// Various functions, mostly string utilities, that are used by most parts of fish.
#include "config.h"

#ifdef HAVE_BACKTRACE_SYMBOLS
#include <cxxabi.h>
#endif

#include <ctype.h>
#include <dlfcn.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <pthread.h>
#include <stdarg.h>
#include <sys/time.h>
#include <termios.h>
#include <unistd.h>

#ifdef HAVE_EXECINFO_H
#include <execinfo.h>
#endif

#ifdef __linux__
// Includes for WSL detection
#include <sys/utsname.h>
#endif

#include <algorithm>
#include <csignal>
#include <cstdlib>
#include <cstring>
#include <cwchar>
#include <memory>

#include "common.h"
#if INCLUDE_RUST_HEADERS
#include "common.rs.h"
#endif
#include "expand.h"
#include "fallback.h"  // IWYU pragma: keep
#include "flog.h"
#include "future_feature_flags.h"
#include "global_safety.h"
#include "iothread.h"
#include "signals.h"
#include "termsize.h"
#include "wcstringutil.h"
#include "wildcard.h"
#include "wutil.h"  // IWYU pragma: keep

// Keep after "common.h"
#ifdef HAVE_SYS_SYSCTL_H
#include <sys/sysctl.h>  // IWYU pragma: keep
#endif
#if defined(__APPLE__)
#include <mach-o/dyld.h>  // IWYU pragma: keep
#endif

struct termios shell_modes;

struct termios *shell_modes_ffi() { return &shell_modes; }

const wcstring g_empty_string{};
const std::vector<wcstring> g_empty_string_list{};

/// This allows us to notice when we've forked.
static relaxed_atomic_bool_t is_forked_proc{false};
/// This allows us to bypass the main thread checks
static relaxed_atomic_bool_t thread_asserts_cfg_for_testing{false};

static relaxed_atomic_t<wchar_t> ellipsis_char;
wchar_t get_ellipsis_char() { return ellipsis_char; }

static relaxed_atomic_t<const wchar_t *> ellipsis_str;
const wchar_t *get_ellipsis_str() { return ellipsis_str; }

static relaxed_atomic_t<const wchar_t *> omitted_newline_str;
const wchar_t *get_omitted_newline_str() { return omitted_newline_str; }

static relaxed_atomic_t<int> omitted_newline_width;
int get_omitted_newline_width() { return omitted_newline_width; }

static relaxed_atomic_t<wchar_t> obfuscation_read_char;
wchar_t get_obfuscation_read_char() { return obfuscation_read_char; }

bool g_profiling_active = false;
void set_profiling_active(bool val) { g_profiling_active = val; }

const wchar_t *program_name;

/// Be able to restore the term's foreground process group.
/// This is set during startup and not modified after.
static relaxed_atomic_t<pid_t> initial_fg_process_group{-1};

#if defined(OS_IS_CYGWIN) || defined(WSL)
// MS Windows tty devices do not currently have either a read or write timestamp. Those
// respective fields of `struct stat` are always the current time. Which means we can't
// use them. So we assume no external program has written to the terminal behind our
// back. This makes multiline promptusable. See issue #2859 and
// https://github.com/Microsoft/BashOnWindows/issues/545
const bool has_working_tty_timestamps = false;
#else
const bool has_working_tty_timestamps = true;
#endif

/// Convert a character to its integer equivalent if it is a valid character for the requested base.
/// Return the integer value if it is valid else -1.
long convert_digit(wchar_t d, int base) {
    long res = -1;
    if ((d <= L'9') && (d >= L'0')) {
        res = d - L'0';
    } else if ((d <= L'z') && (d >= L'a')) {
        res = d + 10 - L'a';
    } else if ((d <= L'Z') && (d >= L'A')) {
        res = d + 10 - L'A';
    }
    if (res >= base) {
        res = -1;
    }

    return res;
}

bool is_windows_subsystem_for_linux() {
#if defined(WSL)
    return true;
#elif not defined(__linux__)
    return false;
#else
    // We are purposely not using std::call_once as it may invoke locking, which is an unnecessary
    // overhead since there's no actual race condition here - even if multiple threads call this
    // routine simultaneously the first time around, we just end up needlessly querying uname(2) one
    // more time.

    static bool wsl_state = [] {
        utsname info;
        uname(&info);

        // Sample utsname.release under WSL, testing for something like `4.4.0-17763-Microsoft`
        if (std::strstr(info.release, "Microsoft") != nullptr) {
            const char *dash = std::strchr(info.release, '-');
            if (dash == nullptr || strtod(dash + 1, nullptr) < 17763) {
                // #5298, #5661: There are acknowledged, published, and (later) fixed issues with
                // job control under early WSL releases that prevent fish from running correctly,
                // with unexpected failures when piping. Fish 3.0 nightly builds worked around this
                // issue with some needlessly complicated code that was later stripped from the
                // fish 3.0 release, so we just bail. Note that fish 2.0 was also broken, but we
                // just didn't warn about it.

                // #6038 & 5101bde: It's been requested that there be some sort of way to disable
                // this check: if the environment variable FISH_NO_WSL_CHECK is present, this test
                // is bypassed. We intentionally do not include this in the error message because
                // it'll only allow fish to run but not to actually work. Here be dragons!
                if (getenv("FISH_NO_WSL_CHECK") == nullptr) {
                    FLOGF(error,
                          "This version of WSL has known bugs that prevent fish from working."
                          "Please upgrade to Windows 10 1809 (17763) or higher to use fish!");
                }
            }

            return true;
        } else {
            return false;
        }
    }();

    // Subsequent calls to this function may take place after fork() and before exec() in
    // postfork.cpp. Make sure we never dynamically allocate any memory in the fast path!
    return wsl_state;
#endif
}

#ifdef HAVE_BACKTRACE_SYMBOLS
// This function produces a stack backtrace with demangled function & method names. It is based on
// https://gist.github.com/fmela/591333 but adapted to the style of the fish project.
[[gnu::noinline]] static std::vector<wcstring> demangled_backtrace(int max_frames,
                                                                   int skip_levels) {
    void *callstack[128];
    const int n_max_frames = sizeof(callstack) / sizeof(callstack[0]);
    int n_frames = backtrace(callstack, n_max_frames);
    char **symbols = backtrace_symbols(callstack, n_frames);
    wchar_t text[1024];
    std::vector<wcstring> backtrace_text;

    if (skip_levels + max_frames < n_frames) n_frames = skip_levels + max_frames;

    for (int i = skip_levels; i < n_frames; i++) {
        Dl_info info;
        if (dladdr(callstack[i], &info) && info.dli_sname) {
            char *demangled = nullptr;
            int status = -1;
            if (info.dli_sname[0] == '_')
                demangled = abi::__cxa_demangle(info.dli_sname, nullptr, nullptr, &status);
            swprintf(text, sizeof(text) / sizeof(wchar_t), L"%-3d %s + %td", i - skip_levels,
                     status == 0                 ? demangled
                     : info.dli_sname == nullptr ? symbols[i]
                                                 : info.dli_sname,
                     static_cast<char *>(callstack[i]) - static_cast<const char *>(info.dli_saddr));
            free(demangled);
        } else {
            swprintf(text, sizeof(text) / sizeof(wchar_t), L"%-3d %s", i - skip_levels, symbols[i]);
        }
        backtrace_text.push_back(text);
    }
    free(symbols);
    return backtrace_text;
}

[[gnu::noinline]] void show_stackframe(int frame_count, int skip_levels) {
    if (frame_count < 1) return;

    std::vector<wcstring> bt = demangled_backtrace(frame_count, skip_levels + 2);
    FLOG(error, L"Backtrace:\n" + join_strings(bt, L'\n') + L'\n');
}

#else   // HAVE_BACKTRACE_SYMBOLS

[[gnu::noinline]] void show_stackframe(int, int) {
    FLOGF(error, L"Sorry, but your system does not support backtraces");
}
#endif  // HAVE_BACKTRACE_SYMBOLS

/// \return the smallest pointer in the range [start, start + len] which is aligned to Align.
/// If there is no such pointer, return \p start + len.
/// alignment must be a power of 2 and in range [1, 64].
/// This is intended to return the end point of the "unaligned prefix" of a vectorized loop.
template <size_t Align>
static inline const char *align_start(const char *start, size_t len) {
    static_assert(Align >= 1 && Align <= 64, "Alignment must be in range [1, 64]");
    static_assert((Align & (Align - 1)) == 0, "Alignment must be power of 2");
    uintptr_t startu = reinterpret_cast<uintptr_t>(start);
    // How much do we have to add to start to make it 0 mod Align?
    // To compute 17 up-aligned by 8, compute its skew 17 % 8, yielding 1,
    // and then we will add 8 - 1. Of course if we align 16 with the same idea, we will
    // add 8 instead of 0, so then mod the sum by Align again.
    // Note all of these mods are optimized to masks.
    uintptr_t add_which_aligns = Align - (startu % Align);
    add_which_aligns %= Align;
    // Add that much but not more than len. If we add 'add_which_aligns' we may overflow the
    // pointer.
    return start + std::min(static_cast<size_t>(add_which_aligns), len);
}

/// \return the largest pointer in the range [start, start + len] which is aligned to Align.
/// If there is no such pointer, return \p start.
/// This is intended to be the start point of the "unaligned suffix" of a vectorized loop.
template <size_t Align>
static inline const char *align_end(const char *start, size_t len) {
    static_assert(Align >= 1 && Align <= 64, "Alignment must be in range [1, 64]");
    static_assert((Align & (Align - 1)) == 0, "Alignment must be power of 2");
    // How much do we have to subtract to align it? Its value, mod Align.
    uintptr_t endu = reinterpret_cast<uintptr_t>(start + len);
    uintptr_t sub_which_aligns = endu % Align;
    return start + len - std::min(static_cast<size_t>(sub_which_aligns), len);
}

/// \return the count of initial characters in \p in which are ASCII.
static size_t count_ascii_prefix(const char *in, size_t in_len) {
    // We'll use aligned reads of this type.
    using WordType = uint32_t;
    const char *aligned_start = align_start<alignof(WordType)>(in, in_len);
    const char *aligned_end = align_end<alignof(WordType)>(in, in_len);

    // Consume the unaligned prefix.
    for (const char *cursor = in; cursor < aligned_start; cursor++) {
        if (cursor[0] & 0x80) return &cursor[0] - in;
    }

    // Consume the aligned middle.
    for (const char *cursor = aligned_start; cursor < aligned_end; cursor += sizeof(WordType)) {
        if (*reinterpret_cast<const WordType *>(cursor) & 0x80808080) {
            if (cursor[0] & 0x80) return &cursor[0] - in;
            if (cursor[1] & 0x80) return &cursor[1] - in;
            if (cursor[2] & 0x80) return &cursor[2] - in;
            return &cursor[3] - in;
        }
    }

    // Consume the unaligned suffix.
    for (const char *cursor = aligned_end; cursor < in + in_len; cursor++) {
        if (cursor[0] & 0x80) return &cursor[0] - in;
    }
    return in_len;
}

/// Converts the narrow character string \c in into its wide equivalent, and return it.
///
/// The string may contain embedded nulls.
///
/// This function encodes illegal character sequences in a reversible way using the private use
/// area.
static wcstring str2wcs_internal(const char *in, const size_t in_len) {
    if (in_len == 0) return wcstring();
    assert(in != nullptr);

    wcstring result;
    result.reserve(in_len);

    size_t in_pos = 0;
    mbstate_t state = {};
    while (in_pos < in_len) {
        // Append any initial sequence of ascii characters.
        // Note we do not support character sets which are not supersets of ASCII.
        size_t ascii_prefix_length = count_ascii_prefix(&in[in_pos], in_len - in_pos);
        result.insert(result.end(), &in[in_pos], &in[in_pos + ascii_prefix_length]);
        in_pos += ascii_prefix_length;
        assert(in_pos <= in_len && "Position overflowed length");
        if (in_pos == in_len) break;

        // We have found a non-ASCII character.
        bool use_encode_direct = false;
        size_t ret = 0;
        wchar_t wc = 0;

        if (false) {
#if defined(HAVE_BROKEN_MBRTOWC_UTF8)
        } else if ((in[in_pos] & 0xF8) == 0xF8) {
            // Protect against broken std::mbrtowc() implementations which attempt to encode UTF-8
            // sequences longer than four bytes (e.g., OS X Snow Leopard).
            use_encode_direct = true;
#endif
        } else if (sizeof(wchar_t) == 2 &&  //!OCLINT(constant if expression)
                   (in[in_pos] & 0xF8) == 0xF0) {
            // Assume we are in a UTF-16 environment (e.g., Cygwin) using a UTF-8 encoding.
            // The bits set check will be true for a four byte UTF-8 sequence that requires
            // two UTF-16 chars. Something that doesn't work with our simple use of std::mbrtowc().
            use_encode_direct = true;
        } else {
            ret = std::mbrtowc(&wc, &in[in_pos], in_len - in_pos, &state);
            // Determine whether to encode this character with our crazy scheme.
            if (wc >= ENCODE_DIRECT_BASE && wc < ENCODE_DIRECT_BASE + 256) {
                use_encode_direct = true;
            } else if ((wc >= 0xD800 && wc <= 0xDFFF) || static_cast<uint32_t>(wc) >= 0x110000) {
                use_encode_direct = true;
            } else if (wc == INTERNAL_SEPARATOR) {
                use_encode_direct = true;
            } else if (ret == static_cast<size_t>(-2)) {
                // Incomplete sequence.
                use_encode_direct = true;
            } else if (ret == static_cast<size_t>(-1)) {
                // Invalid data.
                use_encode_direct = true;
            } else if (ret > in_len - in_pos) {
                // Other error codes? Terrifying, should never happen.
                use_encode_direct = true;
            } else if (sizeof(wchar_t) == 2 && wc >= 0xD800 &&  //!OCLINT(constant if expression)
                       wc <= 0xDFFF) {
                // If we get a surrogate pair char on a UTF-16 system (e.g., Cygwin) then
                // it's guaranteed the UTF-8 decoding is wrong so use direct encoding.
                use_encode_direct = true;
            }
        }

        if (use_encode_direct) {
            wc = ENCODE_DIRECT_BASE + static_cast<unsigned char>(in[in_pos]);
            result.push_back(wc);
            in_pos++;
            std::memset(&state, 0, sizeof state);
        } else if (ret == 0) {  // embedded null byte!
            result.push_back(L'\0');
            in_pos++;
            std::memset(&state, 0, sizeof state);
        } else {  // normal case
            result.push_back(wc);
            in_pos += ret;
        }
    }

    return result;
}

wcstring str2wcstring(const char *in, size_t len) { return str2wcs_internal(in, len); }

wcstring str2wcstring(const char *in) { return str2wcs_internal(in, std::strlen(in)); }

wcstring str2wcstring(const std::string &in) {
    // Handles embedded nulls!
    return str2wcs_internal(in.data(), in.size());
}

wcstring str2wcstring(const std::string &in, size_t len) {
    // Handles embedded nulls!
    return str2wcs_internal(in.data(), len);
}

std::string wcs2string(const wcstring &input) { return wcs2string(input.data(), input.size()); }

std::string wcs2string(const wchar_t *in, size_t len) {
    if (len == 0) return std::string{};
    std::string result;
    wcs2string_appending(in, len, &result);
    return result;
}

std::string wcs2zstring(const wcstring &input) { return wcs2zstring(input.data(), input.size()); }

std::string wcs2zstring(const wchar_t *in, size_t len) {
    if (len == 0) return std::string{};
    std::string result;
    wcs2string_appending(in, len, &result);
    return result;
}

void wcs2string_appending(const wchar_t *in, size_t len, std::string *receiver) {
    assert(receiver && "Null receiver");
    receiver->reserve(receiver->size() + len);
    wcs2string_callback(in, len, [&](const char *buff, size_t bufflen) {
        receiver->append(buff, bufflen);
        return true;
    });
}

/// Test if the character can be encoded using the current locale.
static bool can_be_encoded(wchar_t wc) {
    char converted[MB_LEN_MAX];
    mbstate_t state = {};

    return std::wcrtomb(converted, wc, &state) != static_cast<size_t>(-1);
}

wcstring format_string(const wchar_t *format, ...) {
    va_list va;
    va_start(va, format);
    wcstring result = vformat_string(format, va);
    va_end(va);
    return result;
}

void append_formatv(wcstring &target, const wchar_t *format, va_list va_orig) {
    const int saved_err = errno;
    // As far as I know, there is no way to check if a vswprintf-call failed because of a badly
    // formated string option or because the supplied destination string was to small. In GLIBC,
    // errno seems to be set to EINVAL either way.
    //
    // Because of this, on failure we try to increase the buffer size until the free space is
    // larger than max_size, at which point it will conclude that the error was probably due to a
    // badly formated string option, and return an error. Make sure to null terminate string before
    // that, though.
    const size_t max_size = (128 * 1024 * 1024);
    wchar_t static_buff[256];
    size_t size = 0;
    wchar_t *buff = nullptr;
    int status = -1;
    while (status < 0) {
        // Reallocate if necessary.
        if (size == 0) {
            buff = static_buff;
            size = sizeof static_buff;
        } else {
            size *= 2;
            if (size >= max_size) {
                buff[0] = '\0';
                break;
            }
            buff = static_cast<wchar_t *>(realloc((buff == static_buff ? nullptr : buff), size));
            assert(buff != nullptr);
        }

        // Try printing.
        va_list va;
        va_copy(va, va_orig);
        status = std::vswprintf(buff, size / sizeof(wchar_t), format, va);
        va_end(va);
    }

    target.append(buff);

    if (buff != static_buff) {
        free(buff);
    }

    errno = saved_err;
}

wcstring vformat_string(const wchar_t *format, va_list va_orig) {
    wcstring result;
    append_formatv(result, format, va_orig);
    return result;
}

void append_format(wcstring &str, const wchar_t *format, ...) {
    va_list va;
    va_start(va, format);
    append_formatv(str, format, va);
    va_end(va);
}

const wchar_t *quote_end(const wchar_t *pos, wchar_t quote) {
    while (true) {
        pos++;

        if (!*pos) return nullptr;

        if (*pos == L'\\') {
            pos++;
            if (!*pos) return nullptr;
        } else {
            if (*pos == quote ||
                // Command substitutions also end a double quoted string.  This is how we
                // support command substitutions inside double quotes.
                (quote == L'"' && *pos == L'$' && *(pos + 1) == L'(')) {
                return pos;
            }
        }
    }
    return nullptr;
}

const wchar_t *comment_end(const wchar_t *pos) {
    do {
        pos++;
    } while (*pos && *pos != L'\n');
    return pos;
}

void fish_setlocale() {
    // Use various Unicode symbols if they can be encoded using the current locale, else a simple
    // ASCII char alternative. All of the can_be_encoded() invocations should return the same
    // true/false value since the code points are in the BMP but we're going to be paranoid. This
    // is also technically wrong if we're not in a Unicode locale but we expect (or hope)
    // can_be_encoded() will return false in that case.
    if (can_be_encoded(L'\u2026')) {
        ellipsis_char = L'\u2026';
        ellipsis_str = L"\u2026";
    } else {
        ellipsis_char = L'$';  // "horizontal ellipsis"
        ellipsis_str = L"...";
    }

    if (is_windows_subsystem_for_linux()) {
        // neither of \u23CE and \u25CF can be displayed in the default fonts on Windows, though
        // they can be *encoded* just fine. Use alternative glyphs.
        omitted_newline_str = L"\u00b6";  // "pilcrow"
        omitted_newline_width = 1;
        obfuscation_read_char = L'\u2022';  // "bullet"
    } else if (is_console_session()) {
        omitted_newline_str = L"^J";
        omitted_newline_width = 2;
        obfuscation_read_char = L'*';
    } else {
        if (can_be_encoded(L'\u23CE')) {
            omitted_newline_str = L"\u23CE";  // "return symbol" (⏎)
            omitted_newline_width = 1;
        } else {
            omitted_newline_str = L"^J";
            omitted_newline_width = 2;
        }
        obfuscation_read_char = can_be_encoded(L'\u25CF') ? L'\u25CF' : L'#';  // "black circle"
    }
}

long read_blocked(int fd, void *buf, size_t count) {
    ssize_t res;
    do {
        res = read(fd, buf, count);
    } while (res < 0 && errno == EINTR);
    return res;
}

/// Loop a write request while failure is non-critical. Return -1 and set errno in case of critical
/// error.
ssize_t write_loop(int fd, const char *buff, size_t count) {
    size_t out_cum = 0;
    while (out_cum < count) {
        ssize_t out = write(fd, &buff[out_cum], count - out_cum);
        if (out < 0) {
            if (errno != EAGAIN && errno != EINTR) {
                return -1;
            }
        } else {
            out_cum += static_cast<size_t>(out);
        }
    }
    return static_cast<ssize_t>(out_cum);
}

/// Hack to not print error messages in the tests. Do not call this from functions in this module
/// like `debug()`. It is only intended to suppress diagnostic noise from testing things like the
/// fish parser where we expect a lot of diagnostic messages due to testing error conditions.
bool should_suppress_stderr_for_tests() {
    return program_name && !std::wcscmp(program_name, TESTS_PROGRAM_NAME);
}

// Careful to not negate LLONG_MIN.
static unsigned long long absolute_value(long long x) {
    if (x >= 0) return static_cast<unsigned long long>(x);
    x = -(x + 1);
    return static_cast<unsigned long long>(x) + 1;
}

template <typename CharT>
static void format_safe_impl(CharT *buff, size_t size, unsigned long long val) {
    size_t idx = 0;
    if (val == 0) {
        buff[idx++] = '0';
    } else {
        // Generate the string backwards, then reverse it.
        while (val != 0) {
            buff[idx++] = (val % 10) + '0';
            val /= 10;
        }
        std::reverse(buff, buff + idx);
    }
    buff[idx++] = '\0';
    assert(idx <= size && "Buffer overflowed");
}

void format_long_safe(char buff[64], long val) {
    unsigned long long uval = absolute_value(val);
    if (val >= 0) {
        format_safe_impl(buff, 64, uval);
    } else {
        buff[0] = '-';
        format_safe_impl(buff + 1, 63, uval);
    }
}

void format_long_safe(wchar_t buff[64], long val) {
    unsigned long long uval = absolute_value(val);
    if (val >= 0) {
        format_safe_impl(buff, 64, uval);
    } else {
        buff[0] = '-';
        format_safe_impl(buff + 1, 63, uval);
    }
}

void format_llong_safe(wchar_t buff[64], long long val) {
    unsigned long long uval = absolute_value(val);
    if (val >= 0) {
        format_safe_impl(buff, 64, uval);
    } else {
        buff[0] = '-';
        format_safe_impl(buff + 1, 63, uval);
    }
}

void format_ullong_safe(wchar_t buff[64], unsigned long long val) {
    return format_safe_impl(buff, 64, val);
}

/// Escape a string in a fashion suitable for using as a URL. Store the result in out_str.
static void escape_string_url(const wcstring &in, wcstring &out) {
    auto result = escape_string_url(in.c_str(), in.size());
    if (result) {
        out = *result;
    }
}

/// Escape a string in a fashion suitable for using as a fish var name. Store the result in out_str.
static void escape_string_var(const wcstring &in, wcstring &out) {
    auto result = escape_string_var(in.c_str(), in.size());
    if (result) {
        out = *result;
    }
}

/// Escape a string in a fashion suitable for using in fish script. Store the result in out_str.
static void escape_string_script(const wchar_t *orig_in, size_t in_len, wcstring &out,
                                 escape_flags_t flags) {
    auto result = escape_string_script(orig_in, in_len, flags);
    if (result) {
        out = *result;
    }
}

/// Escapes a string for use in a regex string. Not safe for use with `eval` as only
/// characters reserved by PCRE2 are escaped.
/// \param in is the raw string to be searched for literally when substituted in a PCRE2 expression.
static wcstring escape_string_pcre2(const wcstring &in) {
    wcstring out;
    out.reserve(in.size() * 1.3);  // a wild guess

    for (auto c : in) {
        switch (c) {
            case L'.':
            case L'^':
            case L'$':
            case L'*':
            case L'+':
            case L'(':
            case L')':
            case L'?':
            case L'[':
            case L'{':
            case L'}':
            case L'\\':
            case L'|':
            // these two only *need* to be escaped within a character class, and technically it
            // makes no sense to ever use process substitution output to compose a character class,
            // but...
            case L'-':
            case L']':
                out.push_back('\\');
                __fallthrough__ default : out.push_back(c);
        }
    }

    return out;
}

wcstring escape_string(const wchar_t *in, escape_flags_t flags, escape_string_style_t style) {
    wcstring result;

    switch (style) {
        case STRING_STYLE_SCRIPT: {
            escape_string_script(in, std::wcslen(in), result, flags);
            break;
        }
        case STRING_STYLE_URL: {
            escape_string_url(in, result);
            break;
        }
        case STRING_STYLE_VAR: {
            escape_string_var(in, result);
            break;
        }
        case STRING_STYLE_REGEX: {
            result = escape_string_pcre2(in);
            break;
        }
    }

    return result;
}

wcstring escape_string(const wcstring &in, escape_flags_t flags, escape_string_style_t style) {
    wcstring result;

    switch (style) {
        case STRING_STYLE_SCRIPT: {
            escape_string_script(in.c_str(), in.size(), result, flags);
            break;
        }
        case STRING_STYLE_URL: {
            escape_string_url(in, result);
            break;
        }
        case STRING_STYLE_VAR: {
            escape_string_var(in, result);
            break;
        }
        case STRING_STYLE_REGEX: {
            result = escape_string_pcre2(in);
            break;
        }
    }

    return result;
}

double timef() {
    struct timeval tv;
    assert_with_errno(gettimeofday(&tv, nullptr) != -1);
    return static_cast<timepoint_t>(tv.tv_sec) + 1e-6 * tv.tv_usec;
}

void exit_without_destructors(int code) { _exit(code); }

extern "C" void debug_thread_error();

void save_term_foreground_process_group() { initial_fg_process_group = tcgetpgrp(STDIN_FILENO); }

void restore_term_foreground_process_group_for_exit() {
    // We wish to restore the tty to the initial owner. There's two ways this can go wrong:
    //  1. We may steal the tty from someone else (#7060).
    //  2. The call to tcsetpgrp may deliver SIGSTOP to us, and we will not exit.
    // Hanging on exit seems worse, so ensure that SIGTTOU is ignored so we do not get SIGSTOP.
    // Note initial_fg_process_group == 0 is possible with Linux pid namespaces.
    // This is called during shutdown and from a signal handler. We don't bother to complain on
    // failure because doing so is unlikely to be noticed.
    if (initial_fg_process_group > 0 && initial_fg_process_group != getpgrp()) {
        (void)signal(SIGTTOU, SIG_IGN);
        (void)tcsetpgrp(STDIN_FILENO, initial_fg_process_group);
    }
}

/// Test if the specified character is in a range that fish uses internally to store special tokens.
///
/// NOTE: This is used when tokenizing the input. It is also used when reading input, before
/// tokenization, to replace such chars with REPLACEMENT_WCHAR if they're not part of a quoted
/// string. We don't want external input to be able to feed reserved characters into our
/// lexer/parser or code evaluator.
//
// TODO: Actually implement the replacement as documented above.
bool fish_reserved_codepoint(wchar_t c) {
    return (c >= RESERVED_CHAR_BASE && c < RESERVED_CHAR_END) ||
           (c >= ENCODE_DIRECT_BASE && c < ENCODE_DIRECT_END);
}

/// Reopen stdin, stdout and/or stderr on /dev/null. This is invoked when we find that our tty has
/// become invalid.
void redirect_tty_output() {
    struct termios t;
    int fd = open("/dev/null", O_WRONLY);
    if (fd == -1) {
        __fish_assert("Could not open /dev/null!", __FILE__, __LINE__, errno);
    }
    if (tcgetattr(STDIN_FILENO, &t) == -1 && errno == EIO) dup2(fd, STDIN_FILENO);
    if (tcgetattr(STDOUT_FILENO, &t) == -1 && errno == EIO) dup2(fd, STDOUT_FILENO);
    if (tcgetattr(STDERR_FILENO, &t) == -1 && errno == EIO) dup2(fd, STDERR_FILENO);
    close(fd);
}

/// Display a failed assertion message, dump a stack trace if possible, then die.
[[noreturn]] void __fish_assert(const char *msg, const char *file, size_t line, int error) {
    if (unlikely(error)) {
        FLOGF(error, L"%s:%zu: failed assertion: %s: errno %d (%s)", file, line, msg, error,
              std::strerror(error));
    } else {
        FLOGF(error, L"%s:%zu: failed assertion: %s", file, line, msg);
    }
    show_stackframe(99, 1);
    abort();
}

/// Test if the given char is valid in a variable name.
bool valid_var_name_char(wchar_t chr) { return fish_iswalnum(chr) || chr == L'_'; }

/// Test if the given string is a valid variable name.
bool valid_var_name(const wcstring &str) {
    // Note do not use c_str(), we want to fail on embedded nul bytes.
    return !str.empty() && std::all_of(str.begin(), str.end(), valid_var_name_char);
}

bool valid_var_name(const wchar_t *str) {
    if (str[0] == L'\0') return false;
    for (size_t i = 0; str[i] != L'\0'; i++) {
        if (!valid_var_name_char(str[i])) return false;
    }
    return true;
}

/// Return a path to a directory where we can store temporary files.
std::string get_path_to_tmp_dir() {
    char *env_tmpdir = getenv("TMPDIR");
    if (env_tmpdir) {
        return env_tmpdir;
    }
#if defined(_CS_DARWIN_USER_TEMP_DIR)
    char osx_tmpdir[PATH_MAX];
    size_t n = confstr(_CS_DARWIN_USER_TEMP_DIR, osx_tmpdir, PATH_MAX);
    if (0 < n && n <= PATH_MAX) {
        return osx_tmpdir;
    } else {
        return "/tmp";
    }
#elif defined(P_tmpdir)
    return P_tmpdir;
#elif defined(_PATH_TMP)
    return _PATH_TMP;
#else
    return "/tmp";
#endif
}

// This function attempts to distinguish between a console session (at the actual login vty) and a
// session within a terminal emulator inside a desktop environment or over SSH. Unfortunately
// there are few values of $TERM that we can interpret as being exclusively console sessions, and
// most common operating systems do not use them. The value is cached for the duration of the fish
// session. We err on the side of assuming it's not a console session. This approach isn't
// bullet-proof and that's OK.
bool is_console_session() {
    static const bool console_session = [] {
        char tty_name[PATH_MAX];
        if (ttyname_r(STDIN_FILENO, tty_name, sizeof tty_name) != 0) {
            return false;
        }
        constexpr auto len = const_strlen("/dev/tty");
        const char *TERM = getenv("TERM");
        return
            // Test that the tty matches /dev/(console|dcons|tty[uv\d])
            ((strncmp(tty_name, "/dev/tty", len) == 0 &&
              (tty_name[len] == 'u' || tty_name[len] == 'v' || isdigit(tty_name[len]))) ||
             strcmp(tty_name, "/dev/dcons") == 0 || strcmp(tty_name, "/dev/console") == 0)
            // and that $TERM is simple, e.g. `xterm` or `vt100`, not `xterm-something`
            && (!TERM || !strchr(TERM, '-') || !strcmp(TERM, "sun-color"));
    }();
    return console_session;
}

/// Expose the C++ version of fish_setlocale as fish_setlocale_ffi so the variables we initialize
/// can be init even if the rust version of the function is called instead. This is easier than
/// declaring all those variables as extern, which I'll do in a separate PR.
extern "C" {
void fish_setlocale_ffi() { fish_setlocale(); }
}