/// change.c: functions related to changing text

#include <assert.h>
#include <stdbool.h>
#include <stdint.h>
#include <string.h>

#include "nvim/ascii_defs.h"
#include "nvim/assert_defs.h"
#include "nvim/autocmd.h"
#include "nvim/autocmd_defs.h"
#include "nvim/buffer.h"
#include "nvim/buffer_defs.h"
#include "nvim/buffer_updates.h"
#include "nvim/change.h"
#include "nvim/charset.h"
#include "nvim/cursor.h"
#include "nvim/diff.h"
#include "nvim/drawscreen.h"
#include "nvim/edit.h"
#include "nvim/eval/vars.h"
#include "nvim/ex_cmds_defs.h"
#include "nvim/extmark.h"
#include "nvim/extmark_defs.h"
#include "nvim/fold.h"
#include "nvim/gettext_defs.h"
#include "nvim/globals.h"
#include "nvim/highlight_defs.h"
#include "nvim/indent.h"
#include "nvim/indent_c.h"
#include "nvim/insexpand.h"
#include "nvim/macros_defs.h"
#include "nvim/mark.h"
#include "nvim/mark_defs.h"
#include "nvim/marktree_defs.h"
#include "nvim/mbyte.h"
#include "nvim/mbyte_defs.h"
#include "nvim/memline.h"
#include "nvim/memline_defs.h"
#include "nvim/memory.h"
#include "nvim/message.h"
#include "nvim/move.h"
#include "nvim/option.h"
#include "nvim/option_vars.h"
#include "nvim/os/time.h"
#include "nvim/plines.h"
#include "nvim/pos_defs.h"
#include "nvim/search.h"
#include "nvim/spell.h"
#include "nvim/state.h"
#include "nvim/state_defs.h"
#include "nvim/strings.h"
#include "nvim/textformat.h"
#include "nvim/types_defs.h"
#include "nvim/ui.h"
#include "nvim/undo.h"
#include "nvim/vim_defs.h"

#include "change.c.generated.h"

/// If the file is readonly, give a warning message with the first change.
/// Don't do this for autocommands.
/// Doesn't use emsg(), because it flushes the macro buffer.
/// If we have undone all changes b_changed will be false, but "b_did_warn"
/// will be true.
/// "col" is the column for the message; non-zero when in insert mode and
/// 'showmode' is on.
/// Careful: may trigger autocommands that reload the buffer.
void change_warning(buf_T *buf, int col)
{
  static const char *w_readonly = N_("W10: Warning: Changing a readonly file");

  if (buf->b_did_warn == false
      && curbufIsChanged() == 0
      && !autocmd_busy
      && buf->b_p_ro) {
    buf->b_ro_locked++;
    apply_autocmds(EVENT_FILECHANGEDRO, NULL, NULL, false, buf);
    buf->b_ro_locked--;
    if (!buf->b_p_ro) {
      return;
    }
    // Do what msg() does, but with a column offset if the warning should
    // be after the mode message.
    msg_start();
    if (msg_row == Rows - 1) {
      msg_col = col;
    }
    msg_source(HLF_W);
    msg_ext_set_kind("wmsg");
    msg_puts_hl(_(w_readonly), HLF_W, true);
    set_vim_var_string(VV_WARNINGMSG, _(w_readonly), -1);
    msg_clr_eos();
    msg_end();
    if (msg_silent == 0 && !silent_mode && ui_active()) {
      msg_delay(1002, true);  // give the user time to think about it
    }
    buf->b_did_warn = true;
    redraw_cmdline = false;  // don't redraw and erase the message
    if (msg_row < Rows - 1) {
      showmode();
    }
  }
}

/// Call this function when something in a buffer is changed.
///
/// Most often called through changed_bytes() and changed_lines(), which also
/// mark the area of the display to be redrawn.
///
/// Careful: may trigger autocommands that reload the buffer.
void changed(buf_T *buf)
{
  if (!buf->b_changed) {
    int save_msg_scroll = msg_scroll;

    // Give a warning about changing a read-only file.  This may also
    // check-out the file, thus change "curbuf"!
    change_warning(buf, 0);

    // Create a swap file if that is wanted.
    // Don't do this for "nofile" and "nowrite" buffer types.
    if (buf->b_may_swap && !bt_dontwrite(buf)) {
      bool save_need_wait_return = need_wait_return;

      need_wait_return = false;
      ml_open_file(buf);

      // The ml_open_file() can cause an ATTENTION message.
      // Wait two seconds, to make sure the user reads this unexpected
      // message.  Since we could be anywhere, call wait_return() now,
      // and don't let the emsg() set msg_scroll.
      if (need_wait_return && emsg_silent == 0 && !in_assert_fails && !ui_has(kUIMessages)) {
        msg_delay(2002, true);
        wait_return(true);
        msg_scroll = save_msg_scroll;
      } else {
        need_wait_return = save_need_wait_return;
      }
    }
    changed_internal(buf);
  }
  buf_inc_changedtick(buf);

  // If a pattern is highlighted, the position may now be invalid.
  highlight_match = false;
}

/// Internal part of changed(), no user interaction.
/// Also used for recovery.
void changed_internal(buf_T *buf)
{
  buf->b_changed = true;
  buf->b_changed_invalid = true;
  ml_setflags(buf);
  redraw_buf_status_later(buf);
  redraw_tabline = true;
  need_maketitle = true;  // set window title later
}

/// Invalidate a window's w_valid flags and w_lines[] entries after changing lines.
static void changed_lines_invalidate_win(win_T *wp, linenr_T lnum, colnr_T col, linenr_T lnume,
                                         linenr_T xtra)
{
  // If the changed line is in a range of previously folded lines,
  // compare with the first line in that range.
  if (wp->w_cursor.lnum <= lnum) {
    int i = find_wl_entry(wp, lnum);
    if (i >= 0 && wp->w_cursor.lnum > wp->w_lines[i].wl_lnum) {
      changed_line_abv_curs_win(wp);
    }
  }

  if (wp->w_cursor.lnum > lnum) {
    changed_line_abv_curs_win(wp);
  } else if (wp->w_cursor.lnum == lnum && wp->w_cursor.col >= col) {
    changed_cline_bef_curs(wp);
  }
  if (wp->w_botline >= lnum) {
    if (xtra < 0) {
      invalidate_botline_win(wp);
    } else {
      // Assume that botline doesn't change (inserted lines make
      // other lines scroll down below botline).
      approximate_botline_win(wp);
    }
  }

  // If lines have been inserted/deleted and the buffer has virt_lines, or
  // inline virt_text with 'wrap' enabled, invalidate the line after the changed
  // lines. virt_lines may now be drawn above that line, and inline virt_text
  // may cause that line to wrap.
  if ((xtra < 0 && wp->w_p_wrap && buf_meta_total(wp->w_buffer, kMTMetaInline))
      || (xtra != 0 && buf_meta_total(wp->w_buffer, kMTMetaLines))) {
    lnume++;
  }
  // Check if any w_lines[] entries have become invalid.
  // For entries below the change: Correct the lnums for inserted/deleted lines.
  // Makes it possible to stop displaying after the change.
  for (int i = 0; i < wp->w_lines_valid; i++) {
    if (wp->w_lines[i].wl_valid) {
      if (wp->w_lines[i].wl_lnum >= lnum) {
        // Do not change wl_lnum at index zero, it is used to compare with w_topline.
        // Invalidate it instead.
        if (i == 0 || wp->w_lines[i].wl_lnum < lnume) {
          // line included in change
          wp->w_lines[i].wl_valid = false;
        } else if (xtra != 0) {
          // line below change
          wp->w_lines[i].wl_lnum += xtra;
          wp->w_lines[i].wl_foldend += xtra;
          wp->w_lines[i].wl_lastlnum += xtra;
        }
      } else if (wp->w_lines[i].wl_lastlnum >= lnum) {
        // change somewhere inside this range of folded or concealed lines,
        // may need to be redrawn
        wp->w_lines[i].wl_valid = false;
      }
    }
  }
}

/// Line changed_lines_invalidate_win(), but for all windows displaying a buffer.
void changed_lines_invalidate_buf(buf_T *buf, linenr_T lnum, colnr_T col, linenr_T lnume,
                                  linenr_T xtra)
{
  FOR_ALL_TAB_WINDOWS(tp, wp) {
    if (wp->w_buffer == buf) {
      changed_lines_invalidate_win(wp, lnum, col, lnume, xtra);
    }
  }
}

/// Common code for when a change was made.
/// See changed_lines() for the arguments.
/// Careful: may trigger autocommands that reload the buffer.
static void changed_common(buf_T *buf, linenr_T lnum, colnr_T col, linenr_T lnume, linenr_T xtra)
{
  // mark the buffer as modified
  changed(buf);

  FOR_ALL_WINDOWS_IN_TAB(win, curtab) {
    if (win->w_buffer == buf && win->w_p_diff && diff_internal()) {
      curtab->tp_diff_update = true;
      diff_update_line(lnum);
    }
  }

  // set the '. mark
  if ((cmdmod.cmod_flags & CMOD_KEEPJUMPS) == 0) {
    fmarkv_T view = INIT_FMARKV;
    // Set the markview only if lnum is visible, as changes might be done
    // outside of the current window view.

    if (curwin->w_buffer == buf) {
      if (lnum >= curwin->w_topline && lnum <= curwin->w_botline) {
        view = mark_view_make(curwin, curwin->w_cursor);
      }
    }
    RESET_FMARK(&buf->b_last_change, ((pos_T) { lnum, col, 0 }), buf->handle, view);

    // Create a new entry if a new undo-able change was started or we
    // don't have an entry yet.
    if (buf->b_new_change || buf->b_changelistlen == 0) {
      bool add;
      if (buf->b_changelistlen == 0) {
        add = true;
      } else {
        // Don't create a new entry when the line number is the same
        // as the last one and the column is not too far away.  Avoids
        // creating many entries for typing "xxxxx".
        pos_T *p = &buf->b_changelist[buf->b_changelistlen - 1].mark;
        if (p->lnum != lnum) {
          add = true;
        } else {
          int cols = comp_textwidth(false);
          if (cols == 0) {
            cols = 79;
          }
          add = (p->col + cols < col || col + cols < p->col);
        }
      }
      if (add) {
        // This is the first of a new sequence of undo-able changes
        // and it's at some distance of the last change.  Use a new
        // position in the changelist.
        buf->b_new_change = false;

        if (buf->b_changelistlen == JUMPLISTSIZE) {
          // changelist is full: remove oldest entry
          buf->b_changelistlen = JUMPLISTSIZE - 1;
          memmove(buf->b_changelist, buf->b_changelist + 1,
                  sizeof(buf->b_changelist[0]) * (JUMPLISTSIZE - 1));
          FOR_ALL_TAB_WINDOWS(tp, wp) {
            // Correct position in changelist for other windows on
            // this buffer.
            if (wp->w_buffer == buf && wp->w_changelistidx > 0) {
              wp->w_changelistidx--;
            }
          }
        }
        FOR_ALL_TAB_WINDOWS(tp, wp) {
          // For other windows, if the position in the changelist is
          // at the end it stays at the end.
          if (wp->w_buffer == buf
              && wp->w_changelistidx == buf->b_changelistlen) {
            wp->w_changelistidx++;
          }
        }
        buf->b_changelistlen++;
      }
    }
    buf->b_changelist[buf->b_changelistlen - 1] =
      buf->b_last_change;
    // The current window is always after the last change, so that "g,"
    // takes you back to it.
    if (curwin->w_buffer == buf) {
      curwin->w_changelistidx = buf->b_changelistlen;
    }
  }

  if (curwin->w_buffer == buf && VIsual_active) {
    check_visual_pos();
  }

  FOR_ALL_TAB_WINDOWS(tp, wp) {
    if (wp->w_buffer == buf) {
      // Mark this window to be redrawn later.
      if (!redraw_not_allowed && wp->w_redr_type < UPD_VALID) {
        wp->w_redr_type = UPD_VALID;
      }

      // When inserting/deleting lines and the window has specific lines
      // to be redrawn, w_redraw_top and w_redraw_bot may now be invalid,
      // so just redraw everything.
      if (xtra != 0 && wp->w_redraw_top != 0) {
        redraw_later(wp, UPD_NOT_VALID);
      }

      linenr_T last = lnume + xtra - 1;  // last line after the change

      // Reset "w_skipcol" if the topline length has become smaller to
      // such a degree that nothing will be visible anymore, accounting
      // for 'smoothscroll' <<< or 'listchars' "precedes" marker.
      if (wp->w_skipcol > 0
          && (last < wp->w_topline
              || (wp->w_topline >= lnum
                  && wp->w_topline < lnume
                  && (linetabsize_eol(wp, wp->w_topline)
                      <= wp->w_skipcol + sms_marker_overlap(wp, -1))))) {
        wp->w_skipcol = 0;
      }

      // Check if a change in the buffer has invalidated the cached
      // values for the cursor.
      // Update the folds for this window.  Can't postpone this, because
      // a following operator might work on the whole fold: ">>dd".
      foldUpdate(wp, lnum, last);

      // The change may cause lines above or below the change to become
      // included in a fold.  Set lnum/lnume to the first/last line that
      // might be displayed differently.
      // Set w_cline_folded here as an efficient way to update it when
      // inserting lines just above a closed fold.
      bool folded = hasFoldingWin(wp, lnum, &lnum, NULL, false, NULL);
      if (wp->w_cursor.lnum == lnum) {
        wp->w_cline_folded = folded;
      }
      folded = hasFoldingWin(wp, last, NULL, &last, false, NULL);
      if (wp->w_cursor.lnum == last) {
        wp->w_cline_folded = folded;
      }

      changed_lines_invalidate_win(wp, lnum, col, lnume, xtra);

      // Take care of side effects for setting w_topline when folds have
      // changed.  Esp. when the buffer was changed in another window.
      if (hasAnyFolding(wp)) {
        set_topline(wp, wp->w_topline);
      }

      // If lines have been added or removed, relative numbering always
      // requires an update even if cursor didn't move.
      if (wp->w_p_rnu && xtra != 0) {
        wp->w_last_cursor_lnum_rnu = 0;
      }

      if (wp->w_p_cul && wp->w_last_cursorline >= lnum) {
        if (wp->w_last_cursorline < lnume) {
          // If 'cursorline' was inside the change, it has already
          // been invalidated in w_lines[] by the loop above.
          wp->w_last_cursorline = 0;
        } else {
          // If 'cursorline' was below the change, adjust its lnum.
          wp->w_last_cursorline += xtra;
        }
      }
    }

    if (wp == curwin && xtra != 0 && search_hl_has_cursor_lnum >= lnum) {
      search_hl_has_cursor_lnum += xtra;
    }
  }

  // Call update_screen() later, which checks out what needs to be redrawn,
  // since it notices b_mod_set and then uses b_mod_*.
  set_must_redraw(UPD_VALID);

  // when the cursor line is changed always trigger CursorMoved
  if (last_cursormoved_win == curwin && curwin->w_buffer == buf
      && lnum <= curwin->w_cursor.lnum
      && lnume + (xtra < 0 ? -xtra : xtra) > curwin->w_cursor.lnum) {
    last_cursormoved.lnum = 0;
  }
}

/// Changed bytes within a single line for the current buffer.
/// - marks the windows on this buffer to be redisplayed
/// - marks the buffer changed by calling changed()
/// - invalidates cached values
/// Careful: may trigger autocommands that reload the buffer.
void changed_bytes(linenr_T lnum, colnr_T col)
{
  changed_lines_redraw_buf(curbuf, lnum, lnum + 1, 0);
  changed_common(curbuf, lnum, col, lnum + 1, 0);
  // When text has been changed at the end of the line, possibly the start of
  // the next line may have SpellCap that should be removed or it needs to be
  // displayed.  Schedule the next line for redrawing just in case.
  // Don't do this when displaying '$' at the end of changed text.
  if (spell_check_window(curwin)
      && lnum < curbuf->b_ml.ml_line_count
      && vim_strchr(p_cpo, CPO_DOLLAR) == NULL) {
    redrawWinline(curwin, lnum + 1);
  }
  // notify any channels that are watching
  buf_updates_send_changes(curbuf, lnum, 1, 1);

  // Diff highlighting in other diff windows may need to be updated too.
  if (curwin->w_p_diff) {
    FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
      if (wp->w_p_diff && wp != curwin) {
        redraw_later(wp, UPD_VALID);
        linenr_T wlnum = diff_lnum_win(lnum, wp);
        if (wlnum > 0) {
          changed_lines_redraw_buf(wp->w_buffer, wlnum, wlnum + 1, 0);
        }
      }
    }
  }
}

/// insert/delete bytes at column
///
/// Like changed_bytes() but also adjust extmark for "new" bytes.
void inserted_bytes(linenr_T lnum, colnr_T start_col, int old_col, int new_col)
{
  if (curbuf_splice_pending == 0) {
    extmark_splice_cols(curbuf, (int)lnum - 1, start_col, old_col, new_col, kExtmarkUndo);
  }

  changed_bytes(lnum, start_col);
}

/// Appended "count" lines below line "lnum" in the given buffer.
/// Must be called AFTER the change and after mark_adjust().
/// Takes care of marking the buffer to be redrawn and sets the changed flag.
void appended_lines_buf(buf_T *buf, linenr_T lnum, linenr_T count)
{
  changed_lines(buf, lnum + 1, 0, lnum + 1, count, true);
}

/// Appended "count" lines below line "lnum" in the current buffer.
/// Must be called AFTER the change and after mark_adjust().
/// Takes care of marking the buffer to be redrawn and sets the changed flag.
void appended_lines(linenr_T lnum, linenr_T count)
{
  appended_lines_buf(curbuf, lnum, count);
}

/// Like appended_lines(), but adjust marks first.
void appended_lines_mark(linenr_T lnum, int count)
{
  mark_adjust(lnum + 1, (linenr_T)MAXLNUM, (linenr_T)count, 0, kExtmarkUndo);
  changed_lines(curbuf, lnum + 1, 0, lnum + 1, (linenr_T)count, true);
}

/// Deleted "count" lines at line "lnum" in the given buffer.
/// Must be called AFTER the change and after mark_adjust().
/// Takes care of marking the buffer to be redrawn and sets the changed flag.
void deleted_lines_buf(buf_T *buf, linenr_T lnum, linenr_T count)
{
  changed_lines(buf, lnum, 0, lnum + count, -count, true);
}

/// Deleted "count" lines at line "lnum" in the current buffer.
/// Must be called AFTER the change and after mark_adjust().
/// Takes care of marking the buffer to be redrawn and sets the changed flag.
void deleted_lines(linenr_T lnum, linenr_T count)
{
  deleted_lines_buf(curbuf, lnum, count);
}

/// Like deleted_lines(), but adjust marks first.
/// Make sure the cursor is on a valid line before calling, a GUI callback may
/// be triggered to display the cursor.
void deleted_lines_mark(linenr_T lnum, int count)
{
  bool made_empty = (count > 0) && curbuf->b_ml.ml_flags & ML_EMPTY;

  mark_adjust(lnum, (linenr_T)(lnum + count - 1), MAXLNUM, -(linenr_T)count, kExtmarkNOOP);
  // if we deleted the entire buffer, we need to implicitly add a new empty line
  extmark_adjust(curbuf, lnum, (linenr_T)(lnum + count - 1), MAXLNUM,
                 -(linenr_T)count + (made_empty ? 1 : 0), kExtmarkUndo);
  changed_lines(curbuf, lnum, 0, lnum + (linenr_T)count, (linenr_T)(-count), true);
}

/// Marks the area to be redrawn after a change.
/// Consider also calling changed_lines_invalidate_buf().
///
/// @param buf the buffer where lines were changed
/// @param lnum first line with change
/// @param lnume line below last changed line
/// @param xtra number of extra lines (negative when deleting)
void changed_lines_redraw_buf(buf_T *buf, linenr_T lnum, linenr_T lnume, linenr_T xtra)
{
  // If lines have been deleted and there may be decorations in the buffer, ensure
  // win_update() calculates the height of, and redraws the line to which or whence
  // from its mark may have moved. When lines are deleted, a virt_line mark may
  // have moved be drawn two lines below so increase by one more.
  if (xtra != 0 && buf->b_marktree->n_keys > 0) {
    lnume += 1 + (xtra < 0 && buf_meta_total(buf, kMTMetaLines));
  }

  if (buf->b_mod_set) {
    // find the maximum area that must be redisplayed
    buf->b_mod_top = MIN(buf->b_mod_top, lnum);
    if (lnum < buf->b_mod_bot) {
      // adjust old bot position for xtra lines
      buf->b_mod_bot += xtra;
      buf->b_mod_bot = MAX(buf->b_mod_bot, lnum);
    }
    buf->b_mod_bot = MAX(buf->b_mod_bot, lnume + xtra);
    buf->b_mod_xlines += xtra;
  } else {
    // set the area that must be redisplayed
    buf->b_mod_set = true;
    buf->b_mod_top = lnum;
    buf->b_mod_bot = lnume + xtra;
    buf->b_mod_xlines = xtra;
  }
}

/// Changed lines for a buffer.
/// Must be called AFTER the change and after mark_adjust().
/// - mark the buffer changed by calling changed()
/// - mark the windows on this buffer to be redisplayed
/// - invalidate cached values
/// "lnum" is the first line that needs displaying, "lnume" the first line
/// below the changed lines (BEFORE the change).
/// When only inserting lines, "lnum" and "lnume" are equal.
/// Takes care of calling changed() and updating b_mod_*.
/// Careful: may trigger autocommands that reload the buffer.
///
/// @param lnum  first line with change
/// @param col  column in first line with change
/// @param lnume  line below last changed line
/// @param xtra  number of extra lines (negative when deleting)
/// @param do_buf_event  some callers like undo/redo call changed_lines() and
/// then increment changedtick *again*. This flag allows these callers to send
/// the nvim_buf_lines_event events after they're done modifying changedtick.
void changed_lines(buf_T *buf, linenr_T lnum, colnr_T col, linenr_T lnume, linenr_T xtra,
                   bool do_buf_event)
{
  changed_lines_redraw_buf(buf, lnum, lnume, xtra);

  if (xtra == 0 && curwin->w_p_diff && curwin->w_buffer == buf && !diff_internal()) {
    // When the number of lines doesn't change then mark_adjust() isn't
    // called and other diff buffers still need to be marked for
    // displaying.
    linenr_T wlnum;

    FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
      if (wp->w_p_diff && wp != curwin) {
        redraw_later(wp, UPD_VALID);
        wlnum = diff_lnum_win(lnum, wp);
        if (wlnum > 0) {
          changed_lines_redraw_buf(wp->w_buffer, wlnum, lnume - lnum + wlnum, 0);
        }
      }
    }
  }

  changed_common(buf, lnum, col, lnume, xtra);

  if (do_buf_event) {
    int64_t num_added = (int64_t)(lnume + xtra - lnum);
    int64_t num_removed = lnume - lnum;
    buf_updates_send_changes(buf, lnum, num_added, num_removed);
  }
}

/// Called when the changed flag must be reset for buffer `buf`.
/// When `ff` is true also reset 'fileformat'.
/// When `always_inc_changedtick` is true b:changedtick is incremented even
/// when the changed flag was off.
void unchanged(buf_T *buf, bool ff, bool always_inc_changedtick)
{
  if (buf->b_changed || (ff && file_ff_differs(buf, false))) {
    buf->b_changed = false;
    buf->b_changed_invalid = true;
    ml_setflags(buf);
    if (ff) {
      save_file_ff(buf);
    }
    redraw_buf_status_later(buf);
    redraw_tabline = true;
    need_maketitle = true;  // set window title later
    buf_inc_changedtick(buf);
  } else if (always_inc_changedtick) {
    buf_inc_changedtick(buf);
  }
}

/// Save the current values of 'fileformat' and 'fileencoding', so that we know
/// the file must be considered changed when the value is different.
void save_file_ff(buf_T *buf)
{
  buf->b_start_ffc = (unsigned char)(*buf->b_p_ff);
  buf->b_start_eof = buf->b_p_eof;
  buf->b_start_eol = buf->b_p_eol;
  buf->b_start_bomb = buf->b_p_bomb;

  // Only use free/alloc when necessary, they take time.
  if (buf->b_start_fenc == NULL
      || strcmp(buf->b_start_fenc, buf->b_p_fenc) != 0) {
    xfree(buf->b_start_fenc);
    buf->b_start_fenc = xstrdup(buf->b_p_fenc);
  }
}

/// Return true if 'fileformat' and/or 'fileencoding' has a different value
/// from when editing started (save_file_ff() called).
/// Also when 'endofline' was changed and 'binary' is set, or when 'bomb' was
/// changed and 'binary' is not set.
/// Also when 'endofline' was changed and 'fixeol' is not set.
/// When "ignore_empty" is true don't consider a new, empty buffer to be
/// changed.
bool file_ff_differs(buf_T *buf, bool ignore_empty)
  FUNC_ATTR_NONNULL_ALL FUNC_ATTR_WARN_UNUSED_RESULT
{
  // In a buffer that was never loaded the options are not valid.
  if (buf->b_flags & BF_NEVERLOADED) {
    return false;
  }
  if (ignore_empty
      && (buf->b_flags & BF_NEW)
      && buf->b_ml.ml_line_count == 1
      && *ml_get_buf(buf, 1) == NUL) {
    return false;
  }
  if (buf->b_start_ffc != *buf->b_p_ff) {
    return true;
  }
  if ((buf->b_p_bin || !buf->b_p_fixeol)
      && (buf->b_start_eof != buf->b_p_eof || buf->b_start_eol != buf->b_p_eol)) {
    return true;
  }
  if (!buf->b_p_bin && buf->b_start_bomb != buf->b_p_bomb) {
    return true;
  }
  if (buf->b_start_fenc == NULL) {
    return *buf->b_p_fenc != NUL;
  }
  return strcmp(buf->b_start_fenc, buf->b_p_fenc) != 0;
}

/// Insert string "p" at the cursor position.  Stops at a NUL byte.
/// Handles Replace mode and multi-byte characters.
void ins_bytes(char *p)
{
  ins_bytes_len(p, strlen(p));
}

/// Insert string "p" with length "len" at the cursor position.
/// Handles Replace mode and multi-byte characters.
void ins_bytes_len(char *p, size_t len)
{
  size_t n;
  for (size_t i = 0; i < len; i += n) {
    // avoid reading past p[len]
    n = (size_t)utfc_ptr2len_len(p + i, (int)(len - i));
    ins_char_bytes(p + i, n);
  }
}

/// Insert or replace a single character at the cursor position.
/// When in MODE_REPLACE or MODE_VREPLACE state, replace any existing character.
/// Caller must have prepared for undo.
/// For multi-byte characters we get the whole character, the caller must
/// convert bytes to a character.
void ins_char(int c)
{
  char buf[MB_MAXCHAR + 1];
  size_t n = (size_t)utf_char2bytes(c, buf);

  // When "c" is 0x100, 0x200, etc. we don't want to insert a NUL byte.
  // Happens for CTRL-Vu9900.
  if (buf[0] == 0) {
    buf[0] = '\n';
  }
  ins_char_bytes(buf, n);
}

void ins_char_bytes(char *buf, size_t charlen)
{
  // Break tabs if needed.
  if (virtual_active(curwin) && curwin->w_cursor.coladd > 0) {
    coladvance_force(getviscol());
  }

  size_t col = (size_t)curwin->w_cursor.col;
  linenr_T lnum = curwin->w_cursor.lnum;
  char *oldp = ml_get(lnum);
  size_t linelen = (size_t)ml_get_len(lnum) + 1;  // length of old line including NUL

  // The lengths default to the values for when not replacing.
  size_t oldlen = 0;        // nr of bytes inserted
  size_t newlen = charlen;  // nr of bytes deleted (0 when not replacing)

  if (State & REPLACE_FLAG) {
    if (State & VREPLACE_FLAG) {
      // Disable 'list' temporarily, unless 'cpo' contains the 'L' flag.
      // Returns the old value of list, so when finished,
      // curwin->w_p_list should be set back to this.
      int old_list = curwin->w_p_list;
      if (old_list && vim_strchr(p_cpo, CPO_LISTWM) == NULL) {
        curwin->w_p_list = false;
      }
      // In virtual replace mode each character may replace one or more
      // characters (zero if it's a TAB).  Count the number of bytes to
      // be deleted to make room for the new character, counting screen
      // cells.  May result in adding spaces to fill a gap.
      colnr_T vcol;
      getvcol(curwin, &curwin->w_cursor, NULL, &vcol, NULL);
      colnr_T new_vcol = vcol + win_chartabsize(curwin, buf, vcol);
      while (oldp[col + oldlen] != NUL && vcol < new_vcol) {
        vcol += win_chartabsize(curwin, oldp + col + oldlen, vcol);
        // Don't need to remove a TAB that takes us to the right
        // position.
        if (vcol > new_vcol && oldp[col + oldlen] == TAB) {
          break;
        }
        oldlen += (size_t)utfc_ptr2len(oldp + col + oldlen);
        // Deleted a bit too much, insert spaces.
        if (vcol > new_vcol) {
          newlen += (size_t)(vcol - new_vcol);
        }
      }
      curwin->w_p_list = old_list;
    } else if (oldp[col] != NUL) {
      // normal replace
      oldlen = (size_t)utfc_ptr2len(oldp + col);
    }

    // Push the replaced bytes onto the replace stack, so that they can be
    // put back when BS is used.  The bytes of a multi-byte character are
    // done the other way around, so that the first byte is popped off
    // first (it tells the byte length of the character).
    replace_push_nul();
    replace_push(oldp + col, oldlen);
  }

  char *newp = xmalloc(linelen + newlen - oldlen);

  // Copy bytes before the cursor.
  if (col > 0) {
    memmove(newp, oldp, col);
  }

  // Copy bytes after the changed character(s).
  char *p = newp + col;
  if (linelen > col + oldlen) {
    memmove(p + newlen, oldp + col + oldlen, linelen - col - oldlen);
  }

  // Insert or overwrite the new character.
  memmove(p, buf, charlen);

  // Fill with spaces when necessary.
  for (size_t i = charlen; i < newlen; i++) {
    p[i] = ' ';
  }

  // Replace the line in the buffer.
  ml_replace(lnum, newp, false);

  // mark the buffer as changed and prepare for displaying
  inserted_bytes(lnum, (colnr_T)col, (int)oldlen, (int)newlen);

  // If we're in Insert or Replace mode and 'showmatch' is set, then briefly
  // show the match for right parens and braces.
  if (p_sm && (State & MODE_INSERT)
      && msg_silent == 0
      && !ins_compl_active()) {
    showmatch(utf_ptr2char(buf));
  }

  if (!p_ri || (State & REPLACE_FLAG)) {
    // Normal insert: move cursor right
    curwin->w_cursor.col += (colnr_T)charlen;
  }
  // TODO(Bram): should try to update w_row here, to avoid recomputing it later.
}

/// Insert a string at the cursor position.
/// Note: Does NOT handle Replace mode.
/// Caller must have prepared for undo.
void ins_str(char *s, size_t slen)
{
  linenr_T lnum = curwin->w_cursor.lnum;

  if (virtual_active(curwin) && curwin->w_cursor.coladd > 0) {
    coladvance_force(getviscol());
  }

  colnr_T col = curwin->w_cursor.col;
  char *oldp = ml_get(lnum);
  int oldlen = ml_get_len(lnum);

  char *newp = xmalloc((size_t)oldlen + slen + 1);
  if (col > 0) {
    memmove(newp, oldp, (size_t)col);
  }
  memmove(newp + col, s, slen);
  int bytes = oldlen - col + 1;
  assert(bytes >= 0);
  memmove(newp + col + slen, oldp + col, (size_t)bytes);
  ml_replace(lnum, newp, false);
  inserted_bytes(lnum, col, 0, (int)slen);
  curwin->w_cursor.col += (colnr_T)slen;
}

// Delete one character under the cursor.
// If "fixpos" is true, don't leave the cursor on the NUL after the line.
// Caller must have prepared for undo.
//
// return FAIL for failure, OK otherwise
int del_char(bool fixpos)
{
  // Make sure the cursor is at the start of a character.
  mb_adjust_cursor();
  if (*get_cursor_pos_ptr() == NUL) {
    return FAIL;
  }
  return del_chars(1, fixpos);
}

/// Like del_bytes(), but delete characters instead of bytes.
int del_chars(int count, int fixpos)
{
  int bytes = 0;
  char *p = get_cursor_pos_ptr();
  for (int i = 0; i < count && *p != NUL; i++) {
    int l = utfc_ptr2len(p);
    bytes += l;
    p += l;
  }
  return del_bytes(bytes, fixpos, true);
}

/// Delete "count" bytes under the cursor.
/// If "fixpos" is true, don't leave the cursor on the NUL after the line.
/// Caller must have prepared for undo.
///
/// @param  count           number of bytes to be deleted
/// @param  fixpos_arg      leave the cursor on the NUL after the line
/// @param  use_delcombine  'delcombine' option applies
///
/// @return FAIL for failure, OK otherwise
int del_bytes(colnr_T count, bool fixpos_arg, bool use_delcombine)
{
  linenr_T lnum = curwin->w_cursor.lnum;
  colnr_T col = curwin->w_cursor.col;
  bool fixpos = fixpos_arg;
  char *oldp = ml_get(lnum);
  colnr_T oldlen = ml_get_len(lnum);

  // Can't do anything when the cursor is on the NUL after the line.
  if (col >= oldlen) {
    return FAIL;
  }
  // If "count" is zero there is nothing to do.
  if (count == 0) {
    return OK;
  }
  // If "count" is negative the caller must be doing something wrong.
  if (count < 1) {
    siemsg("E292: Invalid count for del_bytes(): %ld", (int64_t)count);
    return FAIL;
  }

  // If 'delcombine' is set and deleting (less than) one character, only
  // delete the last combining character.
  if (p_deco && use_delcombine && utfc_ptr2len(oldp + col) >= count) {
    char *p0 = oldp + col;
    GraphemeState state = GRAPHEME_STATE_INIT;
    if (utf_composinglike(p0, p0 + utf_ptr2len(p0), &state)) {
      // Find the last composing char, there can be several.
      int n = col;
      do {
        col = n;
        count = utf_ptr2len(oldp + n);
        n += count;
      } while (utf_composinglike(oldp + col, oldp + n, &state));
      fixpos = false;
    }
  }

  // When count is too big, reduce it.
  int movelen = oldlen - col - count + 1;  // includes trailing NUL
  if (movelen <= 1) {
    // If we just took off the last character of a non-blank line, and
    // fixpos is true, we don't want to end up positioned at the NUL,
    // unless "restart_edit" is set or 'virtualedit' contains "onemore".
    if (col > 0 && fixpos && restart_edit == 0
        && (get_ve_flags(curwin) & kOptVeFlagOnemore) == 0) {
      curwin->w_cursor.col--;
      curwin->w_cursor.coladd = 0;
      curwin->w_cursor.col -= utf_head_off(oldp, oldp + curwin->w_cursor.col);
    }
    count = oldlen - col;
    movelen = 1;
  }
  colnr_T newlen = oldlen - count;

  // If the old line has been allocated the deletion can be done in the
  // existing line. Otherwise a new line has to be allocated.
  bool alloc_newp = !ml_line_alloced();     // check if oldp was allocated
  char *newp;
  if (!alloc_newp) {
    ml_add_deleted_len(curbuf->b_ml.ml_line_ptr, oldlen);
    newp = oldp;                            // use same allocated memory
  } else {                                  // need to allocate a new line
    newp = xmallocz((size_t)newlen);
    memmove(newp, oldp, (size_t)col);
  }
  memmove(newp + col, oldp + col + count, (size_t)movelen);
  if (alloc_newp) {
    ml_replace(lnum, newp, false);
  } else {
    curbuf->b_ml.ml_line_textlen = newlen + 1;
  }

  // mark the buffer as changed and prepare for displaying
  inserted_bytes(lnum, col, count, 0);

  return OK;
}

/// open_line: Add a new line below or above the current line.
///
/// For MODE_VREPLACE state, we only add a new line when we get to the end of
/// the file, otherwise we just start replacing the next line.
///
/// Caller must take care of undo.  Since MODE_VREPLACE may affect any number of
/// lines however, it may call u_save_cursor() again when starting to change a
/// new line.
/// "flags": OPENLINE_DELSPACES delete spaces after cursor
///          OPENLINE_DO_COM    format comments
///          OPENLINE_KEEPTRAIL keep trailing spaces
///          OPENLINE_MARKFIX   adjust mark positions after the line break
///          OPENLINE_COM_LIST  format comments with list or 2nd line indent
///          OPENLINE_FORCE_INDENT  set indent from second_line_indent, ignore 'autoindent'
///
/// "second_line_indent": indent for after ^^D in Insert mode or if flag
///                       OPENLINE_COM_LIST
/// "did_do_comment" is set to true when intentionally putting the comment
/// leader in front of the new line.
///
/// @param dir  FORWARD or BACKWARD
///
/// @return true on success, false on failure
bool open_line(int dir, int flags, int second_line_indent, bool *did_do_comment)
{
  char *next_line = NULL;         // copy of the next line
  char *p_extra = NULL;           // what goes to next line
  colnr_T less_cols = 0;          // less columns for mark in new line
  colnr_T less_cols_off = 0;      // columns to skip for mark adjust
  pos_T old_cursor;               // old cursor position
  colnr_T newcol = 0;             // new cursor column
  int newindent = 0;              // auto-indent of the new line
  bool trunc_line = false;        // truncate current line afterwards
  bool retval = false;            // return value
  int extra_len = 0;              // length of p_extra string
  int lead_len;                   // length of comment leader
  int comment_start = 0;          // start index of the comment leader
  char *lead_flags;               // position in 'comments' for comment leader
  char *leader = NULL;            // copy of comment leader
  char *allocated = NULL;         // allocated memory
  char *p;
  char saved_char = NUL;          // init for GCC
  pos_T *pos;
  bool do_si = may_do_si();
  bool no_si = false;             // reset did_si afterwards
  int first_char = NUL;           // init for GCC
  int vreplace_mode;
  bool did_append;                // appended a new line
  int saved_pi = curbuf->b_p_pi;  // copy of preserveindent setting

  linenr_T lnum = curwin->w_cursor.lnum;
  colnr_T mincol = curwin->w_cursor.col + 1;

  // make a copy of the current line so we can mess with it
  char *saved_line = xstrnsave(get_cursor_line_ptr(), (size_t)get_cursor_line_len());

  if (State & VREPLACE_FLAG) {
    // With MODE_VREPLACE we make a copy of the next line, which we will be
    // starting to replace.  First make the new line empty and let vim play
    // with the indenting and comment leader to its heart's content.  Then
    // we grab what it ended up putting on the new line, put back the
    // original line, and call ins_char() to put each new character onto
    // the line, replacing what was there before and pushing the right
    // stuff onto the replace stack.  -- webb.
    if (curwin->w_cursor.lnum < orig_line_count) {
      next_line = xstrnsave(ml_get(curwin->w_cursor.lnum + 1),
                            (size_t)ml_get_len(curwin->w_cursor.lnum + 1));
    } else {
      next_line = xstrdup("");
    }

    // In MODE_VREPLACE state, a NL replaces the rest of the line, and
    // starts replacing the next line, so push all of the characters left
    // on the line onto the replace stack.  We'll push any other characters
    // that might be replaced at the start of the next line (due to
    // autoindent etc) a bit later.
    replace_push_nul();      // Call twice because BS over NL expects it
    replace_push_nul();
    p = saved_line + curwin->w_cursor.col;
    replace_push(p, strlen(p));
    saved_line[curwin->w_cursor.col] = NUL;
  }

  if ((State & MODE_INSERT) && (State & VREPLACE_FLAG) == 0) {
    p_extra = saved_line + curwin->w_cursor.col;
    if (do_si) {  // need first char after new line break
      p = skipwhite(p_extra);
      first_char = (unsigned char)(*p);
    }
    extra_len = (int)strlen(p_extra);
    saved_char = *p_extra;
    *p_extra = NUL;
  }

  u_clearline(curbuf);  // cannot do "U" command when adding lines
  did_si = false;
  ai_col = 0;

  // If we just did an auto-indent, then we didn't type anything on
  // the prior line, and it should be truncated.  Do this even if 'ai' is not
  // set because automatically inserting a comment leader also sets did_ai.
  if (dir == FORWARD && did_ai) {
    trunc_line = true;
  }

  if ((flags & OPENLINE_FORCE_INDENT)) {
    newindent = second_line_indent;
  } else if (curbuf->b_p_ai || do_si) {
    // If 'autoindent' and/or 'smartindent' is set, try to figure out what
    // indent to use for the new line.
    // count white space on current line
    newindent = indent_size_ts(saved_line, curbuf->b_p_ts, curbuf->b_p_vts_array);
    if (newindent == 0 && !(flags & OPENLINE_COM_LIST)) {
      newindent = second_line_indent;  // for ^^D command in insert mode
    }

    // Do smart indenting.
    // In insert/replace mode (only when dir == FORWARD)
    // we may move some text to the next line. If it starts with '{'
    // don't add an indent. Fixes inserting a NL before '{' in line
    //   "if (condition) {"
    if (!trunc_line && do_si && *saved_line != NUL
        && (p_extra == NULL || first_char != '{')) {
      old_cursor = curwin->w_cursor;
      char *ptr = saved_line;
      if (flags & OPENLINE_DO_COM) {
        lead_len = get_leader_len(ptr, NULL, false, true);
      } else {
        lead_len = 0;
      }
      if (dir == FORWARD) {
        // Skip preprocessor directives, unless they are recognised as comments.
        if (lead_len == 0 && ptr[0] == '#') {
          while (ptr[0] == '#' && curwin->w_cursor.lnum > 1) {
            ptr = ml_get(--curwin->w_cursor.lnum);
          }
          newindent = get_indent();
        }
        if (flags & OPENLINE_DO_COM) {
          lead_len = get_leader_len(ptr, NULL, false, true);
        } else {
          lead_len = 0;
        }
        if (lead_len > 0) {
          // This case gets the following right:
          //     \*
          //      * A comment (read '\' as '/').
          //      */
          //     #define IN_THE_WAY
          //     This should line up here;
          p = skipwhite(ptr);
          if (p[0] == '/' && p[1] == '*') {
            p++;
          }
          if (p[0] == '*') {
            for (p++; *p; p++) {
              if (p[0] == '/' && p[-1] == '*') {
                // End of C comment, indent should line up
                // with the line containing the start of
                // the comment.
                curwin->w_cursor.col = (colnr_T)(p - ptr);
                if ((pos = findmatch(NULL, NUL)) != NULL) {
                  curwin->w_cursor.lnum = pos->lnum;
                  newindent = get_indent();
                  break;
                }
                // this may make "ptr" invalid, get it again
                ptr = ml_get(curwin->w_cursor.lnum);
                p = ptr + curwin->w_cursor.col;
              }
            }
          }
        } else {      // Not a comment line
          // Find last non-blank in line
          p = ptr + strlen(ptr) - 1;
          while (p > ptr && ascii_iswhite(*p)) {
            p--;
          }
          char last_char = *p;

          // find the character just before the '{' or ';'
          if (last_char == '{' || last_char == ';') {
            if (p > ptr) {
              p--;
            }
            while (p > ptr && ascii_iswhite(*p)) {
              p--;
            }
          }
          // Try to catch lines that are split over multiple
          // lines.  eg:
          //     if (condition &&
          //             condition) {
          //         Should line up here!
          //     }
          if (*p == ')') {
            curwin->w_cursor.col = (colnr_T)(p - ptr);
            if ((pos = findmatch(NULL, '(')) != NULL) {
              curwin->w_cursor.lnum = pos->lnum;
              newindent = get_indent();
              ptr = get_cursor_line_ptr();
            }
          }
          // If last character is '{' do indent, without
          // checking for "if" and the like.
          if (last_char == '{') {
            did_si = true;              // do indent
            no_si = true;               // don't delete it when '{' typed
            // Look for "if" and the like, use 'cinwords'.
            // Don't do this if the previous line ended in ';' or
            // '}'.
          } else if (last_char != ';' && last_char != '}'
                     && cin_is_cinword(ptr)) {
            did_si = true;
          }
        }
      } else {  // dir == BACKWARD
        // Skip preprocessor directives, unless they are
        // recognised as comments.
        if (lead_len == 0 && ptr[0] == '#') {
          bool was_backslashed = false;

          while ((ptr[0] == '#' || was_backslashed)
                 && curwin->w_cursor.lnum < curbuf->b_ml.ml_line_count) {
            if (*ptr && ptr[strlen(ptr) - 1] == '\\') {
              was_backslashed = true;
            } else {
              was_backslashed = false;
            }
            ptr = ml_get(++curwin->w_cursor.lnum);
          }
          if (was_backslashed) {
            newindent = 0;  // Got to end of file
          } else {
            newindent = get_indent();
          }
        }
        p = skipwhite(ptr);
        if (*p == '}') {            // if line starts with '}': do indent
          did_si = true;
        } else {                    // can delete indent when '{' typed
          can_si_back = true;
        }
      }
      curwin->w_cursor = old_cursor;
    }
    if (do_si) {
      can_si = true;
    }

    did_ai = true;
  }

  // May do indenting after opening a new line.
  bool do_cindent = !p_paste && (curbuf->b_p_cin || *curbuf->b_p_inde != NUL)
                    && in_cinkeys(dir == FORWARD ? KEY_OPEN_FORW : KEY_OPEN_BACK,
                                  ' ', linewhite(curwin->w_cursor.lnum))
                    && !(flags & OPENLINE_FORCE_INDENT);

  // Find out if the current line starts with a comment leader.
  // This may then be inserted in front of the new line.
  end_comment_pending = NUL;
  if (flags & OPENLINE_DO_COM) {
    lead_len = get_leader_len(saved_line, &lead_flags, dir == BACKWARD, true);
    if (lead_len == 0 && curbuf->b_p_cin && do_cindent && dir == FORWARD
        && (!has_format_option(FO_NO_OPEN_COMS) || (flags & OPENLINE_FORMAT))) {
      // Check for a line comment after code.
      comment_start = check_linecomment(saved_line);
      if (comment_start != MAXCOL) {
        lead_len = get_leader_len(saved_line + comment_start, &lead_flags, false, true);
        if (lead_len != 0) {
          lead_len += comment_start;
          if (did_do_comment != NULL) {
            *did_do_comment = true;
          }
        }
      }
    }
  } else {
    lead_len = 0;
  }
  if (lead_len > 0) {
    char *lead_repl = NULL;                 // replaces comment leader
    int lead_repl_len = 0;                  // length of *lead_repl
    char lead_middle[COM_MAX_LEN];          // middle-comment string
    int lead_middle_len;                    // length of the lead_middle
    char lead_end[COM_MAX_LEN];             // end-comment string
    char *comment_end = NULL;               // where lead_end has been found
    int extra_space = false;                // append extra space
    bool require_blank = false;             // requires blank after middle
    char *p2;

    // If the comment leader has the start, middle or end flag, it may not
    // be used or may be replaced with the middle leader.
    for (p = lead_flags; *p && *p != ':'; p++) {
      if (*p == COM_BLANK) {
        require_blank = true;
        continue;
      }
      if (*p == COM_START || *p == COM_MIDDLE) {
        int current_flag = (unsigned char)(*p);
        if (*p == COM_START) {
          // Doing "O" on a start of comment does not insert leader.
          if (dir == BACKWARD) {
            lead_len = 0;
            break;
          }

          // find start of middle part
          copy_option_part(&p, lead_middle, COM_MAX_LEN, ",");
          require_blank = false;
        }

        // Isolate the strings of the middle and end leader.
        while (*p && p[-1] != ':') {  // find end of middle flags
          if (*p == COM_BLANK) {
            require_blank = true;
          }
          p++;
        }
        lead_middle_len = (int)copy_option_part(&p, lead_middle, COM_MAX_LEN, ",");

        while (*p && p[-1] != ':') {  // find end of end flags
          // Check whether we allow automatic ending of comments
          if (*p == COM_AUTO_END) {
            end_comment_pending = -1;  // means we want to set it
          }
          p++;
        }
        size_t n = copy_option_part(&p, lead_end, COM_MAX_LEN, ",");

        if (end_comment_pending == -1) {  // we can set it now
          end_comment_pending = (unsigned char)lead_end[n - 1];
        }

        // If the end of the comment is in the same line, don't use
        // the comment leader.
        if (dir == FORWARD) {
          for (p = saved_line + lead_len; *p; p++) {
            if (strncmp(p, lead_end, n) == 0) {
              comment_end = p;
              lead_len = 0;
              break;
            }
          }
        }

        // Doing "o" on a start of comment inserts the middle leader.
        if (lead_len > 0) {
          if (current_flag == COM_START) {
            lead_repl = lead_middle;
            lead_repl_len = lead_middle_len;
          }

          // If we have hit RETURN immediately after the start
          // comment leader, then put a space after the middle
          // comment leader on the next line.
          if (!ascii_iswhite(saved_line[lead_len - 1])
              && ((p_extra != NULL
                   && (int)curwin->w_cursor.col == lead_len)
                  || (p_extra == NULL
                      && saved_line[lead_len] == NUL)
                  || require_blank)) {
            extra_space = true;
          }
        }
        break;
      }
      if (*p == COM_END) {
        // Doing "o" on the end of a comment does not insert leader.
        // Remember where the end is, might want to use it to find the
        // start (for C-comments).
        if (dir == FORWARD) {
          comment_end = skipwhite(saved_line);
          lead_len = 0;
          break;
        }

        // Doing "O" on the end of a comment inserts the middle leader.
        // Find the string for the middle leader, searching backwards.
        while (p > curbuf->b_p_com && *p != ',') {
          p--;
        }
        for (lead_repl = p; lead_repl > curbuf->b_p_com
             && lead_repl[-1] != ':'; lead_repl--) {}
        lead_repl_len = (int)(p - lead_repl);

        // We can probably always add an extra space when doing "O" on
        // the comment-end
        extra_space = true;

        // Check whether we allow automatic ending of comments
        for (p2 = p; *p2 && *p2 != ':'; p2++) {
          if (*p2 == COM_AUTO_END) {
            end_comment_pending = -1;  // means we want to set it
          }
        }
        if (end_comment_pending == -1) {
          // Find last character in end-comment string
          while (*p2 && *p2 != ',') {
            p2++;
          }
          end_comment_pending = (unsigned char)p2[-1];
        }
        break;
      }
      if (*p == COM_FIRST) {
        // Comment leader for first line only: Don't repeat leader
        // when using "O", blank out leader when using "o".
        if (dir == BACKWARD) {
          lead_len = 0;
        } else {
          lead_repl = "";
          lead_repl_len = 0;
        }
        break;
      }
    }
    if (lead_len > 0) {
      // allocate buffer (may concatenate p_extra later)
      int bytes = lead_len
                  + lead_repl_len
                  + extra_space
                  + extra_len
                  + (second_line_indent > 0 ? second_line_indent : 0)
                  + 1;
      assert(bytes >= 0);
      leader = xmalloc((size_t)bytes);
      allocated = leader;  // remember to free it later

      xmemcpyz(leader, saved_line, (size_t)lead_len);

      // TODO(vim): handle multi-byte and double width chars
      for (int li = 0; li < comment_start; li++) {
        if (!ascii_iswhite(leader[li])) {
          leader[li] = ' ';
        }
      }

      // Replace leader with lead_repl, right or left adjusted
      if (lead_repl != NULL) {
        int c = 0;
        int off = 0;

        for (p = lead_flags; *p != NUL && *p != ':';) {
          if (*p == COM_RIGHT || *p == COM_LEFT) {
            c = (unsigned char)(*p++);
          } else if (ascii_isdigit(*p) || *p == '-') {
            off = getdigits_int(&p, true, 0);
          } else {
            p++;
          }
        }
        if (c == COM_RIGHT) {  // right adjusted leader
          // find last non-white in the leader to line up with
          for (p = leader + lead_len - 1; p > leader
               && ascii_iswhite(*p); p--) {}
          p++;

          // Compute the length of the replaced characters in
          // screen characters, not bytes.
          {
            int repl_size = vim_strnsize(lead_repl, lead_repl_len);
            int old_size = 0;
            char *endp = p;

            while (old_size < repl_size && p > leader) {
              MB_PTR_BACK(leader, p);
              old_size += ptr2cells(p);
            }
            int l = lead_repl_len - (int)(endp - p);
            if (l != 0) {
              memmove(endp + l, endp,
                      (size_t)((leader + lead_len) - endp));
            }
            lead_len += l;
          }
          memmove(p, lead_repl, (size_t)lead_repl_len);
          if (p + lead_repl_len > leader + lead_len) {
            p[lead_repl_len] = NUL;
          }

          // blank-out any other chars from the old leader.
          while (--p >= leader) {
            int l = utf_head_off(leader, p);

            if (l > 1) {
              p -= l;
              if (ptr2cells(p) > 1) {
                p[1] = ' ';
                l--;
              }
              memmove(p + 1, p + l + 1,
                      (size_t)((leader + lead_len) - (p + l + 1)));
              lead_len -= l;
              *p = ' ';
            } else if (!ascii_iswhite(*p)) {
              *p = ' ';
            }
          }
        } else {  // left adjusted leader
          p = skipwhite(leader);
          // Compute the length of the replaced characters in
          // screen characters, not bytes. Move the part that is
          // not to be overwritten.
          {
            int repl_size = vim_strnsize(lead_repl, lead_repl_len);
            int i;
            int l;

            for (i = 0; i < lead_len && p[i] != NUL; i += l) {
              l = utfc_ptr2len(p + i);
              if (vim_strnsize(p, i + l) > repl_size) {
                break;
              }
            }
            if (i != lead_repl_len) {
              memmove(p + lead_repl_len, p + i,
                      (size_t)(lead_len - i - (p - leader)));
              lead_len += lead_repl_len - i;
            }
          }
          memmove(p, lead_repl, (size_t)lead_repl_len);

          // Replace any remaining non-white chars in the old
          // leader by spaces.  Keep Tabs, the indent must
          // remain the same.
          for (p += lead_repl_len; p < leader + lead_len; p++) {
            if (!ascii_iswhite(*p)) {
              // Don't put a space before a TAB.
              if (p + 1 < leader + lead_len && p[1] == TAB) {
                lead_len--;
                memmove(p, p + 1, (size_t)(leader + lead_len - p));
              } else {
                int l = utfc_ptr2len(p);

                if (l > 1) {
                  if (ptr2cells(p) > 1) {
                    // Replace a double-wide char with
                    // two spaces
                    l--;
                    *p++ = ' ';
                  }
                  memmove(p + 1, p + l, (size_t)(leader + lead_len - p));
                  lead_len -= l - 1;
                }
                *p = ' ';
              }
            }
          }
          *p = NUL;
        }

        // Recompute the indent, it may have changed.
        if (curbuf->b_p_ai || do_si) {
          newindent = indent_size_ts(leader, curbuf->b_p_ts, curbuf->b_p_vts_array);
        }

        // Add the indent offset
        if (newindent + off < 0) {
          off = -newindent;
          newindent = 0;
        } else {
          newindent += off;
        }

        // Correct trailing spaces for the shift, so that
        // alignment remains equal.
        while (off > 0 && lead_len > 0
               && leader[lead_len - 1] == ' ') {
          // Don't do it when there is a tab before the space
          if (vim_strchr(skipwhite(leader), '\t') != NULL) {
            break;
          }
          lead_len--;
          off--;
        }

        // If the leader ends in white space, don't add an
        // extra space
        if (lead_len > 0 && ascii_iswhite(leader[lead_len - 1])) {
          extra_space = false;
        }
        leader[lead_len] = NUL;
      }

      if (extra_space) {
        leader[lead_len++] = ' ';
        leader[lead_len] = NUL;
      }

      newcol = lead_len;

      // if a new indent will be set below, remove the indent that
      // is in the comment leader
      if (newindent || did_si) {
        while (lead_len && ascii_iswhite(*leader)) {
          lead_len--;
          newcol--;
          leader++;
        }
      }
      did_si = can_si = false;
    } else if (comment_end != NULL) {
      // We have finished a comment, so we don't use the leader.
      // If this was a C-comment and 'ai' or 'si' is set do a normal
      // indent to align with the line containing the start of the
      // comment.
      if (comment_end[0] == '*' && comment_end[1] == '/'
          && (curbuf->b_p_ai || do_si)) {
        old_cursor = curwin->w_cursor;
        curwin->w_cursor.col = (colnr_T)(comment_end - saved_line);
        if ((pos = findmatch(NULL, NUL)) != NULL) {
          curwin->w_cursor.lnum = pos->lnum;
          newindent = get_indent();
        }
        curwin->w_cursor = old_cursor;
      }
    }
  }

  // (State == MODE_INSERT || State == MODE_REPLACE), only when dir == FORWARD
  if (p_extra != NULL) {
    *p_extra = saved_char;              // restore char that NUL replaced

    // When 'ai' set or "flags" has OPENLINE_DELSPACES, skip to the first
    // non-blank.
    //
    // When in MODE_REPLACE state, put the deleted blanks on the replace
    // stack, preceded by a NUL, so they can be put back when a BS is
    // entered.
    if (REPLACE_NORMAL(State)) {
      replace_push_nul();            // end of extra blanks
    }
    if (curbuf->b_p_ai || (flags & OPENLINE_DELSPACES)) {
      while ((*p_extra == ' ' || *p_extra == '\t')
             && !utf_iscomposing_first(utf_ptr2char(p_extra + 1))) {
        if (REPLACE_NORMAL(State)) {
          replace_push(p_extra, 1);  // always ascii, len = 1
        }
        p_extra++;
        less_cols_off++;
      }
    }

    // columns for marks adjusted for removed columns
    less_cols = (int)(p_extra - saved_line);
  }

  if (p_extra == NULL) {
    p_extra = "";                 // append empty line
  }

  // concatenate leader and p_extra, if there is a leader
  if (lead_len > 0) {
    if (flags & OPENLINE_COM_LIST && second_line_indent > 0) {
      int padding = second_line_indent
                    - (newindent + (int)strlen(leader));

      // Here whitespace is inserted after the comment char.
      // Below, set_indent(newindent, SIN_INSERT) will insert the
      // whitespace needed before the comment char.
      for (int i = 0; i < padding; i++) {
        strcat(leader, " ");
        less_cols--;
        newcol++;
      }
    }
    strcat(leader, p_extra);
    p_extra = leader;
    did_ai = true;          // So truncating blanks works with comments
    less_cols -= lead_len;
  } else {
    end_comment_pending = NUL;  // turns out there was no leader
  }

  curbuf_splice_pending++;
  old_cursor = curwin->w_cursor;
  int old_cmod_flags = cmdmod.cmod_flags;
  char *prompt_moved = NULL;
  if (dir == BACKWARD) {
    // In case of prompt buffer, when we are applying 'normal O' operation on line of prompt,
    // we can't add a new line before the prompt. In this case, we move the prompt text one
    // line below and create a new prompt line as current line.
    if (bt_prompt(curbuf) && curwin->w_cursor.lnum == curbuf->b_prompt_start.mark.lnum) {
      char *prompt_line = ml_get(curwin->w_cursor.lnum);
      char *prompt = prompt_text();
      size_t prompt_len = strlen(prompt);

      if (strncmp(prompt_line, prompt, prompt_len) == 0) {
        STRMOVE(prompt_line, prompt_line + prompt_len);
        // We are moving the lines but the b_prompt_start mark needs to stay in
        // place so freezing marks before making the move.
        cmdmod.cmod_flags = cmdmod.cmod_flags | CMOD_LOCKMARKS;
        ml_replace(curwin->w_cursor.lnum, prompt_line, true);
        prompt_moved = concat_str(prompt, p_extra);
        p_extra = prompt_moved;
      }
    }
    curwin->w_cursor.lnum--;
  }
  if ((State & VREPLACE_FLAG) == 0 || old_cursor.lnum >= orig_line_count) {
    if (ml_append(curwin->w_cursor.lnum, p_extra, 0, false) == FAIL) {
      goto theend;
    }
    // Postpone calling changed_lines(), because it would mess up folding
    // with markers.
    mark_adjust(curwin->w_cursor.lnum + 1, (linenr_T)MAXLNUM, 1, 0, kExtmarkNOOP);
    did_append = true;
  } else {
    // In MODE_VREPLACE state we are starting to replace the next line.
    curwin->w_cursor.lnum++;
    if (curwin->w_cursor.lnum >= Insstart.lnum + vr_lines_changed) {
      // In case we NL to a new line, BS to the previous one, and NL
      // again, we don't want to save the new line for undo twice.
      u_save_cursor();  // errors are ignored!
      vr_lines_changed++;
    }
    ml_replace(curwin->w_cursor.lnum, p_extra, true);
    changed_bytes(curwin->w_cursor.lnum, 0);
    // TODO(vigoux): extmark_splice_cols here??
    curwin->w_cursor.lnum--;
    did_append = false;
  }

  inhibit_delete_count++;
  if (newindent || did_si) {
    curwin->w_cursor.lnum++;
    if (did_si) {
      int sw = get_sw_value(curbuf);

      if (p_sr) {
        newindent -= newindent % sw;
      }
      newindent += sw;
    }
    // Copy the indent
    if (curbuf->b_p_ci) {
      copy_indent(newindent, saved_line);

      // Set the 'preserveindent' option so that any further screwing
      // with the line doesn't entirely destroy our efforts to preserve
      // it.  It gets restored at the function end.
      curbuf->b_p_pi = true;
    } else {
      set_indent(newindent, SIN_INSERT|SIN_NOMARK);
    }
    less_cols -= curwin->w_cursor.col;

    ai_col = curwin->w_cursor.col;

    // In MODE_REPLACE state, for each character in the new indent, there
    // must be a NUL on the replace stack, for when it is deleted with BS
    if (REPLACE_NORMAL(State)) {
      for (colnr_T n = 0; n < curwin->w_cursor.col; n++) {
        replace_push_nul();
      }
    }
    newcol += curwin->w_cursor.col;
    if (no_si) {
      did_si = false;
    }
  }
  inhibit_delete_count--;

  // In MODE_REPLACE state, for each character in the extra leader, there
  // must be a NUL on the replace stack, for when it is deleted with BS.
  if (REPLACE_NORMAL(State)) {
    while (lead_len-- > 0) {
      replace_push_nul();
    }
  }

  curwin->w_cursor = old_cursor;

  if (dir == FORWARD) {
    if (trunc_line || (State & MODE_INSERT)) {
      // truncate current line at cursor
      saved_line[curwin->w_cursor.col] = NUL;
      // Remove trailing white space, unless OPENLINE_KEEPTRAIL used.
      if (trunc_line && !(flags & OPENLINE_KEEPTRAIL)) {
        truncate_spaces(saved_line, (size_t)curwin->w_cursor.col);
      }
      ml_replace(curwin->w_cursor.lnum, saved_line, false);

      int new_len = (int)strlen(saved_line);

      // TODO(vigoux): maybe there is issues there with expandtabs ?
      int cols_spliced = 0;
      if (new_len < curwin->w_cursor.col) {
        extmark_splice_cols(curbuf, (int)curwin->w_cursor.lnum - 1,
                            new_len, curwin->w_cursor.col - new_len, 0, kExtmarkUndo);
        cols_spliced = curwin->w_cursor.col - new_len;
      }

      saved_line = NULL;
      if (did_append) {
        // Always move extmarks - Here we move only the line where the cursor is,
        // the previous mark_adjust() took care of the lines after.
        int cols_added = mincol - 1 + less_cols_off - less_cols;
        extmark_splice(curbuf, (int)lnum - 1, mincol - 1 - cols_spliced,
                       0, less_cols_off, less_cols_off,
                       1, cols_added, 1 + cols_added, kExtmarkUndo);

        changed_lines(curbuf, curwin->w_cursor.lnum, curwin->w_cursor.col,
                      curwin->w_cursor.lnum + 1, 1, true);
        did_append = false;

        // Move marks after the line break to the new line.
        if (flags & OPENLINE_MARKFIX) {
          mark_col_adjust(curwin->w_cursor.lnum,
                          curwin->w_cursor.col + less_cols_off,
                          1, -less_cols, 0);
        }
      } else {
        changed_bytes(curwin->w_cursor.lnum, curwin->w_cursor.col);
      }
    }

    // Put the cursor on the new line.  Careful: the scrollup() above may
    // have moved w_cursor, we must use old_cursor.
    curwin->w_cursor.lnum = old_cursor.lnum + 1;
  }
  if (did_append) {
    // bail out and just get the final length of the line we just manipulated
    bcount_t extra = ml_get_len(curwin->w_cursor.lnum);
    extmark_splice(curbuf, (int)curwin->w_cursor.lnum - 1, 0,
                   0, 0, 0, 1, 0, 1 + extra, kExtmarkUndo);
    changed_lines(curbuf, curwin->w_cursor.lnum, 0, curwin->w_cursor.lnum, 1, true);
  }
  curbuf_splice_pending--;

  curwin->w_cursor.col = newcol;
  curwin->w_cursor.coladd = 0;

  // In MODE_VREPLACE state, we are handling the replace stack ourselves, so
  // stop fixthisline() from doing it (via change_indent()) by telling it
  // we're in normal MODE_INSERT state.
  if (State & VREPLACE_FLAG) {
    vreplace_mode = State;  // So we know to put things right later
    State = MODE_INSERT;
  } else {
    vreplace_mode = 0;
  }

  if (!p_paste) {
    if (leader == NULL
        && !use_indentexpr_for_lisp()
        && curbuf->b_p_lisp
        && curbuf->b_p_ai) {
      // do lisp indenting
      fixthisline(get_lisp_indent);
      ai_col = (colnr_T)getwhitecols_curline();
    } else if (do_cindent || (curbuf->b_p_ai && use_indentexpr_for_lisp())) {
      // do 'cindent' or 'indentexpr' indenting
      do_c_expr_indent();
      ai_col = (colnr_T)getwhitecols_curline();
    }
  }

  if (vreplace_mode != 0) {
    State = vreplace_mode;
  }

  // Finally, MODE_VREPLACE gets the stuff on the new line, then puts back
  // the original line, and inserts the new stuff char by char, pushing old
  // stuff onto the replace stack (via ins_char()).
  if (State & VREPLACE_FLAG) {
    // Put new line in p_extra
    p_extra = xstrnsave(get_cursor_line_ptr(), (size_t)get_cursor_line_len());

    // Put back original line
    ml_replace(curwin->w_cursor.lnum, next_line, false);

    // Insert new stuff into line again
    curwin->w_cursor.col = 0;
    curwin->w_cursor.coladd = 0;
    ins_bytes(p_extra);         // will call changed_bytes()
    xfree(p_extra);
    next_line = NULL;
  }

  retval = true;                // success!
theend:
  curbuf->b_p_pi = saved_pi;
  xfree(saved_line);
  xfree(next_line);
  xfree(allocated);
  xfree(prompt_moved);
  cmdmod.cmod_flags = old_cmod_flags;
  return retval;
}

/// Delete from cursor to end of line.
/// Caller must have prepared for undo.
/// If "fixpos" is true fix the cursor position when done.
void truncate_line(int fixpos)
{
  linenr_T lnum = curwin->w_cursor.lnum;
  colnr_T col = curwin->w_cursor.col;
  char *old_line = ml_get(lnum);
  char *newp = col == 0 ? xstrdup("") : xstrnsave(old_line, (size_t)col);
  int deleted = ml_get_len(lnum) - col;

  ml_replace(lnum, newp, false);

  // mark the buffer as changed and prepare for displaying
  inserted_bytes(lnum, curwin->w_cursor.col, deleted, 0);

  // If "fixpos" is true we don't want to end up positioned at the NUL.
  if (fixpos && curwin->w_cursor.col > 0) {
    curwin->w_cursor.col--;
  }
}

/// Delete "nlines" lines at the cursor.
/// Saves the lines for undo first if "undo" is true.
void del_lines(linenr_T nlines, bool undo)
{
  int n;
  linenr_T first = curwin->w_cursor.lnum;

  if (nlines <= 0) {
    return;
  }

  // save the deleted lines for undo
  if (undo && u_savedel(first, nlines) == FAIL) {
    return;
  }

  for (n = 0; n < nlines;) {
    if (curbuf->b_ml.ml_flags & ML_EMPTY) {  // nothing to delete
      break;
    }

    ml_delete_flags(first, ML_DEL_MESSAGE);
    n++;

    // If we delete the last line in the file, stop
    if (first > curbuf->b_ml.ml_line_count) {
      break;
    }
  }

  // Correct the cursor position before calling deleted_lines_mark(), it may
  // trigger a callback to display the cursor.
  curwin->w_cursor.col = 0;
  check_cursor_lnum(curwin);

  // adjust marks, mark the buffer as changed and prepare for displaying
  deleted_lines_mark(first, n);
}

/// Returns the length in bytes of the prefix of the given string which introduces a comment.
///
/// If this string is not a comment then 0 is returned.
/// When "flags" is not NULL, it is set to point to the flags of the recognized comment leader.
/// "backward" must be true for the "O" command.
/// If "include_space" is set, include trailing whitespace while calculating the length.
int get_leader_len(char *line, char **flags, bool backward, bool include_space)
{
  int j;
  bool got_com = false;
  char part_buf[COM_MAX_LEN];         // buffer for one option part
  char *string;                  // pointer to comment string
  int middle_match_len = 0;
  char *saved_flags = NULL;

  int result = 0;
  int i = 0;
  while (ascii_iswhite(line[i])) {  // leading white space is ignored
    i++;
  }

  // Repeat to match several nested comment strings.
  while (line[i] != NUL) {
    // scan through the 'comments' option for a match
    bool found_one = false;
    for (char *list = curbuf->b_p_com; *list;) {
      // Get one option part into part_buf[].  Advance "list" to next
      // one.  Put "string" at start of string.
      if (!got_com && flags != NULL) {
        *flags = list;              // remember where flags started
      }
      char *prev_list = list;
      copy_option_part(&list, part_buf, COM_MAX_LEN, ",");
      string = vim_strchr(part_buf, ':');
      if (string == NULL) {         // missing ':', ignore this part
        continue;
      }
      *string++ = NUL;              // isolate flags from string

      // If we found a middle match previously, use that match when this
      // is not a middle or end.
      if (middle_match_len != 0
          && vim_strchr(part_buf, COM_MIDDLE) == NULL
          && vim_strchr(part_buf, COM_END) == NULL) {
        break;
      }

      // When we already found a nested comment, only accept further
      // nested comments.
      if (got_com && vim_strchr(part_buf, COM_NEST) == NULL) {
        continue;
      }

      // When 'O' flag present and using "O" command skip this one.
      if (backward && vim_strchr(part_buf, COM_NOBACK) != NULL) {
        continue;
      }

      // Line contents and string must match.
      // When string starts with white space, must have some white space
      // (but the amount does not need to match, there might be a mix of
      // TABs and spaces).
      if (ascii_iswhite(string[0])) {
        if (i == 0 || !ascii_iswhite(line[i - 1])) {
          continue;            // missing white space
        }
        while (ascii_iswhite(string[0])) {
          string++;
        }
      }
      for (j = 0; string[j] != NUL && string[j] == line[i + j]; j++) {}
      if (string[j] != NUL) {
        continue;          // string doesn't match
      }
      // When 'b' flag used, there must be white space or an
      // end-of-line after the string in the line.
      if (vim_strchr(part_buf, COM_BLANK) != NULL
          && !ascii_iswhite(line[i + j]) && line[i + j] != NUL) {
        continue;
      }

      // We have found a match, stop searching unless this is a middle
      // comment. The middle comment can be a substring of the end
      // comment in which case it's better to return the length of the
      // end comment and its flags.  Thus we keep searching with middle
      // and end matches and use an end match if it matches better.
      if (vim_strchr(part_buf, COM_MIDDLE) != NULL) {
        if (middle_match_len == 0) {
          middle_match_len = j;
          saved_flags = prev_list;
        }
        continue;
      }
      if (middle_match_len != 0 && j > middle_match_len) {
        // Use this match instead of the middle match, since it's a
        // longer thus better match.
        middle_match_len = 0;
      }

      if (middle_match_len == 0) {
        i += j;
      }
      found_one = true;
      break;
    }

    if (middle_match_len != 0) {
      // Use the previously found middle match after failing to find a
      // match with an end.
      if (!got_com && flags != NULL) {
        *flags = saved_flags;
      }
      i += middle_match_len;
      found_one = true;
    }

    // No match found, stop scanning.
    if (!found_one) {
      break;
    }

    result = i;

    // Include any trailing white space.
    while (ascii_iswhite(line[i])) {
      i++;
    }

    if (include_space) {
      result = i;
    }

    // If this comment doesn't nest, stop here.
    got_com = true;
    if (vim_strchr(part_buf, COM_NEST) == NULL) {
      break;
    }
  }
  return result;
}

/// Return the offset at which the last comment in line starts. If there is no
/// comment in the whole line, -1 is returned.
///
/// When "flags" is not null, it is set to point to the flags describing the
/// recognized comment leader.
int get_last_leader_offset(char *line, char **flags)
{
  int result = -1;
  int j;
  int lower_check_bound = 0;
  char *com_leader;
  char *com_flags;
  char part_buf[COM_MAX_LEN];         // buffer for one option part

  // Repeat to match several nested comment strings.
  int i = (int)strlen(line);
  while (--i >= lower_check_bound) {
    // scan through the 'comments' option for a match
    bool found_one = false;
    for (char *list = curbuf->b_p_com; *list;) {
      char *flags_save = list;

      // Get one option part into part_buf[].  Advance list to next one.
      // put string at start of string.
      copy_option_part(&list, part_buf, COM_MAX_LEN, ",");
      char *string = vim_strchr(part_buf, ':');
      if (string == NULL) {  // If everything is fine, this cannot actually
                             // happen.
        continue;
      }
      *string++ = NUL;          // Isolate flags from string.
      com_leader = string;

      // Line contents and string must match.
      // When string starts with white space, must have some white space
      // (but the amount does not need to match, there might be a mix of
      // TABs and spaces).
      if (ascii_iswhite(string[0])) {
        if (i == 0 || !ascii_iswhite(line[i - 1])) {
          continue;
        }
        while (ascii_iswhite(*string)) {
          string++;
        }
      }
      for (j = 0; string[j] != NUL && string[j] == line[i + j]; j++) {
        // do nothing
      }
      if (string[j] != NUL) {
        continue;
      }

      // When 'b' flag used, there must be white space or an
      // end-of-line after the string in the line.
      if (vim_strchr(part_buf, COM_BLANK) != NULL
          && !ascii_iswhite(line[i + j]) && line[i + j] != NUL) {
        continue;
      }

      if (vim_strchr(part_buf, COM_MIDDLE) != NULL) {
        // For a middlepart comment, only consider it to match if
        // everything before the current position in the line is
        // whitespace.  Otherwise we would think we are inside a
        // comment if the middle part appears somewhere in the middle
        // of the line.  E.g. for C the "*" appears often.
        for (j = 0; j <= i && ascii_iswhite(line[j]); j++) {}
        if (j < i) {
          continue;
        }
      }

      // We have found a match, stop searching.
      found_one = true;

      if (flags) {
        *flags = flags_save;
      }
      com_flags = flags_save;

      break;
    }

    if (found_one) {
      char part_buf2[COM_MAX_LEN];            // buffer for one option part

      result = i;
      // If this comment nests, continue searching.
      if (vim_strchr(part_buf, COM_NEST) != NULL) {
        continue;
      }

      lower_check_bound = i;

      // Let's verify whether the comment leader found is a substring
      // of other comment leaders. If it is, let's adjust the
      // lower_check_bound so that we make sure that we have determined
      // the comment leader correctly.

      while (ascii_iswhite(*com_leader)) {
        com_leader++;
      }
      int len1 = (int)strlen(com_leader);

      for (char *list = curbuf->b_p_com; *list;) {
        char *flags_save = list;

        copy_option_part(&list, part_buf2, COM_MAX_LEN, ",");
        if (flags_save == com_flags) {
          continue;
        }
        char *string = vim_strchr(part_buf2, ':');
        string++;
        while (ascii_iswhite(*string)) {
          string++;
        }
        int len2 = (int)strlen(string);
        if (len2 == 0) {
          continue;
        }

        // Now we have to verify whether string ends with a substring
        // beginning the com_leader.
        for (int off = (len2 > i ? i : len2); off > 0 && off + len1 > len2;) {
          off--;
          if (!strncmp(string + off, com_leader, (size_t)(len2 - off))) {
            lower_check_bound = MIN(lower_check_bound, i - off);
          }
        }
      }
    }
  }
  return result;
}
