// This is an open source non-commercial project. Dear PVS-Studio, please check
// it. PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com

/*
 * message.c: functions for displaying messages on the command line
 */

#include <assert.h>
#include <inttypes.h>
#include <stdarg.h>
#include <stdbool.h>
#include <string.h>

#include "nvim/api/private/helpers.h"
#include "nvim/ascii.h"
#include "nvim/assert.h"
#include "nvim/charset.h"
#include "nvim/drawscreen.h"
#include "nvim/eval.h"
#include "nvim/ex_docmd.h"
#include "nvim/ex_eval.h"
#include "nvim/ex_getln.h"
#include "nvim/fileio.h"
#include "nvim/func_attr.h"
#include "nvim/garray.h"
#include "nvim/getchar.h"
#include "nvim/grid.h"
#include "nvim/highlight.h"
#include "nvim/indent.h"
#include "nvim/input.h"
#include "nvim/keycodes.h"
#include "nvim/main.h"
#include "nvim/mbyte.h"
#include "nvim/memory.h"
#include "nvim/message.h"
#include "nvim/mouse.h"
#include "nvim/normal.h"
#include "nvim/ops.h"
#include "nvim/option.h"
#include "nvim/os/input.h"
#include "nvim/os/os.h"
#include "nvim/os/time.h"
#include "nvim/regexp.h"
#include "nvim/runtime.h"
#include "nvim/strings.h"
#include "nvim/syntax.h"
#include "nvim/ui.h"
#include "nvim/ui_compositor.h"
#include "nvim/vim.h"

/*
 * To be able to scroll back at the "more" and "hit-enter" prompts we need to
 * store the displayed text and remember where screen lines start.
 */
typedef struct msgchunk_S msgchunk_T;
struct msgchunk_S {
  msgchunk_T *sb_next;
  msgchunk_T *sb_prev;
  char sb_eol;                  // TRUE when line ends after this text
  int sb_msg_col;               // column in which text starts
  int sb_attr;                  // text attributes
  char_u sb_text[1];            // text to be displayed, actually longer
};

// Magic chars used in confirm dialog strings
#define DLG_BUTTON_SEP  '\n'
#define DLG_HOTKEY_CHAR '&'

static int confirm_msg_used = FALSE;            // displaying confirm_msg
#ifdef INCLUDE_GENERATED_DECLARATIONS
# include "message.c.generated.h"
#endif
static char_u *confirm_msg = NULL;            // ":confirm" message
static char_u *confirm_msg_tail;              // tail of confirm_msg

MessageHistoryEntry *first_msg_hist = NULL;
MessageHistoryEntry *last_msg_hist = NULL;
static int msg_hist_len = 0;

static FILE *verbose_fd = NULL;
static int verbose_did_open = FALSE;

bool keep_msg_more = false;    // keep_msg was set by msgmore()

/*
 * When writing messages to the screen, there are many different situations.
 * A number of variables is used to remember the current state:
 * msg_didany       true when messages were written since the last time the
 *                  user reacted to a prompt.
 *                  Reset: After hitting a key for the hit-return prompt,
 *                  hitting <CR> for the command line or input().
 *                  Set: When any message is written to the screen.
 * msg_didout       true when something was written to the current line.
 *                  Reset: When advancing to the next line, when the current
 *                  text can be overwritten.
 *                  Set: When any message is written to the screen.
 * msg_nowait       No extra delay for the last drawn message.
 *                  Used in normal_cmd() before the mode message is drawn.
 * emsg_on_display  There was an error message recently.  Indicates that there
 *                  should be a delay before redrawing.
 * msg_scroll       The next message should not overwrite the current one.
 * msg_scrolled     How many lines the screen has been scrolled (because of
 *                  messages).  Used in update_screen() to scroll the screen
 *                  back.  Incremented each time the screen scrolls a line.
 * msg_scrolled_ign  TRUE when msg_scrolled is non-zero and msg_puts_attr()
 *                  writes something without scrolling should not make
 *                  need_wait_return to be set.  This is a hack to make ":ts"
 *                  work without an extra prompt.
 * lines_left       Number of lines available for messages before the
 *                  more-prompt is to be given.  -1 when not set.
 * need_wait_return true when the hit-return prompt is needed.
 *                  Reset: After giving the hit-return prompt, when the user
 *                  has answered some other prompt.
 *                  Set: When the ruler or typeahead display is overwritten,
 *                  scrolling the screen for some message.
 * keep_msg         Message to be displayed after redrawing the screen, in
 *                  main_loop().
 *                  This is an allocated string or NULL when not used.
 */

// Extended msg state, currently used for external UIs with ext_messages
static const char *msg_ext_kind = NULL;
static Array msg_ext_chunks = ARRAY_DICT_INIT;
static garray_T msg_ext_last_chunk = GA_INIT(sizeof(char), 40);
static sattr_T msg_ext_last_attr = -1;
static size_t msg_ext_cur_len = 0;

static bool msg_ext_overwrite = false;  ///< will overwrite last message
static int msg_ext_visible = 0;  ///< number of messages currently visible

static bool msg_ext_history_visible = false;

/// Shouldn't clear message after leaving cmdline
static bool msg_ext_keep_after_cmdline = false;

static int msg_grid_pos_at_flush = 0;
static int msg_grid_scroll_discount = 0;

static void ui_ext_msg_set_pos(int row, bool scrolled)
{
  char buf[MAX_MCO + 1];
  size_t size = (size_t)utf_char2bytes(curwin->w_p_fcs_chars.msgsep, buf);
  buf[size] = '\0';
  ui_call_msg_set_pos(msg_grid.handle, row, scrolled,
                      (String){ .data = buf, .size = size });
}

void msg_grid_set_pos(int row, bool scrolled)
{
  if (!msg_grid.throttled) {
    ui_ext_msg_set_pos(row, scrolled);
    msg_grid_pos_at_flush = row;
  }
  msg_grid_pos = row;
  if (msg_grid.chars) {
    msg_grid_adj.row_offset = -row;
  }
}

bool msg_use_grid(void)
{
  return default_grid.chars && msg_use_msgsep()
         && !ui_has(kUIMessages);
}

void msg_grid_validate(void)
{
  grid_assign_handle(&msg_grid);
  bool should_alloc = msg_use_grid();
  int max_rows = Rows - (int)p_ch;
  if (should_alloc && (msg_grid.rows != Rows || msg_grid.cols != Columns
                       || !msg_grid.chars)) {
    // TODO(bfredl): eventually should be set to "invalid". I e all callers
    // will use the grid including clear to EOS if necessary.
    grid_alloc(&msg_grid, Rows, Columns, false, true);
    msg_grid.zindex = kZIndexMessages;

    xfree(msg_grid.dirty_col);
    msg_grid.dirty_col = xcalloc((size_t)Rows, sizeof(*msg_grid.dirty_col));

    // Tricky: allow resize while pager is active
    int pos = msg_scrolled ? msg_grid_pos : max_rows;
    ui_comp_put_grid(&msg_grid, pos, 0, msg_grid.rows, msg_grid.cols,
                     false, true);
    ui_call_grid_resize(msg_grid.handle, msg_grid.cols, msg_grid.rows);

    msg_grid.throttled = false;  // don't throttle in 'cmdheight' area
    msg_scrolled_at_flush = msg_scrolled;
    msg_grid.focusable = false;
    msg_grid_adj.target = &msg_grid;
    if (!msg_scrolled) {
      msg_grid_set_pos(max_rows, false);
    }
  } else if (!should_alloc && msg_grid.chars) {
    ui_comp_remove_grid(&msg_grid);
    grid_free(&msg_grid);
    XFREE_CLEAR(msg_grid.dirty_col);
    ui_call_grid_destroy(msg_grid.handle);
    msg_grid.throttled = false;
    msg_grid_adj.row_offset = 0;
    msg_grid_adj.target = &default_grid;
    redraw_cmdline = true;
  } else if (msg_grid.chars && !msg_scrolled && msg_grid_pos != max_rows) {
    msg_grid_set_pos(max_rows, false);
  }

  if (msg_grid.chars && cmdline_row < msg_grid_pos) {
    // TODO(bfredl): this should already be the case, but fails in some
    // "batched" executions where compute_cmdrow() use stale positions or
    // something.
    cmdline_row = msg_grid_pos;
  }
}

/// Displays the string 's' on the status line
/// When terminal not initialized (yet) mch_errmsg(..) is used.
///
/// @return  TRUE if wait_return not called
int msg(char *s)
{
  return msg_attr_keep(s, 0, false, false);
}

/// Like msg() but keep it silent when 'verbosefile' is set.
int verb_msg(char *s)
{
  verbose_enter();
  int n = msg_attr_keep(s, 0, false, false);
  verbose_leave();

  return n;
}

int msg_attr(const char *s, const int attr)
  FUNC_ATTR_NONNULL_ARG(1)
{
  return msg_attr_keep(s, attr, false, false);
}

/// Similar to msg_outtrans_attr, but support newlines and tabs.
void msg_multiline_attr(const char *s, int attr, bool check_int, bool *need_clear)
  FUNC_ATTR_NONNULL_ALL
{
  const char *next_spec = s;

  while (next_spec != NULL) {
    if (check_int && got_int) {
      return;
    }
    next_spec = strpbrk(s, "\t\n\r");

    if (next_spec != NULL) {
      // Printing all char that are before the char found by strpbrk
      msg_outtrans_len_attr((const char_u *)s, (int)(next_spec - s), attr);

      if (*next_spec != TAB && *need_clear) {
        msg_clr_eos();
        *need_clear = false;
      }
      msg_putchar_attr((uint8_t)(*next_spec), attr);
      s = next_spec + 1;
    }
  }

  // Print the rest of the message. We know there is no special
  // character because strpbrk returned NULL
  if (*s != NUL) {
    msg_outtrans_attr((char_u *)s, attr);
  }
}

void msg_multiattr(HlMessage hl_msg, const char *kind, bool history)
{
  no_wait_return++;
  msg_start();
  msg_clr_eos();
  bool need_clear = false;
  for (uint32_t i = 0; i < kv_size(hl_msg); i++) {
    HlMessageChunk chunk = kv_A(hl_msg, i);
    msg_multiline_attr((const char *)chunk.text.data, chunk.attr,
                       true, &need_clear);
  }
  msg_ext_set_kind(kind);
  if (history && kv_size(hl_msg)) {
    add_msg_hist_multiattr(NULL, 0, 0, true, hl_msg);
  }
  no_wait_return--;
  msg_end();
}

/// @param keep set keep_msg if it doesn't scroll
bool msg_attr_keep(const char *s, int attr, bool keep, bool multiline)
  FUNC_ATTR_NONNULL_ALL
{
  static int entered = 0;
  int retval;
  char_u *buf = NULL;

  if (keep && multiline) {
    // Not implemented. 'multiline' is only used by nvim-added messages,
    // which should avoid 'keep' behavior (just show the message at
    // the correct time already).
    abort();
  }

  // Skip messages not match ":filter pattern".
  // Don't filter when there is an error.
  if (!emsg_on_display && message_filtered((char_u *)s)) {
    return true;
  }

  if (attr == 0) {
    set_vim_var_string(VV_STATUSMSG, s, -1);
  }

  /*
   * It is possible that displaying a messages causes a problem (e.g.,
   * when redrawing the window), which causes another message, etc..    To
   * break this loop, limit the recursiveness to 3 levels.
   */
  if (entered >= 3) {
    return TRUE;
  }
  entered++;

  // Add message to history (unless it's a repeated kept message or a
  // truncated message)
  if ((const char_u *)s != keep_msg
      || (*s != '<'
          && last_msg_hist != NULL
          && last_msg_hist->msg != NULL
          && STRCMP(s, last_msg_hist->msg))) {
    add_msg_hist(s, -1, attr, multiline);
  }

  // Truncate the message if needed.
  msg_start();
  buf = msg_strtrunc((char_u *)s, FALSE);
  if (buf != NULL) {
    s = (const char *)buf;
  }

  bool need_clear = true;
  if (multiline) {
    msg_multiline_attr(s, attr, false, &need_clear);
  } else {
    msg_outtrans_attr((char_u *)s, attr);
  }
  if (need_clear) {
    msg_clr_eos();
  }
  retval = msg_end();

  if (keep && retval && vim_strsize((char *)s) < (Rows - cmdline_row - 1) * Columns + sc_col) {
    set_keep_msg((char *)s, 0);
  }

  need_fileinfo = false;

  xfree(buf);
  entered--;
  return retval;
}

/// Truncate a string such that it can be printed without causing a scroll.
///
/// @return  an allocated string or NULL when no truncating is done.
///
/// @param force  always truncate
char_u *msg_strtrunc(char_u *s, int force)
{
  char_u *buf = NULL;
  int len;
  int room;

  // May truncate message to avoid a hit-return prompt
  if ((!msg_scroll && !need_wait_return && shortmess(SHM_TRUNCALL)
       && !exmode_active && msg_silent == 0 && !ui_has(kUIMessages))
      || force) {
    len = vim_strsize((char *)s);
    if (msg_scrolled != 0) {
      // Use all the columns.
      room = (Rows - msg_row) * Columns - 1;
    } else {
      // Use up to 'showcmd' column.
      room = (Rows - msg_row - 1) * Columns + sc_col - 1;
    }
    if (len > room && room > 0) {
      // may have up to 18 bytes per cell (6 per char, up to two
      // composing chars)
      len = (room + 2) * 18;
      buf = xmalloc((size_t)len);
      trunc_string((char *)s, (char *)buf, room, len);
    }
  }
  return buf;
}

/// Truncate a string "s" to "buf" with cell width "room".
/// "s" and "buf" may be equal.
void trunc_string(char *s, char *buf, int room_in, int buflen)
{
  int room = room_in - 3;  // "..." takes 3 chars
  int half;
  int len = 0;
  int e;
  int i;
  int n;

  if (*s == NUL) {
    if (buflen > 0) {
      *buf = NUL;
    }
    return;
  }

  if (room_in < 3) {
    room = 0;
  }
  half = room / 2;

  // First part: Start of the string.
  for (e = 0; len < half && e < buflen; ++e) {
    if (s[e] == NUL) {
      // text fits without truncating!
      buf[e] = NUL;
      return;
    }
    n = ptr2cells(s + e);
    if (len + n > half) {
      break;
    }
    len += n;
    buf[e] = s[e];
    for (n = utfc_ptr2len(s + e); --n > 0;) {
      if (++e == buflen) {
        break;
      }
      buf[e] = s[e];
    }
  }

  // Last part: End of the string.
  half = i = (int)STRLEN(s);
  for (;;) {
    do {
      half = half - utf_head_off((char_u *)s, (char_u *)s + half - 1) - 1;
    } while (half > 0 && utf_iscomposing(utf_ptr2char(s + half)));
    n = ptr2cells(s + half);
    if (len + n > room || half == 0) {
      break;
    }
    len += n;
    i = half;
  }

  if (i <= e + 3) {
    // text fits without truncating
    if (s != buf) {
      len = (int)STRLEN(s);
      if (len >= buflen) {
        len = buflen - 1;
      }
      len = len - e + 1;
      if (len < 1) {
        buf[e - 1] = NUL;
      } else {
        memmove(buf + e, s + e, (size_t)len);
      }
    }
  } else if (e + 3 < buflen) {
    // set the middle and copy the last part
    memmove(buf + e, "...", (size_t)3);
    len = (int)STRLEN(s + i) + 1;
    if (len >= buflen - e - 3) {
      len = buflen - e - 3 - 1;
    }
    memmove(buf + e + 3, s + i, (size_t)len);
    buf[e + 3 + len - 1] = NUL;
  } else {
    // can't fit in the "...", just truncate it
    buf[e - 1] = NUL;
  }
}

/*
 * Note: Caller of smsg() and smsg_attr() must check the resulting string is
 * shorter than IOSIZE!!!
 */

int smsg(const char *s, ...)
  FUNC_ATTR_PRINTF(1, 2)
{
  va_list arglist;

  va_start(arglist, s);
  vim_vsnprintf((char *)IObuff, IOSIZE, s, arglist);
  va_end(arglist);

  return msg((char *)IObuff);
}

int smsg_attr(int attr, const char *s, ...)
  FUNC_ATTR_PRINTF(2, 3)
{
  va_list arglist;

  va_start(arglist, s);
  vim_vsnprintf((char *)IObuff, IOSIZE, s, arglist);
  va_end(arglist);
  return msg_attr((const char *)IObuff, attr);
}

int smsg_attr_keep(int attr, const char *s, ...)
  FUNC_ATTR_PRINTF(2, 3)
{
  va_list arglist;

  va_start(arglist, s);
  vim_vsnprintf((char *)IObuff, IOSIZE, s, arglist);
  va_end(arglist);
  return msg_attr_keep((const char *)IObuff, attr, true, false);
}

/*
 * Remember the last sourcing name/lnum used in an error message, so that it
 * isn't printed each time when it didn't change.
 */
static int last_sourcing_lnum = 0;
static char *last_sourcing_name = NULL;

/// Reset the last used sourcing name/lnum.  Makes sure it is displayed again
/// for the next error message;
void reset_last_sourcing(void)
{
  XFREE_CLEAR(last_sourcing_name);
  last_sourcing_lnum = 0;
}

/// @return  true if "SOURCING_NAME" differs from "last_sourcing_name".
static bool other_sourcing_name(void)
{
  if (SOURCING_NAME != NULL) {
    if (last_sourcing_name != NULL) {
      return strcmp(SOURCING_NAME, last_sourcing_name) != 0;
    }
    return true;
  }
  return false;
}

/// Get the message about the source, as used for an error message
///
/// @return [allocated] String with room for one more character. NULL when no
///                     message is to be given.
static char *get_emsg_source(void)
  FUNC_ATTR_MALLOC FUNC_ATTR_WARN_UNUSED_RESULT
{
  if (SOURCING_NAME != NULL && other_sourcing_name()) {
    char *sname = estack_sfile(ESTACK_NONE);
    char *tofree = sname;

    if (sname == NULL) {
      sname = SOURCING_NAME;
    }

    const char *const p = _("Error detected while processing %s:");
    const size_t buf_len = STRLEN(sname) + strlen(p) + 1;
    char *const buf = xmalloc(buf_len);
    snprintf(buf, buf_len, p, sname);
    xfree(tofree);
    return buf;
  }
  return NULL;
}

/// Get the message about the source lnum, as used for an error message.
///
/// @return [allocated] String with room for one more character. NULL when no
///                     message is to be given.
static char *get_emsg_lnum(void)
  FUNC_ATTR_MALLOC FUNC_ATTR_WARN_UNUSED_RESULT
{
  // lnum is 0 when executing a command from the command line
  // argument, we don't want a line number then
  if (SOURCING_NAME != NULL
      && (other_sourcing_name() || SOURCING_LNUM != last_sourcing_lnum)
      && SOURCING_LNUM != 0) {
    const char *const p = _("line %4ld:");
    const size_t buf_len = 20 + strlen(p);
    char *const buf = xmalloc(buf_len);
    snprintf(buf, buf_len, p, (long)SOURCING_LNUM);
    return buf;
  }
  return NULL;
}

/// Display name and line number for the source of an error.
/// Remember the file name and line number, so that for the next error the info
/// is only displayed if it changed.
void msg_source(int attr)
{
  static bool recursive = false;

  // Bail out if something called here causes an error.
  if (recursive) {
    return;
  }
  recursive = true;

  msg_scroll = true;  // this will take more than one line
  no_wait_return++;
  char *p = get_emsg_source();
  if (p != NULL) {
    msg_attr(p, attr);
    xfree(p);
  }
  p = get_emsg_lnum();
  if (p != NULL) {
    msg_attr(p, HL_ATTR(HLF_N));
    xfree(p);
    last_sourcing_lnum = SOURCING_LNUM;      // only once for each line
  }

  // remember the last sourcing name printed, also when it's empty
  if (SOURCING_NAME == NULL || other_sourcing_name()) {
    XFREE_CLEAR(last_sourcing_name);
    if (SOURCING_NAME != NULL) {
      last_sourcing_name = xstrdup(SOURCING_NAME);
    }
  }
  no_wait_return--;

  recursive = false;
}

/// @return  TRUE if not giving error messages right now:
///            If "emsg_off" is set: no error messages at the moment.
///            If "msg" is in 'debug': do error message but without side effects.
///            If "emsg_skip" is set: never do error messages.
int emsg_not_now(void)
{
  if ((emsg_off > 0 && vim_strchr((char *)p_debug, 'm') == NULL
       && vim_strchr((char *)p_debug, 't') == NULL)
      || emsg_skip > 0) {
    return TRUE;
  }
  return FALSE;
}

static bool emsg_multiline(const char *s, bool multiline)
{
  int attr;
  bool ignore = false;

  // Skip this if not giving error messages at the moment.
  if (emsg_not_now()) {
    return true;
  }

  called_emsg++;

  // If "emsg_severe" is true: When an error exception is to be thrown,
  // prefer this message over previous messages for the same command.
  bool severe = emsg_severe;
  emsg_severe = false;

  if (!emsg_off || vim_strchr((char *)p_debug, 't') != NULL) {
    // Cause a throw of an error exception if appropriate.  Don't display
    // the error message in this case.  (If no matching catch clause will
    // be found, the message will be displayed later on.)  "ignore" is set
    // when the message should be ignored completely (used for the
    // interrupt message).
    if (cause_errthrow(s, severe, &ignore)) {
      if (!ignore) {
        did_emsg = true;
      }
      return true;
    }

    // set "v:errmsg", also when using ":silent! cmd"
    set_vim_var_string(VV_ERRMSG, s, -1);

    /*
     * When using ":silent! cmd" ignore error messages.
     * But do write it to the redirection file.
     */
    if (emsg_silent != 0) {
      if (!emsg_noredir) {
        msg_start();
        char *p = get_emsg_source();
        if (p != NULL) {
          const size_t p_len = strlen(p);
          p[p_len] = '\n';
          redir_write(p, (ptrdiff_t)p_len + 1);
          xfree(p);
        }
        p = get_emsg_lnum();
        if (p != NULL) {
          const size_t p_len = strlen(p);
          p[p_len] = '\n';
          redir_write(p, (ptrdiff_t)p_len + 1);
          xfree(p);
        }
        redir_write(s, (ptrdiff_t)strlen(s));
      }

      // Log (silent) errors as debug messages.
      if (SOURCING_NAME != NULL && SOURCING_LNUM != 0) {
        DLOG("(:silent) %s (%s (line %ld))",
             s, SOURCING_NAME, (long)SOURCING_LNUM);
      } else {
        DLOG("(:silent) %s", s);
      }

      return true;
    }

    // Log editor errors as INFO.
    if (SOURCING_NAME != NULL && SOURCING_LNUM != 0) {
      ILOG("%s (%s (line %ld))", s, SOURCING_NAME, (long)SOURCING_LNUM);
    } else {
      ILOG("%s", s);
    }

    ex_exitval = 1;

    // Reset msg_silent, an error causes messages to be switched back on.
    msg_silent = 0;
    cmd_silent = false;

    if (global_busy) {        // break :global command
      global_busy++;
    }

    if (p_eb) {
      beep_flush();           // also includes flush_buffers()
    } else {
      flush_buffers(FLUSH_MINIMAL);  // flush internal buffers
    }
    did_emsg = true;               // flag for DoOneCmd()
  }

  emsg_on_display = true;     // remember there is an error message
  attr = HL_ATTR(HLF_E);      // set highlight mode for error messages
  if (msg_scrolled != 0) {
    need_wait_return = true;  // needed in case emsg() is called after
  }                           // wait_return has reset need_wait_return
                              // and a redraw is expected because
                              // msg_scrolled is non-zero
  if (msg_ext_kind == NULL) {
    msg_ext_set_kind("emsg");
  }

  // Display name and line number for the source of the error.
  // Sets "msg_scroll".
  msg_source(attr);

  // Display the error message itself.
  msg_nowait = false;  // Wait for this msg.
  return msg_attr_keep(s, attr, false, multiline);
}

/// emsg() - display an error message
///
/// Rings the bell, if appropriate, and calls message() to do the real work
/// When terminal not initialized (yet) mch_errmsg(..) is used.
///
/// @return true if wait_return not called
bool emsg(const char *s)
{
  return emsg_multiline(s, false);
}

void emsg_invreg(int name)
{
  semsg(_("E354: Invalid register name: '%s'"), transchar(name));
}

/// Print an error message with unknown number of arguments
bool semsg(const char *const fmt, ...)
  FUNC_ATTR_PRINTF(1, 2)
{
  bool ret;

  va_list ap;
  va_start(ap, fmt);
  ret = semsgv(fmt, ap);
  va_end(ap);

  return ret;
}

#define MULTILINE_BUFSIZE 8192

bool semsg_multiline(const char *const fmt, ...)
{
  bool ret;
  va_list ap;

  static char errbuf[MULTILINE_BUFSIZE];
  if (emsg_not_now()) {
    return true;
  }

  va_start(ap, fmt);
  vim_vsnprintf(errbuf, sizeof(errbuf), fmt, ap);
  va_end(ap);

  ret = emsg_multiline(errbuf, true);

  return ret;
}

/// Print an error message with unknown number of arguments
static bool semsgv(const char *fmt, va_list ap)
{
  static char errbuf[IOSIZE];
  if (emsg_not_now()) {
    return true;
  }

  vim_vsnprintf(errbuf, sizeof(errbuf), fmt, ap);

  return emsg(errbuf);
}

/// Same as emsg(...), but abort on error when ABORT_ON_INTERNAL_ERROR is
/// defined. It is used for internal errors only, so that they can be
/// detected when fuzzing vim.
void iemsg(const char *s)
{
  if (emsg_not_now()) {
    return;
  }

  emsg(s);
#ifdef ABORT_ON_INTERNAL_ERROR
  set_vim_var_string(VV_ERRMSG, s, -1);
  msg_putchar('\n');  // avoid overwriting the error message
  ui_flush();
  abort();
#endif
}

/// Same as semsg(...) but abort on error when ABORT_ON_INTERNAL_ERROR is
/// defined. It is used for internal errors only, so that they can be
/// detected when fuzzing vim.
void siemsg(const char *s, ...)
{
  if (emsg_not_now()) {
    return;
  }

  va_list ap;
  va_start(ap, s);
  (void)semsgv(s, ap);
  va_end(ap);
#ifdef ABORT_ON_INTERNAL_ERROR
  msg_putchar('\n');  // avoid overwriting the error message
  ui_flush();
  abort();
#endif
}

/// Give an "Internal error" message.
void internal_error(char *where)
{
  siemsg(_(e_intern2), where);
}

static void msg_semsg_event(void **argv)
{
  char *s = argv[0];
  (void)emsg(s);
  xfree(s);
}

void msg_schedule_semsg(const char *const fmt, ...)
  FUNC_ATTR_PRINTF(1, 2)
{
  va_list ap;
  va_start(ap, fmt);
  vim_vsnprintf((char *)IObuff, IOSIZE, fmt, ap);
  va_end(ap);

  char *s = xstrdup((char *)IObuff);
  loop_schedule_deferred(&main_loop, event_create(msg_semsg_event, 1, s));
}

/// Like msg(), but truncate to a single line if p_shm contains 't', or when
/// "force" is true.  This truncates in another way as for normal messages.
/// Careful: The string may be changed by msg_may_trunc()!
///
/// @return  a pointer to the printed message, if wait_return() not called.
char *msg_trunc_attr(char *s, bool force, int attr)
{
  int n;

  // Add message to history before truncating.
  add_msg_hist(s, -1, attr, false);

  char *ts = (char *)msg_may_trunc(force, (char_u *)s);

  msg_hist_off = true;
  n = msg_attr(ts, attr);
  msg_hist_off = false;

  if (n) {
    return ts;
  }
  return NULL;
}

/// Check if message "s" should be truncated at the start (for filenames).
///
/// @return  a pointer to where the truncated message starts.
///
/// @note: May change the message by replacing a character with '<'.
char_u *msg_may_trunc(bool force, char_u *s)
{
  int room;

  room = (Rows - cmdline_row - 1) * Columns + sc_col - 1;
  if ((force || (shortmess(SHM_TRUNC) && !exmode_active))
      && (int)STRLEN(s) - room > 0 && p_ch > 0) {
    int size = vim_strsize((char *)s);

    // There may be room anyway when there are multibyte chars.
    if (size <= room) {
      return s;
    }
    int n;
    for (n = 0; size >= room;) {
      size -= utf_ptr2cells((char *)s + n);
      n += utfc_ptr2len((char *)s + n);
    }
    n--;
    s += n;
    *s = '<';
  }
  return s;
}

void hl_msg_free(HlMessage hl_msg)
{
  for (size_t i = 0; i < kv_size(hl_msg); i++) {
    xfree(kv_A(hl_msg, i).text.data);
  }
  kv_destroy(hl_msg);
}

#define LINE_BUFFER_SIZE 4096

void add_hl_msg_hist(HlMessage hl_msg)
{
  if (kv_size(hl_msg)) {
    add_msg_hist_multiattr(NULL, 0, 0, true, hl_msg);
  }
}

/// @param[in]  len  Length of s or -1.
static void add_msg_hist(const char *s, int len, int attr, bool multiline)
{
  add_msg_hist_multiattr(s, len, attr, multiline, (HlMessage)KV_INITIAL_VALUE);
}

static void add_msg_hist_multiattr(const char *s, int len, int attr, bool multiline,
                                   HlMessage multiattr)
{
  if (msg_hist_off || msg_silent != 0) {
    hl_msg_free(multiattr);
    return;
  }

  // Don't let the message history get too big
  while (msg_hist_len > MAX_MSG_HIST_LEN) {
    (void)delete_first_msg();
  }

  // allocate an entry and add the message at the end of the history
  struct msg_hist *p = xmalloc(sizeof(struct msg_hist));
  if (s) {
    if (len < 0) {
      len = (int)STRLEN(s);
    }
    // remove leading and trailing newlines
    while (len > 0 && *s == '\n') {
      s++;
      len--;
    }
    while (len > 0 && s[len - 1] == '\n') {
      len--;
    }
    p->msg = (char_u *)xmemdupz(s, (size_t)len);
  } else {
    p->msg = NULL;
  }
  p->next = NULL;
  p->attr = attr;
  p->multiline = multiline;
  p->multiattr = multiattr;
  p->kind = msg_ext_kind;
  if (last_msg_hist != NULL) {
    last_msg_hist->next = p;
  }
  last_msg_hist = p;
  if (first_msg_hist == NULL) {
    first_msg_hist = last_msg_hist;
  }
  msg_hist_len++;
}

/// Delete the first (oldest) message from the history.
///
/// @return  FAIL if there are no messages.
int delete_first_msg(void)
{
  struct msg_hist *p;

  if (msg_hist_len <= 0) {
    return FAIL;
  }
  p = first_msg_hist;
  first_msg_hist = p->next;
  if (first_msg_hist == NULL) {  // history is becoming empty
    assert(msg_hist_len == 1);
    last_msg_hist = NULL;
  }
  xfree(p->msg);
  hl_msg_free(p->multiattr);
  xfree(p);
  msg_hist_len--;
  return OK;
}

/// :messages command implementation
void ex_messages(void *const eap_p)
  FUNC_ATTR_NONNULL_ALL
{
  const exarg_T *const eap = (const exarg_T *)eap_p;
  struct msg_hist *p;
  int c = 0;

  if (STRCMP(eap->arg, "clear") == 0) {
    int keep = eap->addr_count == 0 ? 0 : eap->line2;

    while (msg_hist_len > keep) {
      (void)delete_first_msg();
    }
    return;
  }

  if (*eap->arg != NUL) {
    emsg(_(e_invarg));
    return;
  }

  p = first_msg_hist;

  if (eap->addr_count != 0) {
    // Count total messages
    for (; p != NULL && !got_int; p = p->next) {
      c++;
    }

    c -= eap->line2;

    // Skip without number of messages specified
    for (p = first_msg_hist; p != NULL && !got_int && c > 0; p = p->next, c--) {}
  }

  // Display what was not skipped.
  if (ui_has(kUIMessages)) {
    if (msg_silent) {
      return;
    }
    Array entries = ARRAY_DICT_INIT;
    for (; p != NULL; p = p->next) {
      if (kv_size(p->multiattr) || (p->msg && p->msg[0])) {
        Array entry = ARRAY_DICT_INIT;
        ADD(entry, STRING_OBJ(cstr_to_string(p->kind)));
        Array content = ARRAY_DICT_INIT;
        if (kv_size(p->multiattr)) {
          for (uint32_t i = 0; i < kv_size(p->multiattr); i++) {
            HlMessageChunk chunk = kv_A(p->multiattr, i);
            Array content_entry = ARRAY_DICT_INIT;
            ADD(content_entry, INTEGER_OBJ(chunk.attr));
            ADD(content_entry, STRING_OBJ(copy_string(chunk.text)));
            ADD(content, ARRAY_OBJ(content_entry));
          }
        } else if (p->msg && p->msg[0]) {
          Array content_entry = ARRAY_DICT_INIT;
          ADD(content_entry, INTEGER_OBJ(p->attr));
          ADD(content_entry, STRING_OBJ(cstr_to_string((char *)(p->msg))));
          ADD(content, ARRAY_OBJ(content_entry));
        }
        ADD(entry, ARRAY_OBJ(content));
        ADD(entries, ARRAY_OBJ(entry));
      }
    }
    ui_call_msg_history_show(entries);
    api_free_array(entries);
    msg_ext_history_visible = true;
    wait_return(false);
  } else {
    msg_hist_off = true;
    for (; p != NULL && !got_int; p = p->next) {
      if (kv_size(p->multiattr)) {
        msg_multiattr(p->multiattr, p->kind, false);
      } else if (p->msg != NULL) {
        msg_attr_keep((char *)p->msg, p->attr, false, p->multiline);
      }
    }
    msg_hist_off = false;
  }
}

/// Call this after prompting the user.  This will avoid a hit-return message
/// and a delay.
void msg_end_prompt(void)
{
  msg_ext_clear_later();
  need_wait_return = false;
  emsg_on_display = false;
  cmdline_row = msg_row;
  msg_col = 0;
  msg_clr_eos();
  lines_left = -1;
}

/// Wait for the user to hit a key (normally Enter)
///
/// @param redraw  if true, redraw the entire screen NOT_VALID
///                if false, do a normal redraw
///                if -1, don't redraw at all
void wait_return(int redraw)
{
  int c;
  int oldState;
  int tmpState;
  int had_got_int;
  FILE *save_scriptout;

  if (redraw == true) {
    redraw_all_later(NOT_VALID);
  }

  // If using ":silent cmd", don't wait for a return.  Also don't set
  // need_wait_return to do it later.
  if (msg_silent != 0) {
    return;
  }

  if (headless_mode && !ui_active()) {
    return;
  }

  /*
   * When inside vgetc(), we can't wait for a typed character at all.
   * With the global command (and some others) we only need one return at
   * the end. Adjust cmdline_row to avoid the next message overwriting the
   * last one.
   */
  if (vgetc_busy > 0) {
    return;
  }
  need_wait_return = true;
  if (no_wait_return) {
    if (!exmode_active) {
      cmdline_row = msg_row;
    }
    return;
  }

  redir_off = true;             // don't redirect this message
  oldState = State;
  if (quit_more) {
    c = CAR;                    // just pretend CR was hit
    quit_more = FALSE;
    got_int = FALSE;
  } else if (exmode_active) {
    msg_puts(" ");              // make sure the cursor is on the right line
    c = CAR;                    // no need for a return in ex mode
    got_int = FALSE;
  } else {
    // Make sure the hit-return prompt is on screen when 'guioptions' was
    // just changed.
    screenalloc();

    State = MODE_HITRETURN;
    setmouse();
    cmdline_row = msg_row;
    // Avoid the sequence that the user types ":" at the hit-return prompt
    // to start an Ex command, but the file-changed dialog gets in the
    // way.
    if (need_check_timestamps) {
      check_timestamps(false);
    }

    hit_return_msg();

    do {
      // Remember "got_int", if it is set vgetc() probably returns a
      // CTRL-C, but we need to loop then.
      had_got_int = got_int;

      // Don't do mappings here, we put the character back in the
      // typeahead buffer.
      no_mapping++;
      allow_keys++;

      // Temporarily disable Recording. If Recording is active, the
      // character will be recorded later, since it will be added to the
      // typebuf after the loop
      const int save_reg_recording = reg_recording;
      save_scriptout = scriptout;
      reg_recording = 0;
      scriptout = NULL;
      c = safe_vgetc();
      if (had_got_int && !global_busy) {
        got_int = false;
      }
      no_mapping--;
      allow_keys--;
      reg_recording = save_reg_recording;
      scriptout = save_scriptout;

      /*
       * Allow scrolling back in the messages.
       * Also accept scroll-down commands when messages fill the screen,
       * to avoid that typing one 'j' too many makes the messages
       * disappear.
       */
      if (p_more) {
        if (c == 'b' || c == 'k' || c == 'u' || c == 'g'
            || c == K_UP || c == K_PAGEUP) {
          if (msg_scrolled > Rows) {
            // scroll back to show older messages
            do_more_prompt(c);
          } else {
            msg_didout = false;
            c = K_IGNORE;
            msg_col =
              cmdmsg_rl ? Columns - 1 :
              0;
          }
          if (quit_more) {
            c = CAR;                            // just pretend CR was hit
            quit_more = FALSE;
            got_int = FALSE;
          } else if (c != K_IGNORE) {
            c = K_IGNORE;
            hit_return_msg();
          }
        } else if (msg_scrolled > Rows - 2
                   && (c == 'j' || c == 'd' || c == 'f'
                       || c == K_DOWN || c == K_PAGEDOWN)) {
          c = K_IGNORE;
        }
      }
    } while ((had_got_int && c == Ctrl_C)
             || c == K_IGNORE
             || c == K_LEFTDRAG || c == K_LEFTRELEASE
             || c == K_MIDDLEDRAG || c == K_MIDDLERELEASE
             || c == K_RIGHTDRAG || c == K_RIGHTRELEASE
             || c == K_MOUSELEFT || c == K_MOUSERIGHT
             || c == K_MOUSEDOWN || c == K_MOUSEUP
             || c == K_MOUSEMOVE);
    os_breakcheck();
    /*
     * Avoid that the mouse-up event causes visual mode to start.
     */
    if (c == K_LEFTMOUSE || c == K_MIDDLEMOUSE || c == K_RIGHTMOUSE
        || c == K_X1MOUSE || c == K_X2MOUSE) {
      (void)jump_to_mouse(MOUSE_SETPOS, NULL, 0);
    } else if (vim_strchr("\r\n ", c) == NULL && c != Ctrl_C) {
      // Put the character back in the typeahead buffer.  Don't use the
      // stuff buffer, because lmaps wouldn't work.
      ins_char_typebuf(vgetc_char, vgetc_mod_mask);
      do_redraw = true;             // need a redraw even though there is
                                    // typeahead
    }
  }
  redir_off = false;

  // If the user hits ':', '?' or '/' we get a command line from the next
  // line.
  if (c == ':' || c == '?' || c == '/') {
    if (!exmode_active) {
      cmdline_row = msg_row;
    }
    skip_redraw = true;  // skip redraw once
    do_redraw = false;
    msg_ext_keep_after_cmdline = true;
  }

  // If the screen size changed screen_resize() will redraw the screen.
  // Otherwise the screen is only redrawn if 'redraw' is set and no ':'
  // typed.
  tmpState = State;
  State = oldState;  // restore State before screen_resize()
  setmouse();
  msg_check();
  need_wait_return = false;
  did_wait_return = true;
  emsg_on_display = false;      // can delete error message now
  lines_left = -1;              // reset lines_left at next msg_start()
  reset_last_sourcing();
  if (keep_msg != NULL && vim_strsize((char *)keep_msg) >=
      (Rows - cmdline_row - 1) * Columns + sc_col) {
    XFREE_CLEAR(keep_msg);          // don't redisplay message, it's too long
  }

  if (tmpState == MODE_SETWSIZE) {       // got resize event while in vgetc()
    ui_refresh();
  } else if (!skip_redraw) {
    if (redraw == true || (msg_scrolled != 0 && redraw != -1)) {
      redraw_later(curwin, VALID);
    }
    if (ui_has(kUIMessages)) {
      msg_ext_clear(true);
    }
  }
}

/// Write the hit-return prompt.
static void hit_return_msg(void)
{
  int save_p_more = p_more;

  p_more = false;       // don't want to see this message when scrolling back
  if (msg_didout) {     // start on a new line
    msg_putchar('\n');
  }
  msg_ext_set_kind("return_prompt");
  if (got_int) {
    msg_puts(_("Interrupt: "));
  }

  msg_puts_attr(_("Press ENTER or type command to continue"), HL_ATTR(HLF_R));
  if (!msg_use_printf()) {
    msg_clr_eos();
  }
  p_more = save_p_more;
}

/// Set "keep_msg" to "s".  Free the old value and check for NULL pointer.
void set_keep_msg(char *s, int attr)
{
  xfree(keep_msg);
  if (s != NULL && msg_silent == 0) {
    keep_msg = vim_strsave((char_u *)s);
  } else {
    keep_msg = NULL;
  }
  keep_msg_more = false;
  keep_msg_attr = attr;
}

void msgmore(long n)
{
  long pn;

  if (global_busy           // no messages now, wait until global is finished
      || !messaging()) {      // 'lazyredraw' set, don't do messages now
    return;
  }

  // We don't want to overwrite another important message, but do overwrite
  // a previous "more lines" or "fewer lines" message, so that "5dd" and
  // then "put" reports the last action.
  if (keep_msg != NULL && !keep_msg_more) {
    return;
  }

  if (n > 0) {
    pn = n;
  } else {
    pn = -n;
  }

  if (pn > p_report) {
    if (n > 0) {
      vim_snprintf(msg_buf, MSG_BUF_LEN,
                   NGETTEXT("%ld more line", "%ld more lines", pn),
                   pn);
    } else {
      vim_snprintf(msg_buf, MSG_BUF_LEN,
                   NGETTEXT("%ld line less", "%ld fewer lines", pn),
                   pn);
    }
    if (got_int) {
      xstrlcat(msg_buf, _(" (Interrupted)"), MSG_BUF_LEN);
    }
    if (msg(msg_buf)) {
      set_keep_msg(msg_buf, 0);
      keep_msg_more = true;
    }
  }
}

void msg_ext_set_kind(const char *msg_kind)
{
  // Don't change the label of an existing batch:
  msg_ext_ui_flush();

  // TODO(bfredl): would be nice to avoid dynamic scoping, but that would
  // need refactoring the msg_ interface to not be "please pretend nvim is
  // a terminal for a moment"
  msg_ext_kind = msg_kind;
}

/// Prepare for outputting characters in the command line.
void msg_start(void)
{
  int did_return = false;

  if (!msg_silent) {
    XFREE_CLEAR(keep_msg);              // don't display old message now
    need_fileinfo = false;
  }

  const bool no_msg_area = !ui_has_messages();

  if (need_clr_eos || (no_msg_area && redrawing_cmdline)) {
    // Halfway an ":echo" command and getting an (error) message: clear
    // any text from the command.
    need_clr_eos = false;
    msg_clr_eos();
  }

  if (!msg_scroll && full_screen) {     // overwrite last message
    msg_row = cmdline_row;
    msg_col = cmdmsg_rl ? Columns - 1 : 0;
    if (no_msg_area && get_cmdprompt() == NULL) {
      msg_row -= 1;
    }
  } else if (msg_didout || no_msg_area) {  // start message on next line
    msg_putchar('\n');
    did_return = true;
    cmdline_row = msg_row;
  }
  if (!msg_didany || lines_left < 0) {
    msg_starthere();
  }
  if (msg_silent == 0) {
    msg_didout = false;                     // no output on current line yet
  }

  if (ui_has(kUIMessages)) {
    msg_ext_ui_flush();
    if (!msg_scroll && msg_ext_visible) {
      // Will overwrite last message.
      msg_ext_overwrite = true;
    }
  }

  // When redirecting, may need to start a new line.
  if (!did_return) {
    redir_write("\n", 1);
  }
}

/// Note that the current msg position is where messages start.
void msg_starthere(void)
{
  lines_left = cmdline_row;
  msg_didany = false;
}

void msg_putchar(int c)
{
  msg_putchar_attr(c, 0);
}

void msg_putchar_attr(int c, int attr)
{
  char buf[MB_MAXBYTES + 1];

  if (IS_SPECIAL(c)) {
    buf[0] = (char)K_SPECIAL;
    buf[1] = (char)K_SECOND(c);
    buf[2] = (char)K_THIRD(c);
    buf[3] = NUL;
  } else {
    buf[utf_char2bytes(c, (char *)buf)] = NUL;
  }
  msg_puts_attr((const char *)buf, attr);
}

void msg_outnum(long n)
{
  char buf[20];

  snprintf(buf, sizeof(buf), "%ld", n);
  msg_puts(buf);
}

void msg_home_replace(char_u *fname)
{
  msg_home_replace_attr(fname, 0);
}

void msg_home_replace_hl(char_u *fname)
{
  msg_home_replace_attr(fname, HL_ATTR(HLF_D));
}

static void msg_home_replace_attr(char_u *fname, int attr)
{
  char *name = home_replace_save(NULL, (char *)fname);
  msg_outtrans_attr((char_u *)name, attr);
  xfree(name);
}

/// Output 'len' characters in 'str' (including NULs) with translation
/// if 'len' is -1, output up to a NUL character.
/// Use attributes 'attr'.
///
/// @return  the number of characters it takes on the screen.
int msg_outtrans(char *str)
{
  return msg_outtrans_attr((char_u *)str, 0);
}

int msg_outtrans_attr(const char_u *str, int attr)
{
  return msg_outtrans_len_attr(str, (int)STRLEN(str), attr);
}

int msg_outtrans_len(const char_u *str, int len)
{
  return msg_outtrans_len_attr(str, len, 0);
}

/// Output one character at "p".
/// Handles multi-byte characters.
///
/// @return  pointer to the next character.
char_u *msg_outtrans_one(char_u *p, int attr)
{
  int l;

  if ((l = utfc_ptr2len((char *)p)) > 1) {
    msg_outtrans_len_attr(p, l, attr);
    return p + l;
  }
  msg_puts_attr((const char *)transchar_byte(*p), attr);
  return p + 1;
}

int msg_outtrans_len_attr(const char_u *msgstr, int len, int attr)
{
  int retval = 0;
  const char *str = (const char *)msgstr;
  const char *plain_start = (const char *)msgstr;
  char_u *s;
  int mb_l;
  int c;
  int save_got_int = got_int;

  // Only quit when got_int was set in here.
  got_int = false;

  // if MSG_HIST flag set, add message to history
  if (attr & MSG_HIST) {
    add_msg_hist(str, len, attr, false);
    attr &= ~MSG_HIST;
  }

  // If the string starts with a composing character first draw a space on
  // which the composing char can be drawn.
  if (utf_iscomposing(utf_ptr2char((char *)msgstr))) {
    msg_puts_attr(" ", attr);
  }

  /*
   * Go over the string.  Special characters are translated and printed.
   * Normal characters are printed several at a time.
   */
  while (--len >= 0 && !got_int) {
    // Don't include composing chars after the end.
    mb_l = utfc_ptr2len_len((char_u *)str, len + 1);
    if (mb_l > 1) {
      c = utf_ptr2char(str);
      if (vim_isprintc(c)) {
        // Printable multi-byte char: count the cells.
        retval += utf_ptr2cells(str);
      } else {
        // Unprintable multi-byte char: print the printable chars so
        // far and the translation of the unprintable char.
        if (str > plain_start) {
          msg_puts_attr_len(plain_start, str - plain_start, attr);
        }
        plain_start = str + mb_l;
        msg_puts_attr((const char *)transchar(c),
                      (attr == 0 ? HL_ATTR(HLF_8) : attr));
        retval += char2cells(c);
      }
      len -= mb_l - 1;
      str += mb_l;
    } else {
      s = transchar_byte((uint8_t)(*str));
      if (s[1] != NUL) {
        // Unprintable char: print the printable chars so far and the
        // translation of the unprintable char.
        if (str > plain_start) {
          msg_puts_attr_len(plain_start, str - plain_start, attr);
        }
        plain_start = str + 1;
        msg_puts_attr((const char *)s, attr == 0 ? HL_ATTR(HLF_8) : attr);
        retval += (int)STRLEN(s);
      } else {
        retval++;
      }
      str++;
    }
  }

  if (str > plain_start && !got_int) {
    // Print the printable chars at the end.
    msg_puts_attr_len(plain_start, str - plain_start, attr);
  }

  got_int |= save_got_int;

  return retval;
}

void msg_make(char_u *arg)
{
  int i;
  static char_u *str = (char_u *)"eeffoc", *rs = (char_u *)"Plon#dqg#vxjduB";

  arg = (char_u *)skipwhite((char *)arg);
  for (i = 5; *arg && i >= 0; i--) {
    if (*arg++ != str[i]) {
      break;
    }
  }
  if (i < 0) {
    msg_putchar('\n');
    for (i = 0; rs[i]; ++i) {
      msg_putchar(rs[i] - 3);
    }
  }
}

/// Output the string 'str' up to a NUL character.
/// Return the number of characters it takes on the screen.
///
/// If K_SPECIAL is encountered, then it is taken in conjunction with the
/// following character and shown as <F1>, <S-Up> etc.  Any other character
/// which is not printable shown in <> form.
/// If 'from' is TRUE (lhs of a mapping), a space is shown as <Space>.
/// If a character is displayed in one of these special ways, is also
/// highlighted (its highlight name is '8' in the p_hl variable).
/// Otherwise characters are not highlighted.
/// This function is used to show mappings, where we want to see how to type
/// the character/string -- webb
///
/// @param from  true for LHS of a mapping
/// @param maxlen  screen columns, 0 for unlimited
int msg_outtrans_special(const char_u *strstart, bool from, int maxlen)
{
  if (strstart == NULL) {
    return 0;  // Do nothing.
  }
  const char_u *str = strstart;
  int retval = 0;
  int attr = HL_ATTR(HLF_8);

  while (*str != NUL) {
    const char *text;
    // Leading and trailing spaces need to be displayed in <> form.
    if ((str == strstart || str[1] == NUL) && *str == ' ') {
      text = "<Space>";
      str++;
    } else {
      text = str2special((const char **)&str, from, false);
    }
    if (text[0] != NUL && text[1] == NUL) {
      // single-byte character or illegal byte
      text = (char *)transchar_byte((uint8_t)text[0]);
    }
    const int len = vim_strsize((char *)text);
    if (maxlen > 0 && retval + len >= maxlen) {
      break;
    }
    // Highlight special keys
    msg_puts_attr(text, (len > 1
                         && utfc_ptr2len(text) <= 1
                         ? attr : 0));
    retval += len;
  }
  return retval;
}

/// Convert string, replacing key codes with printables
///
/// Used for lhs or rhs of mappings.
///
/// @param[in]  str  String to convert.
/// @param[in]  replace_spaces  Convert spaces into `<Space>`, normally used fo
///                             lhs, but not rhs.
/// @param[in]  replace_lt  Convert `<` into `<lt>`.
///
/// @return [allocated] Converted string.
char *str2special_save(const char *const str, const bool replace_spaces, const bool replace_lt)
  FUNC_ATTR_NONNULL_ALL FUNC_ATTR_WARN_UNUSED_RESULT FUNC_ATTR_MALLOC
  FUNC_ATTR_NONNULL_RET
{
  garray_T ga;
  ga_init(&ga, 1, 40);

  const char *p = str;
  while (*p != NUL) {
    ga_concat(&ga, str2special(&p, replace_spaces, replace_lt));
  }
  ga_append(&ga, NUL);
  return (char *)ga.ga_data;
}

/// Convert character, replacing key with printable representation.
///
/// @param[in,out]  sp  String to convert. Is advanced to the next key code.
/// @param[in]  replace_spaces  Convert spaces into <Space>, normally used for
///                             lhs, but not rhs.
/// @param[in]  replace_lt  Convert `<` into `<lt>`.
///
/// @return Converted key code, in a static buffer. Buffer is always one and the
///         same, so save converted string somewhere before running str2special
///         for the second time.
///         On illegal byte return a string with only that byte.
const char *str2special(const char **const sp, const bool replace_spaces, const bool replace_lt)
  FUNC_ATTR_NONNULL_ALL FUNC_ATTR_WARN_UNUSED_RESULT FUNC_ATTR_NONNULL_RET
{
  static char buf[7];

  {
    // Try to un-escape a multi-byte character.  Return the un-escaped
    // string if it is a multi-byte character.
    const char *const p = mb_unescape(sp);
    if (p != NULL) {
      return p;
    }
  }

  const char *str = *sp;
  int c = (uint8_t)(*str);
  int modifiers = 0;
  bool special = false;
  if (c == K_SPECIAL && str[1] != NUL && str[2] != NUL) {
    if ((uint8_t)str[1] == KS_MODIFIER) {
      modifiers = (uint8_t)str[2];
      str += 3;
      c = (uint8_t)(*str);
    }
    if (c == K_SPECIAL && str[1] != NUL && str[2] != NUL) {
      c = TO_SPECIAL((uint8_t)str[1], (uint8_t)str[2]);
      str += 2;
    }
    if (IS_SPECIAL(c) || modifiers) {  // Special key.
      special = true;
    }
  }

  if (!IS_SPECIAL(c) && MB_BYTE2LEN(c) > 1) {
    *sp = str;
    // Try to un-escape a multi-byte character after modifiers.
    const char *p = mb_unescape(sp);
    if (p != NULL) {
      // Since 'special' is true the multi-byte character 'c' will be
      // processed by get_special_key_name().
      c = utf_ptr2char(p);
    } else {
      // illegal byte
      *sp = str + 1;
    }
  } else {
    // single-byte character, NUL or illegal byte
    *sp = str + (*str == NUL ? 0 : 1);
  }

  // Make special keys and C0 control characters in <> form, also <M-Space>.
  if (special
      || c < ' '
      || (replace_spaces && c == ' ')
      || (replace_lt && c == '<')) {
    return (const char *)get_special_key_name(c, modifiers);
  }
  buf[0] = (char)c;
  buf[1] = NUL;
  return buf;
}

/// Convert string, replacing key codes with printables
///
/// @param[in]  str  String to convert.
/// @param[out]  buf  Buffer to save results to.
/// @param[in]  len  Buffer length.
void str2specialbuf(const char *sp, char *buf, size_t len)
  FUNC_ATTR_NONNULL_ALL
{
  while (*sp) {
    const char *s = str2special(&sp, false, false);
    const size_t s_len = strlen(s);
    if (len <= s_len) {
      break;
    }
    memcpy(buf, s, s_len);
    buf += s_len;
    len -= s_len;
  }
  *buf = NUL;
}

/// print line for :print or :list command
void msg_prt_line(char_u *s, int list)
{
  int c;
  int col = 0;
  int n_extra = 0;
  int c_extra = 0;
  int c_final = 0;
  char_u *p_extra = NULL;  // init to make SASC shut up
  int n;
  int attr = 0;
  char_u *lead = NULL;
  bool in_multispace = false;
  int multispace_pos = 0;
  char_u *trail = NULL;
  int l;

  if (curwin->w_p_list) {
    list = true;
  }

  if (list) {
    // find start of trailing whitespace
    if (curwin->w_p_lcs_chars.trail) {
      trail = s + STRLEN(s);
      while (trail > s && ascii_iswhite(trail[-1])) {
        trail--;
      }
    }
    // find end of leading whitespace
    if (curwin->w_p_lcs_chars.lead || curwin->w_p_lcs_chars.leadmultispace != NULL) {
      lead = s;
      while (ascii_iswhite(lead[0])) {
        lead++;
      }
      // in a line full of spaces all of them are treated as trailing
      if (*lead == NUL) {
        lead = NULL;
      }
    }
  }

  // output a space for an empty line, otherwise the line will be overwritten
  if (*s == NUL && !(list && curwin->w_p_lcs_chars.eol != NUL)) {
    msg_putchar(' ');
  }

  while (!got_int) {
    if (n_extra > 0) {
      n_extra--;
      if (n_extra == 0 && c_final) {
        c = c_final;
      } else if (c_extra) {
        c = c_extra;
      } else {
        assert(p_extra != NULL);
        c = *p_extra++;
      }
    } else if ((l = utfc_ptr2len((char *)s)) > 1) {
      col += utf_ptr2cells((char *)s);
      char buf[MB_MAXBYTES + 1];
      if (l >= MB_MAXBYTES) {
        xstrlcpy(buf, "?", sizeof(buf));
      } else if (curwin->w_p_lcs_chars.nbsp != NUL && list
                 && (utf_ptr2char((char *)s) == 160
                     || utf_ptr2char((char *)s) == 0x202f)) {
        int len = utf_char2bytes(curwin->w_p_lcs_chars.nbsp, buf);
        buf[len] = NUL;
      } else {
        memmove(buf, s, (size_t)l);
        buf[l] = NUL;
      }
      msg_puts(buf);
      s += l;
      continue;
    } else {
      attr = 0;
      c = *s++;
      in_multispace = c == ' ' && ((col > 0 && s[-2] == ' ') || *s == ' ');
      if (!in_multispace) {
        multispace_pos = 0;
      }
      if (c == TAB && (!list || curwin->w_p_lcs_chars.tab1)) {
        // tab amount depends on current column
        n_extra = tabstop_padding(col,
                                  curbuf->b_p_ts,
                                  curbuf->b_p_vts_array) - 1;
        if (!list) {
          c = ' ';
          c_extra = ' ';
          c_final = NUL;
        } else {
          c = (n_extra == 0 && curwin->w_p_lcs_chars.tab3)
              ? curwin->w_p_lcs_chars.tab3
              : curwin->w_p_lcs_chars.tab1;
          c_extra = curwin->w_p_lcs_chars.tab2;
          c_final = curwin->w_p_lcs_chars.tab3;
          attr = HL_ATTR(HLF_0);
        }
      } else if (c == 160 && list && curwin->w_p_lcs_chars.nbsp != NUL) {
        c = curwin->w_p_lcs_chars.nbsp;
        attr = HL_ATTR(HLF_0);
      } else if (c == NUL && list && curwin->w_p_lcs_chars.eol != NUL) {
        p_extra = (char_u *)"";
        c_extra = NUL;
        c_final = NUL;
        n_extra = 1;
        c = curwin->w_p_lcs_chars.eol;
        attr = HL_ATTR(HLF_AT);
        s--;
      } else if (c != NUL && (n = byte2cells(c)) > 1) {
        n_extra = n - 1;
        p_extra = transchar_byte(c);
        c_extra = NUL;
        c_final = NUL;
        c = *p_extra++;
        // Use special coloring to be able to distinguish <hex> from
        // the same in plain text.
        attr = HL_ATTR(HLF_0);
      } else if (c == ' ') {
        if (list && lead != NULL && s <= lead && in_multispace
            && curwin->w_p_lcs_chars.leadmultispace != NULL) {
          c = curwin->w_p_lcs_chars.leadmultispace[multispace_pos++];
          if (curwin->w_p_lcs_chars.leadmultispace[multispace_pos] == NUL) {
            multispace_pos = 0;
          }
          attr = HL_ATTR(HLF_0);
        } else if (lead != NULL && s <= lead && curwin->w_p_lcs_chars.lead != NUL) {
          c = curwin->w_p_lcs_chars.lead;
          attr = HL_ATTR(HLF_0);
        } else if (trail != NULL && s > trail) {
          c = curwin->w_p_lcs_chars.trail;
          attr = HL_ATTR(HLF_0);
        } else if (list && in_multispace
                   && curwin->w_p_lcs_chars.multispace != NULL) {
          c = curwin->w_p_lcs_chars.multispace[multispace_pos++];
          if (curwin->w_p_lcs_chars.multispace[multispace_pos] == NUL) {
            multispace_pos = 0;
          }
          attr = HL_ATTR(HLF_0);
        } else if (list && curwin->w_p_lcs_chars.space != NUL) {
          c = curwin->w_p_lcs_chars.space;
          attr = HL_ATTR(HLF_0);
        }
      }
    }

    if (c == NUL) {
      break;
    }

    msg_putchar_attr(c, attr);
    col++;
  }
  msg_clr_eos();
}

/// Use grid_puts() to output one multi-byte character.
///
/// @return  the pointer "s" advanced to the next character.
static char_u *screen_puts_mbyte(char_u *s, int l, int attr)
{
  int cw;
  attr = hl_combine_attr(HL_ATTR(HLF_MSG), attr);

  msg_didout = true;            // remember that line is not empty
  cw = utf_ptr2cells((char *)s);
  if (cw > 1
      && (cmdmsg_rl ? msg_col <= 1 : msg_col == Columns - 1)) {
    // Doesn't fit, print a highlighted '>' to fill it up.
    msg_screen_putchar('>', HL_ATTR(HLF_AT));
    return s;
  }

  grid_puts_len(&msg_grid_adj, s, l, msg_row, msg_col, attr);
  if (cmdmsg_rl) {
    msg_col -= cw;
    if (msg_col == 0) {
      msg_col = Columns;
      msg_row++;
    }
  } else {
    msg_col += cw;
    if (msg_col >= Columns) {
      msg_col = 0;
      msg_row++;
    }
  }
  return s + l;
}

/// Output a string to the screen at position msg_row, msg_col.
/// Update msg_row and msg_col for the next message.
void msg_puts(const char *s)
{
  msg_puts_attr(s, 0);
}

void msg_puts_title(const char *s)
{
  msg_puts_attr(s, HL_ATTR(HLF_T));
}

/// Show a message in such a way that it always fits in the line.  Cut out a
/// part in the middle and replace it with "..." when necessary.
/// Does not handle multi-byte characters!
void msg_outtrans_long_attr(char_u *longstr, int attr)
{
  msg_outtrans_long_len_attr(longstr, (int)STRLEN(longstr), attr);
}

void msg_outtrans_long_len_attr(char_u *longstr, int len, int attr)
{
  int slen = len;
  int room;

  room = Columns - msg_col;
  if (len > room && room >= 20) {
    slen = (room - 3) / 2;
    msg_outtrans_len_attr(longstr, slen, attr);
    msg_puts_attr("...", HL_ATTR(HLF_8));
  }
  msg_outtrans_len_attr(longstr + len - slen, slen, attr);
}

/// Basic function for writing a message with highlight attributes.
void msg_puts_attr(const char *const s, const int attr)
{
  msg_puts_attr_len(s, -1, attr);
}

/// Write a message with highlight attributes
///
/// @param[in]  str  NUL-terminated message string.
/// @param[in]  len  Length of the string or -1.
/// @param[in]  attr  Highlight attribute.
void msg_puts_attr_len(const char *const str, const ptrdiff_t len, int attr)
  FUNC_ATTR_NONNULL_ALL
{
  assert(len < 0 || memchr(str, 0, (size_t)len) == NULL);
  // If redirection is on, also write to the redirection file.
  redir_write(str, len);

  // Don't print anything when using ":silent cmd".
  if (msg_silent != 0) {
    return;
  }

  // if MSG_HIST flag set, add message to history
  if (attr & MSG_HIST) {
    add_msg_hist(str, (int)len, attr, false);
    attr &= ~MSG_HIST;
  }

  // When writing something to the screen after it has scrolled, requires a
  // wait-return prompt later.  Needed when scrolling, resetting
  // need_wait_return after some prompt, and then outputting something
  // without scrolling
  // Not needed when only using CR to move the cursor.
  bool overflow = false;
  if (ui_has(kUIMessages)) {
    int count = msg_ext_visible + (msg_ext_overwrite ? 0 : 1);
    // TODO(bfredl): possible extension point, let external UI control this
    if (count > 1) {
      overflow = true;
    }
  } else {
    overflow = msg_scrolled != 0;
  }

  if (overflow && !msg_scrolled_ign && strcmp(str, "\r") != 0) {
    need_wait_return = true;
  }
  msg_didany = true;  // remember that something was outputted

  // If there is no valid screen, use fprintf so we can see error messages.
  // If termcap is not active, we may be writing in an alternate console
  // window, cursor positioning may not work correctly (window size may be
  // different, e.g. for Win32 console) or we just don't know where the
  // cursor is.
  if (msg_use_printf()) {
    int saved_msg_col = msg_col;
    msg_puts_printf(str, len);
    if (headless_mode) {
      msg_col = saved_msg_col;
    }
  }
  if (!msg_use_printf() || (headless_mode && default_grid.chars)) {
    msg_puts_display((const char_u *)str, (int)len, attr, false);
  }

  need_fileinfo = false;
}

/// Print a formatted message
///
/// Message printed is limited by #IOSIZE. Must not be used from inside
/// msg_puts_attr().
///
/// @param[in]  attr  Highlight attributes.
/// @param[in]  fmt  Format string.
void msg_printf_attr(const int attr, const char *const fmt, ...)
  FUNC_ATTR_NONNULL_ARG(2) FUNC_ATTR_PRINTF(2, 3)
{
  static char msgbuf[IOSIZE];

  va_list ap;
  va_start(ap, fmt);
  const size_t len = (size_t)vim_vsnprintf(msgbuf, sizeof(msgbuf), fmt, ap);
  va_end(ap);

  msg_scroll = true;
  msg_puts_attr_len(msgbuf, (ptrdiff_t)len, attr);
}

static void msg_ext_emit_chunk(void)
{
  // Color was changed or a message flushed, end current chunk.
  if (msg_ext_last_attr == -1) {
    return;  // no chunk
  }
  Array chunk = ARRAY_DICT_INIT;
  ADD(chunk, INTEGER_OBJ(msg_ext_last_attr));
  msg_ext_last_attr = -1;
  String text = ga_take_string(&msg_ext_last_chunk);
  ADD(chunk, STRING_OBJ(text));
  ADD(msg_ext_chunks, ARRAY_OBJ(chunk));
}

/// The display part of msg_puts_attr_len().
/// May be called recursively to display scroll-back text.
static void msg_puts_display(const char_u *str, int maxlen, int attr, int recurse)
{
  const char_u *s = str;
  const char_u *t_s = str;  // String from "t_s" to "s" is still todo.
  int t_col = 0;  // Screen cells todo, 0 when "t_s" not used.
  int l;
  int cw;
  const char *sb_str = (char *)str;
  int sb_col = msg_col;
  int wrap;
  int did_last_char;

  did_wait_return = false;

  if (ui_has(kUIMessages)) {
    if (attr != msg_ext_last_attr) {
      msg_ext_emit_chunk();
      msg_ext_last_attr = attr;
    }
    // Concat pieces with the same highlight
    size_t len = STRNLEN(str, maxlen);             // -V781
    ga_concat_len(&msg_ext_last_chunk, (char *)str, len);
    msg_ext_cur_len += len;
    return;
  }

  msg_grid_validate();

  cmdline_was_last_drawn = redrawing_cmdline;

  while ((maxlen < 0 || (int)(s - str) < maxlen) && *s != NUL) {
    // We are at the end of the screen line when:
    // - When outputting a newline.
    // - When outputting a character in the last column.
    if (!recurse && msg_row >= Rows - 1
        && (*s == '\n' || (cmdmsg_rl
                           ? (msg_col <= 1
                              || (*s == TAB && msg_col <= 7)
                              || (utf_ptr2cells((char *)s) > 1
                                  && msg_col <= 2))
                           : ((*s != '\r' && msg_col + t_col >= Columns - 1)
                              || (*s == TAB
                                  && msg_col + t_col >= ((Columns - 1) & ~7))
                              || (utf_ptr2cells((char *)s) > 1
                                  && msg_col + t_col >= Columns - 2))))) {
      // The screen is scrolled up when at the last row (some terminals
      // scroll automatically, some don't.  To avoid problems we scroll
      // ourselves).
      if (t_col > 0) {
        // output postponed text
        t_puts(&t_col, t_s, s, attr);
      }

      // When no more prompt and no more room, truncate here
      if (msg_no_more && lines_left == 0) {
        break;
      }

      // Scroll the screen up one line.
      bool has_last_char = (*s >= ' ' && !cmdmsg_rl);
      msg_scroll_up(!has_last_char);

      msg_row = Rows - 2;
      if (msg_col >= Columns) {         // can happen after screen resize
        msg_col = Columns - 1;
      }

      // Display char in last column before showing more-prompt.
      if (has_last_char) {
        if (maxlen >= 0) {
          // Avoid including composing chars after the end.
          l = utfc_ptr2len_len(s, (int)((str + maxlen) - s));
        } else {
          l = utfc_ptr2len((char *)s);
        }
        s = screen_puts_mbyte((char_u *)s, l, attr);
        did_last_char = true;
      } else {
        did_last_char = false;
      }

      // Tricky: if last cell will be written, delay the throttle until
      // after the first scroll. Otherwise we would need to keep track of it.
      if (has_last_char && msg_do_throttle()) {
        if (!msg_grid.throttled) {
          msg_grid_scroll_discount++;
        }
        msg_grid.throttled = true;
      }

      if (p_more) {
        // Store text for scrolling back.
        store_sb_text((char **)&sb_str, (char *)s, attr, &sb_col, true);
      }

      inc_msg_scrolled();
      need_wait_return = true;       // may need wait_return in main()
      redraw_cmdline = true;
      if (cmdline_row > 0 && !exmode_active) {
        cmdline_row--;
      }

      /*
       * If screen is completely filled and 'more' is set then wait
       * for a character.
       */
      if (lines_left > 0) {
        lines_left--;
      }
      if (p_more && lines_left == 0 && State != MODE_HITRETURN
          && !msg_no_more && !exmode_active) {
        if (do_more_prompt(NUL)) {
          s = confirm_msg_tail;
        }
        if (quit_more) {
          return;
        }
      }

      // When we displayed a char in last column need to check if there
      // is still more.
      if (did_last_char) {
        continue;
      }
    }

    wrap = *s == '\n'
           || msg_col + t_col >= Columns
           || (utf_ptr2cells((char *)s) > 1
               && msg_col + t_col >= Columns - 1)
    ;
    if (t_col > 0 && (wrap || *s == '\r' || *s == '\b'
                      || *s == '\t' || *s == BELL)) {
      // Output any postponed text.
      t_puts(&t_col, t_s, s, attr);
    }

    if (wrap && p_more && !recurse) {
      // Store text for scrolling back.
      store_sb_text((char **)&sb_str, (char *)s, attr, &sb_col, true);
    }

    if (*s == '\n') {               // go to next line
      msg_didout = false;           // remember that line is empty
      if (cmdmsg_rl) {
        msg_col = Columns - 1;
      } else {
        msg_col = 0;
      }
      if (++msg_row >= Rows) {        // safety check
        msg_row = Rows - 1;
      }
    } else if (*s == '\r') {      // go to column 0
      msg_col = 0;
    } else if (*s == '\b') {      // go to previous char
      if (msg_col) {
        msg_col--;
      }
    } else if (*s == TAB) {       // translate Tab into spaces
      do {
        msg_screen_putchar(' ', attr);
      } while (msg_col & 7);
    } else if (*s == BELL) {  // beep (from ":sh")
      vim_beep(BO_SH);
    } else if (*s >= 0x20) {  // printable char
      cw = utf_ptr2cells((char *)s);
      if (maxlen >= 0) {
        // avoid including composing chars after the end
        l = utfc_ptr2len_len(s, (int)((str + maxlen) - s));
      } else {
        l = utfc_ptr2len((char *)s);
      }
      // When drawing from right to left or when a double-wide character
      // doesn't fit, draw a single character here.  Otherwise collect
      // characters and draw them all at once later.
      if (cmdmsg_rl || (cw > 1 && msg_col + t_col >= Columns - 1)) {
        if (l > 1) {
          s = screen_puts_mbyte((char_u *)s, l, attr) - 1;
        } else {
          msg_screen_putchar(*s, attr);
        }
      } else {
        // postpone this character until later
        if (t_col == 0) {
          t_s = s;
        }
        t_col += cw;
        s += l - 1;
      }
    }
    s++;
  }

  // Output any postponed text.
  if (t_col > 0) {
    t_puts(&t_col, t_s, s, attr);
  }
  if (p_more && !recurse) {
    store_sb_text((char **)&sb_str, (char *)s, attr, &sb_col, false);
  }

  msg_check();
}

/// @return  true when ":filter pattern" was used and "msg" does not match
///          "pattern".
bool message_filtered(char_u *msg)
{
  if (cmdmod.cmod_filter_regmatch.regprog == NULL) {
    return false;
  }

  bool match = vim_regexec(&cmdmod.cmod_filter_regmatch, (char *)msg, (colnr_T)0);
  return cmdmod.cmod_filter_force ? match : !match;
}

/// including horizontal separator
int msg_scrollsize(void)
{
  return msg_scrolled + (int)p_ch + 1;
}

bool msg_use_msgsep(void)
{
  // the full-screen scroll behavior doesn't really make sense with
  // 'ext_multigrid'
  return ((dy_flags & DY_MSGSEP) || ui_has(kUIMultigrid));
}

bool msg_do_throttle(void)
{
  return msg_use_grid() && !(rdb_flags & RDB_NOTHROTTLE);
}

/// Scroll the screen up one line for displaying the next message line.
void msg_scroll_up(bool may_throttle)
{
  if (may_throttle && msg_do_throttle()) {
    msg_grid.throttled = true;
  }
  msg_did_scroll = true;
  if (msg_use_msgsep()) {
    if (msg_grid_pos > 0) {
      msg_grid_set_pos(msg_grid_pos - 1, true);
    } else {
      grid_del_lines(&msg_grid, 0, 1, msg_grid.rows, 0, msg_grid.cols);
      memmove(msg_grid.dirty_col, msg_grid.dirty_col + 1,
              (size_t)(msg_grid.rows - 1) * sizeof(*msg_grid.dirty_col));
      msg_grid.dirty_col[msg_grid.rows - 1] = 0;
    }
  } else {
    grid_del_lines(&msg_grid_adj, 0, 1, Rows, 0, Columns);
  }

  grid_fill(&msg_grid_adj, Rows - 1, Rows, 0, Columns, ' ', ' ',
            HL_ATTR(HLF_MSG));
}

/// Send throttled message output to UI clients
///
/// The way message.c uses the grid_xx family of functions is quite inefficient
/// relative to the "gridline" UI protocol used by TUI and modern clients.
/// For instance scrolling is done one line at a time. By throttling drawing
/// on the message grid, we can coalesce scrolling to a single grid_scroll
/// per screen update.
///
/// NB: The bookkeeping is quite messy, and rests on a bunch of poorly
/// documented assumptions. For instance that the message area always grows
/// while being throttled, messages are only being output on the last line
/// etc.
///
/// Probably message scrollback storage should be reimplemented as a
/// file_buffer, and message scrolling in TUI be reimplemented as a modal
/// floating window. Then we get throttling "for free" using standard
/// redraw_later code paths.
void msg_scroll_flush(void)
{
  if (msg_grid.throttled) {
    msg_grid.throttled = false;
    int pos_delta = msg_grid_pos_at_flush - msg_grid_pos;
    assert(pos_delta >= 0);
    int delta = MIN(msg_scrolled - msg_scrolled_at_flush, msg_grid.rows);

    if (pos_delta > 0) {
      ui_ext_msg_set_pos(msg_grid_pos, true);
    }

    int to_scroll = delta - pos_delta - msg_grid_scroll_discount;
    assert(to_scroll >= 0);

    // TODO(bfredl): msg_grid_pos should be 0 already when starting scrolling
    // but this sometimes fails in "headless" message printing.
    if (to_scroll > 0 && msg_grid_pos == 0) {
      ui_call_grid_scroll(msg_grid.handle, 0, Rows, 0, Columns, to_scroll, 0);
    }

    for (int i = MAX(Rows - MAX(delta, 1), 0); i < Rows; i++) {
      int row = i - msg_grid_pos;
      assert(row >= 0);
      ui_line(&msg_grid, row, 0, msg_grid.dirty_col[row], msg_grid.cols,
              HL_ATTR(HLF_MSG), false);
      msg_grid.dirty_col[row] = 0;
    }
  }
  msg_scrolled_at_flush = msg_scrolled;
  msg_grid_scroll_discount = 0;
  msg_grid_pos_at_flush = msg_grid_pos;
}

void msg_reset_scroll(void)
{
  if (ui_has(kUIMessages)) {
    msg_ext_clear(true);
    return;
  }
  // TODO(bfredl): some duplicate logic with update_screen(). Later on
  // we should properly disentangle message clear with full screen redraw.
  if (msg_use_grid()) {
    msg_grid.throttled = false;
    // TODO(bfredl): risk for extra flicker i e with
    // "nvim -o has_swap also_has_swap"
    msg_grid_set_pos(Rows - (int)p_ch, false);
    clear_cmdline = true;
    if (msg_grid.chars) {
      // non-displayed part of msg_grid is considered invalid.
      for (int i = 0; i < MIN(msg_scrollsize(), msg_grid.rows); i++) {
        grid_clear_line(&msg_grid, msg_grid.line_offset[i],
                        msg_grid.cols, false);
      }
    }
  } else {
    redraw_all_later(NOT_VALID);
  }
  msg_scrolled = 0;
  msg_scrolled_at_flush = 0;
}

/// Increment "msg_scrolled".
static void inc_msg_scrolled(void)
{
  if (*get_vim_var_str(VV_SCROLLSTART) == NUL) {
    char *p = SOURCING_NAME;
    char *tofree = NULL;

    // v:scrollstart is empty, set it to the script/function name and line
    // number
    if (p == NULL) {
      p = _("Unknown");
    } else {
      size_t len = strlen(p) + 40;
      tofree = xmalloc(len);
      vim_snprintf(tofree, len, _("%s line %" PRId64),
                   p, (int64_t)SOURCING_LNUM);
      p = tofree;
    }
    set_vim_var_string(VV_SCROLLSTART, p, -1);
    xfree(tofree);
  }
  msg_scrolled++;
  if (must_redraw < VALID) {
    must_redraw = VALID;
  }
}

static msgchunk_T *last_msgchunk = NULL;  // last displayed text

typedef enum {
  SB_CLEAR_NONE = 0,
  SB_CLEAR_ALL,
  SB_CLEAR_CMDLINE_BUSY,
  SB_CLEAR_CMDLINE_DONE,
} sb_clear_T;

// When to clear text on next msg.
static sb_clear_T do_clear_sb_text = SB_CLEAR_NONE;

/// Store part of a printed message for displaying when scrolling back.
///
/// @param sb_str  start of string
/// @param s  just after string
/// @param finish  line ends
static void store_sb_text(char **sb_str, char *s, int attr, int *sb_col, int finish)
{
  msgchunk_T *mp;

  if (do_clear_sb_text == SB_CLEAR_ALL
      || do_clear_sb_text == SB_CLEAR_CMDLINE_DONE) {
    clear_sb_text(do_clear_sb_text == SB_CLEAR_ALL);
    msg_sb_eol();  // prevent messages from overlapping
    do_clear_sb_text = SB_CLEAR_NONE;
  }

  if (s > *sb_str) {
    mp = xmalloc((sizeof(msgchunk_T) + (size_t)(s - *sb_str)));
    mp->sb_eol = (char)finish;
    mp->sb_msg_col = *sb_col;
    mp->sb_attr = attr;
    memcpy(mp->sb_text, *sb_str, (size_t)(s - *sb_str));
    mp->sb_text[s - *sb_str] = NUL;

    if (last_msgchunk == NULL) {
      last_msgchunk = mp;
      mp->sb_prev = NULL;
    } else {
      mp->sb_prev = last_msgchunk;
      last_msgchunk->sb_next = mp;
      last_msgchunk = mp;
    }
    mp->sb_next = NULL;
  } else if (finish && last_msgchunk != NULL) {
    last_msgchunk->sb_eol = TRUE;
  }

  *sb_str = s;
  *sb_col = 0;
}

/// Finished showing messages, clear the scroll-back text on the next message.
void may_clear_sb_text(void)
{
  do_clear_sb_text = SB_CLEAR_ALL;
}

/// Starting to edit the command line: do not clear messages now.
void sb_text_start_cmdline(void)
{
  if (do_clear_sb_text == SB_CLEAR_CMDLINE_BUSY) {
    // Invoking command line recursively: the previous-level command line
    // doesn't need to be remembered as it will be redrawn when returning
    // to that level.
    sb_text_restart_cmdline();
  } else {
    msg_sb_eol();
    do_clear_sb_text = SB_CLEAR_CMDLINE_BUSY;
  }
}

/// Redrawing the command line: clear the last unfinished line.
void sb_text_restart_cmdline(void)
{
  // Needed when returning from nested command line.
  do_clear_sb_text = SB_CLEAR_CMDLINE_BUSY;

  if (last_msgchunk == NULL || last_msgchunk->sb_eol) {
    // No unfinished line: don't clear anything.
    return;
  }

  msgchunk_T *tofree = msg_sb_start(last_msgchunk);
  last_msgchunk = tofree->sb_prev;
  if (last_msgchunk != NULL) {
    last_msgchunk->sb_next = NULL;
  }
  while (tofree != NULL) {
    msgchunk_T *tofree_next = tofree->sb_next;
    xfree(tofree);
    tofree = tofree_next;
  }
}

/// Ending to edit the command line: clear old lines but the last one later.
void sb_text_end_cmdline(void)
{
  do_clear_sb_text = SB_CLEAR_CMDLINE_DONE;
}

/// Clear any text remembered for scrolling back.
/// When "all" is FALSE keep the last line.
/// Called when redrawing the screen.
void clear_sb_text(int all)
{
  msgchunk_T *mp;
  msgchunk_T **lastp;

  if (all) {
    lastp = &last_msgchunk;
  } else {
    if (last_msgchunk == NULL) {
      return;
    }
    lastp = &msg_sb_start(last_msgchunk)->sb_prev;
  }

  while (*lastp != NULL) {
    mp = (*lastp)->sb_prev;
    xfree(*lastp);
    *lastp = mp;
  }
}

/// "g<" command.
void show_sb_text(void)
{
  msgchunk_T *mp;

  // Only show something if there is more than one line, otherwise it looks
  // weird, typing a command without output results in one line.
  mp = msg_sb_start(last_msgchunk);
  if (mp == NULL || mp->sb_prev == NULL) {
    vim_beep(BO_MESS);
  } else {
    do_more_prompt('G');
    wait_return(FALSE);
  }
}

/// Move to the start of screen line in already displayed text.
static msgchunk_T *msg_sb_start(msgchunk_T *mps)
{
  msgchunk_T *mp = mps;

  while (mp != NULL && mp->sb_prev != NULL && !mp->sb_prev->sb_eol) {
    mp = mp->sb_prev;
  }
  return mp;
}

/// Mark the last message chunk as finishing the line.
void msg_sb_eol(void)
{
  if (last_msgchunk != NULL) {
    last_msgchunk->sb_eol = TRUE;
  }
}

/// Display a screen line from previously displayed text at row "row".
///
/// @return  a pointer to the text for the next line (can be NULL).
static msgchunk_T *disp_sb_line(int row, msgchunk_T *smp)
{
  msgchunk_T *mp = smp;
  char_u *p;

  for (;;) {
    msg_row = row;
    msg_col = mp->sb_msg_col;
    p = mp->sb_text;
    if (*p == '\n') {       // don't display the line break
      p++;
    }
    msg_puts_display(p, -1, mp->sb_attr, TRUE);
    if (mp->sb_eol || mp->sb_next == NULL) {
      break;
    }
    mp = mp->sb_next;
  }

  return mp->sb_next;
}

/// Output any postponed text for msg_puts_attr_len().
static void t_puts(int *t_col, const char_u *t_s, const char_u *s, int attr)
{
  attr = hl_combine_attr(HL_ATTR(HLF_MSG), attr);
  // Output postponed text.
  msg_didout = true;  // Remember that line is not empty.
  grid_puts_len(&msg_grid_adj, (char_u *)t_s, (int)(s - t_s), msg_row, msg_col,
                attr);
  msg_col += *t_col;
  *t_col = 0;
  // If the string starts with a composing character don't increment the
  // column position for it.
  if (utf_iscomposing(utf_ptr2char((char *)t_s))) {
    msg_col--;
  }
  if (msg_col >= Columns) {
    msg_col = 0;
    msg_row++;
  }
}

/// @return  TRUE when messages should be printed to stdout/stderr:
///          - "batch mode" ("silent mode", -es/-Es)
///          - no UI and not embedded
int msg_use_printf(void)
{
  return !embedded_mode && !ui_active();
}

/// Print a message when there is no valid screen.
static void msg_puts_printf(const char *str, const ptrdiff_t maxlen)
{
  const char *s = str;
  char buf[7];
  char *p;

  if (on_print.type != kCallbackNone) {
    typval_T argv[1];
    argv[0].v_type = VAR_STRING;
    argv[0].v_lock = VAR_UNLOCKED;
    argv[0].vval.v_string = (char *)str;
    typval_T rettv = TV_INITIAL_VALUE;
    callback_call(&on_print, 1, argv, &rettv);
    tv_clear(&rettv);
    return;
  }

  while ((maxlen < 0 || s - str < maxlen) && *s != NUL) {
    int len = utf_ptr2len(s);
    if (!(silent_mode && p_verbose == 0)) {
      // NL --> CR NL translation (for Unix, not for "--version")
      p = &buf[0];
      if (*s == '\n' && !info_message) {
        *p++ = '\r';
      }
      memcpy(p, s, (size_t)len);
      *(p + len) = '\0';
      if (info_message) {
        mch_msg(buf);
      } else {
        mch_errmsg(buf);
      }
    }

    int cw = utf_char2cells(utf_ptr2char(s));
    // primitive way to compute the current column
    if (cmdmsg_rl) {
      if (*s == '\r' || *s == '\n') {
        msg_col = Columns - 1;
      } else {
        msg_col -= cw;
      }
    } else {
      if (*s == '\r' || *s == '\n') {
        msg_col = 0;
      } else {
        msg_col += cw;
      }
    }
    s += len;
  }
  msg_didout = true;  // assume that line is not empty
}

/// Show the more-prompt and handle the user response.
/// This takes care of scrolling back and displaying previously displayed text.
/// When at hit-enter prompt "typed_char" is the already typed character,
/// otherwise it's NUL.
///
/// @return  TRUE when jumping ahead to "confirm_msg_tail".
static int do_more_prompt(int typed_char)
{
  static bool entered = false;
  int used_typed_char = typed_char;
  int oldState = State;
  int c;
  int retval = FALSE;
  int toscroll;
  bool to_redraw = false;
  msgchunk_T *mp_last = NULL;
  msgchunk_T *mp;
  int i;

  // If headless mode is enabled and no input is required, this variable
  // will be true. However If server mode is enabled, the message "--more--"
  // should be displayed.
  bool no_need_more = headless_mode && !embedded_mode;

  // We get called recursively when a timer callback outputs a message. In
  // that case don't show another prompt. Also when at the hit-Enter prompt
  // and nothing was typed.
  if (no_need_more || entered || (State == MODE_HITRETURN && typed_char == 0)) {
    return false;
  }
  entered = true;

  if (typed_char == 'G') {
    // "g<": Find first line on the last page.
    mp_last = msg_sb_start(last_msgchunk);
    for (i = 0; i < Rows - 2 && mp_last != NULL
         && mp_last->sb_prev != NULL; ++i) {
      mp_last = msg_sb_start(mp_last->sb_prev);
    }
  }

  State = MODE_ASKMORE;
  setmouse();
  if (typed_char == NUL) {
    msg_moremsg(FALSE);
  }
  for (;;) {
    /*
     * Get a typed character directly from the user.
     */
    if (used_typed_char != NUL) {
      c = used_typed_char;              // was typed at hit-enter prompt
      used_typed_char = NUL;
    } else {
      c = get_keystroke(resize_events);
    }

    toscroll = 0;
    switch (c) {
    case BS:                    // scroll one line back
    case K_BS:
    case 'k':
    case K_UP:
      toscroll = -1;
      break;

    case CAR:                   // one extra line
    case NL:
    case 'j':
    case K_DOWN:
      toscroll = 1;
      break;

    case 'u':                   // Up half a page
      toscroll = -(Rows / 2);
      break;

    case 'd':                   // Down half a page
      toscroll = Rows / 2;
      break;

    case 'b':                   // one page back
    case K_PAGEUP:
      toscroll = -(Rows - 1);
      break;

    case ' ':                   // one extra page
    case 'f':
    case K_PAGEDOWN:
    case K_LEFTMOUSE:
      toscroll = Rows - 1;
      break;

    case 'g':                   // all the way back to the start
      toscroll = -999999;
      break;

    case 'G':                   // all the way to the end
      toscroll = 999999;
      lines_left = 999999;
      break;

    case ':':                   // start new command line
      if (!confirm_msg_used) {
        // Since got_int is set all typeahead will be flushed, but we
        // want to keep this ':', remember that in a special way.
        typeahead_noflush(':');
        cmdline_row = Rows - 1;                 // put ':' on this line
        skip_redraw = true;                     // skip redraw once
        need_wait_return = false;               // don't wait in main()
      }
      FALLTHROUGH;
    case 'q':                   // quit
    case Ctrl_C:
    case ESC:
      if (confirm_msg_used) {
        // Jump to the choices of the dialog.
        retval = TRUE;
      } else {
        got_int = TRUE;
        quit_more = TRUE;
      }
      // When there is some more output (wrapping line) display that
      // without another prompt.
      lines_left = Rows - 1;
      break;

    case K_EVENT:
      // only resize_events are processed here
      // Attempt to redraw the screen. sb_text doesn't support reflow
      // so this only really works for vertical resize.
      multiqueue_process_events(resize_events);
      to_redraw = true;
      break;

    default:                    // no valid response
      msg_moremsg(TRUE);
      continue;
    }

    // code assumes we only do one at a time
    assert((toscroll == 0) || !to_redraw);

    if (toscroll != 0 || to_redraw) {
      if (toscroll < 0 || to_redraw) {
        // go to start of last line
        if (mp_last == NULL) {
          mp = msg_sb_start(last_msgchunk);
        } else if (mp_last->sb_prev != NULL) {
          mp = msg_sb_start(mp_last->sb_prev);
        } else {
          mp = NULL;
        }

        // go to start of line at top of the screen
        for (i = 0; i < Rows - 2 && mp != NULL && mp->sb_prev != NULL;
             ++i) {
          mp = msg_sb_start(mp->sb_prev);
        }

        if (mp != NULL && (mp->sb_prev != NULL || to_redraw)) {
          // Find line to be displayed at top
          for (i = 0; i > toscroll; i--) {
            if (mp == NULL || mp->sb_prev == NULL) {
              break;
            }
            mp = msg_sb_start(mp->sb_prev);
            if (mp_last == NULL) {
              mp_last = msg_sb_start(last_msgchunk);
            } else {
              mp_last = msg_sb_start(mp_last->sb_prev);
            }
          }

          if (toscroll == -1 && !to_redraw) {
            grid_ins_lines(&msg_grid_adj, 0, 1, Rows, 0, Columns);
            grid_fill(&msg_grid_adj, 0, 1, 0, Columns, ' ', ' ',
                      HL_ATTR(HLF_MSG));
            // display line at top
            (void)disp_sb_line(0, mp);
          } else {
            // redisplay all lines
            // TODO(bfredl): this case is not optimized (though only concerns
            // event fragmentization, not unnecessary scroll events).
            grid_fill(&msg_grid_adj, 0, Rows, 0, Columns, ' ', ' ',
                      HL_ATTR(HLF_MSG));
            for (i = 0; mp != NULL && i < Rows - 1; i++) {
              mp = disp_sb_line(i, mp);
              msg_scrolled++;
            }
            to_redraw = false;
          }
          toscroll = 0;
        }
      } else {
        // First display any text that we scrolled back.
        while (toscroll > 0 && mp_last != NULL) {
          if (msg_do_throttle() && !msg_grid.throttled) {
            // Tricky: we redraw at one line higher than usual. Therefore
            // the non-flushed area is one line larger.
            msg_scrolled_at_flush--;
            msg_grid_scroll_discount++;
          }
          // scroll up, display line at bottom
          msg_scroll_up(true);
          inc_msg_scrolled();
          grid_fill(&msg_grid_adj, Rows - 2, Rows - 1, 0, Columns, ' ', ' ',
                    HL_ATTR(HLF_MSG));
          mp_last = disp_sb_line(Rows - 2, mp_last);
          toscroll--;
        }
      }

      if (toscroll <= 0) {
        // displayed the requested text, more prompt again
        grid_fill(&msg_grid_adj, Rows - 1, Rows, 0, Columns, ' ', ' ',
                  HL_ATTR(HLF_MSG));
        msg_moremsg(false);
        continue;
      }

      // display more text, return to caller
      lines_left = toscroll;
    }

    break;
  }

  // clear the --more-- message
  grid_fill(&msg_grid_adj, Rows - 1, Rows, 0, Columns, ' ', ' ',
            HL_ATTR(HLF_MSG));
  redraw_cmdline = true;
  clear_cmdline = false;
  mode_displayed = false;

  State = oldState;
  setmouse();
  if (quit_more) {
    msg_row = Rows - 1;
    msg_col = 0;
  } else if (cmdmsg_rl) {
    msg_col = Columns - 1;
  }

  entered = false;
  return retval;
}

#if defined(WIN32)
void mch_errmsg(char *str)
{
  assert(str != NULL);
  wchar_t *utf16str;
  int r = utf8_to_utf16(str, -1, &utf16str);
  if (r != 0) {
    fprintf(stderr, "utf8_to_utf16 failed: %d", r);
  } else {
    fwprintf(stderr, L"%ls", utf16str);
    xfree(utf16str);
  }
}

/// Give a message.  To be used when the UI is not initialized yet.
void mch_msg(char *str)
{
  assert(str != NULL);
  wchar_t *utf16str;
  int r = utf8_to_utf16(str, -1, &utf16str);
  if (r != 0) {
    fprintf(stderr, "utf8_to_utf16 failed: %d", r);
  } else {
    wprintf(L"%ls", utf16str);
    xfree(utf16str);
  }
}
#endif  // WIN32

/// Put a character on the screen at the current message position and advance
/// to the next position.  Only for printable ASCII!
static void msg_screen_putchar(int c, int attr)
{
  attr = hl_combine_attr(HL_ATTR(HLF_MSG), attr);
  msg_didout = true;            // remember that line is not empty
  grid_putchar(&msg_grid_adj, c, msg_row, msg_col, attr);
  if (cmdmsg_rl) {
    if (--msg_col == 0) {
      msg_col = Columns;
      msg_row++;
    }
  } else {
    if (++msg_col >= Columns) {
      msg_col = 0;
      msg_row++;
    }
  }
}

void msg_moremsg(int full)
{
  int attr;
  char_u *s = (char_u *)_("-- More --");

  attr = hl_combine_attr(HL_ATTR(HLF_MSG), HL_ATTR(HLF_M));
  grid_puts(&msg_grid_adj, s, Rows - 1, 0, attr);
  if (full) {
    grid_puts(&msg_grid_adj, (char_u *)
              _(" SPACE/d/j: screen/page/line down, b/u/k: up, q: quit "),
              Rows - 1, vim_strsize((char *)s), attr);
  }
}

/// Repeat the message for the current mode: MODE_ASKMORE, MODE_EXTERNCMD,
/// MODE_CONFIRM or exmode_active.
void repeat_message(void)
{
  if (State == MODE_ASKMORE) {
    msg_moremsg(true);          // display --more-- message again
    msg_row = Rows - 1;
  } else if (State == MODE_CONFIRM) {
    display_confirm_msg();      // display ":confirm" message again
    msg_row = Rows - 1;
  } else if (State == MODE_EXTERNCMD) {
    ui_cursor_goto(msg_row, msg_col);     // put cursor back
  } else if (State == MODE_HITRETURN || State == MODE_SETWSIZE) {
    if (msg_row == Rows - 1) {
      // Avoid drawing the "hit-enter" prompt below the previous one,
      // overwrite it.  Esp. useful when regaining focus and a
      // FocusGained autocmd exists but didn't draw anything.
      msg_didout = false;
      msg_col = 0;
      msg_clr_eos();
    }
    hit_return_msg();
    msg_row = Rows - 1;
  }
}

/// Clear from current message position to end of screen.
/// Skip this when ":silent" was used, no need to clear for redirection.
void msg_clr_eos(void)
{
  if (msg_silent == 0 && p_ch > 0) {
    msg_clr_eos_force();
  }
}

/// Clear from current message position to end of screen.
/// Note: msg_col is not updated, so we remember the end of the message
/// for msg_check().
void msg_clr_eos_force(void)
{
  if (ui_has(kUIMessages)) {
    return;
  }
  int msg_startcol = (cmdmsg_rl) ? 0 : msg_col;
  int msg_endcol = (cmdmsg_rl) ? msg_col + 1 : Columns;

  if (msg_grid.chars && msg_row < msg_grid_pos) {
    // TODO(bfredl): ugly, this state should already been validated at this
    // point. But msg_clr_eos() is called in a lot of places.
    msg_row = msg_grid_pos;
  }

  if (ui_has_messages()) {
    grid_fill(&msg_grid_adj, msg_row, msg_row + 1, msg_startcol, msg_endcol,
              ' ', ' ', HL_ATTR(HLF_MSG));
    grid_fill(&msg_grid_adj, msg_row + 1, Rows, 0, Columns,
              ' ', ' ', HL_ATTR(HLF_MSG));
  }

  redraw_cmdline = true;  // overwritten the command line
  if (msg_row < Rows - 1 || msg_col == (cmdmsg_rl ? Columns : 0)) {
    clear_cmdline = false;  // command line has been cleared
    mode_displayed = false;  // mode cleared or overwritten
  }
}

/// Clear the command line.
void msg_clr_cmdline(void)
{
  msg_row = cmdline_row;
  msg_col = 0;
  msg_clr_eos_force();
}

/// end putting a message on the screen
/// call wait_return if the message does not fit in the available space
///
/// @return  TRUE if wait_return not called.
int msg_end(void)
{
  /*
   * If the string is larger than the window,
   * or the ruler option is set and we run into it,
   * we have to redraw the window.
   * Do not do this if we are abandoning the file or editing the command line.
   */
  if (!exiting && need_wait_return && !(State & MODE_CMDLINE)) {
    wait_return(false);
    return false;
  }

  // NOTE: ui_flush() used to be called here. This had to be removed, as it
  // inhibited substantial performance improvements. It is assumed that relevant
  // callers invoke ui_flush() before going into CPU busywork, or restricted
  // event processing after displaying a message to the user.
  msg_ext_ui_flush();
  return true;
}

void msg_ext_ui_flush(void)
{
  if (!ui_has(kUIMessages)) {
    return;
  }

  msg_ext_emit_chunk();
  if (msg_ext_chunks.size > 0) {
    ui_call_msg_show(cstr_as_string((char *)msg_ext_kind),
                     msg_ext_chunks, msg_ext_overwrite);
    if (!msg_ext_overwrite) {
      msg_ext_visible++;
    }
    msg_ext_kind = NULL;
    api_free_array(msg_ext_chunks);
    msg_ext_chunks = (Array)ARRAY_DICT_INIT;
    msg_ext_cur_len = 0;
    msg_ext_overwrite = false;
  }
}

void msg_ext_flush_showmode(void)
{
  // Showmode messages doesn't interrupt normal message flow, so we use
  // separate event. Still reuse the same chunking logic, for simplicity.
  if (ui_has(kUIMessages)) {
    msg_ext_emit_chunk();
    ui_call_msg_showmode(msg_ext_chunks);
    api_free_array(msg_ext_chunks);
    msg_ext_chunks = (Array)ARRAY_DICT_INIT;
    msg_ext_cur_len = 0;
  }
}

void msg_ext_clear(bool force)
{
  if (msg_ext_visible && (!msg_ext_keep_after_cmdline || force)) {
    ui_call_msg_clear();
    msg_ext_visible = 0;
    msg_ext_overwrite = false;  // nothing to overwrite
  }
  if (msg_ext_history_visible) {
    ui_call_msg_history_clear();
    msg_ext_history_visible = false;
  }

  // Only keep once.
  msg_ext_keep_after_cmdline = false;
}

void msg_ext_clear_later(void)
{
  if (msg_ext_is_visible()) {
    msg_ext_need_clear = true;
    if (must_redraw < VALID) {
      must_redraw = VALID;
    }
  }
}

void msg_ext_check_clear(void)
{
  // Redraw after cmdline or prompt is expected to clear messages.
  if (msg_ext_need_clear) {
    msg_ext_clear(true);
    msg_ext_need_clear = false;
  }
}

bool msg_ext_is_visible(void)
{
  return ui_has(kUIMessages) && msg_ext_visible > 0;
}

/// If the written message runs into the shown command or ruler, we have to
/// wait for hit-return and redraw the window later.
void msg_check(void)
{
  if (ui_has(kUIMessages)) {
    return;
  }
  if (msg_row == Rows - 1 && msg_col >= sc_col) {
    need_wait_return = true;
    redraw_cmdline = true;
  }
}

/// May write a string to the redirection file.
///
/// @param maxlen  if -1, write the whole string, otherwise up to "maxlen" bytes.
static void redir_write(const char *const str, const ptrdiff_t maxlen)
{
  const char_u *s = (char_u *)str;
  static int cur_col = 0;

  if (maxlen == 0) {
    return;
  }

  // Don't do anything for displaying prompts and the like.
  if (redir_off) {
    return;
  }

  // If 'verbosefile' is set prepare for writing in that file.
  if (*p_vfile != NUL && verbose_fd == NULL) {
    verbose_open();
  }

  if (redirecting()) {
    // If the string doesn't start with CR or NL, go to msg_col
    if (*s != '\n' && *s != '\r') {
      while (cur_col < msg_col) {
        if (capture_ga) {
          ga_concat_len(capture_ga, " ", 1);
        }
        if (redir_reg) {
          write_reg_contents(redir_reg, (char_u *)" ", 1, true);
        } else if (redir_vname) {
          var_redir_str(" ", -1);
        } else if (redir_fd != NULL) {
          fputs(" ", redir_fd);
        }
        if (verbose_fd != NULL) {
          fputs(" ", verbose_fd);
        }
        cur_col++;
      }
    }

    size_t len = maxlen == -1 ? STRLEN(s) : (size_t)maxlen;
    if (capture_ga) {
      ga_concat_len(capture_ga, str, len);
    }
    if (redir_reg) {
      write_reg_contents(redir_reg, s, (ssize_t)len, true);
    }
    if (redir_vname) {
      var_redir_str((char *)s, (int)maxlen);
    }

    // Write and adjust the current column.
    while (*s != NUL
           && (maxlen < 0 || (int)(s - (const char_u *)str) < maxlen)) {
      if (!redir_reg && !redir_vname && !capture_ga) {
        if (redir_fd != NULL) {
          putc(*s, redir_fd);
        }
      }
      if (verbose_fd != NULL) {
        putc(*s, verbose_fd);
      }
      if (*s == '\r' || *s == '\n') {
        cur_col = 0;
      } else if (*s == '\t') {
        cur_col += (8 - cur_col % 8);
      } else {
        cur_col++;
      }
      s++;
    }

    if (msg_silent != 0) {      // should update msg_col
      msg_col = cur_col;
    }
  }
}

int redirecting(void)
{
  return redir_fd != NULL || *p_vfile != NUL
         || redir_reg || redir_vname || capture_ga != NULL;
}

/// Before giving verbose message.
/// Must always be called paired with verbose_leave()!
void verbose_enter(void)
{
  if (*p_vfile != NUL) {
    msg_silent++;
  }
}

/// After giving verbose message.
/// Must always be called paired with verbose_enter()!
void verbose_leave(void)
{
  if (*p_vfile != NUL) {
    if (--msg_silent < 0) {
      msg_silent = 0;
    }
  }
}

/// Like verbose_enter() and set msg_scroll when displaying the message.
void verbose_enter_scroll(void)
{
  if (*p_vfile != NUL) {
    msg_silent++;
  } else {
    // always scroll up, don't overwrite
    msg_scroll = TRUE;
  }
}

/// Like verbose_leave() and set cmdline_row when displaying the message.
void verbose_leave_scroll(void)
{
  if (*p_vfile != NUL) {
    if (--msg_silent < 0) {
      msg_silent = 0;
    }
  } else {
    cmdline_row = msg_row;
  }
}

/// Called when 'verbosefile' is set: stop writing to the file.
void verbose_stop(void)
{
  if (verbose_fd != NULL) {
    fclose(verbose_fd);
    verbose_fd = NULL;
  }
  verbose_did_open = FALSE;
}

/// Open the file 'verbosefile'.
///
/// @return  FAIL or OK.
int verbose_open(void)
{
  if (verbose_fd == NULL && !verbose_did_open) {
    // Only give the error message once.
    verbose_did_open = TRUE;

    verbose_fd = os_fopen((char *)p_vfile, "a");
    if (verbose_fd == NULL) {
      semsg(_(e_notopen), p_vfile);
      return FAIL;
    }
  }
  return OK;
}

/// Give a warning message (for searching).
/// Use 'w' highlighting and may repeat the message after redrawing
void give_warning(char *message, bool hl)
  FUNC_ATTR_NONNULL_ARG(1)
{
  // Don't do this for ":silent".
  if (msg_silent != 0) {
    return;
  }

  // Don't want a hit-enter prompt here.
  no_wait_return++;

  set_vim_var_string(VV_WARNINGMSG, message, -1);
  XFREE_CLEAR(keep_msg);
  if (hl) {
    keep_msg_attr = HL_ATTR(HLF_W);
  } else {
    keep_msg_attr = 0;
  }

  if (msg_ext_kind == NULL) {
    msg_ext_set_kind("wmsg");
  }

  if (msg_attr((const char *)message, keep_msg_attr) && msg_scrolled == 0) {
    set_keep_msg(message, keep_msg_attr);
  }
  msg_didout = false;  // Overwrite this message.
  msg_nowait = true;   // Don't wait for this message.
  msg_col = 0;

  no_wait_return--;
}

void give_warning2(char_u *const message, char_u *const a1, bool hl)
{
  vim_snprintf((char *)IObuff, IOSIZE, (char *)message, a1);
  give_warning((char *)IObuff, hl);
}

/// Advance msg cursor to column "col".
void msg_advance(int col)
{
  if (msg_silent != 0) {        // nothing to advance to
    msg_col = col;              // for redirection, may fill it up later
    return;
  }
  if (ui_has(kUIMessages)) {
    // TODO(bfredl): use byte count as a basic proxy.
    // later on we might add proper support for formatted messages.
    while (msg_ext_cur_len < (size_t)col) {
      msg_putchar(' ');
    }
    return;
  }
  if (col >= Columns) {         // not enough room
    col = Columns - 1;
  }
  if (cmdmsg_rl) {
    while (msg_col > Columns - col) {
      msg_putchar(' ');
    }
  } else {
    while (msg_col < col) {
      msg_putchar(' ');
    }
  }
}

/// Used for "confirm()" function, and the :confirm command prefix.
/// Versions which haven't got flexible dialogs yet, and console
/// versions, get this generic handler which uses the command line.
///
/// type  = one of:
///         VIM_QUESTION, VIM_INFO, VIM_WARNING, VIM_ERROR or VIM_GENERIC
/// title = title string (can be NULL for default)
/// (neither used in console dialogs at the moment)
///
/// Format of the "buttons" string:
/// "Button1Name\nButton2Name\nButton3Name"
/// The first button should normally be the default/accept
/// The second button should be the 'Cancel' button
/// Other buttons- use your imagination!
/// A '&' in a button name becomes a shortcut, so each '&' should be before a
/// different letter.
///
/// @param textfiel  IObuff for inputdialog(), NULL otherwise
/// @param ex_cmd  when TRUE pressing : accepts default and starts Ex command
/// @returns 0 if cancelled, otherwise the nth button (1-indexed).
int do_dialog(int type, char_u *title, char_u *message, char_u *buttons, int dfltbutton,
              char_u *textfield, int ex_cmd)
{
  int retval = 0;
  char_u *hotkeys;
  int c;
  int i;

  if (silent_mode      // No dialogs in silent mode ("ex -s")
      || !ui_active()  // Without a UI Nvim waits for input forever.
      ) {
    return dfltbutton;  // return default option
  }

  int save_msg_silent = msg_silent;
  int oldState = State;

  msg_silent = 0;  // If dialog prompts for input, user needs to see it! #8788
  State = MODE_CONFIRM;
  setmouse();

  /*
   * Since we wait for a keypress, don't make the
   * user press RETURN as well afterwards.
   */
  no_wait_return++;
  hotkeys = msg_show_console_dialog(message, buttons, dfltbutton);

  for (;;) {
    // Get a typed character directly from the user.
    c = get_keystroke(NULL);
    switch (c) {
    case CAR:                 // User accepts default option
    case NL:
      retval = dfltbutton;
      break;
    case Ctrl_C:              // User aborts/cancels
    case ESC:
      retval = 0;
      break;
    default:                  // Could be a hotkey?
      if (c < 0) {            // special keys are ignored here
        continue;
      }
      if (c == ':' && ex_cmd) {
        retval = dfltbutton;
        ins_char_typebuf(':', 0);
        break;
      }

      // Make the character lowercase, as chars in "hotkeys" are.
      c = mb_tolower(c);
      retval = 1;
      for (i = 0; hotkeys[i]; i++) {
        if (utf_ptr2char((char *)hotkeys + i) == c) {
          break;
        }
        i += utfc_ptr2len((char *)hotkeys + i) - 1;
        retval++;
      }
      if (hotkeys[i]) {
        break;
      }
      // No hotkey match, so keep waiting
      continue;
    }
    break;
  }

  xfree(hotkeys);

  msg_silent = save_msg_silent;
  State = oldState;
  setmouse();
  no_wait_return--;
  msg_end_prompt();

  return retval;
}

/// Copy one character from "*from" to "*to", taking care of multi-byte
/// characters.  Return the length of the character in bytes.
///
/// @param lowercase  make character lower case
static int copy_char(const char_u *from, char_u *to, bool lowercase)
  FUNC_ATTR_NONNULL_ALL
{
  if (lowercase) {
    int c = mb_tolower(utf_ptr2char((char *)from));
    return utf_char2bytes(c, (char *)to);
  }
  int len = utfc_ptr2len((char *)from);
  memmove(to, from, (size_t)len);
  return len;
}

#define HAS_HOTKEY_LEN 30
#define HOTK_LEN MB_MAXBYTES

/// Allocates memory for dialog string & for storing hotkeys
///
/// Finds the size of memory required for the confirm_msg & for storing hotkeys
/// and then allocates the memory for them.
/// has_hotkey array is also filled-up.
///
/// @param message Message which will be part of the confirm_msg
/// @param buttons String containing button names
/// @param[out] has_hotkey An element in this array is set to true if
///                        corresponding button has a hotkey
///
/// @return Pointer to memory allocated for storing hotkeys
static char_u *console_dialog_alloc(const char_u *message, char_u *buttons, bool has_hotkey[])
{
  int lenhotkey = HOTK_LEN;  // count first button
  has_hotkey[0] = false;

  // Compute the size of memory to allocate.
  int len = 0;
  int idx = 0;
  char_u *r = buttons;
  while (*r) {
    if (*r == DLG_BUTTON_SEP) {
      len += 3;                         // '\n' -> ', '; 'x' -> '(x)'
      lenhotkey += HOTK_LEN;            // each button needs a hotkey
      if (idx < HAS_HOTKEY_LEN - 1) {
        has_hotkey[++idx] = false;
      }
    } else if (*r == DLG_HOTKEY_CHAR) {
      r++;
      len++;                    // '&a' -> '[a]'
      if (idx < HAS_HOTKEY_LEN - 1) {
        has_hotkey[idx] = true;
      }
    }

    // Advance to the next character
    MB_PTR_ADV(r);
  }

  len += (int)(STRLEN(message)
               + 2                          // for the NL's
               + STRLEN(buttons)
               + 3);                        // for the ": " and NUL
  lenhotkey++;                               // for the NUL

  // If no hotkey is specified, first char is used.
  if (!has_hotkey[0]) {
    len += 2;                                // "x" -> "[x]"
  }

  // Now allocate space for the strings
  xfree(confirm_msg);
  confirm_msg = xmalloc((size_t)len);
  *confirm_msg = NUL;

  return xmalloc((size_t)lenhotkey);
}

/// Format the dialog string, and display it at the bottom of
/// the screen. Return a string of hotkey chars (if defined) for
/// each 'button'. If a button has no hotkey defined, the first character of
/// the button is used.
/// The hotkeys can be multi-byte characters, but without combining chars.
///
/// @return  an allocated string with hotkeys.
static char_u *msg_show_console_dialog(char_u *message, char_u *buttons, int dfltbutton)
  FUNC_ATTR_NONNULL_RET
{
  bool has_hotkey[HAS_HOTKEY_LEN] = { false };
  char_u *hotk = console_dialog_alloc(message, buttons, has_hotkey);

  copy_hotkeys_and_msg(message, buttons, dfltbutton, has_hotkey, hotk);

  display_confirm_msg();
  return hotk;
}

/// Copies hotkeys & dialog message into the memory allocated for it
///
/// @param message Message which will be part of the confirm_msg
/// @param buttons String containing button names
/// @param default_button_idx Number of default button
/// @param has_hotkey An element in this array is true if corresponding button
///                   has a hotkey
/// @param[out] hotkeys_ptr Pointer to the memory location where hotkeys will be copied
static void copy_hotkeys_and_msg(const char_u *message, char_u *buttons, int default_button_idx,
                                 const bool has_hotkey[], char_u *hotkeys_ptr)
{
  *confirm_msg = '\n';
  STRCPY(confirm_msg + 1, message);

  char_u *msgp = confirm_msg + 1 + STRLEN(message);

  // Define first default hotkey. Keep the hotkey string NUL
  // terminated to avoid reading past the end.
  hotkeys_ptr[copy_char(buttons, hotkeys_ptr, true)] = NUL;

  // Remember where the choices start, displaying starts here when
  // "hotkeys_ptr" typed at the more prompt.
  confirm_msg_tail = msgp;
  *msgp++ = '\n';

  bool first_hotkey = false;  // Is the first char of button a hotkey
  if (!has_hotkey[0]) {
    first_hotkey = true;     // If no hotkey is specified, first char is used
  }

  int idx = 0;
  char_u *r = buttons;
  while (*r) {
    if (*r == DLG_BUTTON_SEP) {
      *msgp++ = ',';
      *msgp++ = ' ';                    // '\n' -> ', '

      // Advance to next hotkey and set default hotkey
      hotkeys_ptr += STRLEN(hotkeys_ptr);
      hotkeys_ptr[copy_char(r + 1, hotkeys_ptr, true)] = NUL;

      if (default_button_idx) {
        default_button_idx--;
      }

      // If no hotkey is specified, first char is used.
      if (idx < HAS_HOTKEY_LEN - 1 && !has_hotkey[++idx]) {
        first_hotkey = true;
      }
    } else if (*r == DLG_HOTKEY_CHAR || first_hotkey) {
      if (*r == DLG_HOTKEY_CHAR) {
        r++;
      }

      first_hotkey = false;
      if (*r == DLG_HOTKEY_CHAR) {                 // '&&a' -> '&a'
        *msgp++ = *r;
      } else {
        // '&a' -> '[a]'
        *msgp++ = (default_button_idx == 1) ? '[' : '(';
        msgp += copy_char(r, msgp, false);
        *msgp++ = (default_button_idx == 1) ? ']' : ')';

        // redefine hotkey
        hotkeys_ptr[copy_char(r, hotkeys_ptr, true)] = NUL;
      }
    } else {
      // everything else copy literally
      msgp += copy_char(r, msgp, false);
    }

    // advance to the next character
    MB_PTR_ADV(r);
  }

  *msgp++ = ':';
  *msgp++ = ' ';
  *msgp = NUL;
}

/// Display the ":confirm" message.  Also called when screen resized.
void display_confirm_msg(void)
{
  // Avoid that 'q' at the more prompt truncates the message here.
  confirm_msg_used++;
  if (confirm_msg != NULL) {
    msg_ext_set_kind("confirm");
    msg_puts_attr((const char *)confirm_msg, HL_ATTR(HLF_M));
  }
  confirm_msg_used--;
}

int vim_dialog_yesno(int type, char_u *title, char_u *message, int dflt)
{
  if (do_dialog(type,
                title == NULL ? (char_u *)_("Question") : title,
                message,
                (char_u *)_("&Yes\n&No"), dflt, NULL, FALSE) == 1) {
    return VIM_YES;
  }
  return VIM_NO;
}

int vim_dialog_yesnocancel(int type, char_u *title, char_u *message, int dflt)
{
  switch (do_dialog(type,
                    title == NULL ? (char_u *)_("Question") : title,
                    message,
                    (char_u *)_("&Yes\n&No\n&Cancel"), dflt, NULL, FALSE)) {
  case 1:
    return VIM_YES;
  case 2:
    return VIM_NO;
  }
  return VIM_CANCEL;
}

int vim_dialog_yesnoallcancel(int type, char_u *title, char_u *message, int dflt)
{
  switch (do_dialog(type,
                    title == NULL ? (char_u *)"Question" : title,
                    message,
                    (char_u *)_("&Yes\n&No\nSave &All\n&Discard All\n&Cancel"),
                    dflt, NULL, FALSE)) {
  case 1:
    return VIM_YES;
  case 2:
    return VIM_NO;
  case 3:
    return VIM_ALL;
  case 4:
    return VIM_DISCARDALL;
  }
  return VIM_CANCEL;
}