif
+
+#if defined(ZIG_OS_WINDOWS)
+
+//static void win32_panic(const char *str) {
+//    DWORD err = GetLastError();
+//    LPSTR messageBuffer = nullptr;
+//    FormatMessageA(
+//        FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
+//        NULL, err, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), (LPSTR)&messageBuffer, 0, NULL);
+//    zig_panic(str, messageBuffer);
+//    LocalFree(messageBuffer);
+//}
+
+static Error os_exec_process_windows(ZigList<const char *> &args,
+        Termination *term, Buf *out_stderr, Buf *out_stdout)
+{
+    Buf command_line = BUF_INIT;
+    os_windows_create_command_line(&command_line, args);
+
+    HANDLE g_hChildStd_IN_Rd = NULL;
+    HANDLE g_hChildStd_IN_Wr = NULL;
+    HANDLE g_hChildStd_OUT_Rd = NULL;
+    HANDLE g_hChildStd_OUT_Wr = NULL;
+    HANDLE g_hChildStd_ERR_Rd = NULL;
+    HANDLE g_hChildStd_ERR_Wr = NULL;
+
+    SECURITY_ATTRIBUTES saAttr;
+    saAttr.nLength = sizeof(SECURITY_ATTRIBUTES);
+    saAttr.bInheritHandle = TRUE;
+    saAttr.lpSecurityDescriptor = NULL;
+
+    if (!CreatePipe(&g_hChildStd_OUT_Rd, &g_hChildStd_OUT_Wr, &saAttr, 0)) {
+        zig_panic("StdoutRd CreatePipe");
+    }
+
+    if (!SetHandleInformation(g_hChildStd_OUT_Rd, HANDLE_FLAG_INHERIT, 0)) {
+        zig_panic("Stdout SetHandleInformation");
+    }
+
+    if (!CreatePipe(&g_hChildStd_ERR_Rd, &g_hChildStd_ERR_Wr, &saAttr, 0)) {
+        zig_panic("stderr CreatePipe");
+    }
+
+    if (!SetHandleInformation(g_hChildStd_ERR_Rd, HANDLE_FLAG_INHERIT, 0)) {
+        zig_panic("stderr SetHandleInformation");
+    }
+
+    if (!CreatePipe(&g_hChildStd_IN_Rd, &g_hChildStd_IN_Wr, &saAttr, 0)) {
+        zig_panic("Stdin CreatePipe");
+    }
+
+    if (!SetHandleInformation(g_hChildStd_IN_Wr, HANDLE_FLAG_INHERIT, 0)) {
+        zig_panic("Stdin SetHandleInformation");
+    }
+
+
+    PROCESS_INFORMATION piProcInfo = {0};
+    STARTUPINFO siStartInfo = {0};
+    siStartInfo.cb = sizeof(STARTUPINFO);
+    siStartInfo.hStdError = g_hChildStd_ERR_Wr;
+    siStartInfo.hStdOutput = g_hChildStd_OUT_Wr;
+    siStartInfo.hStdInput = g_hChildStd_IN_Rd;
+    siStartInfo.dwFlags |= STARTF_USESTDHANDLES;
+
+    const char *exe = args.at(0);
+    BOOL success = CreateProcess(exe, buf_ptr(&command_line), nullptr, nullptr, TRUE, 0, nullptr, nullptr,
+            &siStartInfo, &piProcInfo);
+
+    if (!success) {
+        if (GetLastError() == ERROR_FILE_NOT_FOUND) {
+            CloseHandle(piProcInfo.hProcess);
+            CloseHandle(piProcInfo.hThread);
+            return ErrorFileNotFound;
+        }
+        zig_panic("CreateProcess failed. exe: %s command_line: %s", exe, buf_ptr(&command_line));
+    }
+
+    if (!CloseHandle(g_hChildStd_IN_Wr)) {
+        zig_panic("stdinwr closehandle");
+    }
+
+    CloseHandle(g_hChildStd_IN_Rd);
+    CloseHandle(g_hChildStd_ERR_Wr);
+    CloseHandle(g_hChildStd_OUT_Wr);
+
+    static const size_t BUF_SIZE = 4 * 1024;
+    {
+        DWORD dwRead;
+        char chBuf[BUF_SIZE];
+
+        buf_resize(out_stdout, 0);
+        for (;;) {
+            success = ReadFile( g_hChildStd_OUT_Rd, chBuf, BUF_SIZE, &dwRead, NULL);
+            if (!success || dwRead == 0) break;
+
+            buf_append_mem(out_stdout, chBuf, dwRead);
+        }
+        CloseHandle(g_hChildStd_OUT_Rd);
+    }
+    {
+        DWORD dwRead;
+        char chBuf[BUF_SIZE];
+
+        buf_resize(out_stderr, 0);
+        for (;;) {
+            success = ReadFile( g_hChildStd_ERR_Rd, chBuf, BUF_SIZE, &dwRead, NULL);
+            if (!success || dwRead == 0) break;
+
+            buf_append_mem(out_stderr, chBuf, dwRead);
+        }
+        CloseHandle(g_hChildStd_ERR_Rd);
+    }
+
+    WaitForSingleObject(piProcInfo.hProcess, INFINITE);
+
+    DWORD exit_code;
+    if (!GetExitCodeProcess(piProcInfo.hProcess, &exit_code)) {
+        zig_panic("GetExitCodeProcess failed");
+    }
+    term->how = TerminationIdClean;
+    term->code = exit_code;
+
+    CloseHandle(piProcInfo.hProcess);
+    CloseHandle(piProcInfo.hThread);
+
+    return ErrorNone;
+}
+#endif
+
+Error os_execv(const char *exe, const char **argv) {
+#if defined(ZIG_OS_WINDOWS)
+    return ErrorUnsupportedOperatingSystem;
+#else
+    execv(exe, (char *const *)argv);
+    switch (errno) {
+        case ENOMEM:
+            return ErrorSystemResources;
+        case EIO:
+            return ErrorFileSystem;
+        default:
+            return ErrorUnexpected;
+    }
+#endif
+}
+
+Error os_exec_process(ZigList<const char *> &args,
+        Termination *term, Buf *out_stderr, Buf *out_stdout)
+{
+#if defined(ZIG_OS_WINDOWS)
+    return os_exec_process_windows(args, term, out_stderr, out_stdout);
+#elif defined(ZIG_OS_POSIX)
+    return os_exec_process_posix(args, term, out_stderr, out_stdout);
+#else
+#error "missing os_exec_process implementation"
+#endif
+}
+
+Error os_write_file(Buf *full_path, Buf *contents) {
+#if defined(ZIG_OS_WINDOWS)
+    PathSpace path_space = slice_to_prefixed_file_w(buf_to_slice(full_path));
+    FILE *f = _wfopen(&path_space.data.items[0], L"wb");
+#else
+    FILE *f = fopen(buf_ptr(full_path), "wb");
+#endif
+    if (!f) {
+        zig_panic("os_write_file failed for %s", buf_ptr(full_path));
+    }
+    size_t amt_written = fwrite(buf_ptr(contents), 1, buf_len(contents), f);
+    if (amt_written != (size_t)buf_len(contents))
+        zig_panic("write failed: %s", strerror(errno));
+    if (fclose(f))
+        zig_panic("close failed");
+    return ErrorNone;
+}
+
+static Error copy_open_files(FILE *src_f, FILE *dest_f) {
+    static const size_t buf_size = 2048;
+    char buf[buf_size];
+    for (;;) {
+        size_t amt_read = fread(buf, 1, buf_size, src_f);
+        if (amt_read != buf_size) {
+            if (ferror(src_f)) {
+                return ErrorFileSystem;
+            }
+        }
+        size_t amt_written = fwrite(buf, 1, amt_read, dest_f);
+        if (amt_written != amt_read) {
+            return ErrorFileSystem;
+        }
+        if (feof(src_f)) {
+            return ErrorNone;
+        }
+    }
+}
+
+Error os_dump_file(Buf *src_path, FILE *dest_file) {
+    Error err;
+
+#if defined(ZIG_OS_WINDOWS)
+    PathSpace path_space = slice_to_prefixed_file_w(buf_to_slice(src_path));
+    FILE *src_f = _wfopen(&path_space.data.items[0], L"rb");
+#else
+    FILE *src_f = fopen(buf_ptr(src_path), "rb");
+#endif
+    if (!src_f) {
+        int err = errno;
+        if (err == ENOENT) {
+            return ErrorFileNotFound;
+        } else if (err == EACCES || err == EPERM) {
+            return ErrorAccess;
+        } else {
+            return ErrorFileSystem;
+        }
+    }
+    copy_open_files(src_f, dest_file);
+    if ((err = copy_open_files(src_f, dest_file))) {
+        fclose(src_f);
+        return err;
+    }
+
+    fclose(src_f);
+    return ErrorNone;
+}
+
+#if defined(ZIG_OS_WINDOWS)
+static void windows_filetime_to_os_timestamp(FILETIME *ft, OsTimeStamp *mtime) {
+    mtime->sec = (((ULONGLONG) ft->dwHighDateTime) << 32) + ft->dwLowDateTime;
+    mtime->nsec = 0;
+}
+static FILETIME windows_os_timestamp_to_filetime(OsTimeStamp mtime) {
+    FILETIME result;
+    result.dwHighDateTime = mtime.sec >> 32;
+    result.dwLowDateTime = mtime.sec;
+    return result;
+}
+#endif
+
+static Error set_file_times(OsFile file, OsTimeStamp ts) {
+#if defined(ZIG_OS_WINDOWS)
+    FILETIME ft = windows_os_timestamp_to_filetime(ts);
+    if (SetFileTime(file, nullptr, &ft, &ft) == 0) {
+        return ErrorUnexpected;
+    }
+    return ErrorNone;
+#else
+    struct timespec times[2] = {
+        { (time_t)ts.sec, (long)ts.nsec },
+        { (time_t)ts.sec, (long)ts.nsec },
+    };
+    if (futimens(file, times) == -1) {
+        switch (errno) {
+            case EBADF:
+                zig_panic("futimens EBADF");
+            default:
+                return ErrorUnexpected;
+        }
+    }
+    return ErrorNone;
+#endif
+}
+
+Error os_update_file(Buf *src_path, Buf *dst_path) {
+    Error err;
+
+    OsFile src_file;
+    OsFileAttr src_attr;
+    if ((err = os_file_open_r(src_path, &src_file, &src_attr))) {
+        return err;
+    }
+
+    OsFile dst_file;
+    OsFileAttr dst_attr;
+    if ((err = os_file_open_w(dst_path, &dst_file, &dst_attr, src_attr.mode))) {
+        os_file_close(&src_file);
+        return err;
+    }
+
+    if (src_attr.size == dst_attr.size &&
+        src_attr.mode == dst_attr.mode &&
+        src_attr.mtime.sec == dst_attr.mtime.sec &&
+        src_attr.mtime.nsec == dst_attr.mtime.nsec)
+    {
+        os_file_close(&src_file);
+        os_file_close(&dst_file);
+        return ErrorNone;
+    }
+#if defined(ZIG_OS_WINDOWS)
+    if (SetEndOfFile(dst_file) == 0) {
+        return ErrorUnexpected;
+    }
+#else
+    if (ftruncate(dst_file, 0) == -1) {
+        return ErrorUnexpected;
+    }
+#endif
+#if defined(ZIG_OS_WINDOWS)
+    FILE *src_libc_file = _fdopen(_open_osfhandle((intptr_t)src_file, _O_RDONLY), "rb");
+    FILE *dst_libc_file = _fdopen(_open_osfhandle((intptr_t)dst_file, 0), "wb");
+#else
+    FILE *src_libc_file = fdopen(src_file, "rb");
+    FILE *dst_libc_file = fdopen(dst_file, "wb");
+#endif
+    assert(src_libc_file);
+    assert(dst_libc_file);
+
+    if ((err = copy_open_files(src_libc_file, dst_libc_file))) {
+        fclose(src_libc_file);
+        fclose(dst_libc_file);
+        return err;
+    }
+    if (fflush(dst_libc_file) == -1) {
+        return ErrorUnexpected;
+    }
+    err = set_file_times(dst_file, src_attr.mtime);
+    fclose(src_libc_file);
+    fclose(dst_libc_file);
+    return err;
+}
+
+Error os_copy_file(Buf *src_path, Buf *dest_path) {
+#if defined(ZIG_OS_WINDOWS)
+    PathSpace src_path_space = slice_to_prefixed_file_w(buf_to_slice(src_path));
+    FILE *src_f = _wfopen(&src_path_space.data.items[0], L"rb");
+#else
+    FILE *src_f = fopen(buf_ptr(src_path), "rb");
+#endif
+    if (!src_f) {
+        int err = errno;
+        if (err == ENOENT) {
+            return ErrorFileNotFound;
+        } else if (err == EACCES || err == EPERM) {
+            return ErrorAccess;
+        } else {
+            return ErrorFileSystem;
+        }
+    }
+#if defined(ZIG_OS_WINDOWS)
+    PathSpace dest_path_space = slice_to_prefixed_file_w(buf_to_slice(dest_path));
+    FILE *dest_f = _wfopen(&dest_path_space.data.items[0], L"wb");
+#else
+    FILE *dest_f = fopen(buf_ptr(dest_path), "wb");
+#endif
+    if (!dest_f) {
+        int err = errno;
+        if (err == ENOENT) {
+            fclose(src_f);
+            return ErrorFileNotFound;
+        } else if (err == EACCES || err == EPERM) {
+            fclose(src_f);
+            return ErrorAccess;
+        } else {
+            fclose(src_f);
+            return ErrorFileSystem;
+        }
+    }
+    Error err = copy_open_files(src_f, dest_f);
+    fclose(src_f);
+    fclose(dest_f);
+    return err;
+}
+
+Error os_fetch_file_path(Buf *full_path, Buf *out_contents) {
+#if defined(ZIG_OS_WINDOWS)
+    PathSpace path_space = slice_to_prefixed_file_w(buf_to_slice(full_path));
+    FILE *f = _wfopen(&path_space.data.items[0], L"rb");
+#else
+    FILE *f = fopen(buf_ptr(full_path), "rb");
+#endif
+    if (!f) {
+        switch (errno) {
+            case EACCES:
+                return ErrorAccess;
+            case EINTR:
+                return ErrorInterrupted;
+            case EINVAL:
+                return ErrorInvalidFilename;
+            case ENFILE:
+            case ENOMEM:
+                return ErrorSystemResources;
+            case ENOENT:
+                return ErrorFileNotFound;
+            default:
+                return ErrorFileSystem;
+        }
+    }
+    Error result = os_fetch_file(f, out_contents);
+    fclose(f);
+    return result;
+}
+
+Error os_get_cwd(Buf *out_cwd) {
+#if defined(ZIG_OS_WINDOWS)
+    PathSpace path_space;
+    if (GetCurrentDirectoryW(PATH_MAX_WIDE, &path_space.data.items[0]) == 0) {
+        zig_panic("GetCurrentDirectory failed");
+    }
+    utf16le_ptr_to_utf8(out_cwd, &path_space.data.items[0]);
+    return ErrorNone;
+#elif defined(ZIG_OS_POSIX)
+    char buf[PATH_MAX];
+    char *res = getcwd(buf, PATH_MAX);
+    if (res == nullptr) {
+        zig_panic("unable to get cwd: %s", strerror(errno));
+    }
+    buf_init_from_str(out_cwd, res);
+    return ErrorNone;
+#else
+#error "missing os_get_cwd implementation"
+#endif
+}
+
+#if defined(ZIG_OS_WINDOWS)
+#define is_wprefix(s, prefix) \
+    (wcsncmp((s), (prefix), sizeof(prefix) / sizeof(WCHAR) - 1) == 0)
+static bool is_stderr_cyg_pty(void) {
+    HANDLE stderr_handle = GetStdHandle(STD_ERROR_HANDLE);
+    if (stderr_handle == INVALID_HANDLE_VALUE)
+        return false;
+
+    const int size = sizeof(FILE_NAME_INFO) + sizeof(WCHAR) * MAX_PATH;
+    FILE_NAME_INFO *nameinfo;
+    WCHAR *p = NULL;
+
+    // Cygwin/msys's pty is a pipe.
+    if (GetFileType(stderr_handle) != FILE_TYPE_PIPE) {
+        return 0;
+    }
+    nameinfo = reinterpret_cast<FILE_NAME_INFO *>(heap::c_allocator.allocate<char>(size));
+    if (nameinfo == NULL) {
+        return 0;
+    }
+    // Check the name of the pipe:
+    // '\{cygwin,msys}-XXXXXXXXXXXXXXXX-ptyN-{from,to}-master'
+    if (GetFileInformationByHandleEx(stderr_handle, FileNameInfo, nameinfo, size)) {
+        nameinfo->FileName[nameinfo->FileNameLength / sizeof(WCHAR)] = L'\0';
+        p = nameinfo->FileName;
+        if (is_wprefix(p, L"\\cygwin-")) {      /* Cygwin */
+            p += 8;
+        } else if (is_wprefix(p, L"\\msys-")) { /* MSYS and MSYS2 */
+            p += 6;
+        } else {
+            p = NULL;
+        }
+        if (p != NULL) {
+            while (*p && isxdigit(*p))  /* Skip 16-digit hexadecimal. */
+                ++p;
+            if (is_wprefix(p, L"-pty")) {
+                p += 4;
+            } else {
+                p = NULL;
+            }
+        }
+        if (p != NULL) {
+            while (*p && isdigit(*p))   /* Skip pty number. */
+                ++p;
+            if (is_wprefix(p, L"-from-master")) {
+                //p += 12;
+            } else if (is_wprefix(p, L"-to-master")) {
+                //p += 10;
+            } else {
+                p = NULL;
+            }
+        }
+    }
+    heap::c_allocator.deallocate(reinterpret_cast<char *>(nameinfo), size);
+    return (p != NULL);
+}
+#endif
+
+bool os_stderr_tty(void) {
+#if defined(ZIG_OS_WINDOWS)
+    return _isatty(_fileno(stderr)) != 0 || is_stderr_cyg_pty();
+#elif defined(ZIG_OS_POSIX)
+    return isatty(STDERR_FILENO) != 0;
+#else
+#error "missing os_stderr_tty implementation"
+#endif
+}
+
+Error os_delete_file(Buf *path) {
+    if (remove(buf_ptr(path))) {
+        return ErrorFileSystem;
+    } else {
+        return ErrorNone;
+    }
+}
+
+Error os_rename(Buf *src_path, Buf *dest_path) {
+    if (buf_eql_buf(src_path, dest_path)) {
+        return ErrorNone;
+    }
+#if defined(ZIG_OS_WINDOWS)
+    PathSpace src_path_space = slice_to_prefixed_file_w(buf_to_slice(src_path));
+    PathSpace dest_path_space = slice_to_prefixed_file_w(buf_to_slice(dest_path));
+    if (!MoveFileExW(&src_path_space.data.items[0], &dest_path_space.data.items[0], MOVEFILE_REPLACE_EXISTING | MOVEFILE_WRITE_THROUGH)) {
+        return ErrorFileSystem;
+    }
+#else
+    if (rename(buf_ptr(src_path), buf_ptr(dest_path)) == -1) {
+        return ErrorFileSystem;
+    }
+#endif
+    return ErrorNone;
+}
+
+OsTimeStamp os_timestamp_calendar(void) {
+    OsTimeStamp result;
+#if defined(ZIG_OS_WINDOWS)
+    FILETIME ft;
+    GetSystemTimeAsFileTime(&ft);
+    windows_filetime_to_os_timestamp(&ft, &result);
+#elif defined(__MACH__)
+    mach_timespec_t mts;
+
+    kern_return_t err = clock_get_time(macos_calendar_clock, &mts);
+    assert(!err);
+
+    result.sec = mts.tv_sec;
+    result.nsec = mts.tv_nsec;
+#else
+    struct timespec tms;
+    clock_gettime(CLOCK_REALTIME, &tms);
+
+    result.sec = tms.tv_sec;
+    result.nsec = tms.tv_nsec;
+#endif
+    return result;
+}
+
+OsTimeStamp os_timestamp_monotonic(void) {
+    OsTimeStamp result;
+#if defined(ZIG_OS_WINDOWS)
+    uint64_t counts;
+    QueryPerformanceCounter((LARGE_INTEGER*)&counts);
+    result.sec = counts / windows_perf_freq;
+    result.nsec = (counts % windows_perf_freq) * 1000000000u / windows_perf_freq;
+#elif defined(__MACH__)
+    mach_timespec_t mts;
+
+    kern_return_t err = clock_get_time(macos_monotonic_clock, &mts);
+    assert(!err);
+
+    result.sec = mts.tv_sec;
+    result.nsec = mts.tv_nsec;
+#else
+    struct timespec tms;
+    clock_gettime(CLOCK_MONOTONIC, &tms);
+
+    result.sec = tms.tv_sec;
+    result.nsec = tms.tv_nsec;
+#endif
+    return result;
+}
+
+Error os_make_path(Buf *path) {
+    Buf resolved_path = os_path_resolve(&path, 1);
+
+    size_t end_index = buf_len(&resolved_path);
+    Error err;
+    while (true) {
+        if ((err = os_make_dir(buf_slice(&resolved_path, 0, end_index)))) {
+            if (err == ErrorPathAlreadyExists) {
+                if (end_index == buf_len(&resolved_path))
+                    return ErrorNone;
+            } else if (err == ErrorFileNotFound) {
+                // march end_index backward until next path component
+                while (true) {
+                    end_index -= 1;
+                    if (os_is_sep(buf_ptr(&resolved_path)[end_index]))
+                        break;
+                }
+                continue;
+            } else {
+                return err;
+            }
+        }
+        if (end_index == buf_len(&resolved_path))
+            return ErrorNone;
+        // march end_index forward until next path component
+        while (true) {
+            end_index += 1;
+            if (end_index == buf_len(&resolved_path) || os_is_sep(buf_ptr(&resolved_path)[end_index]))
+                break;
+        }
+    }
+    return ErrorNone;
+}
+
+Error os_make_dir(Buf *path) {
+#if defined(ZIG_OS_WINDOWS)
+    PathSpace path_space = slice_to_prefixed_file_w(buf_to_slice(path));
+    if (memEql(buf_to_slice(path), str("C:\\dev\\tést"))) {
+        for (size_t i = 0; i < path_space.len; i++) {
+            fprintf(stderr, "%d ", path_space.data.items[i]);
+        }
+        fprintf(stderr, "\n");
+    }
+    
+    if (!CreateDirectoryW(&path_space.data.items[0], NULL)) {
+        if (GetLastError() == ERROR_ALREADY_EXISTS)
+            return ErrorPathAlreadyExists;
+        if (GetLastError() == ERROR_PATH_NOT_FOUND)
+            return ErrorFileNotFound;
+        if (GetLastError() == ERROR_ACCESS_DENIED)
+            return ErrorAccess;
+        return ErrorUnexpected;
+    }
+    return ErrorNone;
+#else
+    if (mkdir(buf_ptr(path), 0755) == -1) {
+        if (errno == EEXIST)
+            return ErrorPathAlreadyExists;
+        if (errno == ENOENT)
+            return ErrorFileNotFound;
+        if (errno == EACCES)
+            return ErrorAccess;
+        return ErrorUnexpected;
+    }
+    return ErrorNone;
+#endif
+}
+
+static void init_rand() {
+#if defined(ZIG_OS_WINDOWS)
+    char bytes[sizeof(unsigned)];
+    unsigned seed;
+    RtlGenRandom(bytes, sizeof(unsigned));
+    memcpy(&seed, bytes, sizeof(unsigned));
+    srand(seed);
+#elif defined(ZIG_OS_LINUX)
+    unsigned char *ptr_random = (unsigned char*)getauxval(AT_RANDOM);
+    unsigned seed;
+    memcpy(&seed, ptr_random, sizeof(seed));
+    srand(seed);
+#elif defined(ZIG_OS_FREEBSD) || defined(ZIG_OS_NETBSD)
+    unsigned seed;
+    size_t len = sizeof(seed);
+    int mib[2] = { CTL_KERN, KERN_ARND };
+    if (sysctl(mib, 2, &seed, &len, NULL, 0) != 0) {
+        zig_panic("unable to query random data from sysctl");
+    }
+    srand(seed);
+#else
+    int fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC);
+    if (fd == -1) {
+        zig_panic("unable to open /dev/urandom");
+    }
+    char bytes[sizeof(unsigned)];
+    ssize_t amt_read;
+    while ((amt_read = read(fd, bytes, sizeof(unsigned))) == -1) {
+        if (errno == EINTR) continue;
+        zig_panic("unable to read /dev/urandom");
+    }
+    if (amt_read != sizeof(unsigned)) {
+        zig_panic("unable to read enough bytes from /dev/urandom");
+    }
+    close(fd);
+    unsigned seed;
+    memcpy(&seed, bytes, sizeof(unsigned));
+    srand(seed);
+#endif
+}
+
+int os_init(void) {
+    init_rand();
+#if defined(ZIG_OS_WINDOWS)
+    _setmode(fileno(stdout), _O_BINARY);
+    _setmode(fileno(stderr), _O_BINARY);
+    if (!QueryPerformanceFrequency((LARGE_INTEGER*)&windows_perf_freq)) {
+        return ErrorSystemResources;
+    }
+#elif defined(__MACH__)
+    host_get_clock_service(mach_host_self(), SYSTEM_CLOCK, &macos_monotonic_clock);
+    host_get_clock_service(mach_host_self(), CALENDAR_CLOCK, &macos_calendar_clock);
+#endif
+#if defined(ZIG_OS_POSIX)
+    // Raise the open file descriptor limit.
+    // Code lifted from node.js
+    struct rlimit lim;
+    if (getrlimit(RLIMIT_NOFILE, &lim) == 0 && lim.rlim_cur != lim.rlim_max) {
+        // Do a binary search for the limit.
+        rlim_t min = lim.rlim_cur;
+        rlim_t max = 1 << 20;
+        // But if there's a defined upper bound, don't search, just set it.
+        if (lim.rlim_max != RLIM_INFINITY) {
+            min = lim.rlim_max;
+            max = lim.rlim_max;
+        }
+        do {
+            lim.rlim_cur = min + (max - min) / 2;
+            if (setrlimit(RLIMIT_NOFILE, &lim)) {
+                max = lim.rlim_cur;
+            } else {
+                min = lim.rlim_cur;
+            }
+        } while (min + 1 < max);
+    }
+#endif
+    return 0;
+}
+
+Error os_self_exe_path(Buf *out_path) {
+#if defined(ZIG_OS_WINDOWS)
+    PathSpace path_space;
+    DWORD copied_amt = GetModuleFileNameW(nullptr, &path_space.data.items[0], PATH_MAX_WIDE);
+    if (copied_amt <= 0) {
+        return ErrorFileNotFound;
+    }
+    utf16le_ptr_to_utf8(out_path, &path_space.data.items[0]);
+    return ErrorNone;
+
+#elif defined(ZIG_OS_DARWIN)
+    // How long is the executable's path?
+    uint32_t u32_len = 0;
+    int ret1 = _NSGetExecutablePath(nullptr, &u32_len);
+    assert(ret1 != 0);
+
+    Buf *tmp = buf_alloc_fixed(u32_len);
+
+    // Fill the executable path.
+    int ret2 = _NSGetExecutablePath(buf_ptr(tmp), &u32_len);
+    assert(ret2 == 0);
+
+    // According to libuv project, PATH_MAX*2 works around a libc bug where
+    // the resolved path is sometimes bigger than PATH_MAX.
+    buf_resize(out_path, PATH_MAX*2);
+    char *real_path = realpath(buf_ptr(tmp), buf_ptr(out_path));
+    if (!real_path) {
+        buf_init_from_buf(out_path, tmp);
+        return ErrorNone;
+    }
+
+    // Resize out_path for the correct length.
+    buf_resize(out_path, strlen(buf_ptr(out_path)));
+
+    return ErrorNone;
+#elif defined(ZIG_OS_LINUX)
+    buf_resize(out_path, PATH_MAX);
+    ssize_t amt = readlink("/proc/self/exe", buf_ptr(out_path), buf_len(out_path));
+    if (amt == -1) {
+        return ErrorUnexpected;
+    }
+    buf_resize(out_path, amt);
+    return ErrorNone;
+#elif defined(ZIG_OS_FREEBSD) || defined(ZIG_OS_DRAGONFLY)
+    buf_resize(out_path, PATH_MAX);
+    int mib[4] = { CTL_KERN, KERN_PROC, KERN_PROC_PATHNAME, -1 };
+    size_t cb = PATH_MAX;
+    if (sysctl(mib, 4, buf_ptr(out_path), &cb, nullptr, 0) != 0) {
+        return ErrorUnexpected;
+    }
+    buf_resize(out_path, cb - 1);
+    return ErrorNone;
+#elif defined(ZIG_OS_NETBSD)
+    buf_resize(out_path, PATH_MAX);
+    int mib[4] = { CTL_KERN, KERN_PROC_ARGS, -1, KERN_PROC_PATHNAME };
+    size_t cb = PATH_MAX;
+    if (sysctl(mib, 4, buf_ptr(out_path), &cb, nullptr, 0) != 0) {
+        return ErrorUnexpected;
+    }
+    buf_resize(out_path, cb - 1);
+    return ErrorNone;
+#endif
+    return ErrorFileNotFound;
+}
+
+#define VT_RED "\x1b[31;1m"
+#define VT_GREEN "\x1b[32;1m"
+#define VT_CYAN "\x1b[36;1m"
+#define VT_WHITE "\x1b[37;1m"
+#define VT_BOLD "\x1b[0;1m"
+#define VT_RESET "\x1b[0m"
+
+static void set_color_posix(TermColor color) {
+    switch (color) {
+        case TermColorRed:
+            fprintf(stderr, VT_RED);
+            break;
+        case TermColorGreen:
+            fprintf(stderr, VT_GREEN);
+            break;
+        case TermColorCyan:
+            fprintf(stderr, VT_CYAN);
+            break;
+        case TermColorWhite:
+            fprintf(stderr, VT_WHITE);
+            break;
+        case TermColorBold:
+            fprintf(stderr, VT_BOLD);
+            break;
+        case TermColorReset:
+            fprintf(stderr, VT_RESET);
+            break;
+    }
+}
+
+
+#if defined(ZIG_OS_WINDOWS)
+bool got_orig_console_attrs = false;
+WORD original_console_attributes = FOREGROUND_RED|FOREGROUND_GREEN|FOREGROUND_BLUE;
+#endif
+
+void os_stderr_set_color(TermColor color) {
+#if defined(ZIG_OS_WINDOWS)
+    if (is_stderr_cyg_pty()) {
+        set_color_posix(color);
+        return;
+    }
+    HANDLE stderr_handle = GetStdHandle(STD_ERROR_HANDLE);
+    if (stderr_handle == INVALID_HANDLE_VALUE)
+        zig_panic("unable to get stderr handle");
+    fflush(stderr);
+
+    if (!got_orig_console_attrs) {
+        got_orig_console_attrs = true;
+        CONSOLE_SCREEN_BUFFER_INFO info;
+        if (GetConsoleScreenBufferInfo(stderr_handle, &info)) {
+            original_console_attributes = info.wAttributes;
+        }
+    }
+
+    switch (color) {
+        case TermColorRed:
+            SetConsoleTextAttribute(stderr_handle, FOREGROUND_RED|FOREGROUND_INTENSITY);
+            break;
+        case TermColorGreen:
+            SetConsoleTextAttribute(stderr_handle, FOREGROUND_GREEN|FOREGROUND_INTENSITY);
+            break;
+        case TermColorCyan:
+            SetConsoleTextAttribute(stderr_handle, FOREGROUND_GREEN|FOREGROUND_BLUE|FOREGROUND_INTENSITY);
+            break;
+        case TermColorWhite:
+        case TermColorBold:
+            SetConsoleTextAttribute(stderr_handle,
+                FOREGROUND_RED|FOREGROUND_GREEN|FOREGROUND_BLUE|FOREGROUND_INTENSITY);
+            break;
+        case TermColorReset:
+            SetConsoleTextAttribute(stderr_handle, original_console_attributes);
+            break;
+    }
+#else
+    set_color_posix(color);
+#endif
+}
+
+#if defined(ZIG_OS_WINDOWS)
+// Ported from std/unicode.zig
+struct Utf16LeIterator {
+    uint8_t *bytes;
+    size_t i;
+};
+
+// Ported from std/unicode.zig
+static Utf16LeIterator Utf16LeIterator_init(WCHAR *ptr) {
+    return {(uint8_t*)ptr, 0};
+}
+
+// Ported from std/unicode.zig
+static Optional<uint32_t> Utf16LeIterator_nextCodepoint(Utf16LeIterator *it) {
+    if (it->bytes[it->i] == 0 && it->bytes[it->i + 1] == 0)
+        return {};
+    uint32_t c0 = ((uint32_t)it->bytes[it->i]) | (((uint32_t)it->bytes[it->i + 1]) << 8);
+    if ((c0 & ~((uint32_t)0x03ff)) == 0xd800) {
+        // surrogate pair
+        it->i += 2;
+        assert(it->bytes[it->i] != 0 || it->bytes[it->i + 1] != 0);
+        uint32_t c1 = ((uint32_t)it->bytes[it->i]) | (((uint32_t)it->bytes[it->i + 1]) << 8);
+        assert((c1 & ~((uint32_t)0x03ff)) == 0xdc00);
+        it->i += 2;
+        return Optional<uint32_t>::some(0x10000 + (((c0 & 0x03ff) << 10) | (c1 & 0x03ff)));
+    } else {
+        assert((c0 & ~((uint32_t)0x03ff)) != 0xdc00);
+        it->i += 2;
+        return Optional<uint32_t>::some(c0);
+    }
+}
+
+// Ported from std/unicode.zig
+static uint8_t utf8CodepointSequenceLength(uint32_t c) {
+    if (c < 0x80) return 1;
+    if (c < 0x800) return 2;
+    if (c < 0x10000) return 3;
+    if (c < 0x110000) return 4;
+    zig_unreachable();
+}
+
+// Ported from std.unicode.utf8ByteSequenceLength
+static uint8_t utf8ByteSequenceLength(uint8_t first_byte) {
+    if (first_byte < 0b10000000) return 1;
+    if ((first_byte & 0b11100000) == 0b11000000) return 2;
+    if ((first_byte & 0b11110000) == 0b11100000) return 3;
+    if ((first_byte & 0b11111000) == 0b11110000) return 4;
+    zig_unreachable();
+}
+
+// Ported from std/unicode.zig
+static size_t utf8Encode(uint32_t c, Slice<uint8_t> out) {
+    size_t length = utf8CodepointSequenceLength(c);
+    assert(out.len >= length);
+    switch (length) {
+        // The pattern for each is the same
+        // - Increasing the initial shift by 6 each time
+        // - Each time after the first shorten the shifted
+        //   value to a max of 0b111111 (63)
+        case 1:
+            out.ptr[0] = c; // Can just do 0 + codepoint for initial range
+            break;
+        case 2:
+            out.ptr[0] = 0b11000000 | (c >> 6);
+            out.ptr[1] = 0b10000000 | (c & 0b111111);
+            break;
+        case 3:
+            assert(!(0xd800 <= c && c <= 0xdfff));
+            out.ptr[0] = 0b11100000 | (c >> 12);
+            out.ptr[1] = 0b10000000 | ((c >> 6) & 0b111111);
+            out.ptr[2] = 0b10000000 | (c & 0b111111);
+            break;
+        case 4:
+            out.ptr[0] = 0b11110000 | (c >> 18);
+            out.ptr[1] = 0b10000000 | ((c >> 12) & 0b111111);
+            out.ptr[2] = 0b10000000 | ((c >> 6) & 0b111111);
+            out.ptr[3] = 0b10000000 | (c & 0b111111);
+            break;
+        default:
+            zig_unreachable();
+    }
+    return length;
+}
+
+// Ported from std.unicode.utf8Decode2
+static uint32_t utf8Decode2(Slice<uint8_t> bytes) {
+    assert(bytes.len == 2);
+    assert((bytes.at(0) & 0b11100000) == 0b11000000);
+
+    uint32_t value = bytes.at(0) & 0b00011111;
+    assert((bytes.at(1) & 0b11000000) == 0b10000000);
+    value <<= 6;
+    value |= bytes.at(1) & 0b00111111;
+
+    assert(value >= 0x80);
+    return value;
+}
+
+// Ported from std.unicode.utf8Decode3
+static uint32_t utf8Decode3(Slice<uint8_t> bytes) {
+    assert(bytes.len == 3);
+    assert((bytes.at(0) & 0b11110000) == 0b11100000);
+
+    uint32_t value = bytes.at(0) & 0b00001111;
+    assert((bytes.at(1) & 0b11000000) == 0b10000000);
+    value <<= 6;
+    value |= bytes.at(1) & 0b00111111;
+
+    assert((bytes.at(2) & 0b11000000) == 0b10000000);
+    value <<= 6;
+    value |= bytes.at(2) & 0b00111111;
+
+    assert(value >= 0x80);
+    assert(value < 0xd800 || value > 0xdfff);
+    return value;
+}
+
+// Ported from std.unicode.utf8Decode4
+static uint32_t utf8Decode4(Slice<uint8_t> bytes) {
+    assert(bytes.len == 4);
+    assert((bytes.at(0) & 0b11111000) == 0b11110000);
+
+    uint32_t value = bytes.at(0) & 0b00000111;
+    assert((bytes.at(1) & 0b11000000) == 0b10000000);
+    value <<= 6;
+    value |= bytes.at(1) & 0b00111111;
+
+    assert((bytes.at(2) & 0b11000000) == 0b10000000);
+    value <<= 6;
+    value |= bytes.at(2) & 0b00111111;
+
+    assert((bytes.at(3) & 0b11000000) == 0b10000000);
+    value <<= 6;
+    value |= bytes.at(3) & 0b00111111;
+
+    assert(value >= 0x10000 && value <= 0x10FFFF);
+    return value;
+}
+
+// Ported from std.unicode.utf8Decode
+static uint32_t utf8Decode(Slice<uint8_t> bytes) {
+    switch (bytes.len) {
+        case 1:
+            return bytes.at(0);
+            break;
+        case 2:
+            return utf8Decode2(bytes);
+            break;
+        case 3:
+            return utf8Decode3(bytes);
+            break;
+        case 4:
+            return utf8Decode4(bytes);
+            break;
+        default:
+            zig_unreachable();
+    }
+}
+// Ported from std.unicode.utf16leToUtf8Alloc
+static void utf16le_ptr_to_utf8(Buf *out, WCHAR *utf16le) {
+    // optimistically guess that it will all be ascii.
+    buf_resize(out, 0);
+    size_t out_index = 0;
+    Utf16LeIterator it = Utf16LeIterator_init(utf16le);
+    for (;;) {
+        Optional<uint32_t> opt_codepoint = Utf16LeIterator_nextCodepoint(&it);
+        if (!opt_codepoint.is_some) break;
+        uint32_t codepoint = opt_codepoint.value;
+
+        size_t utf8_len = utf8CodepointSequenceLength(codepoint);
+        buf_resize(out, buf_len(out) + utf8_len);
+        utf8Encode(codepoint, {(uint8_t*)buf_ptr(out)+out_index, buf_len(out)-out_index});
+        out_index += utf8_len;
+    }
+}
+
+// Ported from std.unicode.utf8ToUtf16Le
+static size_t utf8_to_utf16le(WCHAR *utf16_le, Slice<uint8_t> utf8) {
+    size_t dest_i = 0;
+    size_t src_i = 0;
+    while (src_i < utf8.len) {
+        uint8_t n = utf8ByteSequenceLength(utf8.at(src_i));
+        size_t next_src_i = src_i + n;
+        uint32_t codepoint = utf8Decode(utf8.slice(src_i, next_src_i));
+        if (codepoint < 0x10000) {
+            utf16_le[dest_i] = codepoint;
+            dest_i += 1;
+        } else {
+            WCHAR high = ((codepoint - 0x10000) >> 10) + 0xD800;
+            WCHAR low = (codepoint & 0x3FF) + 0xDC00;
+            utf16_le[dest_i] = high;
+            utf16_le[dest_i + 1] = low;
+            dest_i += 2;
+        }
+        src_i = next_src_i;
+    }
+    return dest_i;
+}
+
+// Ported from std.os.windows.sliceToPrefixedFileW
+PathSpace slice_to_prefixed_file_w(Slice<uint8_t> path) {
+    PathSpace path_space;
+    for (size_t idx = 0; idx < path.len; idx++) {
+        assert(path.ptr[idx] != '*' && path.ptr[idx] != '?' && path.ptr[idx] != '"' &&
+               path.ptr[idx] != '<' && path.ptr[idx] != '>' && path.ptr[idx] != '|');
+    }
+
+    size_t start_index;
+    if (memStartsWith(path, str("\\?")) || !isAbsoluteWindows(path)) {
+        start_index = 0;
+    } else {
+        static WCHAR prefix[4] = { u'\\', u'?', u'?', u'\\' };
+        memCopy(path_space.data.slice(), Slice<WCHAR> { prefix, 4 });
+        start_index = 4;
+    }
+
+    path_space.len = start_index + utf8_to_utf16le(path_space.data.slice().sliceFrom(start_index).ptr, path);
+    assert(path_space.len <= path_space.data.len);
+
+    Slice<WCHAR> path_slice = path_space.data.slice().slice(0, path_space.len);
+    for (size_t elem_idx = 0; elem_idx < path_slice.len; elem_idx += 1) {
+        if (path_slice.at(elem_idx) == '/') {
+            path_slice.at(elem_idx) = '\\';
+        }
+    }
+
+    path_space.data.items[path_space.len] = 0;
+    return path_space;
+}
+#endif
+
+// Ported from std.os.getAppDataDir
+Error os_get_app_data_dir(Buf *out_path, const char *appname) {
+#if defined(ZIG_OS_WINDOWS)
+    WCHAR *dir_path_ptr;
+    switch (SHGetKnownFolderPath(FOLDERID_LocalAppData, KF_FLAG_CREATE, nullptr, &dir_path_ptr)) {
+        case S_OK:
+            // defer os.windows.CoTaskMemFree(@ptrCast(*c_void, dir_path_ptr));
+            utf16le_ptr_to_utf8(out_path, dir_path_ptr);
+            CoTaskMemFree(dir_path_ptr);
+            buf_appendf(out_path, "\\%s", appname);
+            return ErrorNone;
+        case E_OUTOFMEMORY:
+            return ErrorNoMem;
+        default:
+            return ErrorUnexpected;
+    }
+    zig_unreachable();
+#elif defined(ZIG_OS_DARWIN)
+    const char *home_dir = getenv("HOME");
+    if (home_dir == nullptr) {
+        // TODO use /etc/passwd
+        return ErrorFileNotFound;
+    }
+    buf_resize(out_path, 0);
+    buf_appendf(out_path, "%s/Library/Application Support/%s", home_dir, appname);
+    return ErrorNone;
+#elif defined(ZIG_OS_POSIX)
+    const char *cache_dir = getenv("XDG_CACHE_HOME");
+    if (cache_dir == nullptr) {
+        cache_dir = getenv("HOME");
+        if (cache_dir == nullptr) {
+            // TODO use /etc/passwd
+            return ErrorFileNotFound;
+        }
+        if (cache_dir[0] == 0) {
+            return ErrorFileNotFound;
+        }
+        buf_init_from_str(out_path, cache_dir);
+        if (buf_ptr(out_path)[buf_len(out_path) - 1] != '/') {
+            buf_append_char(out_path, '/');
+        }
+        buf_appendf(out_path, ".cache/%s", appname);
+    } else {
+        if (cache_dir[0] == 0) {
+            return ErrorFileNotFound;
+        }
+        buf_init_from_str(out_path, cache_dir);
+        if (buf_ptr(out_path)[buf_len(out_path) - 1] != '/') {
+            buf_append_char(out_path, '/');
+        }
+        buf_appendf(out_path, "%s", appname);
+    }
+    return ErrorNone;
+#endif
+}
+
+#if defined(ZIG_OS_LINUX) || defined(ZIG_OS_FREEBSD) || defined(ZIG_OS_NETBSD) || defined(ZIG_OS_DRAGONFLY)
+static int self_exe_shared_libs_callback(struct dl_phdr_info *info, size_t size, void *data) {
+    ZigList<Buf *> *libs = reinterpret_cast< ZigList<Buf *> *>(data);
+    if (info->dlpi_name[0] == '/') {
+        libs->append(buf_create_from_str(info->dlpi_name));
+    }
+    return 0;
+}
+#endif
+
+Error os_self_exe_shared_libs(ZigList<Buf *> &paths) {
+#if defined(ZIG_OS_LINUX) || defined(ZIG_OS_FREEBSD) || defined(ZIG_OS_NETBSD) || defined(ZIG_OS_DRAGONFLY)
+    paths.resize(0);
+    dl_iterate_phdr(self_exe_shared_libs_callback, &paths);
+    return ErrorNone;
+#elif defined(ZIG_OS_DARWIN)
+    paths.resize(0);
+    uint32_t img_count = _dyld_image_count();
+    for (uint32_t i = 0; i != img_count; i += 1) {
+        const char *name = _dyld_get_image_name(i);
+        paths.append(buf_create_from_str(name));
+    }
+    return ErrorNone;
+#elif defined(ZIG_OS_WINDOWS)
+    // zig is built statically on windows, so we can return an empty list
+    paths.resize(0);
+    return ErrorNone;
+#else
+#error unimplemented
+#endif
+}
+
+Error os_file_open_rw(Buf *full_path, OsFile *out_file, OsFileAttr *attr, bool need_write, uint32_t mode) {
+#if defined(ZIG_OS_WINDOWS)
+    PathSpace path_space = slice_to_prefixed_file_w(buf_to_slice(full_path));
+    HANDLE result = CreateFileW(&path_space.data.items[0],
+            need_write ? (GENERIC_READ|GENERIC_WRITE) : GENERIC_READ,
+            need_write ? 0 : FILE_SHARE_READ,
+            nullptr,
+            need_write ? OPEN_ALWAYS : OPEN_EXISTING,
+            FILE_ATTRIBUTE_NORMAL, nullptr);
+
+    if (result == INVALID_HANDLE_VALUE) {
+        DWORD err = GetLastError();
+        switch (err) {
+            case ERROR_SHARING_VIOLATION:
+                return ErrorSharingViolation;
+            case ERROR_ALREADY_EXISTS:
+                return ErrorPathAlreadyExists;
+            case ERROR_FILE_EXISTS:
+                return ErrorPathAlreadyExists;
+            case ERROR_FILE_NOT_FOUND:
+                return ErrorFileNotFound;
+            case ERROR_PATH_NOT_FOUND:
+                return ErrorFileNotFound;
+            case ERROR_ACCESS_DENIED:
+                return ErrorAccess;
+            case ERROR_PIPE_BUSY:
+                return ErrorPipeBusy;
+            default:
+                return ErrorUnexpected;
+        }
+    }
+    *out_file = result;
+
+    if (attr != nullptr) {
+        BY_HANDLE_FILE_INFORMATION file_info;
+        if (!GetFileInformationByHandle(result, &file_info)) {
+            CloseHandle(result);
+            return ErrorUnexpected;
+        }
+        windows_filetime_to_os_timestamp(&file_info.ftLastWriteTime, &attr->mtime);
+        attr->inode = (((uint64_t)file_info.nFileIndexHigh) << 32) | file_info.nFileIndexLow;
+        attr->mode = 0;
+        attr->size = (((uint64_t)file_info.nFileSizeHigh) << 32) | file_info.nFileSizeLow;
+    }
+
+    return ErrorNone;
+#else
+    for (;;) {
+        int fd = open(buf_ptr(full_path),
+                need_write ? (O_RDWR|O_CLOEXEC|O_CREAT) : (O_RDONLY|O_CLOEXEC), mode);
+        if (fd == -1) {
+            switch (errno) {
+                case EINTR:
+                    continue;
+                case EINVAL:
+                    zig_unreachable();
+                case EFAULT:
+                    zig_unreachable();
+                case EACCES:
+                case EPERM:
+                    return ErrorAccess;
+                case EISDIR:
+                    return ErrorIsDir;
+                case ENOENT:
+                    return ErrorFileNotFound;
+                default:
+                    return ErrorFileSystem;
+            }
+        }
+        struct stat statbuf;
+        if (fstat(fd, &statbuf) == -1) {
+            close(fd);
+            return ErrorFileSystem;
+        }
+        if (S_ISDIR(statbuf.st_mode)) {
+            close(fd);
+            return ErrorIsDir;
+        }
+        *out_file = fd;
+
+        if (attr != nullptr) {
+            attr->inode = statbuf.st_ino;
+#if defined(ZIG_OS_DARWIN)
+            attr->mtime.sec = statbuf.st_mtimespec.tv_sec;
+            attr->mtime.nsec = statbuf.st_mtimespec.tv_nsec;
+#else
+            attr->mtime.sec = statbuf.st_mtim.tv_sec;
+            attr->mtime.nsec = statbuf.st_mtim.tv_nsec;
+#endif
+            attr->mode = statbuf.st_mode;
+            attr->size = statbuf.st_size;
+        }
+        return ErrorNone;
+    }
+#endif
+}
+
+Error os_file_open_r(Buf *full_path, OsFile *out_file, OsFileAttr *attr) {
+    return os_file_open_rw(full_path, out_file, attr, false, 0);
+}
+
+Error os_file_open_w(Buf *full_path, OsFile *out_file, OsFileAttr *attr, uint32_t mode) {
+    return os_file_open_rw(full_path, out_file, attr, true, mode);
+}
+
+Error os_file_open_lock_rw(Buf *full_path, OsFile *out_file) {
+#if defined(ZIG_OS_WINDOWS)
+    PathSpace path_space = slice_to_prefixed_file_w(buf_to_slice(full_path));
+    for (;;) {
+        HANDLE result = CreateFileW(&path_space.data.items[0], GENERIC_READ | GENERIC_WRITE,
+            0, nullptr, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, nullptr);
+
+        if (result == INVALID_HANDLE_VALUE) {
+            DWORD err = GetLastError();
+            switch (err) {
+                case ERROR_SHARING_VIOLATION:
+                    // TODO wait for the lock instead of sleeping
+                    Sleep(10);
+                    continue;
+                case ERROR_ALREADY_EXISTS:
+                    return ErrorPathAlreadyExists;
+                case ERROR_FILE_EXISTS:
+                    return ErrorPathAlreadyExists;
+                case ERROR_FILE_NOT_FOUND:
+                    return ErrorFileNotFound;
+                case ERROR_PATH_NOT_FOUND:
+                    return ErrorFileNotFound;
+                case ERROR_ACCESS_DENIED:
+                    return ErrorAccess;
+                case ERROR_PIPE_BUSY:
+                    return ErrorPipeBusy;
+                default:
+                    return ErrorUnexpected;
+            }
+        }
+        *out_file = result;
+        return ErrorNone;
+    }
+#else
+    int fd;
+    for (;;) {
+        fd = open(buf_ptr(full_path), O_RDWR|O_CLOEXEC|O_CREAT, 0666);
+        if (fd == -1) {
+            switch (errno) {
+                case EINTR:
+                    continue;
+                case EINVAL:
+                    zig_unreachable();
+                case EFAULT:
+                    zig_unreachable();
+                case EACCES:
+                case EPERM:
+                    return ErrorAccess;
+                case EISDIR:
+                    return ErrorIsDir;
+                case ENOENT:
+                    return ErrorFileNotFound;
+                case ENOTDIR:
+                    return ErrorNotDir;
+                default:
+                    return ErrorFileSystem;
+            }
+        }
+        break;
+    }
+    for (;;) {
+        struct flock lock;
+        lock.l_type = F_WRLCK;
+        lock.l_whence = SEEK_SET;
+        lock.l_start = 0;
+        lock.l_len = 0;
+        if (fcntl(fd, F_SETLKW, &lock) == -1) {
+            switch (errno) {
+                case EINTR:
+                    continue;
+                case EBADF:
+                    zig_unreachable();
+                case EFAULT:
+                    zig_unreachable();
+                case EINVAL:
+                    zig_unreachable();
+                default:
+                    close(fd);
+                    return ErrorFileSystem;
+            }
+        }
+        break;
+    }
+    *out_file = fd;
+    return ErrorNone;
+#endif
+}
+
+Error os_file_read(OsFile file, void *ptr, size_t *len) {
+#if defined(ZIG_OS_WINDOWS)
+    DWORD amt_read;
+    if (ReadFile(file, ptr, *len, &amt_read, nullptr) == 0)
+        return ErrorUnexpected;
+    *len = amt_read;
+    return ErrorNone;
+#else
+    for (;;) {
+        ssize_t rc = read(file, ptr, *len);
+        if (rc == -1) {
+            switch (errno) {
+                case EINTR:
+                    continue;
+                case EBADF:
+                    zig_unreachable();
+                case EFAULT:
+                    zig_unreachable();
+                case EISDIR:
+                    return ErrorIsDir;
+                default:
+                    return ErrorFileSystem;
+            }
+        }
+        *len = rc;
+        return ErrorNone;
+    }
+#endif
+}
+
+Error os_file_read_all(OsFile file, Buf *contents) {
+    Error err;
+    size_t index = 0;
+    for (;;) {
+        size_t amt = buf_len(contents) - index;
+
+        if (amt < 4096) {
+            buf_resize(contents, buf_len(contents) + (4096 - amt));
+            amt = buf_len(contents) - index;
+        }
+
+        if ((err = os_file_read(file, buf_ptr(contents) + index, &amt)))
+            return err;
+
+        if (amt == 0) {
+            buf_resize(contents, index);
+            return ErrorNone;
+        }
+
+        index += amt;
+    }
+}
+
+Error os_file_overwrite(OsFile file, Buf *contents) {
+#if defined(ZIG_OS_WINDOWS)
+    if (SetFilePointer(file, 0, nullptr, FILE_BEGIN) == INVALID_SET_FILE_POINTER)
+        return ErrorFileSystem;
+    if (!SetEndOfFile(file))
+        return ErrorFileSystem;
+    DWORD bytes_written;
+    if (!WriteFile(file, buf_ptr(contents), buf_len(contents), &bytes_written, nullptr))
+        return ErrorFileSystem;
+    return ErrorNone;
+#else
+    if (lseek(file, 0, SEEK_SET) == -1)
+        return ErrorUnexpectedSeekFailure;
+    if (ftruncate(file, 0) == -1)
+        return ErrorUnexpectedFileTruncationFailure;
+    for (;;) {
+        if (write(file, buf_ptr(contents), buf_len(contents)) == -1) {
+            switch (errno) {
+                case EINTR:
+                    continue;
+                case EINVAL:
+                    zig_unreachable();
+                case EBADF:
+                    zig_unreachable();
+                case EFAULT:
+                    zig_unreachable();
+                case EDQUOT:
+                    return ErrorDiskQuota;
+                case ENOSPC:
+                    return ErrorDiskSpace;
+                case EFBIG:
+                    return ErrorFileTooBig;
+                case EIO:
+                    return ErrorFileSystem;
+                case EPERM:
+                    return ErrorAccess;
+                default:
+                    return ErrorUnexpectedWriteFailure;
+            }
+        }
+        return ErrorNone;
+    }
+#endif
+}
+
+void os_file_close(OsFile *file) {
+#if defined(ZIG_OS_WINDOWS)
+    CloseHandle(*file);
+    *file = NULL;
+#else
+    close(*file);
+    *file = -1;
+#endif
+}