// cmdexpand.c: functions for command-line completion

#include <assert.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>

#include "nvim/api/private/defs.h"
#include "nvim/api/private/helpers.h"
#include "nvim/arglist.h"
#include "nvim/ascii_defs.h"
#include "nvim/autocmd.h"
#include "nvim/buffer.h"
#include "nvim/charset.h"
#include "nvim/cmdexpand.h"
#include "nvim/cmdhist.h"
#include "nvim/drawscreen.h"
#include "nvim/eval.h"
#include "nvim/eval/funcs.h"
#include "nvim/eval/typval.h"
#include "nvim/eval/typval_defs.h"
#include "nvim/eval/userfunc.h"
#include "nvim/ex_cmds.h"
#include "nvim/ex_docmd.h"
#include "nvim/ex_getln.h"
#include "nvim/garray.h"
#include "nvim/garray_defs.h"
#include "nvim/getchar.h"
#include "nvim/gettext.h"
#include "nvim/globals.h"
#include "nvim/grid.h"
#include "nvim/hashtab.h"
#include "nvim/help.h"
#include "nvim/highlight.h"
#include "nvim/highlight_group.h"
#include "nvim/keycodes.h"
#include "nvim/log.h"
#include "nvim/lua/executor.h"
#include "nvim/macros_defs.h"
#include "nvim/mapping.h"
#include "nvim/mbyte.h"
#include "nvim/memory.h"
#include "nvim/menu.h"
#include "nvim/message.h"
#include "nvim/option.h"
#include "nvim/option_vars.h"
#include "nvim/os/fs.h"
#include "nvim/os/lang.h"
#include "nvim/os/os.h"
#include "nvim/path.h"
#include "nvim/popupmenu.h"
#include "nvim/profile.h"
#include "nvim/regexp.h"
#include "nvim/runtime.h"
#include "nvim/search.h"
#include "nvim/sign.h"
#include "nvim/statusline.h"
#include "nvim/strings.h"
#include "nvim/syntax.h"
#include "nvim/tag.h"
#include "nvim/types_defs.h"
#include "nvim/ui.h"
#include "nvim/usercmd.h"
#include "nvim/vim_defs.h"
#include "nvim/window.h"

/// Type used by call_user_expand_func
typedef void *(*user_expand_func_T)(const char *, int, typval_T *);

#ifdef INCLUDE_GENERATED_DECLARATIONS
# include "cmdexpand.c.generated.h"
#endif

static int cmd_showtail;  ///< Only show path tail in lists ?

/// "compl_match_array" points the currently displayed list of entries in the
/// popup menu.  It is NULL when there is no popup menu.
static pumitem_T *compl_match_array = NULL;
static int compl_match_arraysize;
/// First column in cmdline of the matched item for completion.
static int compl_startcol;
static int compl_selected;

#define SHOW_MATCH(m) (showtail ? showmatches_gettail(matches[m], false) : matches[m])

/// Returns true if fuzzy completion is supported for a given cmdline completion
/// context.
static bool cmdline_fuzzy_completion_supported(const expand_T *const xp)
  FUNC_ATTR_WARN_UNUSED_RESULT FUNC_ATTR_NONNULL_ALL FUNC_ATTR_PURE
{
  return (wop_flags & WOP_FUZZY)
         && xp->xp_context != EXPAND_BOOL_SETTINGS
         && xp->xp_context != EXPAND_COLORS
         && xp->xp_context != EXPAND_COMPILER
         && xp->xp_context != EXPAND_DIRECTORIES
         && xp->xp_context != EXPAND_FILES
         && xp->xp_context != EXPAND_FILES_IN_PATH
         && xp->xp_context != EXPAND_FILETYPE
         && xp->xp_context != EXPAND_HELP
         && xp->xp_context != EXPAND_LUA
         && xp->xp_context != EXPAND_OLD_SETTING
         && xp->xp_context != EXPAND_STRING_SETTING
         && xp->xp_context != EXPAND_SETTING_SUBTRACT
         && xp->xp_context != EXPAND_OWNSYNTAX
         && xp->xp_context != EXPAND_PACKADD
         && xp->xp_context != EXPAND_RUNTIME
         && xp->xp_context != EXPAND_SHELLCMD
         && xp->xp_context != EXPAND_TAGS
         && xp->xp_context != EXPAND_TAGS_LISTFILES
         && xp->xp_context != EXPAND_USER_LIST
         && xp->xp_context != EXPAND_USER_LUA;
}

/// Returns true if fuzzy completion for cmdline completion is enabled and
/// "fuzzystr" is not empty.  If search pattern is empty, then don't use fuzzy
/// matching.
bool cmdline_fuzzy_complete(const char *const fuzzystr)
  FUNC_ATTR_WARN_UNUSED_RESULT FUNC_ATTR_NONNULL_ALL FUNC_ATTR_PURE
{
  return (wop_flags & WOP_FUZZY) && *fuzzystr != NUL;
}

/// Sort function for the completion matches.
/// <SNR> functions should be sorted to the end.
static int sort_func_compare(const void *s1, const void *s2)
{
  char *p1 = *(char **)s1;
  char *p2 = *(char **)s2;

  if (*p1 != '<' && *p2 == '<') {
    return -1;
  }
  if (*p1 == '<' && *p2 != '<') {
    return 1;
  }
  return strcmp(p1, p2);
}

/// Escape special characters in the cmdline completion matches.
static void wildescape(expand_T *xp, const char *str, int numfiles, char **files)
{
  char *p;
  const int vse_what = xp->xp_context == EXPAND_BUFFERS ? VSE_BUFFER : VSE_NONE;

  if (xp->xp_context == EXPAND_FILES
      || xp->xp_context == EXPAND_FILES_IN_PATH
      || xp->xp_context == EXPAND_SHELLCMD
      || xp->xp_context == EXPAND_BUFFERS
      || xp->xp_context == EXPAND_DIRECTORIES) {
    // Insert a backslash into a file name before a space, \, %, #
    // and wildmatch characters, except '~'.
    for (int i = 0; i < numfiles; i++) {
      // for ":set path=" we need to escape spaces twice
      if (xp->xp_backslash & XP_BS_THREE) {
        char *pat = (xp->xp_backslash & XP_BS_COMMA) ? " ," : " ";
        p = vim_strsave_escaped(files[i], pat);
        xfree(files[i]);
        files[i] = p;
#if defined(BACKSLASH_IN_FILENAME)
        p = vim_strsave_escaped(files[i], " ");
        xfree(files[i]);
        files[i] = p;
#endif
      } else if (xp->xp_backslash & XP_BS_COMMA) {
        if (vim_strchr(files[i], ',') != NULL) {
          p = vim_strsave_escaped(files[i], ",");
          xfree(files[i]);
          files[i] = p;
        }
      }
#ifdef BACKSLASH_IN_FILENAME
      p = vim_strsave_fnameescape(files[i], vse_what);
#else
      p = vim_strsave_fnameescape(files[i], xp->xp_shell ? VSE_SHELL : vse_what);
#endif
      xfree(files[i]);
      files[i] = p;

      // If 'str' starts with "\~", replace "~" at start of
      // files[i] with "\~".
      if (str[0] == '\\' && str[1] == '~' && files[i][0] == '~') {
        escape_fname(&files[i]);
      }
    }
    xp->xp_backslash = XP_BS_NONE;

    // If the first file starts with a '+' escape it.  Otherwise it
    // could be seen as "+cmd".
    if (*files[0] == '+') {
      escape_fname(&files[0]);
    }
  } else if (xp->xp_context == EXPAND_TAGS) {
    // Insert a backslash before characters in a tag name that
    // would terminate the ":tag" command.
    for (int i = 0; i < numfiles; i++) {
      p = vim_strsave_escaped(files[i], "\\|\"");
      xfree(files[i]);
      files[i] = p;
    }
  }
}

/// Escape special characters in the cmdline completion matches.
static void ExpandEscape(expand_T *xp, char *str, int numfiles, char **files, int options)
{
  // May change home directory back to "~"
  if (options & WILD_HOME_REPLACE) {
    tilde_replace(str, numfiles, files);
  }

  if (options & WILD_ESCAPE) {
    wildescape(xp, str, numfiles, files);
  }
}

/// Return FAIL if this is not an appropriate context in which to do
/// completion of anything, return OK if it is (even if there are no matches).
/// For the caller, this means that the character is just passed through like a
/// normal character (instead of being expanded).  This allows :s/^I^D etc.
///
/// @param options  extra options for ExpandOne()
/// @param escape  if true, escape the returned matches
int nextwild(expand_T *xp, int type, int options, bool escape)
{
  CmdlineInfo *const ccline = get_cmdline_info();
  char *p2;

  if (xp->xp_numfiles == -1) {
    set_expand_context(xp);
    cmd_showtail = expand_showtail(xp);
  }

  if (xp->xp_context == EXPAND_UNSUCCESSFUL) {
    beep_flush();
    return OK;      // Something illegal on command line
  }
  if (xp->xp_context == EXPAND_NOTHING) {
    // Caller can use the character as a normal char instead
    return FAIL;
  }

  // If cmd_silent is set then don't show the dots, because redrawcmd() below
  // won't remove them.
  if (!cmd_silent && !(ui_has(kUICmdline) || ui_has(kUIWildmenu))) {
    msg_puts("...");  // show that we are busy
    ui_flush();
  }

  int i = (int)(xp->xp_pattern - ccline->cmdbuff);
  assert(ccline->cmdpos >= i);
  xp->xp_pattern_len = (size_t)ccline->cmdpos - (size_t)i;

  if (type == WILD_NEXT || type == WILD_PREV
      || type == WILD_PAGEUP || type == WILD_PAGEDOWN
      || type == WILD_PUM_WANT) {
    // Get next/previous match for a previous expanded pattern.
    p2 = ExpandOne(xp, NULL, NULL, 0, type);
  } else {
    char *p1;
    if (cmdline_fuzzy_completion_supported(xp)) {
      // If fuzzy matching, don't modify the search string
      p1 = xstrnsave(xp->xp_pattern, xp->xp_pattern_len);
    } else {
      p1 = addstar(xp->xp_pattern, xp->xp_pattern_len, xp->xp_context);
    }
    // Translate string into pattern and expand it.
    const int use_options = (options
                             | WILD_HOME_REPLACE
                             | WILD_ADD_SLASH
                             | WILD_SILENT
                             | (escape ? WILD_ESCAPE : 0)
                             | (p_wic ? WILD_ICASE : 0));
    p2 = ExpandOne(xp, p1, xstrnsave(&ccline->cmdbuff[i], xp->xp_pattern_len),
                   use_options, type);
    xfree(p1);

    // xp->xp_pattern might have been modified by ExpandOne (for example,
    // in lua completion), so recompute the pattern index and length
    i = (int)(xp->xp_pattern - ccline->cmdbuff);
    xp->xp_pattern_len = (size_t)ccline->cmdpos - (size_t)i;

    // Longest match: make sure it is not shorter, happens with :help.
    if (p2 != NULL && type == WILD_LONGEST) {
      int j;
      for (j = 0; (size_t)j < xp->xp_pattern_len; j++) {
        if (ccline->cmdbuff[i + j] == '*'
            || ccline->cmdbuff[i + j] == '?') {
          break;
        }
      }
      if ((int)strlen(p2) < j) {
        XFREE_CLEAR(p2);
      }
    }
  }

  if (p2 != NULL && !got_int) {
    int difflen = (int)strlen(p2) - (int)(xp->xp_pattern_len);
    if (ccline->cmdlen + difflen + 4 > ccline->cmdbufflen) {
      realloc_cmdbuff(ccline->cmdlen + difflen + 4);
      xp->xp_pattern = ccline->cmdbuff + i;
    }
    assert(ccline->cmdpos <= ccline->cmdlen);
    memmove(&ccline->cmdbuff[ccline->cmdpos + difflen],
            &ccline->cmdbuff[ccline->cmdpos],
            (size_t)ccline->cmdlen - (size_t)ccline->cmdpos + 1);
    memmove(&ccline->cmdbuff[i], p2, strlen(p2));
    ccline->cmdlen += difflen;
    ccline->cmdpos += difflen;
  }
  xfree(p2);

  redrawcmd();
  cursorcmd();

  // When expanding a ":map" command and no matches are found, assume that
  // the key is supposed to be inserted literally
  if (xp->xp_context == EXPAND_MAPPINGS && p2 == NULL) {
    return FAIL;
  }

  if (xp->xp_numfiles <= 0 && p2 == NULL) {
    beep_flush();
  } else if (xp->xp_numfiles == 1) {
    // free expanded pattern
    (void)ExpandOne(xp, NULL, NULL, 0, WILD_FREE);
  }

  return OK;
}

/// Create and display a cmdline completion popup menu with items from
/// "matches".
static int cmdline_pum_create(CmdlineInfo *ccline, expand_T *xp, char **matches, int numMatches,
                              int showtail)
{
  assert(numMatches >= 0);
  // Add all the completion matches
  compl_match_arraysize = numMatches;
  compl_match_array = xmalloc(sizeof(pumitem_T) * (size_t)compl_match_arraysize);
  for (int i = 0; i < numMatches; i++) {
    compl_match_array[i] = (pumitem_T){
      .pum_text = SHOW_MATCH(i),
      .pum_info = NULL,
      .pum_extra = NULL,
      .pum_kind = NULL,
    };
  }

  // Compute the popup menu starting column
  char *endpos = showtail ? showmatches_gettail(xp->xp_pattern, true) : xp->xp_pattern;
  if (ui_has(kUICmdline)) {
    compl_startcol = (int)(endpos - ccline->cmdbuff);
  } else {
    compl_startcol = cmd_screencol((int)(endpos - ccline->cmdbuff));
  }

  // no default selection
  compl_selected = -1;

  cmdline_pum_display(true);

  return EXPAND_OK;
}

void cmdline_pum_display(bool changed_array)
{
  pum_display(compl_match_array, compl_match_arraysize, compl_selected,
              changed_array, compl_startcol);
}

/// Returns true if the cmdline completion popup menu is being displayed.
bool cmdline_pum_active(void)
{
  // compl_match_array != NULL should already imply pum_visible() in Nvim.
  return compl_match_array != NULL;
}

/// Remove the cmdline completion popup menu (if present), free the list of items.
void cmdline_pum_remove(void)
{
  pum_undisplay(true);
  XFREE_CLEAR(compl_match_array);
}

void cmdline_pum_cleanup(CmdlineInfo *cclp)
{
  cmdline_pum_remove();
  wildmenu_cleanup(cclp);
}

/// Return the number of characters that should be skipped in the wildmenu
/// These are backslashes used for escaping.  Do show backslashes in help tags.
static int skip_wildmenu_char(expand_T *xp, char *s)
{
  if ((rem_backslash(s) && xp->xp_context != EXPAND_HELP)
      || ((xp->xp_context == EXPAND_MENUS || xp->xp_context == EXPAND_MENUNAMES)
          && (s[0] == '\t' || (s[0] == '\\' && s[1] != NUL)))) {
#ifndef BACKSLASH_IN_FILENAME
    // TODO(bfredl): Why in the actual fuck are we special casing the
    // shell variety deep in the redraw logic? Shell special snowflakiness
    // should already be eliminated multiple layers before reaching the
    // screen infracstructure.
    if (xp->xp_shell && csh_like_shell() && s[1] == '\\' && s[2] == '!') {
      return 2;
    }
#endif
    return 1;
  }
  return 0;
}

/// Get the length of an item as it will be shown in the status line.
static int wildmenu_match_len(expand_T *xp, char *s)
{
  int len = 0;

  int emenu = (xp->xp_context == EXPAND_MENUS
               || xp->xp_context == EXPAND_MENUNAMES);

  // Check for menu separators - replace with '|'.
  if (emenu && menu_is_separator(s)) {
    return 1;
  }

  while (*s != NUL) {
    s += skip_wildmenu_char(xp, s);
    len += ptr2cells(s);
    MB_PTR_ADV(s);
  }

  return len;
}

/// Show wildchar matches in the status line.
/// Show at least the "match" item.
/// We start at item "first_match" in the list and show all matches that fit.
///
/// If inversion is possible we use it. Else '=' characters are used.
///
/// @param matches  list of matches
static void redraw_wildmenu(expand_T *xp, int num_matches, char **matches, int match, int showtail)
{
  int len;
  int clen;                     // length in screen cells
  int attr;
  int i;
  bool highlight = true;
  char *selstart = NULL;
  int selstart_col = 0;
  char *selend = NULL;
  static int first_match = 0;
  bool add_left = false;
  int l;

  if (matches == NULL) {        // interrupted completion?
    return;
  }

  char *buf = xmalloc((size_t)Columns * MB_MAXBYTES + 1);

  if (match == -1) {    // don't show match but original text
    match = 0;
    highlight = false;
  }
  // count 1 for the ending ">"
  clen = wildmenu_match_len(xp, SHOW_MATCH(match)) + 3;
  if (match == 0) {
    first_match = 0;
  } else if (match < first_match) {
    // jumping left, as far as we can go
    first_match = match;
    add_left = true;
  } else {
    // check if match fits on the screen
    for (i = first_match; i < match; i++) {
      clen += wildmenu_match_len(xp, SHOW_MATCH(i)) + 2;
    }
    if (first_match > 0) {
      clen += 2;
    }
    // jumping right, put match at the left
    if (clen > Columns) {
      first_match = match;
      // if showing the last match, we can add some on the left
      clen = 2;
      for (i = match; i < num_matches; i++) {
        clen += wildmenu_match_len(xp, SHOW_MATCH(i)) + 2;
        if (clen >= Columns) {
          break;
        }
      }
      if (i == num_matches) {
        add_left = true;
      }
    }
  }
  if (add_left) {
    while (first_match > 0) {
      clen += wildmenu_match_len(xp, SHOW_MATCH(first_match - 1)) + 2;
      if (clen >= Columns) {
        break;
      }
      first_match--;
    }
  }

  int fillchar = fillchar_status(&attr, curwin);

  if (first_match == 0) {
    *buf = NUL;
    len = 0;
  } else {
    STRCPY(buf, "< ");
    len = 2;
  }
  clen = len;

  i = first_match;
  while (clen + wildmenu_match_len(xp, SHOW_MATCH(i)) + 2 < Columns) {
    if (i == match) {
      selstart = buf + len;
      selstart_col = clen;
    }

    char *s = SHOW_MATCH(i);
    // Check for menu separators - replace with '|'
    int emenu = (xp->xp_context == EXPAND_MENUS || xp->xp_context == EXPAND_MENUNAMES);
    if (emenu && menu_is_separator(s)) {
      STRCPY(buf + len, transchar('|'));
      l = (int)strlen(buf + len);
      len += l;
      clen += l;
    } else {
      for (; *s != NUL; s++) {
        s += skip_wildmenu_char(xp, s);
        clen += ptr2cells(s);
        if ((l = utfc_ptr2len(s)) > 1) {
          strncpy(buf + len, s, (size_t)l);  // NOLINT(runtime/printf)
          s += l - 1;
          len += l;
        } else {
          STRCPY(buf + len, transchar_byte((uint8_t)(*s)));
          len += (int)strlen(buf + len);
        }
      }
    }
    if (i == match) {
      selend = buf + len;
    }

    *(buf + len++) = ' ';
    *(buf + len++) = ' ';
    clen += 2;
    if (++i == num_matches) {
      break;
    }
  }

  if (i != num_matches) {
    *(buf + len++) = '>';
    clen++;
  }

  buf[len] = NUL;

  int row = cmdline_row - 1;
  if (row >= 0) {
    if (wild_menu_showing == 0 || wild_menu_showing == WM_LIST) {
      if (msg_scrolled > 0) {
        // Put the wildmenu just above the command line.  If there is
        // no room, scroll the screen one line up.
        if (cmdline_row == Rows - 1) {
          msg_scroll_up(false, false);
          msg_scrolled++;
        } else {
          cmdline_row++;
          row++;
        }
        wild_menu_showing = WM_SCROLLED;
      } else {
        // Create status line if needed by setting 'laststatus' to 2.
        // Set 'winminheight' to zero to avoid that the window is
        // resized.
        if (lastwin->w_status_height == 0 && global_stl_height() == 0) {
          save_p_ls = (int)p_ls;
          save_p_wmh = (int)p_wmh;
          p_ls = 2;
          p_wmh = 0;
          last_status(false);
        }
        wild_menu_showing = WM_SHOWN;
      }
    }

    // Tricky: wildmenu can be drawn either over a status line, or at empty
    // scrolled space in the message output
    grid_line_start((wild_menu_showing == WM_SCROLLED) ? &msg_grid_adj : &default_grid, row);

    grid_line_puts(0, buf, -1, attr);
    if (selstart != NULL && highlight) {
      *selend = NUL;
      grid_line_puts(selstart_col, selstart, -1, HL_ATTR(HLF_WM));
    }

    grid_line_fill(clen, Columns, fillchar, attr);

    grid_line_flush();
  }

  win_redraw_last_status(topframe);
  xfree(buf);
}

/// Get the next or prev cmdline completion match. The index of the match is set
/// in "xp->xp_selected"
static char *get_next_or_prev_match(int mode, expand_T *xp)
{
  if (xp->xp_numfiles <= 0) {
    return NULL;
  }

  int findex = xp->xp_selected;

  if (mode == WILD_PREV) {
    if (findex == -1) {
      findex = xp->xp_numfiles;
    }
    findex--;
  } else if (mode == WILD_NEXT) {
    findex++;
  } else if (mode == WILD_PAGEUP) {
    if (findex == 0) {
      // at the first entry, don't select any entries
      findex = -1;
    } else if (findex == -1) {
      // no entry is selected. select the last entry
      findex = xp->xp_numfiles - 1;
    } else {
      // go up by the pum height
      int ht = pum_get_height();
      if (ht > 3) {
        ht -= 2;
      }
      findex -= ht;
      if (findex < 0) {
        // few entries left, select the first entry
        findex = 0;
      }
    }
  } else if (mode == WILD_PAGEDOWN) {
    if (findex == xp->xp_numfiles - 1) {
      // at the last entry, don't select any entries
      findex = -1;
    } else if (findex == -1) {
      // no entry is selected. select the first entry
      findex = 0;
    } else {
      // go down by the pum height
      int ht = pum_get_height();
      if (ht > 3) {
        ht -= 2;
      }
      findex += ht;
      if (findex >= xp->xp_numfiles) {
        // few entries left, select the last entry
        findex = xp->xp_numfiles - 1;
      }
    }
  } else {  // mode == WILD_PUM_WANT
    assert(pum_want.active);
    findex = pum_want.item;
  }

  // When wrapping around, return the original string, set findex to -1.
  if (findex < 0) {
    if (xp->xp_orig == NULL) {
      findex = xp->xp_numfiles - 1;
    } else {
      findex = -1;
    }
  }
  if (findex >= xp->xp_numfiles) {
    if (xp->xp_orig == NULL) {
      findex = 0;
    } else {
      findex = -1;
    }
  }
  if (compl_match_array) {
    compl_selected = findex;
    cmdline_pum_display(false);
  } else if (p_wmnu) {
    redraw_wildmenu(xp, xp->xp_numfiles, xp->xp_files, findex, cmd_showtail);
  }
  xp->xp_selected = findex;

  return xstrdup(findex == -1 ? xp->xp_orig : xp->xp_files[findex]);
}

/// Start the command-line expansion and get the matches.
static char *ExpandOne_start(int mode, expand_T *xp, char *str, int options)
{
  int non_suf_match;  // number without matching suffix
  char *ss = NULL;

  // Do the expansion.
  if (ExpandFromContext(xp, str, &xp->xp_files, &xp->xp_numfiles, options) == FAIL) {
#ifdef FNAME_ILLEGAL
    // Illegal file name has been silently skipped.  But when there
    // are wildcards, the real problem is that there was no match,
    // causing the pattern to be added, which has illegal characters.
    if (!(options & WILD_SILENT) && (options & WILD_LIST_NOTFOUND)) {
      semsg(_(e_nomatch2), str);
    }
#endif
  } else if (xp->xp_numfiles == 0) {
    if (!(options & WILD_SILENT)) {
      semsg(_(e_nomatch2), str);
    }
  } else {
    // Escape the matches for use on the command line.
    ExpandEscape(xp, str, xp->xp_numfiles, xp->xp_files, options);

    // Check for matching suffixes in file names.
    if (mode != WILD_ALL && mode != WILD_ALL_KEEP && mode != WILD_LONGEST) {
      if (xp->xp_numfiles) {
        non_suf_match = xp->xp_numfiles;
      } else {
        non_suf_match = 1;
      }
      if ((xp->xp_context == EXPAND_FILES
           || xp->xp_context == EXPAND_DIRECTORIES)
          && xp->xp_numfiles > 1) {
        // More than one match; check suffix.
        // The files will have been sorted on matching suffix in
        // expand_wildcards, only need to check the first two.
        non_suf_match = 0;
        for (int i = 0; i < 2; i++) {
          if (match_suffix(xp->xp_files[i])) {
            non_suf_match++;
          }
        }
      }
      if (non_suf_match != 1) {
        // Can we ever get here unless it's while expanding
        // interactively?  If not, we can get rid of this all
        // together. Don't really want to wait for this message
        // (and possibly have to hit return to continue!).
        if (!(options & WILD_SILENT)) {
          emsg(_(e_toomany));
        } else if (!(options & WILD_NO_BEEP)) {
          beep_flush();
        }
      }
      if (!(non_suf_match != 1 && mode == WILD_EXPAND_FREE)) {
        ss = xstrdup(xp->xp_files[0]);
      }
    }
  }

  return ss;
}

/// Return the longest common part in the list of cmdline completion matches.
static char *find_longest_match(expand_T *xp, int options)
{
  size_t len = 0;

  for (size_t mb_len; xp->xp_files[0][len]; len += mb_len) {
    mb_len = (size_t)utfc_ptr2len(&xp->xp_files[0][len]);
    int c0 = utf_ptr2char(&xp->xp_files[0][len]);
    int i;
    for (i = 1; i < xp->xp_numfiles; i++) {
      int ci = utf_ptr2char(&xp->xp_files[i][len]);

      if (p_fic && (xp->xp_context == EXPAND_DIRECTORIES
                    || xp->xp_context == EXPAND_FILES
                    || xp->xp_context == EXPAND_SHELLCMD
                    || xp->xp_context == EXPAND_BUFFERS)) {
        if (mb_tolower(c0) != mb_tolower(ci)) {
          break;
        }
      } else if (c0 != ci) {
        break;
      }
    }
    if (i < xp->xp_numfiles) {
      if (!(options & WILD_NO_BEEP)) {
        vim_beep(BO_WILD);
      }
      break;
    }
  }

  return xmemdupz(xp->xp_files[0], len);
}

/// Do wildcard expansion on the string "str".
/// Chars that should not be expanded must be preceded with a backslash.
/// Return a pointer to allocated memory containing the new string.
/// Return NULL for failure.
///
/// "orig" is the originally expanded string, copied to allocated memory.  It
/// should either be kept in "xp->xp_orig" or freed.  When "mode" is WILD_NEXT
/// or WILD_PREV "orig" should be NULL.
///
/// Results are cached in xp->xp_files and xp->xp_numfiles, except when "mode"
/// is WILD_EXPAND_FREE or WILD_ALL.
///
/// mode = WILD_FREE:        just free previously expanded matches
/// mode = WILD_EXPAND_FREE: normal expansion, do not keep matches
/// mode = WILD_EXPAND_KEEP: normal expansion, keep matches
/// mode = WILD_NEXT:        use next match in multiple match, wrap to first
/// mode = WILD_PREV:        use previous match in multiple match, wrap to first
/// mode = WILD_ALL:         return all matches concatenated
/// mode = WILD_LONGEST:     return longest matched part
/// mode = WILD_ALL_KEEP:    get all matches, keep matches
/// mode = WILD_APPLY:       apply the item selected in the cmdline completion
///                          popup menu and close the menu.
/// mode = WILD_CANCEL:      cancel and close the cmdline completion popup and
///                          use the original text.
/// mode = WILD_PUM_WANT:    use the match at index pum_want.item
///
/// options = WILD_LIST_NOTFOUND:    list entries without a match
/// options = WILD_HOME_REPLACE:     do home_replace() for buffer names
/// options = WILD_USE_NL:           Use '\n' for WILD_ALL
/// options = WILD_NO_BEEP:          Don't beep for multiple matches
/// options = WILD_ADD_SLASH:        add a slash after directory names
/// options = WILD_KEEP_ALL:         don't remove 'wildignore' entries
/// options = WILD_SILENT:           don't print warning messages
/// options = WILD_ESCAPE:           put backslash before special chars
/// options = WILD_ICASE:            ignore case for files
///
/// The variables xp->xp_context and xp->xp_backslash must have been set!
///
/// @param orig  allocated copy of original of expanded string
char *ExpandOne(expand_T *xp, char *str, char *orig, int options, int mode)
{
  char *ss = NULL;
  int orig_saved = false;

  // first handle the case of using an old match
  if (mode == WILD_NEXT || mode == WILD_PREV
      || mode == WILD_PAGEUP || mode == WILD_PAGEDOWN
      || mode == WILD_PUM_WANT) {
    return get_next_or_prev_match(mode, xp);
  }

  if (mode == WILD_CANCEL) {
    ss = xstrdup(xp->xp_orig ? xp->xp_orig : "");
  } else if (mode == WILD_APPLY) {
    ss = xstrdup(xp->xp_selected == -1
                 ? (xp->xp_orig ? xp->xp_orig : "")
                 : xp->xp_files[xp->xp_selected]);
  }

  // free old names
  if (xp->xp_numfiles != -1 && mode != WILD_ALL && mode != WILD_LONGEST) {
    FreeWild(xp->xp_numfiles, xp->xp_files);
    xp->xp_numfiles = -1;
    XFREE_CLEAR(xp->xp_orig);

    // The entries from xp_files may be used in the PUM, remove it.
    if (compl_match_array != NULL) {
      cmdline_pum_remove();
    }
  }
  xp->xp_selected = 0;

  if (mode == WILD_FREE) {      // only release file name
    return NULL;
  }

  if (xp->xp_numfiles == -1 && mode != WILD_APPLY && mode != WILD_CANCEL) {
    xfree(xp->xp_orig);
    xp->xp_orig = orig;
    orig_saved = true;

    ss = ExpandOne_start(mode, xp, str, options);
  }

  // Find longest common part
  if (mode == WILD_LONGEST && xp->xp_numfiles > 0) {
    ss = find_longest_match(xp, options);
    xp->xp_selected = -1;  // next p_wc gets first one
  }

  // Concatenate all matching names.  Unless interrupted, this can be slow
  // and the result probably won't be used.
  if (mode == WILD_ALL && xp->xp_numfiles > 0 && !got_int) {
    size_t len = 0;
    for (int i = 0; i < xp->xp_numfiles; i++) {
      if (i > 0) {
        if (xp->xp_prefix == XP_PREFIX_NO) {
          len += 2;   // prefix "no"
        } else if (xp->xp_prefix == XP_PREFIX_INV) {
          len += 3;   // prefix "inv"
        }
      }
      len += strlen(xp->xp_files[i]) + 1;
    }
    ss = xmalloc(len);
    *ss = NUL;
    char *ssp = ss;
    for (int i = 0; i < xp->xp_numfiles; i++) {
      if (i > 0) {
        if (xp->xp_prefix == XP_PREFIX_NO) {
          ssp = xstpcpy(ssp, "no");
        } else if (xp->xp_prefix == XP_PREFIX_INV) {
          ssp = xstpcpy(ssp, "inv");
        }
      }
      ssp = xstpcpy(ssp, xp->xp_files[i]);

      if (i != xp->xp_numfiles - 1) {
        ssp = xstpcpy(ssp, (options & WILD_USE_NL) ? "\n" : " ");
      }
    }
  }

  if (mode == WILD_EXPAND_FREE || mode == WILD_ALL) {
    ExpandCleanup(xp);
  }

  // Free "orig" if it wasn't stored in "xp->xp_orig".
  if (!orig_saved) {
    xfree(orig);
  }

  return ss;
}

/// Prepare an expand structure for use.
void ExpandInit(expand_T *xp)
  FUNC_ATTR_NONNULL_ALL
{
  CLEAR_POINTER(xp);
  xp->xp_backslash = XP_BS_NONE;
  xp->xp_prefix = XP_PREFIX_NONE;
  xp->xp_numfiles = -1;
}

/// Cleanup an expand structure after use.
void ExpandCleanup(expand_T *xp)
{
  if (xp->xp_numfiles >= 0) {
    FreeWild(xp->xp_numfiles, xp->xp_files);
    xp->xp_numfiles = -1;
  }
  XFREE_CLEAR(xp->xp_orig);
}

/// Display one line of completion matches. Multiple matches are displayed in
/// each line (used by wildmode=list and CTRL-D)
///
/// @param matches      list of completion match names
/// @param numMatches   number of completion matches in "matches"
/// @param lines        number of output lines
/// @param linenr       line number of matches to display
/// @param maxlen       maximum number of characters in each line
/// @param showtail     display only the tail of the full path of a file name
/// @param dir_attr     highlight attribute to use for directory names
static void showmatches_oneline(expand_T *xp, char **matches, int numMatches, int lines, int linenr,
                                int maxlen, int showtail, int dir_attr)
{
  char *p;
  int lastlen = 999;
  for (int j = linenr; j < numMatches; j += lines) {
    if (xp->xp_context == EXPAND_TAGS_LISTFILES) {
      msg_outtrans(matches[j], HL_ATTR(HLF_D));
      p = matches[j] + strlen(matches[j]) + 1;
      msg_advance(maxlen + 1);
      msg_puts(p);
      msg_advance(maxlen + 3);
      msg_outtrans_long(p + 2, HL_ATTR(HLF_D));
      break;
    }
    for (int i = maxlen - lastlen; --i >= 0;) {
      msg_putchar(' ');
    }
    bool isdir;
    if (xp->xp_context == EXPAND_FILES
        || xp->xp_context == EXPAND_SHELLCMD
        || xp->xp_context == EXPAND_BUFFERS) {
      // highlight directories
      if (xp->xp_numfiles != -1) {
        // Expansion was done before and special characters
        // were escaped, need to halve backslashes.  Also
        // $HOME has been replaced with ~/.
        char *exp_path = expand_env_save_opt(matches[j], true);
        char *path = exp_path != NULL ? exp_path : matches[j];
        char *halved_slash = backslash_halve_save(path);
        isdir = os_isdir(halved_slash);
        xfree(exp_path);
        if (halved_slash != path) {
          xfree(halved_slash);
        }
      } else {
        // Expansion was done here, file names are literal.
        isdir = os_isdir(matches[j]);
      }
      if (showtail) {
        p = SHOW_MATCH(j);
      } else {
        home_replace(NULL, matches[j], NameBuff, MAXPATHL, true);
        p = NameBuff;
      }
    } else {
      isdir = false;
      p = SHOW_MATCH(j);
    }
    lastlen = msg_outtrans(p, isdir ? dir_attr : 0);
  }
  if (msg_col > 0) {  // when not wrapped around
    msg_clr_eos();
    msg_putchar('\n');
  }
}

/// Show all matches for completion on the command line.
/// Returns EXPAND_NOTHING when the character that triggered expansion should
/// be inserted like a normal character.
int showmatches(expand_T *xp, int wildmenu)
{
  CmdlineInfo *const ccline = get_cmdline_info();
  int numMatches;
  char **matches;
  int j;
  int maxlen;
  int lines;
  int columns;
  int attr;
  int showtail;

  if (xp->xp_numfiles == -1) {
    set_expand_context(xp);
    int i = expand_cmdline(xp, ccline->cmdbuff, ccline->cmdpos,
                           &numMatches, &matches);
    showtail = expand_showtail(xp);
    if (i != EXPAND_OK) {
      return i;
    }
  } else {
    numMatches = xp->xp_numfiles;
    matches = xp->xp_files;
    showtail = cmd_showtail;
  }

  bool compl_use_pum = (ui_has(kUICmdline)
                        ? ui_has(kUIPopupmenu)
                        : wildmenu && (wop_flags & WOP_PUM))
                       || ui_has(kUIWildmenu);

  if (compl_use_pum) {
    // cmdline completion popup menu (with wildoptions=pum)
    return cmdline_pum_create(ccline, xp, matches, numMatches, showtail);
  }

  if (!wildmenu) {
    msg_didany = false;                 // lines_left will be set
    msg_start();                        // prepare for paging
    msg_putchar('\n');
    ui_flush();
    cmdline_row = msg_row;
    msg_didany = false;                 // lines_left will be set again
    msg_start();                        // prepare for paging
  }

  if (got_int) {
    got_int = false;            // only int. the completion, not the cmd line
  } else if (wildmenu) {
    redraw_wildmenu(xp, numMatches, matches, -1, showtail);
  } else {
    // find the length of the longest file name
    maxlen = 0;
    for (int i = 0; i < numMatches; i++) {
      if (!showtail && (xp->xp_context == EXPAND_FILES
                        || xp->xp_context == EXPAND_SHELLCMD
                        || xp->xp_context == EXPAND_BUFFERS)) {
        home_replace(NULL, matches[i], NameBuff, MAXPATHL, true);
        j = vim_strsize(NameBuff);
      } else {
        j = vim_strsize(SHOW_MATCH(i));
      }
      if (j > maxlen) {
        maxlen = j;
      }
    }

    if (xp->xp_context == EXPAND_TAGS_LISTFILES) {
      lines = numMatches;
    } else {
      // compute the number of columns and lines for the listing
      maxlen += 2;          // two spaces between file names
      columns = (Columns + 2) / maxlen;
      if (columns < 1) {
        columns = 1;
      }
      lines = (numMatches + columns - 1) / columns;
    }

    attr = HL_ATTR(HLF_D);      // find out highlighting for directories

    if (xp->xp_context == EXPAND_TAGS_LISTFILES) {
      msg_puts_attr(_("tagname"), HL_ATTR(HLF_T));
      msg_clr_eos();
      msg_advance(maxlen - 3);
      msg_puts_attr(_(" kind file\n"), HL_ATTR(HLF_T));
    }

    // list the files line by line
    for (int i = 0; i < lines; i++) {
      showmatches_oneline(xp, matches, numMatches, lines, i, maxlen, showtail, attr);
      if (got_int) {
        got_int = false;
        break;
      }
    }

    // we redraw the command below the lines that we have just listed
    // This is a bit tricky, but it saves a lot of screen updating.
    cmdline_row = msg_row;      // will put it back later
  }

  if (xp->xp_numfiles == -1) {
    FreeWild(numMatches, matches);
  }

  return EXPAND_OK;
}

/// path_tail() version for showmatches() and redraw_wildmenu():
/// Return the tail of file name path "s", ignoring a trailing "/".
static char *showmatches_gettail(char *s, bool eager)
{
  char *t = s;
  bool had_sep = false;

  for (char *p = s; *p != NUL;) {
    if (vim_ispathsep(*p)
#ifdef BACKSLASH_IN_FILENAME
        && !rem_backslash(p)
#endif
        ) {
      if (eager) {
        t = p + 1;
      } else {
        had_sep = true;
      }
    } else if (had_sep) {
      t = p;
      had_sep = false;
    }
    MB_PTR_ADV(p);
  }
  return t;
}

/// Return true if we only need to show the tail of completion matches.
/// When not completing file names or there is a wildcard in the path false is
/// returned.
static bool expand_showtail(expand_T *xp)
{
  // When not completing file names a "/" may mean something different.
  if (xp->xp_context != EXPAND_FILES
      && xp->xp_context != EXPAND_SHELLCMD
      && xp->xp_context != EXPAND_DIRECTORIES) {
    return false;
  }

  char *end = path_tail(xp->xp_pattern);
  if (end == xp->xp_pattern) {          // there is no path separator
    return false;
  }

  for (char *s = xp->xp_pattern; s < end; s++) {
    // Skip escaped wildcards.  Only when the backslash is not a path
    // separator, on DOS the '*' "path\*\file" must not be skipped.
    if (rem_backslash(s)) {
      s++;
    } else if (vim_strchr("*?[", (uint8_t)(*s)) != NULL) {
      return false;
    }
  }
  return true;
}

/// Prepare a string for expansion.
///
/// When expanding file names: The string will be used with expand_wildcards().
/// Copy "fname[len]" into allocated memory and add a '*' at the end.
/// When expanding other names: The string will be used with regcomp().  Copy
/// the name into allocated memory and prepend "^".
///
/// @param context EXPAND_FILES etc.
char *addstar(char *fname, size_t len, int context)
  FUNC_ATTR_NONNULL_RET
{
  char *retval;

  if (context != EXPAND_FILES
      && context != EXPAND_FILES_IN_PATH
      && context != EXPAND_SHELLCMD
      && context != EXPAND_DIRECTORIES) {
    // Matching will be done internally (on something other than files).
    // So we convert the file-matching-type wildcards into our kind for
    // use with vim_regcomp().  First work out how long it will be:

    // For help tags the translation is done in find_help_tags().
    // For a tag pattern starting with "/" no translation is needed.
    if (context == EXPAND_HELP
        || context == EXPAND_COLORS
        || context == EXPAND_COMPILER
        || context == EXPAND_OWNSYNTAX
        || context == EXPAND_FILETYPE
        || context == EXPAND_PACKADD
        || context == EXPAND_RUNTIME
        || ((context == EXPAND_TAGS_LISTFILES || context == EXPAND_TAGS)
            && fname[0] == '/')
        || context == EXPAND_CHECKHEALTH
        || context == EXPAND_LUA) {
      retval = xstrnsave(fname, len);
    } else {
      size_t new_len = len + 2;                // +2 for '^' at start, NUL at end
      for (size_t i = 0; i < len; i++) {
        if (fname[i] == '*' || fname[i] == '~') {
          new_len++;                    // '*' needs to be replaced by ".*"
                                        // '~' needs to be replaced by "\~"
        }
        // Buffer names are like file names.  "." should be literal
        if (context == EXPAND_BUFFERS && fname[i] == '.') {
          new_len++;                    // "." becomes "\."
        }
        // Custom expansion takes care of special things, match
        // backslashes literally (perhaps also for other types?)
        if ((context == EXPAND_USER_DEFINED
             || context == EXPAND_USER_LIST) && fname[i] == '\\') {
          new_len++;                    // '\' becomes "\\"
        }
      }
      retval = xmalloc(new_len);
      {
        retval[0] = '^';
        size_t j = 1;
        for (size_t i = 0; i < len; i++, j++) {
          // Skip backslash.  But why?  At least keep it for custom
          // expansion.
          if (context != EXPAND_USER_DEFINED
              && context != EXPAND_USER_LIST
              && fname[i] == '\\'
              && ++i == len) {
            break;
          }

          switch (fname[i]) {
          case '*':
            retval[j++] = '.';
            break;
          case '~':
            retval[j++] = '\\';
            break;
          case '?':
            retval[j] = '.';
            continue;
          case '.':
            if (context == EXPAND_BUFFERS) {
              retval[j++] = '\\';
            }
            break;
          case '\\':
            if (context == EXPAND_USER_DEFINED
                || context == EXPAND_USER_LIST) {
              retval[j++] = '\\';
            }
            break;
          }
          retval[j] = fname[i];
        }
        retval[j] = NUL;
      }
    }
  } else {
    retval = xmalloc(len + 4);
    xstrlcpy(retval, fname, len + 1);

    // Don't add a star to *, ~, ~user, $var or `cmd`.
    // * would become **, which walks the whole tree.
    // ~ would be at the start of the file name, but not the tail.
    // $ could be anywhere in the tail.
    // ` could be anywhere in the file name.
    // When the name ends in '$' don't add a star, remove the '$'.
    char *tail = path_tail(retval);
    int ends_in_star = (len > 0 && retval[len - 1] == '*');
#ifndef BACKSLASH_IN_FILENAME
    for (ssize_t k = (ssize_t)len - 2; k >= 0; k--) {
      if (retval[k] != '\\') {
        break;
      }
      ends_in_star = !ends_in_star;
    }
#endif
    if ((*retval != '~' || tail != retval)
        && !ends_in_star
        && vim_strchr(tail, '$') == NULL
        && vim_strchr(retval, '`') == NULL) {
      retval[len++] = '*';
    } else if (len > 0 && retval[len - 1] == '$') {
      len--;
    }
    retval[len] = NUL;
  }
  return retval;
}

/// Must parse the command line so far to work out what context we are in.
/// Completion can then be done based on that context.
/// This routine sets the variables:
///  xp->xp_pattern          The start of the pattern to be expanded within
///                              the command line (ends at the cursor).
///  xp->xp_context          The type of thing to expand.  Will be one of:
///
///  EXPAND_UNSUCCESSFUL     Used sometimes when there is something illegal on
///                          the command line, like an unknown command.  Caller
///                          should beep.
///  EXPAND_NOTHING          Unrecognised context for completion, use char like
///                          a normal char, rather than for completion.  eg
///                          :s/^I/
///  EXPAND_COMMANDS         Cursor is still touching the command, so complete
///                          it.
///  EXPAND_BUFFERS          Complete file names for :buf and :sbuf commands.
///  EXPAND_FILES            After command with EX_XFILE set, or after setting
///                          with P_EXPAND set.  eg :e ^I, :w>>^I
///  EXPAND_DIRECTORIES      In some cases this is used instead of the latter
///                          when we know only directories are of interest.
///                          E.g.  :set dir=^I  and  :cd ^I
///  EXPAND_SHELLCMD         After ":!cmd", ":r !cmd"  or ":w !cmd".
///  EXPAND_SETTINGS         Complete variable names.  eg :set d^I
///  EXPAND_BOOL_SETTINGS    Complete boolean variables only,  eg :set no^I
///  EXPAND_TAGS             Complete tags from the files in p_tags.  eg :ta a^I
///  EXPAND_TAGS_LISTFILES   As above, but list filenames on ^D, after :tselect
///  EXPAND_HELP             Complete tags from the file 'helpfile'/tags
///  EXPAND_EVENTS           Complete event names
///  EXPAND_SYNTAX           Complete :syntax command arguments
///  EXPAND_HIGHLIGHT        Complete highlight (syntax) group names
///  EXPAND_AUGROUP          Complete autocommand group names
///  EXPAND_USER_VARS        Complete user defined variable names, eg :unlet a^I
///  EXPAND_MAPPINGS         Complete mapping and abbreviation names,
///                            eg :unmap a^I , :cunab x^I
///  EXPAND_FUNCTIONS        Complete internal or user defined function names,
///                            eg :call sub^I
///  EXPAND_USER_FUNC        Complete user defined function names, eg :delf F^I
///  EXPAND_EXPRESSION       Complete internal or user defined function/variable
///                          names in expressions, eg :while s^I
///  EXPAND_ENV_VARS         Complete environment variable names
///  EXPAND_USER             Complete user names
void set_expand_context(expand_T *xp)
{
  CmdlineInfo *const ccline = get_cmdline_info();

  // only expansion for ':', '>' and '=' command-lines
  if (ccline->cmdfirstc != ':'
      && ccline->cmdfirstc != '>' && ccline->cmdfirstc != '='
      && !ccline->input_fn) {
    xp->xp_context = EXPAND_NOTHING;
    return;
  }
  set_cmd_context(xp, ccline->cmdbuff, ccline->cmdlen, ccline->cmdpos, true);
}

/// Sets the index of a built-in or user defined command "cmd" in eap->cmdidx.
/// For user defined commands, the completion context is set in "xp" and the
/// completion flags in "complp".
///
/// @return  a pointer to the text after the command or NULL for failure.
static const char *set_cmd_index(const char *cmd, exarg_T *eap, expand_T *xp, int *complp)
{
  const char *p = NULL;
  const bool fuzzy = cmdline_fuzzy_complete(cmd);

  // Isolate the command and search for it in the command table.
  // Exceptions:
  // - the 'k' command can directly be followed by any character, but do
  // accept "keepmarks", "keepalt" and "keepjumps". As fuzzy matching can
  // find matches anywhere in the command name, do this only for command
  // expansion based on regular expression and not for fuzzy matching.
  // - the 's' command can be followed directly by 'c', 'g', 'i', 'I' or 'r'
  if (!fuzzy && (*cmd == 'k' && cmd[1] != 'e')) {
    eap->cmdidx = CMD_k;
    p = cmd + 1;
  } else {
    p = cmd;
    while (ASCII_ISALPHA(*p) || *p == '*') {  // Allow * wild card
      p++;
    }
    // a user command may contain digits
    if (ASCII_ISUPPER(cmd[0])) {
      while (ASCII_ISALNUM(*p) || *p == '*') {
        p++;
      }
    }
    // for python 3.x: ":py3*" commands completion
    if (cmd[0] == 'p' && cmd[1] == 'y' && p == cmd + 2 && *p == '3') {
      p++;
      while (ASCII_ISALPHA(*p) || *p == '*') {
        p++;
      }
    }
    // check for non-alpha command
    if (p == cmd && vim_strchr("@*!=><&~#", (uint8_t)(*p)) != NULL) {
      p++;
    }
    size_t len = (size_t)(p - cmd);

    if (len == 0) {
      xp->xp_context = EXPAND_UNSUCCESSFUL;
      return NULL;
    }

    eap->cmdidx = excmd_get_cmdidx(cmd, len);

    // User defined commands support alphanumeric characters.
    // Also when doing fuzzy expansion for non-shell commands, support
    // alphanumeric characters.
    if ((cmd[0] >= 'A' && cmd[0] <= 'Z')
        || (fuzzy && eap->cmdidx != CMD_bang && *p != NUL)) {
      while (ASCII_ISALNUM(*p) || *p == '*') {  // Allow * wild card
        p++;
      }
    }
  }

  // If the cursor is touching the command, and it ends in an alphanumeric
  // character, complete the command name.
  if (*p == NUL && ASCII_ISALNUM(p[-1])) {
    return NULL;
  }

  if (eap->cmdidx == CMD_SIZE) {
    if (*cmd == 's' && vim_strchr("cgriI", (uint8_t)cmd[1]) != NULL) {
      eap->cmdidx = CMD_substitute;
      p = cmd + 1;
    } else if (cmd[0] >= 'A' && cmd[0] <= 'Z') {
      eap->cmd = (char *)cmd;
      p = find_ucmd(eap, (char *)p, NULL, xp, complp);
      if (p == NULL) {
        eap->cmdidx = CMD_SIZE;  // Ambiguous user command.
      }
    }
  }
  if (eap->cmdidx == CMD_SIZE) {
    // Not still touching the command and it was an illegal one
    xp->xp_context = EXPAND_UNSUCCESSFUL;
    return NULL;
  }

  return p;
}

/// Set the completion context for a command argument with wild card characters.
static void set_context_for_wildcard_arg(exarg_T *eap, const char *arg, bool usefilter,
                                         expand_T *xp, int *complp)
{
  bool in_quote = false;
  const char *bow = NULL;  // Beginning of word.
  size_t len = 0;

  // Allow spaces within back-quotes to count as part of the argument
  // being expanded.
  xp->xp_pattern = skipwhite(arg);
  const char *p = xp->xp_pattern;
  while (*p != NUL) {
    int c = utf_ptr2char(p);
    if (c == '\\' && p[1] != NUL) {
      p++;
    } else if (c == '`') {
      if (!in_quote) {
        xp->xp_pattern = (char *)p;
        bow = p + 1;
      }
      in_quote = !in_quote;
      // An argument can contain just about everything, except
      // characters that end the command and white space.
    } else if (c == '|' || c == '\n' || c == '"' || ascii_iswhite(c)) {
      len = 0;  // avoid getting stuck when space is in 'isfname'
      while (*p != NUL) {
        c = utf_ptr2char(p);
        if (c == '`' || vim_isfilec_or_wc(c)) {
          break;
        }
        len = (size_t)utfc_ptr2len(p);
        MB_PTR_ADV(p);
      }
      if (in_quote) {
        bow = p;
      } else {
        xp->xp_pattern = (char *)p;
      }
      p -= len;
    }
    MB_PTR_ADV(p);
  }

  // If we are still inside the quotes, and we passed a space, just
  // expand from there.
  if (bow != NULL && in_quote) {
    xp->xp_pattern = (char *)bow;
  }
  xp->xp_context = EXPAND_FILES;

  // For a shell command more chars need to be escaped.
  if (usefilter || eap->cmdidx == CMD_bang || eap->cmdidx == CMD_terminal) {
#ifndef BACKSLASH_IN_FILENAME
    xp->xp_shell = true;
#endif
    // When still after the command name expand executables.
    if (xp->xp_pattern == skipwhite(arg)) {
      xp->xp_context = EXPAND_SHELLCMD;
    }
  }

  // Check for environment variable.
  if (*xp->xp_pattern == '$') {
    for (p = xp->xp_pattern + 1; *p != NUL; p++) {
      if (!vim_isIDc((uint8_t)(*p))) {
        break;
      }
    }
    if (*p == NUL) {
      xp->xp_context = EXPAND_ENV_VARS;
      xp->xp_pattern++;
      // Avoid that the assignment uses EXPAND_FILES again.
      if (*complp != EXPAND_USER_DEFINED && *complp != EXPAND_USER_LIST) {
        *complp = EXPAND_ENV_VARS;
      }
    }
  }
  // Check for user names.
  if (*xp->xp_pattern == '~') {
    for (p = xp->xp_pattern + 1; *p != NUL && *p != '/'; p++) {}
    // Complete ~user only if it partially matches a user name.
    // A full match ~user<Tab> will be replaced by user's home
    // directory i.e. something like ~user<Tab> -> /home/user/
    if (*p == NUL && p > xp->xp_pattern + 1 && match_user(xp->xp_pattern + 1) >= 1) {
      xp->xp_context = EXPAND_USER;
      xp->xp_pattern++;
    }
  }
}

/// Set the completion context for the "++opt=arg" argument.  Always returns NULL.
static const char *set_context_in_argopt(expand_T *xp, const char *arg)
{
  char *p = vim_strchr(arg, '=');
  if (p == NULL) {
    xp->xp_pattern = (char *)arg;
  } else {
    xp->xp_pattern = p + 1;
  }

  xp->xp_context = EXPAND_ARGOPT;
  return NULL;
}

/// Set the completion context for the :filter command. Returns a pointer to the
/// next command after the :filter command.
static const char *set_context_in_filter_cmd(expand_T *xp, const char *arg)
{
  if (*arg != NUL) {
    arg = skip_vimgrep_pat((char *)arg, NULL, NULL);
  }
  if (arg == NULL || *arg == NUL) {
    xp->xp_context = EXPAND_NOTHING;
    return NULL;
  }
  return skipwhite(arg);
}

/// Set the completion context for the :match command. Returns a pointer to the
/// next command after the :match command.
static const char *set_context_in_match_cmd(expand_T *xp, const char *arg)
{
  if (*arg == NUL || !ends_excmd(*arg)) {
    // also complete "None"
    set_context_in_echohl_cmd(xp, arg);
    arg = skipwhite(skiptowhite(arg));
    if (*arg != NUL) {
      xp->xp_context = EXPAND_NOTHING;
      arg = skip_regexp((char *)arg + 1, (uint8_t)(*arg), magic_isset());
    }
  }
  return find_nextcmd(arg);
}

/// Returns a pointer to the next command after a :global or a :v command.
/// Returns NULL if there is no next command.
static const char *find_cmd_after_global_cmd(const char *arg)
{
  const int delim = (uint8_t)(*arg);  // Get the delimiter.
  if (delim) {
    arg++;  // Skip delimiter if there is one.
  }

  while (arg[0] != NUL && (uint8_t)arg[0] != delim) {
    if (arg[0] == '\\' && arg[1] != NUL) {
      arg++;
    }
    arg++;
  }
  if (arg[0] != NUL) {
    return arg + 1;
  }

  return NULL;
}

/// Returns a pointer to the next command after a :substitute or a :& command.
/// Returns NULL if there is no next command.
static const char *find_cmd_after_substitute_cmd(const char *arg)
{
  const int delim = (uint8_t)(*arg);
  if (delim) {
    // Skip "from" part.
    arg++;
    arg = skip_regexp((char *)arg, delim, magic_isset());

    if (arg[0] != NUL && arg[0] == delim) {
      // Skip "to" part.
      arg++;
      while (arg[0] != NUL && (uint8_t)arg[0] != delim) {
        if (arg[0] == '\\' && arg[1] != NUL) {
          arg++;
        }
        arg++;
      }
      if (arg[0] != NUL) {  // Skip delimiter.
        arg++;
      }
    }
  }
  while (arg[0] && strchr("|\"#", arg[0]) == NULL) {
    arg++;
  }
  if (arg[0] != NUL) {
    return arg;
  }

  return NULL;
}

/// Returns a pointer to the next command after a :isearch/:dsearch/:ilist
/// :dlist/:ijump/:psearch/:djump/:isplit/:dsplit command.
/// Returns NULL if there is no next command.
static const char *find_cmd_after_isearch_cmd(expand_T *xp, const char *arg)
{
  // Skip count.
  arg = skipwhite(skipdigits(arg));
  if (*arg != '/') {
    return NULL;
  }

  // Match regexp, not just whole words.
  for (++arg; *arg && *arg != '/'; arg++) {
    if (*arg == '\\' && arg[1] != NUL) {
      arg++;
    }
  }
  if (*arg) {
    arg = skipwhite(arg + 1);

    // Check for trailing illegal characters.
    if (*arg == NUL || strchr("|\"\n", *arg) == NULL) {
      xp->xp_context = EXPAND_NOTHING;
    } else {
      return arg;
    }
  }

  return NULL;
}

/// Set the completion context for the :unlet command. Always returns NULL.
static const char *set_context_in_unlet_cmd(expand_T *xp, const char *arg)
{
  while ((xp->xp_pattern = strchr(arg, ' ')) != NULL) {
    arg = xp->xp_pattern + 1;
  }

  xp->xp_context = EXPAND_USER_VARS;
  xp->xp_pattern = (char *)arg;

  if (*xp->xp_pattern == '$') {
    xp->xp_context = EXPAND_ENV_VARS;
    xp->xp_pattern++;
  }

  return NULL;
}

/// Set the completion context for the :language command. Always returns NULL.
static const char *set_context_in_lang_cmd(expand_T *xp, const char *arg)
{
  const char *p = skiptowhite(arg);
  if (*p == NUL) {
    xp->xp_context = EXPAND_LANGUAGE;
    xp->xp_pattern = (char *)arg;
  } else {
    if (strncmp(arg, "messages", (size_t)(p - arg)) == 0
        || strncmp(arg, "ctype", (size_t)(p - arg)) == 0
        || strncmp(arg, "time", (size_t)(p - arg)) == 0
        || strncmp(arg, "collate", (size_t)(p - arg)) == 0) {
      xp->xp_context = EXPAND_LOCALES;
      xp->xp_pattern = skipwhite(p);
    } else {
      xp->xp_context = EXPAND_NOTHING;
    }
  }

  return NULL;
}

static enum {
  EXP_BREAKPT_ADD,  ///< expand ":breakadd" sub-commands
  EXP_BREAKPT_DEL,  ///< expand ":breakdel" sub-commands
  EXP_PROFDEL,      ///< expand ":profdel" sub-commands
} breakpt_expand_what;

/// Set the completion context for the :breakadd command. Always returns NULL.
static const char *set_context_in_breakadd_cmd(expand_T *xp, const char *arg, cmdidx_T cmdidx)
{
  xp->xp_context = EXPAND_BREAKPOINT;
  xp->xp_pattern = (char *)arg;

  if (cmdidx == CMD_breakadd) {
    breakpt_expand_what = EXP_BREAKPT_ADD;
  } else if (cmdidx == CMD_breakdel) {
    breakpt_expand_what = EXP_BREAKPT_DEL;
  } else {
    breakpt_expand_what = EXP_PROFDEL;
  }

  const char *p = skipwhite(arg);
  if (*p == NUL) {
    return NULL;
  }
  const char *subcmd_start = p;

  if (strncmp("file ", p, 5) == 0 || strncmp("func ", p, 5) == 0) {
    // :breakadd file [lnum] <filename>
    // :breakadd func [lnum] <funcname>
    p += 4;
    p = skipwhite(p);

    // skip line number (if specified)
    if (ascii_isdigit(*p)) {
      p = skipdigits(p);
      if (*p != ' ') {
        xp->xp_context = EXPAND_NOTHING;
        return NULL;
      }
      p = skipwhite(p);
    }
    if (strncmp("file", subcmd_start, 4) == 0) {
      xp->xp_context = EXPAND_FILES;
    } else {
      xp->xp_context = EXPAND_USER_FUNC;
    }
    xp->xp_pattern = (char *)p;
  } else if (strncmp("expr ", p, 5) == 0) {
    // :breakadd expr <expression>
    xp->xp_context = EXPAND_EXPRESSION;
    xp->xp_pattern = skipwhite(p + 5);
  }

  return NULL;
}

static const char *set_context_in_scriptnames_cmd(expand_T *xp, const char *arg)
{
  xp->xp_context = EXPAND_NOTHING;
  xp->xp_pattern = NULL;

  char *p = skipwhite(arg);
  if (ascii_isdigit(*p)) {
    return NULL;
  }

  xp->xp_context = EXPAND_SCRIPTNAMES;
  xp->xp_pattern = p;

  return NULL;
}

/// Set the completion context in "xp" for command "cmd" with index "cmdidx".
/// The argument to the command is "arg" and the argument flags is "argt".
/// For user-defined commands and for environment variables, "context" has the
/// completion type.
///
/// @return  a pointer to the next command, or NULL if there is no next command.
static const char *set_context_by_cmdname(const char *cmd, cmdidx_T cmdidx, expand_T *xp,
                                          const char *arg, uint32_t argt, int context, bool forceit)
{
  switch (cmdidx) {
  case CMD_find:
  case CMD_sfind:
  case CMD_tabfind:
    if (xp->xp_context == EXPAND_FILES) {
      xp->xp_context = EXPAND_FILES_IN_PATH;
    }
    break;
  case CMD_cd:
  case CMD_chdir:
  case CMD_lcd:
  case CMD_lchdir:
  case CMD_tcd:
  case CMD_tchdir:
    if (xp->xp_context == EXPAND_FILES) {
      xp->xp_context = EXPAND_DIRECTORIES;
    }
    break;
  case CMD_help:
    xp->xp_context = EXPAND_HELP;
    xp->xp_pattern = (char *)arg;
    break;

  // Command modifiers: return the argument.
  // Also for commands with an argument that is a command.
  case CMD_aboveleft:
  case CMD_argdo:
  case CMD_belowright:
  case CMD_botright:
  case CMD_browse:
  case CMD_bufdo:
  case CMD_cdo:
  case CMD_cfdo:
  case CMD_confirm:
  case CMD_debug:
  case CMD_folddoclosed:
  case CMD_folddoopen:
  case CMD_hide:
  case CMD_horizontal:
  case CMD_keepalt:
  case CMD_keepjumps:
  case CMD_keepmarks:
  case CMD_keeppatterns:
  case CMD_ldo:
  case CMD_leftabove:
  case CMD_lfdo:
  case CMD_lockmarks:
  case CMD_noautocmd:
  case CMD_noswapfile:
  case CMD_rightbelow:
  case CMD_sandbox:
  case CMD_silent:
  case CMD_tab:
  case CMD_tabdo:
  case CMD_topleft:
  case CMD_verbose:
  case CMD_vertical:
  case CMD_windo:
    return arg;

  case CMD_filter:
    return set_context_in_filter_cmd(xp, arg);

  case CMD_match:
    return set_context_in_match_cmd(xp, arg);

  // All completion for the +cmdline_compl feature goes here.

  case CMD_command:
    return set_context_in_user_cmd(xp, arg);

  case CMD_delcommand:
    xp->xp_context = EXPAND_USER_COMMANDS;
    xp->xp_pattern = (char *)arg;
    break;

  case CMD_global:
  case CMD_vglobal:
    return find_cmd_after_global_cmd(arg);
  case CMD_and:
  case CMD_substitute:
    return find_cmd_after_substitute_cmd(arg);
  case CMD_isearch:
  case CMD_dsearch:
  case CMD_ilist:
  case CMD_dlist:
  case CMD_ijump:
  case CMD_psearch:
  case CMD_djump:
  case CMD_isplit:
  case CMD_dsplit:
    return find_cmd_after_isearch_cmd(xp, arg);
  case CMD_autocmd:
    return set_context_in_autocmd(xp, (char *)arg, false);

  case CMD_doautocmd:
  case CMD_doautoall:
    return set_context_in_autocmd(xp, (char *)arg, true);
  case CMD_set:
    set_context_in_set_cmd(xp, (char *)arg, 0);
    break;
  case CMD_setglobal:
    set_context_in_set_cmd(xp, (char *)arg, OPT_GLOBAL);
    break;
  case CMD_setlocal:
    set_context_in_set_cmd(xp, (char *)arg, OPT_LOCAL);
    break;
  case CMD_tag:
  case CMD_stag:
  case CMD_ptag:
  case CMD_ltag:
  case CMD_tselect:
  case CMD_stselect:
  case CMD_ptselect:
  case CMD_tjump:
  case CMD_stjump:
  case CMD_ptjump:
    if (wop_flags & WOP_TAGFILE) {
      xp->xp_context = EXPAND_TAGS_LISTFILES;
    } else {
      xp->xp_context = EXPAND_TAGS;
    }
    xp->xp_pattern = (char *)arg;
    break;
  case CMD_augroup:
    xp->xp_context = EXPAND_AUGROUP;
    xp->xp_pattern = (char *)arg;
    break;
  case CMD_syntax:
    set_context_in_syntax_cmd(xp, arg);
    break;
  case CMD_const:
  case CMD_let:
  case CMD_if:
  case CMD_elseif:
  case CMD_while:
  case CMD_for:
  case CMD_echo:
  case CMD_echon:
  case CMD_execute:
  case CMD_echomsg:
  case CMD_echoerr:
  case CMD_call:
  case CMD_return:
  case CMD_cexpr:
  case CMD_caddexpr:
  case CMD_cgetexpr:
  case CMD_lexpr:
  case CMD_laddexpr:
  case CMD_lgetexpr:
    set_context_for_expression(xp, (char *)arg, cmdidx);
    break;

  case CMD_unlet:
    return set_context_in_unlet_cmd(xp, arg);
  case CMD_function:
  case CMD_delfunction:
    xp->xp_context = EXPAND_USER_FUNC;
    xp->xp_pattern = (char *)arg;
    break;

  case CMD_echohl:
    set_context_in_echohl_cmd(xp, arg);
    break;
  case CMD_highlight:
    set_context_in_highlight_cmd(xp, arg);
    break;
  case CMD_sign:
    set_context_in_sign_cmd(xp, (char *)arg);
    break;
  case CMD_bdelete:
  case CMD_bwipeout:
  case CMD_bunload:
    while ((xp->xp_pattern = strchr(arg, ' ')) != NULL) {
      arg = xp->xp_pattern + 1;
    }
    FALLTHROUGH;
  case CMD_buffer:
  case CMD_sbuffer:
  case CMD_checktime:
    xp->xp_context = EXPAND_BUFFERS;
    xp->xp_pattern = (char *)arg;
    break;
  case CMD_diffget:
  case CMD_diffput:
    // If current buffer is in diff mode, complete buffer names
    // which are in diff mode, and different than current buffer.
    xp->xp_context = EXPAND_DIFF_BUFFERS;
    xp->xp_pattern = (char *)arg;
    break;

  case CMD_USER:
  case CMD_USER_BUF:
    return set_context_in_user_cmdarg(cmd, arg, argt, context, xp, forceit);

  case CMD_map:
  case CMD_noremap:
  case CMD_nmap:
  case CMD_nnoremap:
  case CMD_vmap:
  case CMD_vnoremap:
  case CMD_omap:
  case CMD_onoremap:
  case CMD_imap:
  case CMD_inoremap:
  case CMD_cmap:
  case CMD_cnoremap:
  case CMD_lmap:
  case CMD_lnoremap:
  case CMD_smap:
  case CMD_snoremap:
  case CMD_xmap:
  case CMD_xnoremap:
    return set_context_in_map_cmd(xp, (char *)cmd, (char *)arg, forceit, false,
                                  false, cmdidx);
  case CMD_unmap:
  case CMD_nunmap:
  case CMD_vunmap:
  case CMD_ounmap:
  case CMD_iunmap:
  case CMD_cunmap:
  case CMD_lunmap:
  case CMD_sunmap:
  case CMD_xunmap:
    return set_context_in_map_cmd(xp, (char *)cmd, (char *)arg, forceit, false,
                                  true, cmdidx);
  case CMD_mapclear:
  case CMD_nmapclear:
  case CMD_vmapclear:
  case CMD_omapclear:
  case CMD_imapclear:
  case CMD_cmapclear:
  case CMD_lmapclear:
  case CMD_smapclear:
  case CMD_xmapclear:
    xp->xp_context = EXPAND_MAPCLEAR;
    xp->xp_pattern = (char *)arg;
    break;

  case CMD_abbreviate:
  case CMD_noreabbrev:
  case CMD_cabbrev:
  case CMD_cnoreabbrev:
  case CMD_iabbrev:
  case CMD_inoreabbrev:
    return set_context_in_map_cmd(xp, (char *)cmd, (char *)arg, forceit, true,
                                  false, cmdidx);
  case CMD_unabbreviate:
  case CMD_cunabbrev:
  case CMD_iunabbrev:
    return set_context_in_map_cmd(xp, (char *)cmd, (char *)arg, forceit, true,
                                  true, cmdidx);
  case CMD_menu:
  case CMD_noremenu:
  case CMD_unmenu:
  case CMD_amenu:
  case CMD_anoremenu:
  case CMD_aunmenu:
  case CMD_nmenu:
  case CMD_nnoremenu:
  case CMD_nunmenu:
  case CMD_vmenu:
  case CMD_vnoremenu:
  case CMD_vunmenu:
  case CMD_omenu:
  case CMD_onoremenu:
  case CMD_ounmenu:
  case CMD_imenu:
  case CMD_inoremenu:
  case CMD_iunmenu:
  case CMD_cmenu:
  case CMD_cnoremenu:
  case CMD_cunmenu:
  case CMD_tlmenu:
  case CMD_tlnoremenu:
  case CMD_tlunmenu:
  case CMD_tmenu:
  case CMD_tunmenu:
  case CMD_popup:
  case CMD_emenu:
    return set_context_in_menu_cmd(xp, cmd, (char *)arg, forceit);

  case CMD_colorscheme:
    xp->xp_context = EXPAND_COLORS;
    xp->xp_pattern = (char *)arg;
    break;

  case CMD_compiler:
    xp->xp_context = EXPAND_COMPILER;
    xp->xp_pattern = (char *)arg;
    break;

  case CMD_ownsyntax:
    xp->xp_context = EXPAND_OWNSYNTAX;
    xp->xp_pattern = (char *)arg;
    break;

  case CMD_setfiletype:
    xp->xp_context = EXPAND_FILETYPE;
    xp->xp_pattern = (char *)arg;
    break;

  case CMD_packadd:
    xp->xp_context = EXPAND_PACKADD;
    xp->xp_pattern = (char *)arg;
    break;

  case CMD_runtime:
    set_context_in_runtime_cmd(xp, arg);
    break;

  case CMD_language:
    return set_context_in_lang_cmd(xp, arg);

  case CMD_profile:
    set_context_in_profile_cmd(xp, arg);
    break;
  case CMD_checkhealth:
    xp->xp_context = EXPAND_CHECKHEALTH;
    xp->xp_pattern = (char *)arg;
    break;

  case CMD_messages:
    xp->xp_context = EXPAND_MESSAGES;
    xp->xp_pattern = (char *)arg;
    break;

  case CMD_history:
    xp->xp_context = EXPAND_HISTORY;
    xp->xp_pattern = (char *)arg;
    break;
  case CMD_syntime:
    xp->xp_context = EXPAND_SYNTIME;
    xp->xp_pattern = (char *)arg;
    break;

  case CMD_argdelete:
    while ((xp->xp_pattern = vim_strchr(arg, ' ')) != NULL) {
      arg = (xp->xp_pattern + 1);
    }
    xp->xp_context = EXPAND_ARGLIST;
    xp->xp_pattern = (char *)arg;
    break;

  case CMD_breakadd:
  case CMD_profdel:
  case CMD_breakdel:
    return set_context_in_breakadd_cmd(xp, arg, cmdidx);

  case CMD_scriptnames:
    return set_context_in_scriptnames_cmd(xp, arg);

  case CMD_lua:
  case CMD_equal:
    xp->xp_context = EXPAND_LUA;
    break;

  default:
    break;
  }
  return NULL;
}

/// This is all pretty much copied from do_one_cmd(), with all the extra stuff
/// we don't need/want deleted.  Maybe this could be done better if we didn't
/// repeat all this stuff.  The only problem is that they may not stay
/// perfectly compatible with each other, but then the command line syntax
/// probably won't change that much -- webb.
///
/// @param buff  buffer for command string
static const char *set_one_cmd_context(expand_T *xp, const char *buff)
{
  size_t len = 0;
  exarg_T ea;
  int context = EXPAND_NOTHING;
  bool forceit = false;
  bool usefilter = false;  // Filter instead of file name.

  ExpandInit(xp);
  xp->xp_pattern = (char *)buff;
  xp->xp_line = (char *)buff;
  xp->xp_context = EXPAND_COMMANDS;  // Default until we get past command
  ea.argt = 0;

  // 1. skip comment lines and leading space, colons or bars
  const char *cmd;
  for (cmd = buff; vim_strchr(" \t:|", (uint8_t)(*cmd)) != NULL; cmd++) {}
  xp->xp_pattern = (char *)cmd;

  if (*cmd == NUL) {
    return NULL;
  }
  if (*cmd == '"') {  // ignore comment lines
    xp->xp_context = EXPAND_NOTHING;
    return NULL;
  }

  // 3. skip over a range specifier of the form: addr [,addr] [;addr] ..
  cmd = skip_range(cmd, &xp->xp_context);
  xp->xp_pattern = (char *)cmd;
  if (*cmd == NUL) {
    return NULL;
  }
  if (*cmd == '"') {
    xp->xp_context = EXPAND_NOTHING;
    return NULL;
  }

  if (*cmd == '|' || *cmd == '\n') {
    return cmd + 1;  // There's another command
  }

  // Get the command index.
  const char *p = set_cmd_index(cmd, &ea, xp, &context);
  if (p == NULL) {
    return NULL;
  }

  xp->xp_context = EXPAND_NOTHING;  // Default now that we're past command

  if (*p == '!') {  // forced commands
    forceit = true;
    p++;
  }

  // 6. parse arguments
  if (!IS_USER_CMDIDX(ea.cmdidx)) {
    ea.argt = excmd_get_argt(ea.cmdidx);
  }

  const char *arg = skipwhite(p);

  // Does command allow "++argopt" argument?
  if (ea.argt & EX_ARGOPT) {
    while (*arg != NUL && strncmp(arg, "++", 2) == 0) {
      p = arg + 2;
      while (*p && !ascii_isspace(*p)) {
        MB_PTR_ADV(p);
      }

      // Still touching the command after "++"?
      if (*p == NUL) {
        if (ea.argt & EX_ARGOPT) {
          return set_context_in_argopt(xp, arg + 2);
        }
      }

      arg = skipwhite(p);
    }
  }

  if (ea.cmdidx == CMD_write || ea.cmdidx == CMD_update) {
    if (*arg == '>') {  // append
      if (*++arg == '>') {
        arg++;
      }
      arg = skipwhite(arg);
    } else if (*arg == '!' && ea.cmdidx == CMD_write) {  // :w !filter
      arg++;
      usefilter = true;
    }
  }

  if (ea.cmdidx == CMD_read) {
    usefilter = forceit;  // :r! filter if forced
    if (*arg == '!') {    // :r !filter
      arg++;
      usefilter = true;
    }
  }

  if (ea.cmdidx == CMD_lshift || ea.cmdidx == CMD_rshift) {
    while (*arg == *cmd) {  // allow any number of '>' or '<'
      arg++;
    }
    arg = skipwhite(arg);
  }

  // Does command allow "+command"?
  if ((ea.argt & EX_CMDARG) && !usefilter && *arg == '+') {
    // Check if we're in the +command
    p = arg + 1;
    arg = skip_cmd_arg((char *)arg, false);

    // Still touching the command after '+'?
    if (*arg == NUL) {
      return p;
    }

    // Skip space(s) after +command to get to the real argument.
    arg = skipwhite(arg);
  }

  // Check for '|' to separate commands and '"' to start comments.
  // Don't do this for ":read !cmd" and ":write !cmd".
  if ((ea.argt & EX_TRLBAR) && !usefilter) {
    p = arg;
    // ":redir @" is not the start of a comment
    if (ea.cmdidx == CMD_redir && p[0] == '@' && p[1] == '"') {
      p += 2;
    }
    while (*p) {
      if (*p == Ctrl_V) {
        if (p[1] != NUL) {
          p++;
        }
      } else if ((*p == '"' && !(ea.argt & EX_NOTRLCOM))
                 || *p == '|'
                 || *p == '\n') {
        if (*(p - 1) != '\\') {
          if (*p == '|' || *p == '\n') {
            return p + 1;
          }
          return NULL;  // It's a comment
        }
      }
      MB_PTR_ADV(p);
    }
  }

  if (!(ea.argt & EX_EXTRA) && *arg != NUL && strchr("|\"", *arg) == NULL) {
    // no arguments allowed but there is something
    return NULL;
  }

  // Find start of last argument (argument just before cursor):
  p = buff;
  xp->xp_pattern = (char *)p;
  len = strlen(buff);
  while (*p && p < buff + len) {
    if (*p == ' ' || *p == TAB) {
      // argument starts after a space
      xp->xp_pattern = (char *)++p;
    } else {
      if (*p == '\\' && *(p + 1) != NUL) {
        p++;  // skip over escaped character
      }
      MB_PTR_ADV(p);
    }
  }

  if (ea.argt & EX_XFILE) {
    set_context_for_wildcard_arg(&ea, arg, usefilter, xp, &context);
  }

  // Switch on command name.
  return set_context_by_cmdname(cmd, ea.cmdidx, xp, arg, ea.argt, context, forceit);
}

/// Set the completion context in "xp" for command "str"
///
/// @param str  start of command line
/// @param len  length of command line (excl. NUL)
/// @param col  position of cursor
/// @param use_ccline  use ccline for info
void set_cmd_context(expand_T *xp, char *str, int len, int col, int use_ccline)
{
  CmdlineInfo *const ccline = get_cmdline_info();
  char old_char = NUL;

  // Avoid a UMR warning from Purify, only save the character if it has been
  // written before.
  if (col < len) {
    old_char = str[col];
  }
  str[col] = NUL;
  const char *nextcomm = str;

  if (use_ccline && ccline->cmdfirstc == '=') {
    // pass CMD_SIZE because there is no real command
    set_context_for_expression(xp, str, CMD_SIZE);
  } else if (use_ccline && ccline->input_fn) {
    xp->xp_context = ccline->xp_context;
    xp->xp_pattern = ccline->cmdbuff;
    xp->xp_arg = ccline->xp_arg;
  } else {
    while (nextcomm != NULL) {
      nextcomm = set_one_cmd_context(xp, nextcomm);
    }
  }

  // Store the string here so that call_user_expand_func() can get to them
  // easily.
  xp->xp_line = str;
  xp->xp_col = col;

  str[col] = old_char;
}

/// Expand the command line "str" from context "xp".
/// "xp" must have been set by set_cmd_context().
/// xp->xp_pattern points into "str", to where the text that is to be expanded
/// starts.
/// Returns EXPAND_UNSUCCESSFUL when there is something illegal before the
/// cursor.
/// Returns EXPAND_NOTHING when there is nothing to expand, might insert the
/// key that triggered expansion literally.
/// Returns EXPAND_OK otherwise.
///
/// @param str  start of command line
/// @param col  position of cursor
/// @param matchcount  return: nr of matches
/// @param matches  return: array of pointers to matches
int expand_cmdline(expand_T *xp, const char *str, int col, int *matchcount, char ***matches)
{
  char *file_str = NULL;
  int options = WILD_ADD_SLASH|WILD_SILENT;

  if (xp->xp_context == EXPAND_UNSUCCESSFUL) {
    beep_flush();
    return EXPAND_UNSUCCESSFUL;      // Something illegal on command line
  }
  if (xp->xp_context == EXPAND_NOTHING) {
    // Caller can use the character as a normal char instead
    return EXPAND_NOTHING;
  }

  // add star to file name, or convert to regexp if not exp. files.
  assert((str + col) - xp->xp_pattern >= 0);
  xp->xp_pattern_len = (size_t)((str + col) - xp->xp_pattern);
  if (cmdline_fuzzy_completion_supported(xp)) {
    // If fuzzy matching, don't modify the search string
    file_str = xstrdup(xp->xp_pattern);
  } else {
    file_str = addstar(xp->xp_pattern, xp->xp_pattern_len, xp->xp_context);
  }

  if (p_wic) {
    options += WILD_ICASE;
  }

  // find all files that match the description
  if (ExpandFromContext(xp, file_str, matches, matchcount, options) == FAIL) {
    *matchcount = 0;
    *matches = NULL;
  }
  xfree(file_str);

  return EXPAND_OK;
}

/// Expand file or directory names.
static int expand_files_and_dirs(expand_T *xp, char *pat, char ***matches, int *numMatches,
                                 int flags, int options)
{
  bool free_pat = false;

  // for ":set path=" and ":set tags=" halve backslashes for escaped space
  if (xp->xp_backslash != XP_BS_NONE) {
    free_pat = true;
    pat = xstrdup(pat);
    for (int i = 0; pat[i]; i++) {
      if (pat[i] == '\\') {
        if (xp->xp_backslash & XP_BS_THREE
            && pat[i + 1] == '\\'
            && pat[i + 2] == '\\'
            && pat[i + 3] == ' ') {
          STRMOVE(pat + i, pat + i + 3);
        } else if (xp->xp_backslash & XP_BS_ONE
                   && pat[i + 1] == ' ') {
          STRMOVE(pat + i, pat + i + 1);
        } else if ((xp->xp_backslash & XP_BS_COMMA)
                   && pat[i + 1] == '\\'
                   && pat[i + 2] == ',') {
          STRMOVE(pat + i, pat + i + 2);
#ifdef BACKSLASH_IN_FILENAME
        } else if ((xp->xp_backslash & XP_BS_COMMA)
                   && pat[i + 1] == ',') {
          STRMOVE(pat + i, pat + i + 1);
#endif
        }
      }
    }
  }

  if (xp->xp_context == EXPAND_FILES) {
    flags |= EW_FILE;
  } else if (xp->xp_context == EXPAND_FILES_IN_PATH) {
    flags |= (EW_FILE | EW_PATH);
  } else {
    flags = (flags | EW_DIR) & ~EW_FILE;
  }
  if (options & WILD_ICASE) {
    flags |= EW_ICASE;
  }

  // Expand wildcards, supporting %:h and the like.
  int ret = expand_wildcards_eval(&pat, numMatches, matches, flags);
  if (free_pat) {
    xfree(pat);
  }
#ifdef BACKSLASH_IN_FILENAME
  if (p_csl[0] != NUL && (options & WILD_IGNORE_COMPLETESLASH) == 0) {
    for (int j = 0; j < *numMatches; j++) {
      char *ptr = (*matches)[j];
      while (*ptr != NUL) {
        if (p_csl[0] == 's' && *ptr == '\\') {
          *ptr = '/';
        } else if (p_csl[0] == 'b' && *ptr == '/') {
          *ptr = '\\';
        }
        ptr += utfc_ptr2len(ptr);
      }
    }
  }
#endif
  return ret;
}

/// Function given to ExpandGeneric() to obtain the possible arguments of the
/// ":breakadd {expr, file, func, here}" command.
/// ":breakdel {func, file, here}" command.
static char *get_breakadd_arg(expand_T *xp FUNC_ATTR_UNUSED, int idx)
{
  char *opts[] = { "expr", "file", "func", "here" };

  if (idx >= 0 && idx <= 3) {
    // breakadd {expr, file, func, here}
    if (breakpt_expand_what == EXP_BREAKPT_ADD) {
      return opts[idx];
    } else if (breakpt_expand_what == EXP_BREAKPT_DEL) {
      // breakdel {func, file, here}
      if (idx <= 2) {
        return opts[idx + 1];
      }
    } else {
      // profdel {func, file}
      if (idx <= 1) {
        return opts[idx + 1];
      }
    }
  }
  return NULL;
}

/// Function given to ExpandGeneric() to obtain the possible arguments for the
/// ":scriptnames" command.
static char *get_scriptnames_arg(expand_T *xp FUNC_ATTR_UNUSED, int idx)
{
  if (!SCRIPT_ID_VALID(idx + 1)) {
    return NULL;
  }

  scriptitem_T *si = SCRIPT_ITEM(idx + 1);
  home_replace(NULL, si->sn_name, NameBuff, MAXPATHL, true);
  return NameBuff;
}

/// Function given to ExpandGeneric() to obtain the possible arguments of the
/// ":messages {clear}" command.
static char *get_messages_arg(expand_T *xp FUNC_ATTR_UNUSED, int idx)
{
  if (idx == 0) {
    return "clear";
  }
  return NULL;
}

static char *get_mapclear_arg(expand_T *xp FUNC_ATTR_UNUSED, int idx)
{
  if (idx == 0) {
    return "<buffer>";
  }
  return NULL;
}

/// Completion for |:checkhealth| command.
///
/// Given to ExpandGeneric() to obtain all available heathcheck names.
/// @param[in] idx  Index of the healthcheck item.
/// @param[in] xp  Not used.
static char *get_healthcheck_names(expand_T *xp FUNC_ATTR_UNUSED, int idx)
{
  static Object names = OBJECT_INIT;
  static unsigned last_gen = 0;

  if (last_gen != get_cmdline_last_prompt_id() || last_gen == 0) {
    Array a = ARRAY_DICT_INIT;
    Error err = ERROR_INIT;
    Object res = nlua_exec(STATIC_CSTR_AS_STRING("return vim.health._complete()"), a, &err);
    api_clear_error(&err);
    api_free_object(names);
    names = res;
    last_gen = get_cmdline_last_prompt_id();
  }

  if (names.type == kObjectTypeArray && idx < (int)names.data.array.size) {
    return names.data.array.items[idx].data.string.data;
  }
  return NULL;
}

/// Do the expansion based on xp->xp_context and "rmp".
static int ExpandOther(char *pat, expand_T *xp, regmatch_T *rmp, char ***matches, int *numMatches)
{
  typedef CompleteListItemGetter ExpandFunc;
  static struct expgen {
    int context;
    ExpandFunc func;
    int ic;
    int escaped;
  } tab[] = {
    { EXPAND_COMMANDS, get_command_name, false, true },
    { EXPAND_MAPCLEAR, get_mapclear_arg, true, true },
    { EXPAND_MESSAGES, get_messages_arg, true, true },
    { EXPAND_HISTORY, get_history_arg, true, true },
    { EXPAND_USER_COMMANDS, get_user_commands, false, true },
    { EXPAND_USER_ADDR_TYPE, get_user_cmd_addr_type, false, true },
    { EXPAND_USER_CMD_FLAGS, get_user_cmd_flags, false, true },
    { EXPAND_USER_NARGS, get_user_cmd_nargs, false, true },
    { EXPAND_USER_COMPLETE, get_user_cmd_complete, false, true },
    { EXPAND_USER_VARS, get_user_var_name, false, true },
    { EXPAND_FUNCTIONS, get_function_name, false, true },
    { EXPAND_USER_FUNC, get_user_func_name, false, true },
    { EXPAND_EXPRESSION, get_expr_name, false, true },
    { EXPAND_MENUS, get_menu_name, false, true },
    { EXPAND_MENUNAMES, get_menu_names, false, true },
    { EXPAND_SYNTAX, get_syntax_name, true, true },
    { EXPAND_SYNTIME, get_syntime_arg, true, true },
    { EXPAND_HIGHLIGHT, get_highlight_name, true, false },
    { EXPAND_EVENTS, expand_get_event_name, true, false },
    { EXPAND_AUGROUP, expand_get_augroup_name, true, false },
    { EXPAND_SIGN, get_sign_name, true, true },
    { EXPAND_PROFILE, get_profile_name, true, true },
    { EXPAND_LANGUAGE, get_lang_arg, true, false },
    { EXPAND_LOCALES, get_locales, true, false },
    { EXPAND_ENV_VARS, get_env_name, true, true },
    { EXPAND_USER, get_users, true, false },
    { EXPAND_ARGLIST, get_arglist_name, true, false },
    { EXPAND_BREAKPOINT, get_breakadd_arg, true, true },
    { EXPAND_SCRIPTNAMES, get_scriptnames_arg, true, false },
    { EXPAND_CHECKHEALTH, get_healthcheck_names, true, false },
  };
  int ret = FAIL;

  // Find a context in the table and call the ExpandGeneric() with the
  // right function to do the expansion.
  for (int i = 0; i < (int)ARRAY_SIZE(tab); i++) {
    if (xp->xp_context == tab[i].context) {
      if (tab[i].ic) {
        rmp->rm_ic = true;
      }
      ExpandGeneric(pat, xp, rmp, matches, numMatches, tab[i].func, tab[i].escaped);
      ret = OK;
      break;
    }
  }

  return ret;
}

/// Map wild expand options to flags for expand_wildcards()
static int map_wildopts_to_ewflags(int options)
{
  int flags = EW_DIR;       // include directories
  if (options & WILD_LIST_NOTFOUND) {
    flags |= EW_NOTFOUND;
  }
  if (options & WILD_ADD_SLASH) {
    flags |= EW_ADDSLASH;
  }
  if (options & WILD_KEEP_ALL) {
    flags |= EW_KEEPALL;
  }
  if (options & WILD_SILENT) {
    flags |= EW_SILENT;
  }
  if (options & WILD_NOERROR) {
    flags |= EW_NOERROR;
  }
  if (options & WILD_ALLLINKS) {
    flags |= EW_ALLLINKS;
  }

  return flags;
}

/// Do the expansion based on xp->xp_context and "pat".
///
/// @param options  WILD_ flags
static int ExpandFromContext(expand_T *xp, char *pat, char ***matches, int *numMatches, int options)
{
  regmatch_T regmatch = { .rm_ic = false };
  int ret;
  int flags = map_wildopts_to_ewflags(options);
  const bool fuzzy = cmdline_fuzzy_complete(pat)
                     && cmdline_fuzzy_completion_supported(xp);

  if (xp->xp_context == EXPAND_FILES
      || xp->xp_context == EXPAND_DIRECTORIES
      || xp->xp_context == EXPAND_FILES_IN_PATH) {
    return expand_files_and_dirs(xp, pat, matches, numMatches, flags, options);
  }

  *matches = NULL;
  *numMatches = 0;
  if (xp->xp_context == EXPAND_HELP) {
    // With an empty argument we would get all the help tags, which is
    // very slow.  Get matches for "help" instead.
    if (find_help_tags(*pat == NUL ? "help" : pat,
                       numMatches, matches, false) == OK) {
      cleanup_help_tags(*numMatches, *matches);
      return OK;
    }
    return FAIL;
  }

  if (xp->xp_context == EXPAND_SHELLCMD) {
    expand_shellcmd(pat, matches, numMatches, flags);
    return OK;
  }
  if (xp->xp_context == EXPAND_OLD_SETTING) {
    return ExpandOldSetting(numMatches, matches);
  }
  if (xp->xp_context == EXPAND_BUFFERS) {
    return ExpandBufnames(pat, numMatches, matches, options);
  }
  if (xp->xp_context == EXPAND_DIFF_BUFFERS) {
    return ExpandBufnames(pat, numMatches, matches, options | BUF_DIFF_FILTER);
  }
  if (xp->xp_context == EXPAND_TAGS
      || xp->xp_context == EXPAND_TAGS_LISTFILES) {
    return expand_tags(xp->xp_context == EXPAND_TAGS, pat, numMatches, matches);
  }
  if (xp->xp_context == EXPAND_COLORS) {
    char *directories[] = { "colors", NULL };
    return ExpandRTDir(pat, DIP_START + DIP_OPT, numMatches, matches, directories);
  }
  if (xp->xp_context == EXPAND_COMPILER) {
    char *directories[] = { "compiler", NULL };
    return ExpandRTDir(pat, 0, numMatches, matches, directories);
  }
  if (xp->xp_context == EXPAND_OWNSYNTAX) {
    char *directories[] = { "syntax", NULL };
    return ExpandRTDir(pat, 0, numMatches, matches, directories);
  }
  if (xp->xp_context == EXPAND_FILETYPE) {
    char *directories[] = { "syntax", "indent", "ftplugin", NULL };
    return ExpandRTDir(pat, 0, numMatches, matches, directories);
  }
  if (xp->xp_context == EXPAND_USER_LIST) {
    return ExpandUserList(xp, matches, numMatches);
  }
  if (xp->xp_context == EXPAND_USER_LUA) {
    return ExpandUserLua(xp, numMatches, matches);
  }
  if (xp->xp_context == EXPAND_PACKADD) {
    return ExpandPackAddDir(pat, numMatches, matches);
  }
  if (xp->xp_context == EXPAND_RUNTIME) {
    return expand_runtime_cmd(pat, numMatches, matches);
  }

  // When expanding a function name starting with s:, match the <SNR>nr_
  // prefix.
  char *tofree = NULL;
  if (xp->xp_context == EXPAND_USER_FUNC && strncmp(pat, "^s:", 3) == 0) {
    const size_t len = strlen(pat) + 20;

    tofree = xmalloc(len);
    snprintf(tofree, len, "^<SNR>\\d\\+_%s", pat + 3);
    pat = tofree;
  }

  if (xp->xp_context == EXPAND_LUA) {
    ILOG("PAT %s", pat);
    return nlua_expand_pat(xp, pat, numMatches, matches);
  }

  if (!fuzzy) {
    regmatch.regprog = vim_regcomp(pat, magic_isset() ? RE_MAGIC : 0);
    if (regmatch.regprog == NULL) {
      return FAIL;
    }

    // set ignore-case according to p_ic, p_scs and pat
    regmatch.rm_ic = ignorecase(pat);
  }

  if (xp->xp_context == EXPAND_SETTINGS
      || xp->xp_context == EXPAND_BOOL_SETTINGS) {
    ret = ExpandSettings(xp, &regmatch, pat, numMatches, matches, fuzzy);
  } else if (xp->xp_context == EXPAND_STRING_SETTING) {
    ret = ExpandStringSetting(xp, &regmatch, numMatches, matches);
  } else if (xp->xp_context == EXPAND_SETTING_SUBTRACT) {
    ret = ExpandSettingSubtract(xp, &regmatch, numMatches, matches);
  } else if (xp->xp_context == EXPAND_MAPPINGS) {
    ret = ExpandMappings(pat, &regmatch, numMatches, matches);
  } else if (xp->xp_context == EXPAND_ARGOPT) {
    ret = expand_argopt(pat, xp, &regmatch, matches, numMatches);
  } else if (xp->xp_context == EXPAND_USER_DEFINED) {
    ret = ExpandUserDefined(pat, xp, &regmatch, matches, numMatches);
  } else {
    ret = ExpandOther(pat, xp, &regmatch, matches, numMatches);
  }

  if (!fuzzy) {
    vim_regfree(regmatch.regprog);
  }
  xfree(tofree);

  return ret;
}

/// Expand a list of names.
///
/// Generic function for command line completion.  It calls a function to
/// obtain strings, one by one.  The strings are matched against a regexp
/// program.  Matching strings are copied into an array, which is returned.
///
/// @param func  returns a string from the list
void ExpandGeneric(const char *const pat, expand_T *xp, regmatch_T *regmatch, char ***matches,
                   int *numMatches, CompleteListItemGetter func, bool escaped)
{
  const bool fuzzy = cmdline_fuzzy_complete(pat);
  *matches = NULL;
  *numMatches = 0;

  garray_T ga;
  if (!fuzzy) {
    ga_init(&ga, sizeof(char *), 30);
  } else {
    ga_init(&ga, sizeof(fuzmatch_str_T), 30);
  }

  for (int i = 0;; i++) {
    char *str = (*func)(xp, i);
    if (str == NULL) {  // End of list.
      break;
    }
    if (*str == NUL) {  // Skip empty strings.
      continue;
    }

    bool match;
    int score = 0;
    if (xp->xp_pattern[0] != NUL) {
      if (!fuzzy) {
        match = vim_regexec(regmatch, str, 0);
      } else {
        score = fuzzy_match_str(str, pat);
        match = (score != 0);
      }
    } else {
      match = true;
    }

    if (!match) {
      continue;
    }

    if (escaped) {
      str = vim_strsave_escaped(str, " \t\\.");
    } else {
      str = xstrdup(str);
    }

    if (fuzzy) {
      GA_APPEND(fuzmatch_str_T, &ga, ((fuzmatch_str_T){
        .idx = ga.ga_len,
        .str = str,
        .score = score,
      }));
    } else {
      GA_APPEND(char *, &ga, str);
    }

    if (func == get_menu_names) {
      // Test for separator added by get_menu_names().
      str += strlen(str) - 1;
      if (*str == '\001') {
        *str = '.';
      }
    }
  }

  if (ga.ga_len == 0) {
    return;
  }

  // Sort the matches when using regular expression matching and sorting
  // applies to the completion context. Menus and scriptnames should be kept
  // in the specified order.
  const bool sort_matches = !fuzzy
                            && xp->xp_context != EXPAND_MENUNAMES
                            && xp->xp_context != EXPAND_STRING_SETTING
                            && xp->xp_context != EXPAND_MENUS
                            && xp->xp_context != EXPAND_SCRIPTNAMES
                            && xp->xp_context != EXPAND_ARGOPT;

  // <SNR> functions should be sorted to the end.
  const bool funcsort = xp->xp_context == EXPAND_EXPRESSION
                        || xp->xp_context == EXPAND_FUNCTIONS
                        || xp->xp_context == EXPAND_USER_FUNC;

  // Sort the matches.
  if (sort_matches) {
    if (funcsort) {
      // <SNR> functions should be sorted to the end.
      qsort(ga.ga_data, (size_t)ga.ga_len, sizeof(char *), sort_func_compare);
    } else {
      sort_strings(ga.ga_data, ga.ga_len);
    }
  }

  if (!fuzzy) {
    *matches = ga.ga_data;
    *numMatches = ga.ga_len;
  } else {
    fuzzymatches_to_strmatches(ga.ga_data, matches, ga.ga_len, funcsort);
    *numMatches = ga.ga_len;
  }

  // Reset the variables used for special highlight names expansion, so that
  // they don't show up when getting normal highlight names by ID.
  reset_expand_highlight();
}

/// Expand shell command matches in one directory of $PATH.
static void expand_shellcmd_onedir(char *buf, char *s, size_t l, char *pat, char ***matches,
                                   int *numMatches, int flags, hashtab_T *ht, garray_T *gap)
{
  xstrlcpy(buf, s, l + 1);
  add_pathsep(buf);
  l = strlen(buf);
  xstrlcpy(buf + l, pat, MAXPATHL - l);

  // Expand matches in one directory of $PATH.
  int ret = expand_wildcards(1, &buf, numMatches, matches, flags);
  if (ret != OK) {
    return;
  }

  ga_grow(gap, *numMatches);

  for (int i = 0; i < *numMatches; i++) {
    char *name = (*matches)[i];

    if (strlen(name) > l) {
      // Check if this name was already found.
      hash_T hash = hash_hash(name + l);
      hashitem_T *hi =
        hash_lookup(ht, name + l, strlen(name + l), hash);
      if (HASHITEM_EMPTY(hi)) {
        // Remove the path that was prepended.
        STRMOVE(name, name + l);
        ((char **)gap->ga_data)[gap->ga_len++] = name;
        hash_add_item(ht, hi, name, hash);
        name = NULL;
      }
    }
    xfree(name);
  }
  xfree(*matches);
}

/// Complete a shell command.
///
/// @param      filepat     is a pattern to match with command names.
/// @param[out] matches     is pointer to array of pointers to matches.
///                         *matches will either be set to NULL or point to
///                         allocated memory.
/// @param[out] numMatches  is pointer to number of matches.
/// @param      flagsarg    is a combination of EW_* flags.
static void expand_shellcmd(char *filepat, char ***matches, int *numMatches, int flagsarg)
  FUNC_ATTR_NONNULL_ALL
{
  char *path = NULL;
  garray_T ga;
  char *buf = xmalloc(MAXPATHL);
  char *e;
  int flags = flagsarg;
  bool did_curdir = false;

  // for ":set path=" and ":set tags=" halve backslashes for escaped space
  char *pat = xstrdup(filepat);
  for (int i = 0; pat[i]; i++) {
    if (pat[i] == '\\' && pat[i + 1] == ' ') {
      STRMOVE(pat + i, pat + i + 1);
    }
  }

  flags |= EW_FILE | EW_EXEC | EW_SHELLCMD;

  bool mustfree = false;  // Track memory allocation for *path.
  if (pat[0] == '.' && (vim_ispathsep(pat[1])
                        || (pat[1] == '.' && vim_ispathsep(pat[2])))) {
    path = ".";
  } else {
    // For an absolute name we don't use $PATH.
    if (!path_is_absolute(pat)) {
      path = vim_getenv("PATH");
    }
    if (path == NULL) {
      path = "";
    } else {
      mustfree = true;
    }
  }

  // Go over all directories in $PATH.  Expand matches in that directory and
  // collect them in "ga". When "." is not in $PATH also expand for the
  // current directory, to find "subdir/cmd".
  ga_init(&ga, (int)sizeof(char *), 10);
  hashtab_T found_ht;
  hash_init(&found_ht);
  for (char *s = path;; s = e) {
    e = vim_strchr(s, ENV_SEPCHAR);
    if (e == NULL) {
      e = s + strlen(s);
    }

    if (*s == NUL) {
      if (did_curdir) {
        break;
      }
      // Find directories in the current directory, path is empty.
      did_curdir = true;
      flags |= EW_DIR;
    } else if (strncmp(s, ".", (size_t)(e - s)) == 0) {
      did_curdir = true;
      flags |= EW_DIR;
    } else {
      // Do not match directories inside a $PATH item.
      flags &= ~EW_DIR;
    }

    size_t l = (size_t)(e - s);
    if (l > MAXPATHL - 5) {
      break;
    }
    expand_shellcmd_onedir(buf, s, l, pat, matches, numMatches, flags, &found_ht, &ga);
    if (*e != NUL) {
      e++;
    }
  }
  *matches = ga.ga_data;
  *numMatches = ga.ga_len;

  xfree(buf);
  xfree(pat);
  if (mustfree) {
    xfree(path);
  }
  hash_clear(&found_ht);
}

/// Call "user_expand_func()" to invoke a user defined Vim script function and
/// return the result (either a string, a List or NULL).
static void *call_user_expand_func(user_expand_func_T user_expand_func, expand_T *xp)
  FUNC_ATTR_NONNULL_ALL
{
  CmdlineInfo *const ccline = get_cmdline_info();
  char keep = 0;
  typval_T args[4];
  const sctx_T save_current_sctx = current_sctx;

  if (xp->xp_arg == NULL || xp->xp_arg[0] == '\0' || xp->xp_line == NULL) {
    return NULL;
  }

  if (ccline->cmdbuff != NULL) {
    keep = ccline->cmdbuff[ccline->cmdlen];
    ccline->cmdbuff[ccline->cmdlen] = 0;
  }

  char *pat = xstrnsave(xp->xp_pattern, xp->xp_pattern_len);
  args[0].v_type = VAR_STRING;
  args[1].v_type = VAR_STRING;
  args[2].v_type = VAR_NUMBER;
  args[3].v_type = VAR_UNKNOWN;
  args[0].vval.v_string = pat;
  args[1].vval.v_string = xp->xp_line;
  args[2].vval.v_number = xp->xp_col;

  current_sctx = xp->xp_script_ctx;

  void *const ret = user_expand_func(xp->xp_arg, 3, args);

  current_sctx = save_current_sctx;
  if (ccline->cmdbuff != NULL) {
    ccline->cmdbuff[ccline->cmdlen] = keep;
  }

  xfree(pat);
  return ret;
}

/// Expand names with a function defined by the user (EXPAND_USER_DEFINED and
/// EXPAND_USER_LIST).
static int ExpandUserDefined(const char *const pat, expand_T *xp, regmatch_T *regmatch,
                             char ***matches, int *numMatches)
{
  const bool fuzzy = cmdline_fuzzy_complete(pat);
  *matches = NULL;
  *numMatches = 0;

  char *const retstr = call_user_expand_func(call_func_retstr, xp);
  if (retstr == NULL) {
    return FAIL;
  }

  garray_T ga;
  if (!fuzzy) {
    ga_init(&ga, (int)sizeof(char *), 3);
  } else {
    ga_init(&ga, (int)sizeof(fuzmatch_str_T), 3);
  }

  for (char *s = retstr, *e; *s != NUL; s = e) {
    e = vim_strchr(s, '\n');
    if (e == NULL) {
      e = s + strlen(s);
    }
    const char keep = *e;
    *e = NUL;

    bool match;
    int score = 0;
    if (xp->xp_pattern[0] != NUL) {
      if (!fuzzy) {
        match = vim_regexec(regmatch, s, 0);
      } else {
        score = fuzzy_match_str(s, pat);
        match = (score != 0);
      }
    } else {
      match = true;               // match everything
    }

    *e = keep;

    if (match) {
      if (!fuzzy) {
        GA_APPEND(char *, &ga, xmemdupz(s, (size_t)(e - s)));
      } else {
        GA_APPEND(fuzmatch_str_T, &ga, ((fuzmatch_str_T){
          .idx = ga.ga_len,
          .str = xmemdupz(s, (size_t)(e - s)),
          .score = score,
        }));
      }
    }

    if (*e != NUL) {
      e++;
    }
  }
  xfree(retstr);

  if (ga.ga_len == 0) {
    return OK;
  }

  if (!fuzzy) {
    *matches = ga.ga_data;
    *numMatches = ga.ga_len;
  } else {
    fuzzymatches_to_strmatches(ga.ga_data, matches, ga.ga_len, false);
    *numMatches = ga.ga_len;
  }
  return OK;
}

/// Expand names with a list returned by a function defined by the user.
static int ExpandUserList(expand_T *xp, char ***matches, int *numMatches)
{
  *matches = NULL;
  *numMatches = 0;
  list_T *const retlist = call_user_expand_func(call_func_retlist, xp);
  if (retlist == NULL) {
    return FAIL;
  }

  garray_T ga;
  ga_init(&ga, (int)sizeof(char *), 3);
  // Loop over the items in the list.
  TV_LIST_ITER_CONST(retlist, li, {
    if (TV_LIST_ITEM_TV(li)->v_type != VAR_STRING
        || TV_LIST_ITEM_TV(li)->vval.v_string == NULL) {
      continue;  // Skip non-string items and empty strings.
    }

    GA_APPEND(char *, &ga, xstrdup(TV_LIST_ITEM_TV(li)->vval.v_string));
  });
  tv_list_unref(retlist);

  *matches = ga.ga_data;
  *numMatches = ga.ga_len;
  return OK;
}

static int ExpandUserLua(expand_T *xp, int *num_file, char ***file)
{
  typval_T rettv;
  nlua_call_user_expand_func(xp, &rettv);
  if (rettv.v_type != VAR_LIST) {
    tv_clear(&rettv);
    return FAIL;
  }

  list_T *const retlist = rettv.vval.v_list;

  garray_T ga;
  ga_init(&ga, (int)sizeof(char *), 3);
  // Loop over the items in the list.
  TV_LIST_ITER_CONST(retlist, li, {
    if (TV_LIST_ITEM_TV(li)->v_type != VAR_STRING
        || TV_LIST_ITEM_TV(li)->vval.v_string == NULL) {
      continue;  // Skip non-string items and empty strings.
    }

    GA_APPEND(char *, &ga, xstrdup(TV_LIST_ITEM_TV(li)->vval.v_string));
  });
  tv_list_unref(retlist);

  *file = ga.ga_data;
  *num_file = ga.ga_len;
  return OK;
}

/// Expand `file` for all comma-separated directories in `path`.
/// Adds matches to `ga`.
/// If "dirs" is true only expand directory names.
void globpath(char *path, char *file, garray_T *ga, int expand_options, bool dirs)
{
  expand_T xpc;
  ExpandInit(&xpc);
  xpc.xp_context = dirs ? EXPAND_DIRECTORIES : EXPAND_FILES;

  char *buf = xmalloc(MAXPATHL);

  // Loop over all entries in {path}.
  while (*path != NUL) {
    // Copy one item of the path to buf[] and concatenate the file name.
    copy_option_part(&path, buf, MAXPATHL, ",");
    if (strlen(buf) + strlen(file) + 2 < MAXPATHL) {
      add_pathsep(buf);
      STRCAT(buf, file);  // NOLINT

      char **p;
      int num_p = 0;
      (void)ExpandFromContext(&xpc, buf, &p, &num_p, WILD_SILENT | expand_options);
      if (num_p > 0) {
        ExpandEscape(&xpc, buf, num_p, p, WILD_SILENT | expand_options);

        // Concatenate new results to previous ones.
        ga_grow(ga, num_p);
        // take over the pointers and put them in "ga"
        for (int i = 0; i < num_p; i++) {
          ((char **)ga->ga_data)[ga->ga_len] = p[i];
          ga->ga_len++;
        }
        xfree(p);
      }
    }
  }

  xfree(buf);
}

/// Translate some keys pressed when 'wildmenu' is used.
int wildmenu_translate_key(CmdlineInfo *cclp, int key, expand_T *xp, int did_wild_list)
{
  int c = key;

  if (did_wild_list) {
    if (c == K_LEFT) {
      c = Ctrl_P;
    } else if (c == K_RIGHT) {
      c = Ctrl_N;
    }
  }

  // Hitting CR after "emenu Name.": complete submenu
  if (xp->xp_context == EXPAND_MENUNAMES
      && cclp->cmdpos > 1
      && cclp->cmdbuff[cclp->cmdpos - 1] == '.'
      && cclp->cmdbuff[cclp->cmdpos - 2] != '\\'
      && (c == '\n' || c == '\r' || c == K_KENTER)) {
    c = K_DOWN;
  }

  return c;
}

/// Delete characters on the command line, from "from" to the current position.
static void cmdline_del(CmdlineInfo *cclp, int from)
{
  assert(cclp->cmdpos <= cclp->cmdlen);
  memmove(cclp->cmdbuff + from, cclp->cmdbuff + cclp->cmdpos,
          (size_t)cclp->cmdlen - (size_t)cclp->cmdpos + 1);
  cclp->cmdlen -= cclp->cmdpos - from;
  cclp->cmdpos = from;
}

/// Handle a key pressed when the wild menu for the menu names
/// (EXPAND_MENUNAMES) is displayed.
static int wildmenu_process_key_menunames(CmdlineInfo *cclp, int key, expand_T *xp)
{
  // Hitting <Down> after "emenu Name.": complete submenu
  if (key == K_DOWN && cclp->cmdpos > 0
      && cclp->cmdbuff[cclp->cmdpos - 1] == '.') {
    key = (int)p_wc;
    KeyTyped = true;  // in case the key was mapped
  } else if (key == K_UP) {
    // Hitting <Up>: Remove one submenu name in front of the
    // cursor
    int found = false;

    int j = (int)(xp->xp_pattern - cclp->cmdbuff);
    int i = 0;
    while (--j > 0) {
      // check for start of menu name
      if (cclp->cmdbuff[j] == ' '
          && cclp->cmdbuff[j - 1] != '\\') {
        i = j + 1;
        break;
      }
      // check for start of submenu name
      if (cclp->cmdbuff[j] == '.'
          && cclp->cmdbuff[j - 1] != '\\') {
        if (found) {
          i = j + 1;
          break;
        } else {
          found = true;
        }
      }
    }
    if (i > 0) {
      cmdline_del(cclp, i);
    }
    key = (int)p_wc;
    KeyTyped = true;  // in case the key was mapped
    xp->xp_context = EXPAND_NOTHING;
  }

  return key;
}

/// Handle a key pressed when the wild menu for file names (EXPAND_FILES) or
/// directory names (EXPAND_DIRECTORIES) or shell command names
/// (EXPAND_SHELLCMD) is displayed.
static int wildmenu_process_key_filenames(CmdlineInfo *cclp, int key, expand_T *xp)
{
  char upseg[5];
  upseg[0] = PATHSEP;
  upseg[1] = '.';
  upseg[2] = '.';
  upseg[3] = PATHSEP;
  upseg[4] = NUL;

  if (key == K_DOWN
      && cclp->cmdpos > 0
      && cclp->cmdbuff[cclp->cmdpos - 1] == PATHSEP
      && (cclp->cmdpos < 3
          || cclp->cmdbuff[cclp->cmdpos - 2] != '.'
          || cclp->cmdbuff[cclp->cmdpos - 3] != '.')) {
    // go down a directory
    key = (int)p_wc;
    KeyTyped = true;  // in case the key was mapped
  } else if (strncmp(xp->xp_pattern, upseg + 1, 3) == 0 && key == K_DOWN) {
    // If in a direct ancestor, strip off one ../ to go down
    int found = false;

    int j = cclp->cmdpos;
    int i = (int)(xp->xp_pattern - cclp->cmdbuff);
    while (--j > i) {
      j -= utf_head_off(cclp->cmdbuff, cclp->cmdbuff + j);
      if (vim_ispathsep(cclp->cmdbuff[j])) {
        found = true;
        break;
      }
    }
    if (found
        && cclp->cmdbuff[j - 1] == '.'
        && cclp->cmdbuff[j - 2] == '.'
        && (vim_ispathsep(cclp->cmdbuff[j - 3]) || j == i + 2)) {
      cmdline_del(cclp, j - 2);
      key = (int)p_wc;
      KeyTyped = true;  // in case the key was mapped
    }
  } else if (key == K_UP) {
    // go up a directory
    int found = false;

    int j = cclp->cmdpos - 1;
    int i = (int)(xp->xp_pattern - cclp->cmdbuff);
    while (--j > i) {
      j -= utf_head_off(cclp->cmdbuff, cclp->cmdbuff + j);
      if (vim_ispathsep(cclp->cmdbuff[j])
#ifdef BACKSLASH_IN_FILENAME
          && vim_strchr(" *?[{`$%#", (uint8_t)cclp->cmdbuff[j + 1]) == NULL
#endif
          ) {
        if (found) {
          i = j + 1;
          break;
        } else {
          found = true;
        }
      }
    }

    if (!found) {
      j = i;
    } else if (strncmp(cclp->cmdbuff + j, upseg, 4) == 0) {
      j += 4;
    } else if (strncmp(cclp->cmdbuff + j, upseg + 1, 3) == 0
               && j == i) {
      j += 3;
    } else {
      j = 0;
    }

    if (j > 0) {
      // TODO(tarruda): this is only for DOS/Unix systems - need to put in
      // machine-specific stuff here and in upseg init
      cmdline_del(cclp, j);
      put_on_cmdline(upseg + 1, 3, false);
    } else if (cclp->cmdpos > i) {
      cmdline_del(cclp, i);
    }

    // Now complete in the new directory. Set KeyTyped in case the
    // Up key came from a mapping.
    key = (int)p_wc;
    KeyTyped = true;
  }

  return key;
}

/// Handle a key pressed when wild menu is displayed
int wildmenu_process_key(CmdlineInfo *cclp, int key, expand_T *xp)
{
  // Special translations for 'wildmenu'
  if (xp->xp_context == EXPAND_MENUNAMES) {
    return wildmenu_process_key_menunames(cclp, key, xp);
  }
  if (xp->xp_context == EXPAND_FILES
      || xp->xp_context == EXPAND_DIRECTORIES
      || xp->xp_context == EXPAND_SHELLCMD) {
    return wildmenu_process_key_filenames(cclp, key, xp);
  }

  return key;
}

/// Free expanded names when finished walking through the matches
void wildmenu_cleanup(CmdlineInfo *cclp)
{
  if (!p_wmnu || wild_menu_showing == 0) {
    return;
  }

  const bool skt = KeyTyped;
  const int old_RedrawingDisabled = RedrawingDisabled;

  if (cclp->input_fn) {
    RedrawingDisabled = 0;
  }

  if (wild_menu_showing == WM_SCROLLED) {
    // Entered command line, move it up
    cmdline_row--;
    redrawcmd();
    wild_menu_showing = 0;
  } else if (save_p_ls != -1) {
    // restore 'laststatus' and 'winminheight'
    p_ls = save_p_ls;
    p_wmh = save_p_wmh;
    last_status(false);
    update_screen();  // redraw the screen NOW
    redrawcmd();
    save_p_ls = -1;
    wild_menu_showing = 0;
    // don't redraw statusline if WM_LIST is showing
  } else if (wild_menu_showing != WM_LIST) {
    win_redraw_last_status(topframe);
    wild_menu_showing = 0;  // must be before redraw_statuslines #8385
    redraw_statuslines();
  } else {
    wild_menu_showing = 0;
  }
  KeyTyped = skt;
  if (cclp->input_fn) {
    RedrawingDisabled = old_RedrawingDisabled;
  }
}

/// "getcompletion()" function
void f_getcompletion(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
{
  expand_T xpc;
  bool filtered = false;
  int options = WILD_SILENT | WILD_USE_NL | WILD_ADD_SLASH
                | WILD_NO_BEEP | WILD_HOME_REPLACE;

  if (tv_check_for_string_arg(argvars, 1) == FAIL) {
    return;
  }
  const char *const type = tv_get_string(&argvars[1]);

  if (argvars[2].v_type != VAR_UNKNOWN) {
    filtered = (bool)tv_get_number_chk(&argvars[2], NULL);
  }

  if (p_wic) {
    options |= WILD_ICASE;
  }

  // For filtered results, 'wildignore' is used
  if (!filtered) {
    options |= WILD_KEEP_ALL;
  }

  if (argvars[0].v_type != VAR_STRING) {
    emsg(_(e_invarg));
    return;
  }
  const char *pattern = tv_get_string(&argvars[0]);

  if (strcmp(type, "cmdline") == 0) {
    const int cmdline_len = (int)strlen(pattern);
    set_cmd_context(&xpc, (char *)pattern, cmdline_len, cmdline_len, false);
    xpc.xp_pattern_len = strlen(xpc.xp_pattern);
    xpc.xp_col = cmdline_len;
    goto theend;
  }

  ExpandInit(&xpc);
  xpc.xp_pattern = (char *)pattern;
  xpc.xp_pattern_len = strlen(xpc.xp_pattern);
  xpc.xp_line = (char *)pattern;

  xpc.xp_context = cmdcomplete_str_to_type(type);
  if (xpc.xp_context == EXPAND_NOTHING) {
    semsg(_(e_invarg2), type);
    return;
  }

  if (xpc.xp_context == EXPAND_USER_DEFINED) {
    // Must be "custom,funcname" pattern
    if (strncmp(type, "custom,", 7) != 0) {
      semsg(_(e_invarg2), type);
      return;
    }

    xpc.xp_arg = (char *)(type + 7);
  }

  if (xpc.xp_context == EXPAND_USER_LIST) {
    // Must be "customlist,funcname" pattern
    if (strncmp(type, "customlist,", 11) != 0) {
      semsg(_(e_invarg2), type);
      return;
    }

    xpc.xp_arg = (char *)(type + 11);
  }

  if (xpc.xp_context == EXPAND_MENUS) {
    set_context_in_menu_cmd(&xpc, "menu", xpc.xp_pattern, false);
    xpc.xp_pattern_len = strlen(xpc.xp_pattern);
  }
  if (xpc.xp_context == EXPAND_SIGN) {
    set_context_in_sign_cmd(&xpc, xpc.xp_pattern);
    xpc.xp_pattern_len = strlen(xpc.xp_pattern);
  }
  if (xpc.xp_context == EXPAND_RUNTIME) {
    set_context_in_runtime_cmd(&xpc, xpc.xp_pattern);
    xpc.xp_pattern_len = strlen(xpc.xp_pattern);
  }

theend:
  ;
  char *pat;
  if (cmdline_fuzzy_completion_supported(&xpc)) {
    // when fuzzy matching, don't modify the search string
    pat = xstrdup(xpc.xp_pattern);
  } else {
    pat = addstar(xpc.xp_pattern, xpc.xp_pattern_len, xpc.xp_context);
  }

  ExpandOne(&xpc, pat, NULL, options, WILD_ALL_KEEP);
  tv_list_alloc_ret(rettv, xpc.xp_numfiles);

  for (int i = 0; i < xpc.xp_numfiles; i++) {
    tv_list_append_string(rettv->vval.v_list, xpc.xp_files[i], -1);
  }
  xfree(pat);
  ExpandCleanup(&xpc);
}