fish-shell/src/screen.cpp

// High level library for handling the terminal screen.
//
// The screen library allows the interactive reader to write its output to screen efficiently by
// keeping an internal representation of the current screen contents and trying to find the most
// efficient way for transforming that to the desired screen content.
//
#include "config.h"

#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <termios.h>
#include <unistd.h>

#include <cstdint>
#include <cstring>
#include <cwchar>

#if HAVE_CURSES_H
#include <curses.h>  // IWYU pragma: keep
#elif HAVE_NCURSES_H
#include <ncurses.h>
#elif HAVE_NCURSES_CURSES_H
#include <ncurses/curses.h>
#endif
#if HAVE_TERM_H
#include <term.h>
#elif HAVE_NCURSES_TERM_H
#include <ncurses/term.h>
#endif

#include <algorithm>
#include <string>
#include <vector>

#include "common.h"
#include "env.h"
#include "fallback.h"  // IWYU pragma: keep
#include "flog.h"
#include "global_safety.h"
#include "highlight.h"
#include "output.h"
#include "pager.h"
#include "screen.h"
#include "termsize.h"

/// The number of characters to indent new blocks.
#define INDENT_STEP 4u

/// RAII class to begin and end buffering around an outputter.
namespace {
class scoped_buffer_t : noncopyable_t, nonmovable_t {
    outputter_t &outp_;

   public:
    explicit scoped_buffer_t(outputter_t &outp) : outp_(outp) { outp_.begin_buffering(); }

    ~scoped_buffer_t() { outp_.end_buffering(); }
};
}  // namespace

// Singleton of the cached escape sequences seen in prompts and similar strings.
// Note this is deliberately exported so that init_curses can clear it.
layout_cache_t layout_cache_t::shared;

void screen_clear_layout_cache_ffi() { layout_cache_t::shared.clear(); }

/// Tests if the specified narrow character sequence is present at the specified position of the
/// specified wide character string. All of \c seq must match, but str may be longer than seq.
static size_t try_sequence(const char *seq, const wchar_t *str) {
    for (size_t i = 0;; i++) {
        if (!seq[i]) return i;
        if (seq[i] != str[i]) return 0;
    }

    DIE("unexpectedly fell off end of try_sequence()");
    return 0;  // this should never be executed
}

static bool midnight_commander_hack = false;

void screen_set_midnight_commander_hack() { midnight_commander_hack = true; }

/// Returns the number of columns left until the next tab stop, given the current cursor position.
static size_t next_tab_stop(size_t current_line_width) {
    // Assume tab stops every 8 characters if undefined.
    size_t tab_width = init_tabs > 0 ? static_cast<size_t>(init_tabs) : 8;
    return ((current_line_width / tab_width) + 1) * tab_width;
}

int line_t::wcswidth_min_0(size_t max) const {
    int result = 0;
    for (size_t idx = 0, end = std::min(max, text.size()); idx < end; idx++) {
        auto w = fish_wcwidth_visible(text[idx].character);
        // A backspace at the start of the line does nothing.
        if (w > 0 || result > 0) {
            result += w;
        }
    }
    return result;
}

/// Whether we permit soft wrapping. If so, in some cases we don't explicitly move to the second
/// physical line on a wrapped logical line; instead we just output it.
static bool allow_soft_wrap() {
    // Should we be looking at eat_newline_glitch as well?
    return auto_right_margin;
}

/// Does this look like the escape sequence for setting a screen name?
static bool is_screen_name_escape_seq(const wchar_t *code, size_t *resulting_length) {
    // Tmux escapes start with `\ePtmux;` and end also in `\e\\`,
    // so we can just handle them here.
    static const wchar_t *tmux_seq = L"Ptmux;";
    static const size_t tmux_seq_len = std::wcslen(tmux_seq);
    bool is_tmux = false;
    if (code[1] != L'k') {
        if (wcsncmp(&code[1], tmux_seq, tmux_seq_len) == 0) {
            is_tmux = true;
        } else {
            return false;
        }
    }
    const wchar_t *const screen_name_end_sentinel = L"\x1B\\";
    size_t offset = 2;
    while (true) {
        const wchar_t *screen_name_end = std::wcsstr(&code[offset], screen_name_end_sentinel);
        if (screen_name_end == nullptr) {
            // Consider just <esc>k to be the code.
            // (note: for the tmux sequence this is broken, but since we have no idea...)
            *resulting_length = 2;
            break;
        } else {
            // The tmux sequence requires that all escapes in the payload sequence
            // be doubled. So if we have \e\e\\ that's still not the end.
            if (is_tmux) {
                size_t esc_count = 0;
                const wchar_t *i = screen_name_end;
                while (i > code && *(i - 1) == L'\x1B' && --i) esc_count++;
                if (esc_count % 2 == 1) {
                    offset = screen_name_end - code + 1;
                    continue;
                }
            }
            const wchar_t *escape_sequence_end =
                screen_name_end + std::wcslen(screen_name_end_sentinel);
            *resulting_length = escape_sequence_end - code;
            break;
        }
    }
    return true;
}

/// Operating System Command (OSC) escape codes, used by iTerm2 and others:
/// ESC followed by ], terminated by either BEL or escape + backslash.
/// See https://invisible-island.net/xterm/ctlseqs/ctlseqs.html
/// and https://iterm2.com/documentation-escape-codes.html .
static bool is_osc_escape_seq(const wchar_t *code, size_t *resulting_length) {
    bool found = false;
    if (code[1] == ']') {
        // Start at 2 to skip over <esc>].
        size_t cursor = 2;
        for (; code[cursor] != L'\0'; cursor++) {
            // Consume a sequence of characters up to <esc>\ or <bel>.
            if (code[cursor] == '\x07' || (code[cursor] == '\\' && code[cursor - 1] == '\x1B')) {
                found = true;
                break;
            }
        }
        if (found) {
            *resulting_length = cursor + 1;
        }
    }
    return found;
}

/// Generic VT100 three byte sequence: CSI followed by something in the range @ through _.
static bool is_three_byte_escape_seq(const wchar_t *code, size_t *resulting_length) {
    bool found = false;
    if (code[1] == L'[' && (code[2] >= L'@' && code[2] <= L'_')) {
        *resulting_length = 3;
        found = true;
    }
    return found;
}

/// Generic VT100 two byte sequence: <esc> followed by something in the range @ through _.
static bool is_two_byte_escape_seq(const wchar_t *code, size_t *resulting_length) {
    bool found = false;
    if (code[1] >= L'@' && code[1] <= L'_') {
        *resulting_length = 2;
        found = true;
    }
    return found;
}

/// Generic VT100 CSI-style sequence. <esc>, followed by zero or more ASCII characters NOT in
/// the range [@,_], followed by one character in that range.
/// This will also catch color sequences.
static bool is_csi_style_escape_seq(const wchar_t *code, size_t *resulting_length) {
    if (code[1] != L'[') {
        return false;
    }

    // Start at 2 to skip over <esc>[
    size_t cursor = 2;
    for (; code[cursor] != L'\0'; cursor++) {
        // Consume a sequence of ASCII characters not in the range [@, ~].
        wchar_t widechar = code[cursor];

        // If we're not in ASCII, just stop.
        if (widechar > 127) break;

        // If we're the end character, then consume it and then stop.
        if (widechar >= L'@' && widechar <= L'~') {
            cursor++;
            break;
        }
    }
    // cursor now indexes just beyond the end of the sequence (or at the terminating zero).
    *resulting_length = cursor;
    return true;
}

/// Detect whether the escape sequence sets one of the terminal attributes that affects how text is
/// displayed other than the color.
static bool is_visual_escape_seq(const wchar_t *code, size_t *resulting_length) {
    if (!cur_term) return false;
    const char *const esc2[] = {
        enter_bold_mode,     exit_attribute_mode, enter_underline_mode,   exit_underline_mode,
        enter_standout_mode, exit_standout_mode,  enter_blink_mode,       enter_protected_mode,
        enter_italics_mode,  exit_italics_mode,   enter_reverse_mode,     enter_shadow_mode,
        exit_shadow_mode,    enter_standout_mode, exit_standout_mode,     enter_secure_mode,
        enter_dim_mode,      enter_blink_mode,    enter_alt_charset_mode, exit_alt_charset_mode};

    for (auto p : esc2) {
        if (!p) continue;
        // Test both padded and unpadded version, just to be safe. Most versions of fish_tparm don't
        // actually seem to do anything these days.
        size_t esc_seq_len =
            std::max(try_sequence(fish_tparm(const_cast<char *>(p)), code), try_sequence(p, code));
        if (esc_seq_len) {
            *resulting_length = esc_seq_len;
            return true;
        }
    }

    return false;
}

/// Returns the number of characters in the escape code starting at 'code'. We only handle sequences
/// that begin with \x1B. If it doesn't we return zero. We also return zero if we don't recognize
/// the escape sequence based on querying terminfo and other heuristics.
maybe_t<size_t> escape_code_length(const wchar_t *code) {
    assert(code != nullptr);
    if (*code != L'\x1B') return none();

    size_t esc_seq_len = 0;
    bool found = is_visual_escape_seq(code, &esc_seq_len);
    if (!found) found = is_screen_name_escape_seq(code, &esc_seq_len);
    if (!found) found = is_osc_escape_seq(code, &esc_seq_len);
    if (!found) found = is_three_byte_escape_seq(code, &esc_seq_len);
    if (!found) found = is_csi_style_escape_seq(code, &esc_seq_len);
    if (!found) found = is_two_byte_escape_seq(code, &esc_seq_len);

    return found ? maybe_t<size_t>{esc_seq_len} : none();
}

size_t layout_cache_t::escape_code_length(const wchar_t *code) {
    assert(code != nullptr);
    if (*code != L'\x1B') return 0;

    size_t esc_seq_len = this->find_escape_code(code);
    if (esc_seq_len) return esc_seq_len;

    auto found = ::escape_code_length(code);
    if (found.has_value()) {
        this->add_escape_code(wcstring(code, *found));
        esc_seq_len = *found;
    }
    return esc_seq_len;
}

const layout_cache_t::prompt_cache_entry_t *layout_cache_t::find_prompt_layout(
    const wcstring &input, size_t max_line_width) {
    auto start = prompt_cache_.begin();
    auto end = prompt_cache_.end();
    for (auto iter = start; iter != end; ++iter) {
        if (iter->text == input && iter->max_line_width == max_line_width) {
            // Found it. Move it to the front if not already there.
            if (iter != start) prompt_cache_.splice(start, prompt_cache_, iter);
            return &*prompt_cache_.begin();
        }
    }
    return nullptr;
}

void layout_cache_t::add_prompt_layout(prompt_cache_entry_t entry) {
    prompt_cache_.emplace_front(std::move(entry));
    if (prompt_cache_.size() > prompt_cache_max_size) {
        prompt_cache_.pop_back();
    }
}

/// \return whether \p c ends a measuring run.
static bool is_run_terminator(wchar_t c) {
    return c == L'\0' || c == L'\n' || c == L'\r' || c == L'\f';
}

/// Measure a run of characters in \p input starting at \p start.
/// Stop when we reach a run terminator, and return its index in \p out_end (if not null).
/// Note \0 is a run terminator so there will always be one.
/// We permit escape sequences to have run terminators other than \0. That is, escape sequences may
/// have embedded newlines, etc.; it's unclear if this is possible but we allow it.
static size_t measure_run_from(const wchar_t *input, size_t start, size_t *out_end,
                               layout_cache_t &cache) {
    size_t width = 0;
    size_t idx = start;
    for (; !is_run_terminator(input[idx]); idx++) {
        if (input[idx] == L'\x1B') {
            // This is the start of an escape code; we assume it has width 0.
            // -1 because we are going to increment in the loop.
            size_t len = cache.escape_code_length(&input[idx]);
            if (len > 0) idx += len - 1;
        } else if (input[idx] == L'\t') {
            width = next_tab_stop(width);
        } else {
            // Ordinary char. Add its width with care to ignore control chars which have width -1.
            auto w = fish_wcwidth_visible(input[idx]);
            // A backspace at the start of the line does nothing.
            if (w != -1 || width > 0) {
                width += w;
            }
        }
    }
    if (out_end) *out_end = idx;
    return width;
}

/// Attempt to truncate the prompt run \p run, which has width \p width, to \p no more than
/// desired_width. \return the resulting width and run by reference.
static void truncate_run(wcstring *run, size_t desired_width, size_t *width,
                         layout_cache_t &cache) {
    size_t curr_width = *width;
    if (curr_width <= desired_width) {
        return;
    }

    // Bravely prepend ellipsis char and skip it.
    // Ellipsis is always width 1.
    wchar_t ellipsis = get_ellipsis_char();
    run->insert(0, 1, ellipsis);  // index, count, char
    curr_width += 1;

    // Start removing characters after ellipsis.
    // Note we modify 'run' inside this loop.
    size_t idx = 1;
    while (curr_width > desired_width && idx < run->size()) {
        wchar_t c = run->at(idx);
        assert(!is_run_terminator(c) && "Should not have run terminator inside run");
        if (c == L'\x1B') {
            size_t len = cache.escape_code_length(run->c_str() + idx);
            idx += std::max(len, (size_t)1);
        } else if (c == '\t') {
            // Tabs would seem to be quite annoying to measure while truncating.
            // We simply remove these and start over.
            run->erase(idx, 1);
            curr_width = measure_run_from(run->c_str(), 0, nullptr, cache);
            idx = 0;
        } else {
            size_t char_width = fish_wcwidth_visible(c);
            curr_width -= std::min(curr_width, char_width);
            run->erase(idx, 1);
        }
    }
    *width = curr_width;
}

prompt_layout_t layout_cache_t::calc_prompt_layout(const wcstring &prompt_str,
                                                   wcstring *out_trunc_prompt,
                                                   size_t max_line_width) {
    // FIXME: we could avoid allocating trunc_prompt if max_line_width is SIZE_T_MAX.
    if (const auto *entry = this->find_prompt_layout(prompt_str, max_line_width)) {
        if (out_trunc_prompt) out_trunc_prompt->assign(entry->trunc_text);
        return entry->layout;
    }

    size_t prompt_len = prompt_str.size();
    const wchar_t *prompt = prompt_str.c_str();

    prompt_layout_t layout = {{}, 0, 0};
    wcstring trunc_prompt;

    size_t run_start = 0;
    while (run_start < prompt_len) {
        size_t run_end;
        size_t line_width = measure_run_from(prompt, run_start, &run_end, *this);
        if (line_width <= max_line_width) {
            // No truncation needed on this line.
            trunc_prompt.append(&prompt[run_start], run_end - run_start);
        } else {
            // Truncation needed on this line.
            wcstring run_storage(&prompt[run_start], run_end - run_start);
            truncate_run(&run_storage, max_line_width, &line_width, *this);
            trunc_prompt.append(run_storage);
        }
        layout.max_line_width = std::max(layout.max_line_width, line_width);
        layout.last_line_width = line_width;

        wchar_t endc = prompt[run_end];
        if (endc) {
            if (endc == L'\n' || endc == L'\f') {
                layout.line_breaks.push_back(trunc_prompt.size());
                // If the prompt ends in a new line, that's one empy last line.
                if (run_end == prompt_str.size() - 1) layout.last_line_width = 0;
            }
            trunc_prompt.push_back(endc);
            run_start = run_end + 1;
        } else {
            break;
        }
    }
    this->add_prompt_layout(prompt_cache_entry_t{prompt, max_line_width, trunc_prompt, layout});
    if (out_trunc_prompt) {
        *out_trunc_prompt = std::move(trunc_prompt);
    }
    return layout;
}

static size_t calc_prompt_lines(const wcstring &prompt) {
    // Hack for the common case where there's no newline at all. I don't know if a newline can
    // appear in an escape sequence, so if we detect a newline we have to defer to
    // calc_prompt_width_and_lines.
    size_t result = 1;
    if (prompt.find_first_of(L"\n\f") != wcstring::npos) {
        result = layout_cache_t::shared.calc_prompt_layout(prompt).line_breaks.size() + 1;
    }
    return result;
}

/// Stat stdout and stderr and save result. This should be done before calling a function that may
/// cause output.
void screen_t::save_status() {
    fstat(STDOUT_FILENO, &this->prev_buff_1);
    fstat(STDERR_FILENO, &this->prev_buff_2);
}

/// Stat stdout and stderr and compare result to previous result in reader_save_status. Repaint if
/// modification time has changed.
void screen_t::check_status() {
    fflush(stdout);
    fflush(stderr);
    if (!has_working_tty_timestamps) {
        // We can't reliably determine if the terminal has been written to behind our back so we
        // just assume that hasn't happened and hope for the best. This is important for multi-line
        // prompts to work correctly.
        return;
    }

    struct stat post_buff_1 {};
    struct stat post_buff_2 {};
    fstat(STDOUT_FILENO, &post_buff_1);
    fstat(STDERR_FILENO, &post_buff_2);

    bool changed = (this->prev_buff_1.st_mtime != post_buff_1.st_mtime) ||
                   (this->prev_buff_2.st_mtime != post_buff_2.st_mtime);

#if defined HAVE_STRUCT_STAT_ST_MTIMESPEC_TV_NSEC
    changed = changed ||
              this->prev_buff_1.st_mtimespec.tv_nsec != post_buff_1.st_mtimespec.tv_nsec ||
              this->prev_buff_2.st_mtimespec.tv_nsec != post_buff_2.st_mtimespec.tv_nsec;
#elif defined HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC
    changed = changed || this->prev_buff_1.st_mtim.tv_nsec != post_buff_1.st_mtim.tv_nsec ||
              this->prev_buff_2.st_mtim.tv_nsec != post_buff_2.st_mtim.tv_nsec;
#endif

    if (changed) {
        // Ok, someone has been messing with our screen. We will want to repaint. However, we do not
        // know where the cursor is. It is our best bet that we are still on the same line, so we
        // move to the beginning of the line, reset the modelled screen contents, and then set the
        // modeled cursor y-pos to its earlier value.
        int prev_line = this->actual.cursor.y;
        this->reset_line(true /* repaint prompt */);
        this->actual.cursor.y = prev_line;
    }
}

void screen_t::desired_append_char(wchar_t b, highlight_spec_t c, int indent, size_t prompt_width,
                                   size_t bwidth) {
    int line_no = this->desired.cursor.y;

    if (b == L'\n') {
        // Current line is definitely hard wrapped.
        // Create the next line.
        this->desired.create_line(this->desired.cursor.y + 1);
        this->desired.line(this->desired.cursor.y).is_soft_wrapped = false;
        int line_no = ++this->desired.cursor.y;
        this->desired.cursor.x = 0;
        size_t indentation = prompt_width + static_cast<size_t>(indent) * INDENT_STEP;
        line_t &line = this->desired.line(line_no);
        line.indentation = indentation;
        for (size_t i = 0; i < indentation; i++) {
            desired_append_char(L' ', highlight_spec_t{}, indent, prompt_width, 1);
        }
    } else if (b == L'\r') {
        line_t &current = this->desired.line(line_no);
        current.clear();
        this->desired.cursor.x = 0;
    } else {
        int screen_width = this->desired.screen_width;
        int cw = bwidth;

        this->desired.create_line(line_no);

        // Check if we are at the end of the line. If so, continue on the next line.
        if ((this->desired.cursor.x + cw) > screen_width) {
            // Current line is soft wrapped (assuming we support it).
            this->desired.line(this->desired.cursor.y).is_soft_wrapped = true;

            line_no = static_cast<int>(this->desired.line_count());
            this->desired.add_line();
            this->desired.cursor.y++;
            this->desired.cursor.x = 0;
        }

        line_t &line = this->desired.line(line_no);
        line.append(b, c);
        this->desired.cursor.x += cw;

        // Maybe wrap the cursor to the next line, even if the line itself did not wrap. This
        // avoids wonkiness in the last column.
        if (this->desired.cursor.x >= screen_width) {
            line.is_soft_wrapped = true;
            this->desired.cursor.x = 0;
            this->desired.cursor.y++;
        }
    }
}

void screen_t::move(int new_x, int new_y) {
    if (this->actual.cursor.x == new_x && this->actual.cursor.y == new_y) return;

    const scoped_buffer_t buffering(outp());

    // If we are at the end of our window, then either the cursor stuck to the edge or it didn't. We
    // don't know! We can fix it up though.
    if (this->actual.cursor.x == this->actual.screen_width) {
        // Either issue a cr to go back to the beginning of this line, or a nl to go to the
        // beginning of the next one, depending on what we think is more efficient.
        if (new_y <= this->actual.cursor.y) {
            this->outp().push_back('\r');
        } else {
            this->outp().push_back('\n');
            this->actual.cursor.y++;
        }
        // Either way we're not in the first column.
        this->actual.cursor.x = 0;
    }

    int i;
    int x_steps, y_steps;

    const char *str;
    auto &outp = this->outp();

    y_steps = new_y - this->actual.cursor.y;

    if (y_steps < 0) {
        str = cursor_up;
    } else if (y_steps > 0) {
        str = cursor_down;
        if ((shell_modes.c_oflag & ONLCR) != 0 &&
            std::strcmp(str, "\n") == 0) {  // See GitHub issue #4505.
            // Most consoles use a simple newline as the cursor down escape.
            // If ONLCR is enabled (which it normally is) this will of course
            // also move the cursor to the beginning of the line.
            // We could do:
            // if (std::strcmp(cursor_up, "\x1B[A") == 0) str = "\x1B[B";
            // else ... but that doesn't work for unknown reasons.
            this->actual.cursor.x = 0;
        }
    }

    for (i = 0; i < abs(y_steps); i++) {
        outp.writembs(str);
    }

    x_steps = new_x - this->actual.cursor.x;

    if (x_steps && new_x == 0) {
        outp.push_back('\r');
        x_steps = 0;
    }

    const char *multi_str = nullptr;
    if (x_steps < 0) {
        str = cursor_left;
        multi_str = parm_left_cursor;
    } else {
        str = cursor_right;
        multi_str = parm_right_cursor;
    }

    // Use the bulk ('multi') output for cursor movement if it is supported and it would be shorter
    // Note that this is required to avoid some visual glitches in iTerm (issue #1448).
    bool use_multi = multi_str != nullptr && multi_str[0] != '\0' &&
                     abs(x_steps) * std::strlen(str) > std::strlen(multi_str);
    if (use_multi && cur_term) {
        char *multi_param = fish_tparm(const_cast<char *>(multi_str), abs(x_steps));
        writembs(outp, multi_param);
    } else {
        for (i = 0; i < abs(x_steps); i++) {
            writembs(outp, str);
        }
    }

    this->actual.cursor.x = new_x;
    this->actual.cursor.y = new_y;
}

/// Convert a wide character to a multibyte string and append it to the buffer.
void screen_t::write_char(wchar_t c, size_t width) {
    scoped_buffer_t buffering(outp());
    this->actual.cursor.x += width;
    this->outp().writech(c);
    if (this->actual.cursor.x == this->actual.screen_width && allow_soft_wrap()) {
        this->soft_wrap_location = screen_data_t::cursor_t{0, this->actual.cursor.y + 1};

        // Note that our cursor position may be a lie: Apple Terminal makes the right cursor stick
        // to the margin, while Ubuntu makes it "go off the end" (but still doesn't wrap). We rely
        // on s_move to fix this up.
    } else {
        this->soft_wrap_location = none();
    }
}

/// Send the specified string through tputs and append the output to the screen's outputter.
void screen_t::write_mbs(const char *s) { writembs(this->outp(), s); }

/// Convert a wide string to a multibyte string and append it to the buffer.
void screen_t::write_str(const wchar_t *s) { this->outp().writestr(s); }
void screen_t::write_str(const wcstring &s) { this->outp().writestr(s.c_str()); }

/// Returns the length of the "shared prefix" of the two lines, which is the run of matching text
/// and colors. If the prefix ends on a combining character, do not include the previous character
/// in the prefix.
static size_t line_shared_prefix(const line_t &a, const line_t &b) {
    size_t idx, max = std::min(a.size(), b.size());
    for (idx = 0; idx < max; idx++) {
        wchar_t ac = a.char_at(idx), bc = b.char_at(idx);

        // We're done if the text or colors are different.
        if (ac != bc || a.color_at(idx) != b.color_at(idx)) {
            if (idx > 0) {
                const line_t *c = nullptr;
                // Possible combining mark, go back until we hit _two_ printable characters or idx
                // of 0.
                if (fish_wcwidth(a.char_at(idx)) < 1) {
                    c = &a;
                } else if (fish_wcwidth(b.char_at(idx)) < 1) {
                    c = &b;
                }

                if (c) {
                    while (idx > 1 && (fish_wcwidth(c->char_at(idx - 1)) < 1 ||
                                       fish_wcwidth(c->char_at(idx)) < 1))
                        idx--;
                    if (idx == 1 && fish_wcwidth(c->char_at(idx)) < 1) idx = 0;
                }
            }
            break;
        }
    }
    return idx;
}

// We are about to output one or more characters onto the screen at the given x, y. If we are at the
// end of previous line, and the previous line is marked as soft wrapping, then tweak the screen so
// we believe we are already in the target position. This lets the terminal take care of wrapping,
// which means that if you copy and paste the text, it won't have an embedded newline.
bool screen_t::handle_soft_wrap(int x, int y) {
    if (this->soft_wrap_location && x == this->soft_wrap_location->x &&
        y == this->soft_wrap_location->y) {  //!OCLINT
        // We can soft wrap; but do we want to?
        if (this->desired.line(y - 1).is_soft_wrapped && allow_soft_wrap()) {
            // Yes. Just update the actual cursor; that will cause us to elide emitting the commands
            // to move here, so we will just output on "one big line" (which the terminal soft
            // wraps.
            this->actual.cursor = this->soft_wrap_location.value();
        }
    }
    return false;
}

/// Update the screen to match the desired output.
void screen_t::update(const wcstring &left_prompt, const wcstring &right_prompt,
                      const environment_t &vars) {
    // Helper function to set a resolved color, using the caching resolver.
    highlight_color_resolver_t color_resolver{};
    auto set_color = [&](highlight_spec_t c) {
        this->outp().set_color(color_resolver.resolve_spec(c, false, vars),
                               color_resolver.resolve_spec(c, true, vars));
    };

    layout_cache_t &cached_layouts = layout_cache_t::shared;
    const scoped_buffer_t buffering(outp());

    // Determine size of left and right prompt. Note these have already been truncated.
    const prompt_layout_t left_prompt_layout = cached_layouts.calc_prompt_layout(left_prompt);
    const size_t left_prompt_width = left_prompt_layout.last_line_width;
    const size_t right_prompt_width =
        cached_layouts.calc_prompt_layout(right_prompt).last_line_width;

    // Figure out how many following lines we need to clear (probably 0).
    size_t actual_lines_before_reset = this->actual_lines_before_reset;
    this->actual_lines_before_reset = 0;

    bool need_clear_lines = this->need_clear_lines;
    bool need_clear_screen = this->need_clear_screen;
    bool has_cleared_screen = false;

    const int screen_width = this->desired.screen_width;

    if (this->actual.screen_width != screen_width) {
        // Ensure we don't issue a clear screen for the very first output, to avoid issue #402.
        if (this->actual.screen_width > 0) {
            need_clear_screen = true;
            this->move(0, 0);
            this->reset_line();

            need_clear_lines = need_clear_lines || this->need_clear_lines;
            need_clear_screen = need_clear_screen || this->need_clear_screen;
        }
        this->actual.screen_width = screen_width;
    }

    this->need_clear_lines = false;
    this->need_clear_screen = false;

    // Determine how many lines have stuff on them; we need to clear lines with stuff that we don't
    // want.
    const size_t lines_with_stuff = std::max(actual_lines_before_reset, this->actual.line_count());
    if (this->desired.line_count() < lines_with_stuff) need_clear_screen = true;

    // Output the left prompt if it has changed.
    if (left_prompt != this->actual_left_prompt) {
        this->move(0, 0);
        size_t start = 0;
        for (const size_t line_break : left_prompt_layout.line_breaks) {
            this->write_str(left_prompt.substr(start, line_break - start));
            if (clr_eol) {
                this->write_mbs(clr_eol);
            }
            start = line_break;
        }
        this->write_str(left_prompt.substr(start));
        this->actual_left_prompt = left_prompt;
        this->actual.cursor.x = static_cast<int>(left_prompt_width);
    }

    // Output all lines.
    for (size_t i = 0; i < this->desired.line_count(); i++) {
        const line_t &o_line = this->desired.line(i);
        line_t &s_line = this->actual.create_line(i);
        size_t start_pos = i == 0 ? left_prompt_width : 0;
        int current_width = 0;
        bool has_cleared_line = false;

        // If this is the last line, maybe we should clear the screen.
        // Don't issue clr_eos if we think the cursor will end up in the last column - see #6951.
        const bool should_clear_screen_this_line =
            need_clear_screen && i + 1 == this->desired.line_count() && clr_eos != nullptr &&
            !(this->desired.cursor.x == 0 &&
              this->desired.cursor.y == static_cast<int>(this->desired.line_count()));

        // skip_remaining is how many columns are unchanged on this line.
        // Note that skip_remaining is a width, not a character count.
        size_t skip_remaining = start_pos;

        const size_t shared_prefix = line_shared_prefix(o_line, s_line);
        size_t skip_prefix = shared_prefix;
        if (shared_prefix < o_line.indentation) {
            if (o_line.indentation > s_line.indentation && !has_cleared_screen && clr_eol &&
                clr_eos) {
                set_color(highlight_spec_t{});
                this->move(0, static_cast<int>(i));
                this->write_mbs(should_clear_screen_this_line ? clr_eos : clr_eol);
                has_cleared_screen = should_clear_screen_this_line;
                has_cleared_line = true;
            }
            skip_prefix = o_line.indentation;
        }

        // Compute how much we should skip. At a minimum we skip over the prompt. But also skip
        // over the shared prefix of what we want to output now, and what we output before, to
        // avoid repeatedly outputting it.
        if (skip_prefix > 0) {
            size_t skip_width =
                shared_prefix < skip_prefix ? skip_prefix : o_line.wcswidth_min_0(shared_prefix);
            if (skip_width > skip_remaining) skip_remaining = skip_width;
        }

        if (!should_clear_screen_this_line) {
            // If we're soft wrapped, and if we're going to change the first character of the next
            // line, don't skip over the last two characters so that we maintain soft-wrapping.
            if (o_line.is_soft_wrapped && i + 1 < this->desired.line_count()) {
                bool next_line_will_change = true;
                if (i + 1 < this->actual.line_count()) {  //!OCLINT
                    if (line_shared_prefix(this->desired.line(i + 1), this->actual.line(i + 1)) >
                        0) {
                        next_line_will_change = false;
                    }
                }
                if (next_line_will_change) {
                    skip_remaining = std::min(skip_remaining,
                                              static_cast<size_t>(this->actual.screen_width - 2));
                }
            }
        }

        // Skip over skip_remaining width worth of characters.
        size_t j = 0;
        for (; j < o_line.size(); j++) {
            size_t width = fish_wcwidth_visible(o_line.char_at(j));
            if (skip_remaining < width) break;
            skip_remaining -= width;
            current_width += width;
        }

        // Skip over zero-width characters (e.g. combining marks at the end of the prompt).
        for (; j < o_line.size(); j++) {
            int width = fish_wcwidth_visible(o_line.char_at(j));
            if (width > 0) break;
        }

        // Now actually output stuff.
        for (;; j++) {
            bool done = j >= o_line.size();
            // Clear the screen if we have not done so yet.
            // If we are about to output into the last column, clear the screen first. If we clear
            // the screen after we output into the last column, it can erase the last character due
            // to the sticky right cursor. If we clear the screen too early, we can defeat soft
            // wrapping.
            if (should_clear_screen_this_line && !has_cleared_screen &&
                (done || j + 1 == static_cast<size_t>(screen_width))) {
                set_color(highlight_spec_t{});
                this->move(current_width, static_cast<int>(i));
                this->write_mbs(clr_eos);
                has_cleared_screen = true;
            }
            if (done) break;

            this->handle_soft_wrap(current_width, static_cast<int>(i));
            this->move(current_width, static_cast<int>(i));
            set_color(o_line.color_at(j));
            auto width = fish_wcwidth_visible(o_line.char_at(j));
            this->write_char(o_line.char_at(j), width);
            current_width += width;
        }

        bool clear_remainder = false;
        // Clear the remainder of the line if we need to clear and if we didn't write to the end of
        // the line. If we did write to the end of the line, the "sticky right edge" (as part of
        // auto_right_margin) means that we'll be clearing the last character we wrote!
        if (has_cleared_screen || has_cleared_line) {
            // Already cleared everything.
            clear_remainder = false;
        } else if (need_clear_lines && current_width < screen_width) {
            clear_remainder = true;
        } else if (right_prompt_width < this->last_right_prompt_width) {
            clear_remainder = true;
        } else {
            // This wcswidth shows up strong in the profile.
            // Only do it if the previous line could conceivably be wider.
            // That means if it is a prefix of the current one we can skip it.
            if (s_line.text.size() != shared_prefix) {
                int prev_width = s_line.wcswidth_min_0();
                clear_remainder = prev_width > current_width;
            }
        }
        if (clear_remainder && clr_eol) {
            set_color(highlight_spec_t{});
            this->move(current_width, static_cast<int>(i));
            this->write_mbs(clr_eol);
        }

        // Output any rprompt if this is the first line.
        if (i == 0 && right_prompt_width > 0) {  //!OCLINT(Use early exit/continue)
            // Move the cursor to the beginning of the line first to be independent of the width.
            // This helps prevent staircase effects if fish and the terminal disagree.
            this->move(0, 0);
            this->move(static_cast<int>(screen_width - right_prompt_width), static_cast<int>(i));
            set_color(highlight_spec_t{});
            this->write_str(right_prompt);
            this->actual.cursor.x += right_prompt_width;

            // We output in the last column. Some terms (Linux) push the cursor further right, past
            // the window. Others make it "stick." Since we don't really know which is which, issue
            // a cr so it goes back to the left.
            //
            // However, if the user is resizing the window smaller, then it's possible the cursor
            // wrapped. If so, then a cr will go to the beginning of the following line! So instead
            // issue a bunch of "move left" commands to get back onto the line, and then jump to the
            // front of it.
            this->move(this->actual.cursor.x - static_cast<int>(right_prompt_width),
                       this->actual.cursor.y);
            this->write_str(L"\r");
            this->actual.cursor.x = 0;
        }
    }

    // Also move the cursor to the beginning of the line here,
    // in case we're wrong about the width anywhere.
    // Don't do it when running in midnight_commander because of
    // https://midnight-commander.org/ticket/4258.
    if (!midnight_commander_hack) {
        this->move(0, 0);
    }

    // Clear remaining lines (if any) if we haven't cleared the screen.
    if (!has_cleared_screen && need_clear_screen && clr_eol) {
        set_color(highlight_spec_t{});
        for (size_t i = this->desired.line_count(); i < lines_with_stuff; i++) {
            this->move(0, static_cast<int>(i));
            this->write_mbs(clr_eol);
        }
    }

    this->move(this->desired.cursor.x, this->desired.cursor.y);
    set_color(highlight_spec_t{});

    // We have now synced our actual screen against our desired screen. Note that this is a big
    // assignment!
    this->actual = this->desired;
    this->last_right_prompt_width = right_prompt_width;
}

/// Returns true if we are using a dumb terminal.
static bool is_dumb() {
    if (!cur_term) return true;
    return !cursor_up || !cursor_down || !cursor_left || !cursor_right;
}

namespace {
struct screen_layout_t {
    // The left prompt that we're going to use.
    wcstring left_prompt;
    // How much space to leave for it.
    size_t left_prompt_space;
    // The right prompt.
    wcstring right_prompt;
    // The autosuggestion.
    wcstring autosuggestion;
};
}  // namespace

// Given a vector whose indexes are offsets and whose values are the widths of the string if
// truncated at that offset, return the offset that fits in the given width. Returns
// width_by_offset.size() - 1 if they all fit. The first value in width_by_offset is assumed to be
// 0.
static size_t truncation_offset_for_width(const std::vector<size_t> &width_by_offset,
                                          size_t max_width) {
    assert(!width_by_offset.empty() && width_by_offset.at(0) == 0);
    size_t i;
    for (i = 1; i < width_by_offset.size(); i++) {
        if (width_by_offset.at(i) > max_width) break;
    }
    // i is the first index that did not fit; i-1 is therefore the last that did.
    return i - 1;
}

static screen_layout_t compute_layout(screen_t *s, size_t screen_width,
                                      const wcstring &left_untrunc_prompt,
                                      const wcstring &right_untrunc_prompt,
                                      const wcstring &commandline,
                                      const wcstring &autosuggestion_str) {
    UNUSED(s);
    screen_layout_t result = {};

    // Truncate both prompts to screen width (#904).
    wcstring left_prompt;
    prompt_layout_t left_prompt_layout =
        layout_cache_t::shared.calc_prompt_layout(left_untrunc_prompt, &left_prompt, screen_width);

    wcstring right_prompt;
    prompt_layout_t right_prompt_layout = layout_cache_t::shared.calc_prompt_layout(
        right_untrunc_prompt, &right_prompt, screen_width);

    size_t left_prompt_width = left_prompt_layout.last_line_width;
    size_t right_prompt_width = right_prompt_layout.last_line_width;

    if (left_prompt_width + right_prompt_width > screen_width) {
        // Nix right_prompt.
        right_prompt = L"";
        right_prompt_width = 0;
    }

    // Now we should definitely fit.
    assert(left_prompt_width + right_prompt_width <= screen_width);

    // Get the width of the first line, and if there is more than one line.
    bool multiline = false;
    size_t first_line_width = 0;
    for (auto c : commandline) {
        if (c == L'\n') {
            multiline = true;
            break;
        } else {
            first_line_width += fish_wcwidth_visible(c);
        }
    }
    const size_t first_command_line_width = first_line_width;

    // If we have more than one line, ensure we have no autosuggestion.
    const wchar_t *autosuggestion = autosuggestion_str.c_str();
    size_t autosuggest_total_width = 0;
    std::vector<size_t> autosuggest_truncated_widths;
    if (multiline) {
        autosuggestion = L"";
    } else {
        autosuggest_truncated_widths.reserve(1 + autosuggestion_str.size());
        for (size_t i = 0; autosuggestion[i] != L'\0'; i++) {
            autosuggest_truncated_widths.push_back(autosuggest_total_width);
            autosuggest_total_width += fish_wcwidth_visible(autosuggestion[i]);
        }
    }

    // Here are the layouts we try in turn:
    //
    // 1. Left prompt visible, right prompt visible, command line visible, autosuggestion visible.
    //
    // 2. Left prompt visible, right prompt visible, command line visible, autosuggestion truncated
    // (possibly to zero).
    //
    // 3. Left prompt visible, right prompt hidden, command line visible, autosuggestion visible
    //
    // 4. Left prompt visible, right prompt hidden, command line visible, autosuggestion truncated
    //
    // 5. Newline separator (left prompt visible, right prompt hidden, command line visible,
    // autosuggestion visible).
    //
    // A remark about layout #4: if we've pushed the command line to a new line, why can't we draw
    // the right prompt? The issue is resizing: if you resize the window smaller, then the right
    // prompt will wrap to the next line. This means that we can't go back to the line that we were
    // on, and things turn to chaos very quickly.
    size_t calculated_width;
    bool done = false;

    // Case 1
    if (!done) {
        calculated_width = left_prompt_width + right_prompt_width + first_command_line_width +
                           autosuggest_total_width;
        if (calculated_width <= screen_width) {
            result.left_prompt = left_prompt;
            result.left_prompt_space = left_prompt_width;
            result.right_prompt = right_prompt;
            result.autosuggestion = autosuggestion;
            done = true;
        }
    }

    // Case 2. Note that we require strict inequality so that there's always at least one space
    // between the left edge and the rprompt.
    if (!done) {
        calculated_width = left_prompt_width + right_prompt_width + first_command_line_width;
        if (calculated_width <= screen_width) {
            result.left_prompt = left_prompt;
            result.left_prompt_space = left_prompt_width;
            result.right_prompt = right_prompt;

            // Need at least two characters to show an autosuggestion.
            size_t available_autosuggest_space =
                screen_width - (left_prompt_width + right_prompt_width + first_command_line_width);
            if (autosuggest_total_width > 0 && available_autosuggest_space > 2) {
                size_t truncation_offset = truncation_offset_for_width(
                    autosuggest_truncated_widths, available_autosuggest_space - 2);
                result.autosuggestion = wcstring(autosuggestion, truncation_offset);
                result.autosuggestion.push_back(get_ellipsis_char());
            }
            done = true;
        }
    }

    // Case 3
    if (!done) {
        calculated_width = left_prompt_width + first_command_line_width + autosuggest_total_width;
        if (calculated_width <= screen_width) {
            result.left_prompt = left_prompt;
            result.left_prompt_space = left_prompt_width;
            result.autosuggestion = autosuggestion;
            done = true;
        }
    }

    // Case 4
    if (!done) {
        calculated_width = left_prompt_width + first_command_line_width;
        if (calculated_width <= screen_width) {
            result.left_prompt = left_prompt;
            result.left_prompt_space = left_prompt_width;

            // Need at least two characters to show an autosuggestion.
            size_t available_autosuggest_space =
                screen_width - (left_prompt_width + first_command_line_width);
            if (autosuggest_total_width > 0 && available_autosuggest_space > 2) {
                size_t truncation_offset = truncation_offset_for_width(
                    autosuggest_truncated_widths, available_autosuggest_space - 2);
                result.autosuggestion = wcstring(autosuggestion, truncation_offset);
                result.autosuggestion.push_back(get_ellipsis_char());
            }
            done = true;
        }
    }

    // Case 5
    if (!done) {
        result.left_prompt = left_prompt;
        result.left_prompt_space = left_prompt_width;
        result.autosuggestion = autosuggestion;
    }

    return result;
}

void screen_t::write(const wcstring &left_prompt, const wcstring &right_prompt,
                     const wcstring &commandline, size_t explicit_len,
                     const std::vector<highlight_spec_t> &colors, const std::vector<int> &indent,
                     size_t cursor_pos, const environment_t &vars, pager_t &pager,
                     page_rendering_t &page_rendering, bool cursor_is_within_pager) {
    termsize_t curr_termsize = termsize_last();
    int screen_width = curr_termsize.width;
    static relaxed_atomic_t<uint32_t> s_repaints{0};
    FLOGF(screen, "Repaint %u", static_cast<unsigned>(++s_repaints));
    screen_data_t::cursor_t cursor_arr;

    // Turn the command line into the explicit portion and the autosuggestion.
    const wcstring explicit_command_line = commandline.substr(0, explicit_len);
    const wcstring autosuggestion = commandline.substr(explicit_len);

    // If we are using a dumb terminal, don't try any fancy stuff, just print out the text.
    // right_prompt not supported.
    if (is_dumb()) {
        const std::string prompt_narrow = wcs2string(left_prompt);
        const std::string command_line_narrow = wcs2string(explicit_command_line);

        write_loop(STDOUT_FILENO, "\r", 1);
        write_loop(STDOUT_FILENO, prompt_narrow.c_str(), prompt_narrow.size());
        write_loop(STDOUT_FILENO, command_line_narrow.c_str(), command_line_narrow.size());

        return;
    }

    this->check_status();

    // Completely ignore impossibly small screens.
    if (screen_width < 4) {
        return;
    }

    // Compute a layout.
    const screen_layout_t layout = compute_layout(this, screen_width, left_prompt, right_prompt,
                                                  explicit_command_line, autosuggestion);

    // Determine whether, if we have an autosuggestion, it was truncated.
    this->autosuggestion_is_truncated =
        !autosuggestion.empty() && autosuggestion != layout.autosuggestion;

    // Clear the desired screen and set its width.
    this->desired.screen_width = screen_width;
    this->desired.resize(0);
    this->desired.cursor.x = this->desired.cursor.y = 0;

    // Append spaces for the left prompt.
    for (size_t i = 0; i < layout.left_prompt_space; i++) {
        desired_append_char(L' ', highlight_spec_t{}, 0, layout.left_prompt_space, 1);
    }

    // If overflowing, give the prompt its own line to improve the situation.
    size_t first_line_prompt_space = layout.left_prompt_space;

    // Reconstruct the command line.
    wcstring effective_commandline = explicit_command_line + layout.autosuggestion;

    // Output the command line.
    size_t i;
    for (i = 0; i < effective_commandline.size(); i++) {
        // Grab the current cursor's x,y position if this character matches the cursor's offset.
        if (!cursor_is_within_pager && i == cursor_pos) {
            cursor_arr = this->desired.cursor;
        }
        desired_append_char(effective_commandline.at(i), colors[i], indent[i],
                            first_line_prompt_space,
                            fish_wcwidth_visible(effective_commandline.at(i)));
    }

    // Cursor may have been at the end too.
    if (!cursor_is_within_pager && i == cursor_pos) {
        cursor_arr = this->desired.cursor;
    }

    int full_line_count = this->desired.cursor.y + 1;

    // Now that we've output everything, set the cursor to the position that we saved in the loop
    // above.
    this->desired.cursor = cursor_arr;

    if (cursor_is_within_pager) {
        this->desired.cursor.x = static_cast<int>(cursor_pos);
        this->desired.cursor.y = static_cast<int>(this->desired.line_count());
    }

    // Re-render our completions page if necessary. Limit the term size of the pager to the true
    // term size, minus the number of lines consumed by our string.
    pager.set_term_size(
        termsize_t{std::max((rust::isize)1, curr_termsize.width),
                   std::max((rust::isize)1, curr_termsize.height - full_line_count)});
    pager.update_rendering(&page_rendering);
    // Append pager_data (none if empty).
    this->desired.append_lines(page_rendering.screen_data);

    this->update(layout.left_prompt, layout.right_prompt, vars);
    this->save_status();
}

void screen_t::reset_line(bool repaint_prompt) {
    // Remember how many lines we had output to, so we can clear the remaining lines in the next
    // call to s_update. This prevents leaving junk underneath the cursor when resizing a window
    // wider such that it reduces our desired line count.
    this->actual_lines_before_reset =
        std::max(this->actual_lines_before_reset, this->actual.line_count());

    if (repaint_prompt) {
        // If the prompt is multi-line, we need to move up to the prompt's initial line. We do this
        // by lying to ourselves and claiming that we're really below what we consider "line 0"
        // (which is the last line of the prompt). This will cause us to move up to try to get back
        // to line 0, but really we're getting back to the initial line of the prompt.
        const size_t prompt_line_count = calc_prompt_lines(this->actual_left_prompt);
        assert(prompt_line_count >= 1);
        this->actual.cursor.y += (prompt_line_count - 1);
        this->actual_left_prompt.clear();
    }
    this->actual.resize(0);
    this->need_clear_lines = true;

    // This should prevent resetting the cursor position during the next repaint.
    write_loop(STDOUT_FILENO, "\r", 1);
    this->actual.cursor.x = 0;

    fstat(STDOUT_FILENO, &this->prev_buff_1);
    fstat(STDERR_FILENO, &this->prev_buff_2);
}

void screen_t::reset_abandoning_line(int screen_width) {
    this->actual.cursor.y = 0;
    this->actual.resize(0);
    this->actual_left_prompt.clear();
    this->need_clear_lines = true;

    // Do the PROMPT_SP hack.
    wcstring abandon_line_string;
    abandon_line_string.reserve(screen_width + 32);

    // Don't need to check for fish_wcwidth errors; this is done when setting up
    // omitted_newline_char in common.cpp.
    int non_space_width = get_omitted_newline_width();
    // We do `>` rather than `>=` because the code below might require one extra space.
    if (screen_width > non_space_width) {
        bool justgrey = true;
        if (cur_term && enter_dim_mode) {
            std::string dim = fish_tparm(const_cast<char *>(enter_dim_mode));
            if (!dim.empty()) {
                // Use dim if they have it, so the color will be based on their actual normal
                // color and the background of the terminal.
                abandon_line_string.append(str2wcstring(dim));
                justgrey = false;
            }
        }
        if (cur_term && justgrey && set_a_foreground) {
            if (max_colors >= 238) {
                // draw the string in a particular grey
                abandon_line_string.append(
                    str2wcstring(fish_tparm(const_cast<char *>(set_a_foreground), 237)));
            } else if (max_colors >= 9) {
                // bright black (the ninth color, looks grey)
                abandon_line_string.append(
                    str2wcstring(fish_tparm(const_cast<char *>(set_a_foreground), 8)));
            } else if (max_colors >= 2 && enter_bold_mode) {
                // we might still get that color by setting black and going bold for bright
                abandon_line_string.append(
                    str2wcstring(fish_tparm(const_cast<char *>(enter_bold_mode))));
                abandon_line_string.append(
                    str2wcstring(fish_tparm(const_cast<char *>(set_a_foreground), 0)));
            }
        }

        abandon_line_string.append(get_omitted_newline_str());

        if (cur_term && exit_attribute_mode) {
            abandon_line_string.append(str2wcstring(fish_tparm(
                const_cast<char *>(exit_attribute_mode))));  // normal text ANSI escape sequence
        }

        int newline_glitch_width = TERM_HAS_XN ? 0 : 1;
        abandon_line_string.append(screen_width - non_space_width - newline_glitch_width, L' ');
    }

    abandon_line_string.push_back(L'\r');
    abandon_line_string.append(get_omitted_newline_str());
    // Now we are certainly on a new line. But we may have dropped the omitted newline char on
    // it. So append enough spaces to overwrite the omitted newline char, and then clear all the
    // spaces from the new line.
    abandon_line_string.append(non_space_width, L' ');
    abandon_line_string.push_back(L'\r');
    // Clear entire line. Zsh doesn't do this. Fish added this with commit 4417a6ee: If you have
    // a prompt preceded by a new line, you'll get a line full of spaces instead of an empty
    // line above your prompt. This doesn't make a difference in normal usage, but copying and
    // pasting your terminal log becomes a pain. This commit clears that line, making it an
    // actual empty line.
    if (!is_dumb() && clr_eol) {
        abandon_line_string.append(str2wcstring(clr_eol));
    }

    const std::string narrow_abandon_line_string = wcs2string(abandon_line_string);
    write_loop(STDOUT_FILENO, narrow_abandon_line_string.c_str(),
               narrow_abandon_line_string.size());
    this->actual.cursor.x = 0;

    fstat(STDOUT_FILENO, &this->prev_buff_1);
    fstat(STDERR_FILENO, &this->prev_buff_2);
}

void screen_force_clear_to_end() {
    if (clr_eos) {
        writembs(stdoutput(), clr_eos);
    }
}

screen_t::screen_t() : outp_(stdoutput()) {}

bool screen_t::cursor_is_wrapped_to_own_line() const {
    // Note == comparison against the line count is correct: we do not create a line just for the
    // cursor. If there is a line containing the cursor, then it means that line has contents and we
    // should return false.
    // Don't consider dumb terminals to have wrapping for the purposes of this function.
    return actual.cursor.x == 0 && static_cast<size_t>(actual.cursor.y) == actual.line_count() &&
           !is_dumb();
}