vim-patch:8.2.1262: src/ex_cmds.c file is too big (#19811)

Problem:    src/ex_cmds.c file is too big.
Solution:   Move help related code to src/help.c. (Yegappan Lakshmanan,
            closes vim/vim#6506)
https://github.com/vim/vim/commit/f868ba89039045b25efe83d12ca501d657e170e8

10 files changed, 1199 insertions, 1173 deletions

diff --git a/src/nvim/buffer.c b/src/nvim/buffer.c
index 18915f1042..08c2746d7b 100644
--- a/src/nvim/buffer.c
+++ b/src/nvim/buffer.c
@@ -52,6 +52,7 @@
 #include "nvim/garray.h"
 #include "nvim/getchar.h"
 #include "nvim/hashtab.h"
+#include "nvim/help.h"
 #include "nvim/highlight_group.h"
 #include "nvim/indent.h"
 #include "nvim/indent_c.h"
diff --git a/src/nvim/ex_cmds.c b/src/nvim/ex_cmds.c
index 327834b646..842ebc4612 100644
--- a/src/nvim/ex_cmds.c
+++ b/src/nvim/ex_cmds.c
@@ -38,6 +38,7 @@
 #include "nvim/fold.h"
 #include "nvim/garray.h"
 #include "nvim/getchar.h"
+#include "nvim/help.h"
 #include "nvim/highlight.h"
 #include "nvim/highlight_group.h"
 #include "nvim/indent.h"
@@ -4779,1124 +4780,6 @@ bool prepare_tagpreview(bool undo_sync)
   return false;
 }
 
-/// ":help": open a read-only window on a help file
-void ex_help(exarg_T *eap)
-{
-  char *arg;
-  char *tag;
-  FILE *helpfd;          // file descriptor of help file
-  int n;
-  int i;
-  win_T *wp;
-  int num_matches;
-  char **matches;
-  char *p;
-  int empty_fnum = 0;
-  int alt_fnum = 0;
-  buf_T *buf;
-  int len;
-  char *lang;
-  const bool old_KeyTyped = KeyTyped;
-
-  if (eap != NULL) {
-    /*
-     * A ":help" command ends at the first LF, or at a '|' that is
-     * followed by some text.  Set nextcmd to the following command.
-     */
-    for (arg = eap->arg; *arg; arg++) {
-      if (*arg == '\n' || *arg == '\r'
-          || (*arg == '|' && arg[1] != NUL && arg[1] != '|')) {
-        *arg++ = NUL;
-        eap->nextcmd = arg;
-        break;
-      }
-    }
-    arg = eap->arg;
-
-    if (eap->forceit && *arg == NUL && !curbuf->b_help) {
-      emsg(_("E478: Don't panic!"));
-      return;
-    }
-
-    if (eap->skip) {        // not executing commands
-      return;
-    }
-  } else {
-    arg = "";
-  }
-
-  // remove trailing blanks
-  p = arg + STRLEN(arg) - 1;
-  while (p > arg && ascii_iswhite(*p) && p[-1] != '\\') {
-    *p-- = NUL;
-  }
-
-  // Check for a specified language
-  lang = check_help_lang(arg);
-
-  // When no argument given go to the index.
-  if (*arg == NUL) {
-    arg = "help.txt";
-  }
-
-  /*
-   * Check if there is a match for the argument.
-   */
-  n = find_help_tags(arg, &num_matches, &matches, eap != NULL && eap->forceit);
-
-  i = 0;
-  if (n != FAIL && lang != NULL) {
-    // Find first item with the requested language.
-    for (i = 0; i < num_matches; ++i) {
-      len = (int)STRLEN(matches[i]);
-      if (len > 3 && matches[i][len - 3] == '@'
-          && STRICMP(matches[i] + len - 2, lang) == 0) {
-        break;
-      }
-    }
-  }
-  if (i >= num_matches || n == FAIL) {
-    if (lang != NULL) {
-      semsg(_("E661: Sorry, no '%s' help for %s"), lang, arg);
-    } else {
-      semsg(_("E149: Sorry, no help for %s"), arg);
-    }
-    if (n != FAIL) {
-      FreeWild(num_matches, matches);
-    }
-    return;
-  }
-
-  // The first match (in the requested language) is the best match.
-  tag = xstrdup(matches[i]);
-  FreeWild(num_matches, matches);
-
-  /*
-   * Re-use an existing help window or open a new one.
-   * Always open a new one for ":tab help".
-   */
-  if (!bt_help(curwin->w_buffer) || cmdmod.cmod_tab != 0) {
-    if (cmdmod.cmod_tab != 0) {
-      wp = NULL;
-    } else {
-      wp = NULL;
-      FOR_ALL_WINDOWS_IN_TAB(wp2, curtab) {
-        if (bt_help(wp2->w_buffer)) {
-          wp = wp2;
-          break;
-        }
-      }
-    }
-    if (wp != NULL && wp->w_buffer->b_nwindows > 0) {
-      win_enter(wp, true);
-    } else {
-      // There is no help window yet.
-      // Try to open the file specified by the "helpfile" option.
-      if ((helpfd = os_fopen((char *)p_hf, READBIN)) == NULL) {
-        smsg(_("Sorry, help file \"%s\" not found"), p_hf);
-        goto erret;
-      }
-      fclose(helpfd);
-
-      // Split off help window; put it at far top if no position
-      // specified, the current window is vertically split and
-      // narrow.
-      n = WSP_HELP;
-      if (cmdmod.cmod_split == 0 && curwin->w_width != Columns
-          && curwin->w_width < 80) {
-        n |= WSP_TOP;
-      }
-      if (win_split(0, n) == FAIL) {
-        goto erret;
-      }
-
-      if (curwin->w_height < p_hh) {
-        win_setheight((int)p_hh);
-      }
-
-      /*
-       * Open help file (do_ecmd() will set b_help flag, readfile() will
-       * set b_p_ro flag).
-       * Set the alternate file to the previously edited file.
-       */
-      alt_fnum = curbuf->b_fnum;
-      (void)do_ecmd(0, NULL, NULL, NULL, ECMD_LASTL,
-                    ECMD_HIDE + ECMD_SET_HELP,
-                    NULL);  // buffer is still open, don't store info
-
-      if ((cmdmod.cmod_flags & CMOD_KEEPALT) == 0) {
-        curwin->w_alt_fnum = alt_fnum;
-      }
-      empty_fnum = curbuf->b_fnum;
-    }
-  }
-
-  restart_edit = 0;               // don't want insert mode in help file
-
-  // Restore KeyTyped, setting 'filetype=help' may reset it.
-  // It is needed for do_tag top open folds under the cursor.
-  KeyTyped = old_KeyTyped;
-
-  do_tag((char_u *)tag, DT_HELP, 1, false, true);
-
-  // Delete the empty buffer if we're not using it.  Careful: autocommands
-  // may have jumped to another window, check that the buffer is not in a
-  // window.
-  if (empty_fnum != 0 && curbuf->b_fnum != empty_fnum) {
-    buf = buflist_findnr(empty_fnum);
-    if (buf != NULL && buf->b_nwindows == 0) {
-      wipe_buffer(buf, true);
-    }
-  }
-
-  // keep the previous alternate file
-  if (alt_fnum != 0 && curwin->w_alt_fnum == empty_fnum
-      && (cmdmod.cmod_flags & CMOD_KEEPALT) == 0) {
-    curwin->w_alt_fnum = alt_fnum;
-  }
-
-erret:
-  xfree(tag);
-}
-
-/// In an argument search for a language specifiers in the form "@xx".
-/// Changes the "@" to NUL if found, and returns a pointer to "xx".
-///
-/// @return  NULL if not found.
-char *check_help_lang(char *arg)
-{
-  int len = (int)STRLEN(arg);
-
-  if (len >= 3 && arg[len - 3] == '@' && ASCII_ISALPHA(arg[len - 2])
-      && ASCII_ISALPHA(arg[len - 1])) {
-    arg[len - 3] = NUL;                 // remove the '@'
-    return arg + len - 2;
-  }
-  return NULL;
-}
-
-/// Return a heuristic indicating how well the given string matches.  The
-/// smaller the number, the better the match.  This is the order of priorities,
-/// from best match to worst match:
-///      - Match with least alphanumeric characters is better.
-///      - Match with least total characters is better.
-///      - Match towards the start is better.
-///      - Match starting with "+" is worse (feature instead of command)
-/// Assumption is made that the matched_string passed has already been found to
-/// match some string for which help is requested.  webb.
-///
-/// @param offset      offset for match
-/// @param wrong_case  no matching case
-///
-/// @return  a heuristic indicating how well the given string matches.
-int help_heuristic(char *matched_string, int offset, int wrong_case)
-  FUNC_ATTR_PURE
-{
-  int num_letters;
-  char *p;
-
-  num_letters = 0;
-  for (p = matched_string; *p; p++) {
-    if (ASCII_ISALNUM(*p)) {
-      num_letters++;
-    }
-  }
-
-  /*
-   * Multiply the number of letters by 100 to give it a much bigger
-   * weighting than the number of characters.
-   * If there only is a match while ignoring case, add 5000.
-   * If the match starts in the middle of a word, add 10000 to put it
-   * somewhere in the last half.
-   * If the match is more than 2 chars from the start, multiply by 200 to
-   * put it after matches at the start.
-   */
-  if (offset > 0
-      && ASCII_ISALNUM(matched_string[offset])
-      && ASCII_ISALNUM(matched_string[offset - 1])) {
-    offset += 10000;
-  } else if (offset > 2) {
-    offset *= 200;
-  }
-  if (wrong_case) {
-    offset += 5000;
-  }
-  // Features are less interesting than the subjects themselves, but "+"
-  // alone is not a feature.
-  if (matched_string[0] == '+' && matched_string[1] != NUL) {
-    offset += 100;
-  }
-  return 100 * num_letters + (int)STRLEN(matched_string) + offset;
-}
-
-/// Compare functions for qsort() below, that checks the help heuristics number
-/// that has been put after the tagname by find_tags().
-static int help_compare(const void *s1, const void *s2)
-{
-  char *p1;
-  char *p2;
-
-  p1 = *(char **)s1 + strlen(*(char **)s1) + 1;
-  p2 = *(char **)s2 + strlen(*(char **)s2) + 1;
-
-  // Compare by help heuristic number first.
-  int cmp = strcmp(p1, p2);
-  if (cmp != 0) {
-    return cmp;
-  }
-
-  // Compare by strings as tie-breaker when same heuristic number.
-  return strcmp(*(char **)s1, *(char **)s2);
-}
-
-/// Find all help tags matching "arg", sort them and return in matches[], with
-/// the number of matches in num_matches.
-/// The matches will be sorted with a "best" match algorithm.
-/// When "keep_lang" is true try keeping the language of the current buffer.
-int find_help_tags(const char *arg, int *num_matches, char ***matches, bool keep_lang)
-{
-  int i;
-
-  // Specific tags that either have a specific replacement or won't go
-  // through the generic rules.
-  static char *(except_tbl[][2]) = {
-    { "*",           "star" },
-    { "g*",          "gstar" },
-    { "[*",          "[star" },
-    { "]*",          "]star" },
-    { ":*",          ":star" },
-    { "/*",          "/star" },  // NOLINT
-    { "/\\*",        "/\\\\star" },
-    { "\"*",         "quotestar" },
-    { "**",          "starstar" },
-    { "cpo-*",       "cpo-star" },
-    { "/\\(\\)",     "/\\\\(\\\\)" },
-    { "/\\%(\\)",    "/\\\\%(\\\\)" },
-    { "?",           "?" },
-    { "??",          "??" },
-    { ":?",          ":?" },
-    { "?<CR>",       "?<CR>" },
-    { "g?",          "g?" },
-    { "g?g?",        "g?g?" },
-    { "g??",         "g??" },
-    { "-?",          "-?" },
-    { "q?",          "q?" },
-    { "v_g?",        "v_g?" },
-    { "/\\?",        "/\\\\?" },
-    { "/\\z(\\)",    "/\\\\z(\\\\)" },
-    { "\\=",         "\\\\=" },
-    { ":s\\=",       ":s\\\\=" },
-    { "[count]",     "\\[count]" },
-    { "[quotex]",    "\\[quotex]" },
-    { "[range]",     "\\[range]" },
-    { ":[range]",    ":\\[range]" },
-    { "[pattern]",   "\\[pattern]" },
-    { "\\|",         "\\\\bar" },
-    { "\\%$",        "/\\\\%\\$" },
-    { "s/\\~",       "s/\\\\\\~" },
-    { "s/\\U",       "s/\\\\U" },
-    { "s/\\L",       "s/\\\\L" },
-    { "s/\\1",       "s/\\\\1" },
-    { "s/\\2",       "s/\\\\2" },
-    { "s/\\3",       "s/\\\\3" },
-    { "s/\\9",       "s/\\\\9" },
-    { NULL, NULL }
-  };
-
-  static const char *(expr_table[]) = {
-    "!=?", "!~?", "<=?", "<?", "==?", "=~?",
-    ">=?", ">?", "is?", "isnot?"
-  };
-  char *d = (char *)IObuff;       // assume IObuff is long enough!
-  d[0] = NUL;
-
-  if (STRNICMP(arg, "expr-", 5) == 0) {
-    // When the string starting with "expr-" and containing '?' and matches
-    // the table, it is taken literally (but ~ is escaped).  Otherwise '?'
-    // is recognized as a wildcard.
-    for (i = (int)ARRAY_SIZE(expr_table); --i >= 0;) {
-      if (STRCMP(arg + 5, expr_table[i]) == 0) {
-        for (int si = 0, di = 0;; si++) {
-          if (arg[si] == '~') {
-            d[di++] = '\\';
-          }
-          d[di++] = arg[si];
-          if (arg[si] == NUL) {
-            break;
-          }
-        }
-        break;
-      }
-    }
-  } else {
-    // Recognize a few exceptions to the rule.  Some strings that contain
-    // '*'are changed to "star", otherwise '*' is recognized as a wildcard.
-    for (i = 0; except_tbl[i][0] != NULL; i++) {
-      if (STRCMP(arg, except_tbl[i][0]) == 0) {
-        STRCPY(d, except_tbl[i][1]);
-        break;
-      }
-    }
-  }
-
-  if (d[0] == NUL) {  // no match in table
-    // Replace "\S" with "/\\S", etc.  Otherwise every tag is matched.
-    // Also replace "\%^" and "\%(", they match every tag too.
-    // Also "\zs", "\z1", etc.
-    // Also "\@<", "\@=", "\@<=", etc.
-    // And also "\_$" and "\_^".
-    if (arg[0] == '\\'
-        && ((arg[1] != NUL && arg[2] == NUL)
-            || (vim_strchr("%_z@", arg[1]) != NULL
-                && arg[2] != NUL))) {
-      vim_snprintf(d, IOSIZE, "/\\\\%s", arg + 1);
-      // Check for "/\\_$", should be "/\\_\$"
-      if (d[3] == '_' && d[4] == '$') {
-        STRCPY(d + 4, "\\$");
-      }
-    } else {
-      // Replace:
-      // "[:...:]" with "\[:...:]"
-      // "[++...]" with "\[++...]"
-      // "\{" with "\\{"               -- matching "} \}"
-      if ((arg[0] == '[' && (arg[1] == ':'
-                             || (arg[1] == '+' && arg[2] == '+')))
-          || (arg[0] == '\\' && arg[1] == '{')) {
-        *d++ = '\\';
-      }
-
-      // If tag starts with "('", skip the "(". Fixes CTRL-] on ('option'.
-      if (*arg == '(' && arg[1] == '\'') {
-        arg++;
-      }
-      for (const char *s = arg; *s; s++) {
-        // Replace "|" with "bar" and '"' with "quote" to match the name of
-        // the tags for these commands.
-        // Replace "*" with ".*" and "?" with "." to match command line
-        // completion.
-        // Insert a backslash before '~', '$' and '.' to avoid their
-        // special meaning.
-        if ((char_u *)d - IObuff > IOSIZE - 10) {           // getting too long!?
-          break;
-        }
-        switch (*s) {
-        case '|':
-          STRCPY(d, "bar");
-          d += 3;
-          continue;
-        case '"':
-          STRCPY(d, "quote");
-          d += 5;
-          continue;
-        case '*':
-          *d++ = '.';
-          break;
-        case '?':
-          *d++ = '.';
-          continue;
-        case '$':
-        case '.':
-        case '~':
-          *d++ = '\\';
-          break;
-        }
-
-        /*
-         * Replace "^x" by "CTRL-X". Don't do this for "^_" to make
-         * ":help i_^_CTRL-D" work.
-         * Insert '-' before and after "CTRL-X" when applicable.
-         */
-        if (*s < ' '
-            || (*s == '^' && s[1]
-                && (ASCII_ISALPHA(s[1]) || vim_strchr("?@[\\]^", s[1]) != NULL))) {
-          if ((char_u *)d > IObuff && d[-1] != '_' && d[-1] != '\\') {
-            *d++ = '_';                 // prepend a '_' to make x_CTRL-x
-          }
-          STRCPY(d, "CTRL-");
-          d += 5;
-          if (*s < ' ') {
-            *d++ = (char)(*s + '@');
-            if (d[-1] == '\\') {
-              *d++ = '\\';              // double a backslash
-            }
-          } else {
-            *d++ = *++s;
-          }
-          if (s[1] != NUL && s[1] != '_') {
-            *d++ = '_';                 // append a '_'
-          }
-          continue;
-        } else if (*s == '^') {         // "^" or "CTRL-^" or "^_"
-          *d++ = '\\';
-        }
-        /*
-         * Insert a backslash before a backslash after a slash, for search
-         * pattern tags: "/\|" --> "/\\|".
-         */
-        else if (s[0] == '\\' && s[1] != '\\'
-                 && *arg == '/' && s == arg + 1) {
-          *d++ = '\\';
-        }
-
-        // "CTRL-\_" -> "CTRL-\\_" to avoid the special meaning of "\_" in
-        // "CTRL-\_CTRL-N"
-        if (STRNICMP(s, "CTRL-\\_", 7) == 0) {
-          STRCPY(d, "CTRL-\\\\");
-          d += 7;
-          s += 6;
-        }
-
-        *d++ = *s;
-
-        // If tag contains "({" or "([", tag terminates at the "(".
-        // This is for help on functions, e.g.: abs({expr}).
-        if (*s == '(' && (s[1] == '{' || s[1] == '[')) {
-          break;
-        }
-
-        // If tag starts with ', toss everything after a second '. Fixes
-        // CTRL-] on 'option'. (would include the trailing '.').
-        if (*s == '\'' && s > arg && *arg == '\'') {
-          break;
-        }
-        // Also '{' and '}'. Fixes CTRL-] on '{address}'.
-        if (*s == '}' && s > arg && *arg == '{') {
-          break;
-        }
-      }
-      *d = NUL;
-
-      if (*IObuff == '`') {
-        if ((char_u *)d > IObuff + 2 && d[-1] == '`') {
-          // remove the backticks from `command`
-          memmove(IObuff, IObuff + 1, STRLEN(IObuff));
-          d[-2] = NUL;
-        } else if ((char_u *)d > IObuff + 3 && d[-2] == '`' && d[-1] == ',') {
-          // remove the backticks and comma from `command`,
-          memmove(IObuff, IObuff + 1, STRLEN(IObuff));
-          d[-3] = NUL;
-        } else if ((char_u *)d > IObuff + 4 && d[-3] == '`'
-                   && d[-2] == '\\' && d[-1] == '.') {
-          // remove the backticks and dot from `command`\.
-          memmove(IObuff, IObuff + 1, STRLEN(IObuff));
-          d[-4] = NUL;
-        }
-      }
-    }
-  }
-
-  *matches = NULL;
-  *num_matches = 0;
-  int flags = TAG_HELP | TAG_REGEXP | TAG_NAMES | TAG_VERBOSE | TAG_NO_TAGFUNC;
-  if (keep_lang) {
-    flags |= TAG_KEEP_LANG;
-  }
-  if (find_tags(IObuff, num_matches, matches, flags, MAXCOL, NULL) == OK
-      && *num_matches > 0) {
-    // Sort the matches found on the heuristic number that is after the
-    // tag name.
-    qsort((void *)(*matches), (size_t)(*num_matches),
-          sizeof(char_u *), help_compare);
-    // Delete more than TAG_MANY to reduce the size of the listing.
-    while (*num_matches > TAG_MANY) {
-      xfree((*matches)[--*num_matches]);
-    }
-  }
-  return OK;
-}
-
-/// Called when starting to edit a buffer for a help file.
-static void prepare_help_buffer(void)
-{
-  curbuf->b_help = true;
-  set_string_option_direct("buftype", -1, "help", OPT_FREE|OPT_LOCAL, 0);
-
-  // Always set these options after jumping to a help tag, because the
-  // user may have an autocommand that gets in the way.
-  // Accept all ASCII chars for keywords, except ' ', '*', '"', '|', and
-  // latin1 word characters (for translated help files).
-  // Only set it when needed, buf_init_chartab() is some work.
-  char *p = "!-~,^*,^|,^\",192-255";
-  if (STRCMP(curbuf->b_p_isk, p) != 0) {
-    set_string_option_direct("isk", -1, p, OPT_FREE|OPT_LOCAL, 0);
-    check_buf_options(curbuf);
-    (void)buf_init_chartab(curbuf, FALSE);
-  }
-
-  // Don't use the global foldmethod.
-  set_string_option_direct("fdm", -1, "manual", OPT_FREE|OPT_LOCAL, 0);
-
-  curbuf->b_p_ts = 8;         // 'tabstop' is 8.
-  curwin->w_p_list = FALSE;   // No list mode.
-
-  curbuf->b_p_ma = FALSE;     // Not modifiable.
-  curbuf->b_p_bin = FALSE;    // Reset 'bin' before reading file.
-  curwin->w_p_nu = 0;         // No line numbers.
-  curwin->w_p_rnu = 0;        // No relative line numbers.
-  RESET_BINDING(curwin);      // No scroll or cursor binding.
-  curwin->w_p_arab = FALSE;   // No arabic mode.
-  curwin->w_p_rl  = FALSE;    // Help window is left-to-right.
-  curwin->w_p_fen = FALSE;    // No folding in the help window.
-  curwin->w_p_diff = FALSE;   // No 'diff'.
-  curwin->w_p_spell = FALSE;  // No spell checking.
-
-  set_buflisted(FALSE);
-}
-
-/// After reading a help file: May cleanup a help buffer when syntax
-/// highlighting is not used.
-void fix_help_buffer(void)
-{
-  linenr_T lnum;
-  char *line;
-  bool in_example = false;
-
-  // Set filetype to "help".
-  if (STRCMP(curbuf->b_p_ft, "help") != 0) {
-    curbuf->b_ro_locked++;
-    set_option_value("ft", 0L, "help", OPT_LOCAL);
-    curbuf->b_ro_locked--;
-  }
-
-  if (!syntax_present(curwin)) {
-    for (lnum = 1; lnum <= curbuf->b_ml.ml_line_count; lnum++) {
-      line = (char *)ml_get_buf(curbuf, lnum, false);
-      const size_t len = STRLEN(line);
-      if (in_example && len > 0 && !ascii_iswhite(line[0])) {
-        // End of example: non-white or '<' in first column.
-        if (line[0] == '<') {
-          // blank-out a '<' in the first column
-          line = (char *)ml_get_buf(curbuf, lnum, true);
-          line[0] = ' ';
-        }
-        in_example = false;
-      }
-      if (!in_example && len > 0) {
-        if (line[len - 1] == '>' && (len == 1 || line[len - 2] == ' ')) {
-          // blank-out a '>' in the last column (start of example)
-          line = (char *)ml_get_buf(curbuf, lnum, true);
-          line[len - 1] = ' ';
-          in_example = true;
-        } else if (line[len - 1] == '~') {
-          // blank-out a '~' at the end of line (header marker)
-          line = (char *)ml_get_buf(curbuf, lnum, true);
-          line[len - 1] = ' ';
-        }
-      }
-    }
-  }
-
-  /*
-   * In the "help.txt" and "help.abx" file, add the locally added help
-   * files.  This uses the very first line in the help file.
-   */
-  char *const fname = path_tail(curbuf->b_fname);
-  if (FNAMECMP(fname, "help.txt") == 0
-      || (FNAMENCMP(fname, "help.", 5) == 0
-          && ASCII_ISALPHA(fname[5])
-          && ASCII_ISALPHA(fname[6])
-          && TOLOWER_ASC(fname[7]) == 'x'
-          && fname[8] == NUL)) {
-    for (lnum = 1; lnum < curbuf->b_ml.ml_line_count; lnum++) {
-      line = (char *)ml_get_buf(curbuf, lnum, false);
-      if (strstr(line, "*local-additions*") == NULL) {
-        continue;
-      }
-
-      // Go through all directories in 'runtimepath', skipping
-      // $VIMRUNTIME.
-      char *p = (char *)p_rtp;
-      while (*p != NUL) {
-        copy_option_part(&p, (char *)NameBuff, MAXPATHL, ",");
-        char *const rt = vim_getenv("VIMRUNTIME");
-        if (rt != NULL
-            && path_full_compare(rt, (char *)NameBuff, false, true) != kEqualFiles) {
-          int fcount;
-          char **fnames;
-          char *s;
-          vimconv_T vc;
-          char *cp;
-
-          // Find all "doc/ *.txt" files in this directory.
-          if (!add_pathsep((char *)NameBuff)
-              || STRLCAT(NameBuff, "doc/*.??[tx]",
-                         sizeof(NameBuff)) >= MAXPATHL) {
-            emsg(_(e_fnametoolong));
-            continue;
-          }
-
-          // Note: We cannot just do `&NameBuff` because it is a statically sized array
-          //       so `NameBuff == &NameBuff` according to C semantics.
-          char *buff_list[1] = { (char *)NameBuff };
-          if (gen_expand_wildcards(1, buff_list, &fcount,
-                                   &fnames, EW_FILE|EW_SILENT) == OK
-              && fcount > 0) {
-            // If foo.abx is found use it instead of foo.txt in
-            // the same directory.
-            for (int i1 = 0; i1 < fcount; i1++) {
-              for (int i2 = 0; i2 < fcount; i2++) {
-                if (i1 == i2) {
-                  continue;
-                }
-                if (fnames[i1] == NULL || fnames[i2] == NULL) {
-                  continue;
-                }
-                const char *const f1 = fnames[i1];
-                const char *const f2 = fnames[i2];
-                const char *const t1 = path_tail(f1);
-                const char *const t2 = path_tail(f2);
-                const char *const e1 = (char *)STRRCHR(t1, '.');
-                const char *const e2 = (char *)STRRCHR(t2, '.');
-                if (e1 == NULL || e2 == NULL) {
-                  continue;
-                }
-                if (FNAMECMP(e1, ".txt") != 0
-                    && FNAMECMP(e1, fname + 4) != 0) {
-                  // Not .txt and not .abx, remove it.
-                  XFREE_CLEAR(fnames[i1]);
-                  continue;
-                }
-                if (e1 - f1 != e2 - f2
-                    || FNAMENCMP(f1, f2, e1 - f1) != 0) {
-                  continue;
-                }
-                if (FNAMECMP(e1, ".txt") == 0
-                    && FNAMECMP(e2, fname + 4) == 0) {
-                  // use .abx instead of .txt
-                  XFREE_CLEAR(fnames[i1]);
-                }
-              }
-            }
-            for (int fi = 0; fi < fcount; fi++) {
-              if (fnames[fi] == NULL) {
-                continue;
-              }
-
-              FILE *const fd = os_fopen(fnames[fi], "r");
-              if (fd == NULL) {
-                continue;
-              }
-              vim_fgets(IObuff, IOSIZE, fd);
-              if (IObuff[0] == '*'
-                  && (s = vim_strchr((char *)IObuff + 1, '*'))
-                  != NULL) {
-                TriState this_utf = kNone;
-                // Change tag definition to a
-                // reference and remove <CR>/<NL>.
-                IObuff[0] = '|';
-                *s = '|';
-                while (*s != NUL) {
-                  if (*s == '\r' || *s == '\n') {
-                    *s = NUL;
-                  }
-                  // The text is utf-8 when a byte
-                  // above 127 is found and no
-                  // illegal byte sequence is found.
-                  if ((char_u)(*s) >= 0x80 && this_utf != kFalse) {
-                    this_utf = kTrue;
-                    const int l = utf_ptr2len(s);
-                    if (l == 1) {
-                      this_utf = kFalse;
-                    }
-                    s += l - 1;
-                  }
-                  s++;
-                }
-                // The help file is latin1 or utf-8;
-                // conversion to the current
-                // 'encoding' may be required.
-                vc.vc_type = CONV_NONE;
-                convert_setup(&vc,
-                              (char_u *)(this_utf == kTrue ? "utf-8" : "latin1"),
-                              p_enc);
-                if (vc.vc_type == CONV_NONE) {
-                  // No conversion needed.
-                  cp = (char *)IObuff;
-                } else {
-                  // Do the conversion.  If it fails
-                  // use the unconverted text.
-                  cp = (char *)string_convert(&vc, IObuff, NULL);
-                  if (cp == NULL) {
-                    cp = (char *)IObuff;
-                  }
-                }
-                convert_setup(&vc, NULL, NULL);
-
-                ml_append(lnum, cp, (colnr_T)0, false);
-                if ((char_u *)cp != IObuff) {
-                  xfree(cp);
-                }
-                lnum++;
-              }
-              fclose(fd);
-            }
-            FreeWild(fcount, fnames);
-          }
-        }
-        xfree(rt);
-      }
-      break;
-    }
-  }
-}
-
-/// ":exusage"
-void ex_exusage(exarg_T *eap)
-{
-  do_cmdline_cmd("help ex-cmd-index");
-}
-
-/// ":viusage"
-void ex_viusage(exarg_T *eap)
-{
-  do_cmdline_cmd("help normal-index");
-}
-
-/// Generate tags in one help directory
-///
-/// @param dir  Path to the doc directory
-/// @param ext  Suffix of the help files (".txt", ".itx", ".frx", etc.)
-/// @param tagname  Name of the tags file ("tags" for English, "tags-fr" for
-///                 French)
-/// @param add_help_tags  Whether to add the "help-tags" tag
-/// @param ignore_writeerr  ignore write error
-static void helptags_one(char *dir, const char *ext, const char *tagfname, bool add_help_tags,
-                         bool ignore_writeerr)
-  FUNC_ATTR_NONNULL_ALL
-{
-  garray_T ga;
-  int filecount;
-  char **files;
-  char *p1, *p2;
-  char *s;
-  TriState utf8 = kNone;
-  bool mix = false;             // detected mixed encodings
-
-  // Find all *.txt files.
-  size_t dirlen = STRLCPY(NameBuff, dir, sizeof(NameBuff));
-  if (dirlen >= MAXPATHL
-      || STRLCAT(NameBuff, "/**/*", sizeof(NameBuff)) >= MAXPATHL  // NOLINT
-      || STRLCAT(NameBuff, ext, sizeof(NameBuff)) >= MAXPATHL) {
-    emsg(_(e_fnametoolong));
-    return;
-  }
-
-  // Note: We cannot just do `&NameBuff` because it is a statically sized array
-  //       so `NameBuff == &NameBuff` according to C semantics.
-  char *buff_list[1] = { (char *)NameBuff };
-  const int res = gen_expand_wildcards(1, buff_list, &filecount, &files,
-                                       EW_FILE|EW_SILENT);
-  if (res == FAIL || filecount == 0) {
-    if (!got_int) {
-      semsg(_("E151: No match: %s"), NameBuff);
-    }
-    if (res != FAIL) {
-      FreeWild(filecount, files);
-    }
-    return;
-  }
-
-  //
-  // Open the tags file for writing.
-  // Do this before scanning through all the files.
-  //
-  memcpy(NameBuff, dir, dirlen + 1);
-  if (!add_pathsep((char *)NameBuff)
-      || STRLCAT(NameBuff, tagfname, sizeof(NameBuff)) >= MAXPATHL) {
-    emsg(_(e_fnametoolong));
-    return;
-  }
-
-  FILE *const fd_tags = os_fopen((char *)NameBuff, "w");
-  if (fd_tags == NULL) {
-    if (!ignore_writeerr) {
-      semsg(_("E152: Cannot open %s for writing"), NameBuff);
-    }
-    FreeWild(filecount, files);
-    return;
-  }
-
-  // If using the "++t" argument or generating tags for "$VIMRUNTIME/doc"
-  // add the "help-tags" tag.
-  ga_init(&ga, (int)sizeof(char_u *), 100);
-  if (add_help_tags
-      || path_full_compare("$VIMRUNTIME/doc", dir, false, true) == kEqualFiles) {
-    size_t s_len = 18 + STRLEN(tagfname);
-    s = xmalloc(s_len);
-    snprintf(s, s_len, "help-tags\t%s\t1\n", tagfname);
-    GA_APPEND(char *, &ga, s);
-  }
-
-  // Go over all the files and extract the tags.
-  for (int fi = 0; fi < filecount && !got_int; fi++) {
-    FILE *const fd = os_fopen(files[fi], "r");
-    if (fd == NULL) {
-      semsg(_("E153: Unable to open %s for reading"), files[fi]);
-      continue;
-    }
-    const char *const fname = files[fi] + dirlen + 1;
-
-    bool firstline = true;
-    while (!vim_fgets(IObuff, IOSIZE, fd) && !got_int) {
-      if (firstline) {
-        // Detect utf-8 file by a non-ASCII char in the first line.
-        TriState this_utf8 = kNone;
-        for (s = (char *)IObuff; *s != NUL; s++) {
-          if ((char_u)(*s) >= 0x80) {
-            this_utf8 = kTrue;
-            const int l = utf_ptr2len(s);
-            if (l == 1) {
-              // Illegal UTF-8 byte sequence.
-              this_utf8 = kFalse;
-              break;
-            }
-            s += l - 1;
-          }
-        }
-        if (this_utf8 == kNone) {           // only ASCII characters found
-          this_utf8 = kFalse;
-        }
-        if (utf8 == kNone) {                // first file
-          utf8 = this_utf8;
-        } else if (utf8 != this_utf8) {
-          semsg(_("E670: Mix of help file encodings within a language: %s"),
-                files[fi]);
-          mix = !got_int;
-          got_int = TRUE;
-        }
-        firstline = false;
-      }
-      p1 = vim_strchr((char *)IObuff, '*');                        // find first '*'
-      while (p1 != NULL) {
-        p2 = strchr((const char *)p1 + 1, '*');  // Find second '*'.
-        if (p2 != NULL && p2 > p1 + 1) {                   // Skip "*" and "**".
-          for (s = p1 + 1; s < p2; s++) {
-            if (*s == ' ' || *s == '\t' || *s == '|') {
-              break;
-            }
-          }
-
-          // Only accept a *tag* when it consists of valid
-          // characters, there is white space before it and is
-          // followed by a white character or end-of-line.
-          if (s == p2
-              && ((char_u *)p1 == IObuff || p1[-1] == ' ' || p1[-1] == '\t')
-              && (vim_strchr(" \t\n\r", s[1]) != NULL
-                  || s[1] == '\0')) {
-            *p2 = '\0';
-            p1++;
-            size_t s_len= (size_t)(p2 - p1) + STRLEN(fname) + 2;
-            s = xmalloc(s_len);
-            GA_APPEND(char *, &ga, s);
-            snprintf(s, s_len, "%s\t%s", p1, fname);
-
-            // find next '*'
-            p2 = vim_strchr(p2 + 1, '*');
-          }
-        }
-        p1 = p2;
-      }
-      line_breakcheck();
-    }
-
-    fclose(fd);
-  }
-
-  FreeWild(filecount, files);
-
-  if (!got_int && ga.ga_data != NULL) {
-    // Sort the tags.
-    sort_strings(ga.ga_data, ga.ga_len);
-
-    // Check for duplicates.
-    for (int i = 1; i < ga.ga_len; i++) {
-      p1 = ((char **)ga.ga_data)[i - 1];
-      p2 = ((char **)ga.ga_data)[i];
-      while (*p1 == *p2) {
-        if (*p2 == '\t') {
-          *p2 = NUL;
-          vim_snprintf((char *)NameBuff, MAXPATHL,
-                       _("E154: Duplicate tag \"%s\" in file %s/%s"),
-                       ((char_u **)ga.ga_data)[i], dir, p2 + 1);
-          emsg((char *)NameBuff);
-          *p2 = '\t';
-          break;
-        }
-        p1++;
-        p2++;
-      }
-    }
-
-    if (utf8 == kTrue) {
-      fprintf(fd_tags, "!_TAG_FILE_ENCODING\tutf-8\t//\n");
-    }
-
-    // Write the tags into the file.
-    for (int i = 0; i < ga.ga_len; i++) {
-      s = ((char **)ga.ga_data)[i];
-      if (STRNCMP(s, "help-tags\t", 10) == 0) {
-        // help-tags entry was added in formatted form
-        fputs(s, fd_tags);
-      } else {
-        fprintf(fd_tags, "%s\t/" "*", s);
-        for (p1 = s; *p1 != '\t'; p1++) {
-          // insert backslash before '\\' and '/'
-          if (*p1 == '\\' || *p1 == '/') {
-            putc('\\', fd_tags);
-          }
-          putc(*p1, fd_tags);
-        }
-        fprintf(fd_tags, "*\n");
-      }
-    }
-  }
-  if (mix) {
-    got_int = false;        // continue with other languages
-  }
-
-  GA_DEEP_CLEAR_PTR(&ga);
-  fclose(fd_tags);          // there is no check for an error...
-}
-
-/// Generate tags in one help directory, taking care of translations.
-static void do_helptags(char *dirname, bool add_help_tags, bool ignore_writeerr)
-  FUNC_ATTR_NONNULL_ALL
-{
-  int len;
-  garray_T ga;
-  char lang[2];
-  char ext[5];
-  char fname[8];
-  int filecount;
-  char **files;
-
-  // Get a list of all files in the help directory and in subdirectories.
-  STRLCPY(NameBuff, dirname, sizeof(NameBuff));
-  if (!add_pathsep((char *)NameBuff)
-      || STRLCAT(NameBuff, "**", sizeof(NameBuff)) >= MAXPATHL) {
-    emsg(_(e_fnametoolong));
-    return;
-  }
-
-  // Note: We cannot just do `&NameBuff` because it is a statically sized array
-  //       so `NameBuff == &NameBuff` according to C semantics.
-  char *buff_list[1] = { (char *)NameBuff };
-  if (gen_expand_wildcards(1, buff_list, &filecount, &files,
-                           EW_FILE|EW_SILENT) == FAIL
-      || filecount == 0) {
-    semsg(_("E151: No match: %s"), NameBuff);
-    return;
-  }
-
-  // Go over all files in the directory to find out what languages are
-  // present.
-  int j;
-  ga_init(&ga, 1, 10);
-  for (int i = 0; i < filecount; i++) {
-    len = (int)STRLEN(files[i]);
-    if (len <= 4) {
-      continue;
-    }
-
-    if (STRICMP(files[i] + len - 4, ".txt") == 0) {
-      // ".txt" -> language "en"
-      lang[0] = 'e';
-      lang[1] = 'n';
-    } else if (files[i][len - 4] == '.'
-               && ASCII_ISALPHA(files[i][len - 3])
-               && ASCII_ISALPHA(files[i][len - 2])
-               && TOLOWER_ASC(files[i][len - 1]) == 'x') {
-      // ".abx" -> language "ab"
-      lang[0] = (char)TOLOWER_ASC(files[i][len - 3]);
-      lang[1] = (char)TOLOWER_ASC(files[i][len - 2]);
-    } else {
-      continue;
-    }
-
-    // Did we find this language already?
-    for (j = 0; j < ga.ga_len; j += 2) {
-      if (STRNCMP(lang, ((char_u *)ga.ga_data) + j, 2) == 0) {
-        break;
-      }
-    }
-    if (j == ga.ga_len) {
-      // New language, add it.
-      ga_grow(&ga, 2);
-      ((char *)ga.ga_data)[ga.ga_len++] = lang[0];
-      ((char *)ga.ga_data)[ga.ga_len++] = lang[1];
-    }
-  }
-
-  /*
-   * Loop over the found languages to generate a tags file for each one.
-   */
-  for (j = 0; j < ga.ga_len; j += 2) {
-    STRCPY(fname, "tags-xx");
-    fname[5] = ((char *)ga.ga_data)[j];
-    fname[6] = ((char *)ga.ga_data)[j + 1];
-    if (fname[5] == 'e' && fname[6] == 'n') {
-      // English is an exception: use ".txt" and "tags".
-      fname[4] = NUL;
-      STRCPY(ext, ".txt");
-    } else {
-      // Language "ab" uses ".abx" and "tags-ab".
-      STRCPY(ext, ".xxx");
-      ext[1] = fname[5];
-      ext[2] = fname[6];
-    }
-    helptags_one(dirname, (char *)ext, (char *)fname, add_help_tags, ignore_writeerr);
-  }
-
-  ga_clear(&ga);
-  FreeWild(filecount, files);
-}
-
-static void helptags_cb(char *fname, void *cookie)
-  FUNC_ATTR_NONNULL_ALL
-{
-  do_helptags(fname, *(bool *)cookie, true);
-}
-
-/// ":helptags"
-void ex_helptags(exarg_T *eap)
-{
-  expand_T xpc;
-  char *dirname;
-  bool add_help_tags = false;
-
-  // Check for ":helptags ++t {dir}".
-  if (STRNCMP(eap->arg, "++t", 3) == 0 && ascii_iswhite(eap->arg[3])) {
-    add_help_tags = true;
-    eap->arg = skipwhite(eap->arg + 3);
-  }
-
-  if (STRCMP(eap->arg, "ALL") == 0) {
-    do_in_path(p_rtp, "doc", DIP_ALL + DIP_DIR, helptags_cb, &add_help_tags);
-  } else {
-    ExpandInit(&xpc);
-    xpc.xp_context = EXPAND_DIRECTORIES;
-    dirname = (char *)ExpandOne(&xpc, (char_u *)eap->arg, NULL,
-                                WILD_LIST_NOTFOUND|WILD_SILENT, WILD_EXPAND_FREE);
-    if (dirname == NULL || !os_isdir((char_u *)dirname)) {
-      semsg(_("E150: Not a directory: %s"), eap->arg);
-    } else {
-      do_helptags(dirname, add_help_tags, false);
-    }
-    xfree(dirname);
-  }
-}
-
-/// ":helpclose": Close one help window
-void ex_helpclose(exarg_T *eap)
-{
-  FOR_ALL_WINDOWS_IN_TAB(win, curtab) {
-    if (bt_help(win->w_buffer)) {
-      win_close(win, false, eap->forceit);
-      return;
-    }
-  }
-}
-
 /// Shows the effects of the :substitute command being typed ('inccommand').
 /// If inccommand=split, shows a preview window and later restores the layout.
 ///
diff --git a/src/nvim/ex_cmds.h b/src/nvim/ex_cmds.h
index a55e74a789..3aaba9ce42 100644
--- a/src/nvim/ex_cmds.h
+++ b/src/nvim/ex_cmds.h
@@ -20,9 +20,9 @@
 #define ECMD_NOWINENTER      0x40    // do not trigger BufWinEnter
 
 // for lnum argument in do_ecmd()
-#define ECMD_LASTL      (linenr_T)0     // use last position in loaded file
-#define ECMD_LAST       ((linenr_T) - 1)  // use last position in all files
-#define ECMD_ONE        (linenr_T)1     // use first line
+#define ECMD_LASTL      (linenr_T)0       // use last position in loaded file
+#define ECMD_LAST       ((linenr_T)(-1))  // use last position in all files
+#define ECMD_ONE        (linenr_T)1       // use first line
 
 /// Previous :substitute replacement string definition
 typedef struct {
diff --git a/src/nvim/ex_docmd.c b/src/nvim/ex_docmd.c
index e723fd02a9..799acbbb9e 100644
--- a/src/nvim/ex_docmd.c
+++ b/src/nvim/ex_docmd.c
@@ -40,6 +40,7 @@
 #include "nvim/getchar.h"
 #include "nvim/globals.h"
 #include "nvim/hardcopy.h"
+#include "nvim/help.h"
 #include "nvim/highlight_group.h"
 #include "nvim/if_cscope.h"
 #include "nvim/input.h"
diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index bce5ec3ce5..f82f9d3bac 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -39,6 +39,7 @@
 #include "nvim/garray.h"
 #include "nvim/getchar.h"
 #include "nvim/globals.h"
+#include "nvim/help.h"
 #include "nvim/highlight.h"
 #include "nvim/highlight_defs.h"
 #include "nvim/highlight_group.h"
@@ -5025,58 +5026,6 @@ int expand_cmdline(expand_T *xp, char_u *str, int col, int *matchcount, char ***
   return EXPAND_OK;
 }
 
-// Cleanup matches for help tags:
-// Remove "@ab" if the top of 'helplang' is "ab" and the language of the first
-// tag matches it.  Otherwise remove "@en" if "en" is the only language.
-static void cleanup_help_tags(int num_file, char **file)
-{
-  char_u buf[4];
-  char_u *p = buf;
-
-  if (p_hlg[0] != NUL && (p_hlg[0] != 'e' || p_hlg[1] != 'n')) {
-    *p++ = '@';
-    *p++ = p_hlg[0];
-    *p++ = p_hlg[1];
-  }
-  *p = NUL;
-
-  for (int i = 0; i < num_file; i++) {
-    int len = (int)STRLEN(file[i]) - 3;
-    if (len <= 0) {
-      continue;
-    }
-    if (STRCMP(file[i] + len, "@en") == 0) {
-      // Sorting on priority means the same item in another language may
-      // be anywhere.  Search all items for a match up to the "@en".
-      int j;
-      for (j = 0; j < num_file; j++) {
-        if (j != i
-            && (int)STRLEN(file[j]) == len + 3
-            && STRNCMP(file[i], file[j], len + 1) == 0) {
-          break;
-        }
-      }
-      if (j == num_file) {
-        // item only exists with @en, remove it
-        file[i][len] = NUL;
-      }
-    }
-  }
-
-  if (*buf != NUL) {
-    for (int i = 0; i < num_file; i++) {
-      int len = (int)STRLEN(file[i]) - 3;
-      if (len <= 0) {
-        continue;
-      }
-      if (STRCMP(file[i] + len, buf) == 0) {
-        // remove the default language
-        file[i][len] = NUL;
-      }
-    }
-  }
-}
-
 typedef char *(*ExpandFunc)(expand_T *, int);
 
 /// Do the expansion based on xp->xp_context and "pat".
diff --git a/src/nvim/help.c b/src/nvim/help.c
new file mode 100644
index 0000000000..172d389e74
--- /dev/null
+++ b/src/nvim/help.c
@@ -0,0 +1,1178 @@
+// This is an open source non-commercial project. Dear PVS-Studio, please check
+// it. PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
+
+// help.c: functions for Vim help
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "nvim/buffer.h"
+#include "nvim/charset.h"
+#include "nvim/ex_cmds.h"
+#include "nvim/ex_docmd.h"
+#include "nvim/ex_getln.h"
+#include "nvim/fileio.h"
+#include "nvim/garray.h"
+#include "nvim/globals.h"
+#include "nvim/help.h"
+#include "nvim/memory.h"
+#include "nvim/option.h"
+#include "nvim/os/input.h"
+#include "nvim/path.h"
+#include "nvim/strings.h"
+#include "nvim/syntax.h"
+#include "nvim/tag.h"
+#include "nvim/vim.h"
+#include "nvim/window.h"
+
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "help.c.generated.h"
+#endif
+
+/// ":help": open a read-only window on a help file
+void ex_help(exarg_T *eap)
+{
+  char *arg;
+  char *tag;
+  FILE *helpfd;          // file descriptor of help file
+  int n;
+  int i;
+  win_T *wp;
+  int num_matches;
+  char **matches;
+  char *p;
+  int empty_fnum = 0;
+  int alt_fnum = 0;
+  buf_T *buf;
+  int len;
+  char *lang;
+  const bool old_KeyTyped = KeyTyped;
+
+  if (eap != NULL) {
+    // A ":help" command ends at the first LF, or at a '|' that is
+    // followed by some text.  Set nextcmd to the following command.
+    for (arg = eap->arg; *arg; arg++) {
+      if (*arg == '\n' || *arg == '\r'
+          || (*arg == '|' && arg[1] != NUL && arg[1] != '|')) {
+        *arg++ = NUL;
+        eap->nextcmd = arg;
+        break;
+      }
+    }
+    arg = eap->arg;
+
+    if (eap->forceit && *arg == NUL && !curbuf->b_help) {
+      emsg(_("E478: Don't panic!"));
+      return;
+    }
+
+    if (eap->skip) {        // not executing commands
+      return;
+    }
+  } else {
+    arg = "";
+  }
+
+  // remove trailing blanks
+  p = arg + STRLEN(arg) - 1;
+  while (p > arg && ascii_iswhite(*p) && p[-1] != '\\') {
+    *p-- = NUL;
+  }
+
+  // Check for a specified language
+  lang = check_help_lang(arg);
+
+  // When no argument given go to the index.
+  if (*arg == NUL) {
+    arg = "help.txt";
+  }
+
+  // Check if there is a match for the argument.
+  n = find_help_tags(arg, &num_matches, &matches, eap != NULL && eap->forceit);
+
+  i = 0;
+  if (n != FAIL && lang != NULL) {
+    // Find first item with the requested language.
+    for (i = 0; i < num_matches; i++) {
+      len = (int)STRLEN(matches[i]);
+      if (len > 3 && matches[i][len - 3] == '@'
+          && STRICMP(matches[i] + len - 2, lang) == 0) {
+        break;
+      }
+    }
+  }
+  if (i >= num_matches || n == FAIL) {
+    if (lang != NULL) {
+      semsg(_("E661: Sorry, no '%s' help for %s"), lang, arg);
+    } else {
+      semsg(_("E149: Sorry, no help for %s"), arg);
+    }
+    if (n != FAIL) {
+      FreeWild(num_matches, matches);
+    }
+    return;
+  }
+
+  // The first match (in the requested language) is the best match.
+  tag = xstrdup(matches[i]);
+  FreeWild(num_matches, matches);
+
+  // Re-use an existing help window or open a new one.
+  // Always open a new one for ":tab help".
+  if (!bt_help(curwin->w_buffer) || cmdmod.cmod_tab != 0) {
+    if (cmdmod.cmod_tab != 0) {
+      wp = NULL;
+    } else {
+      wp = NULL;
+      FOR_ALL_WINDOWS_IN_TAB(wp2, curtab) {
+        if (bt_help(wp2->w_buffer)) {
+          wp = wp2;
+          break;
+        }
+      }
+    }
+    if (wp != NULL && wp->w_buffer->b_nwindows > 0) {
+      win_enter(wp, true);
+    } else {
+      // There is no help window yet.
+      // Try to open the file specified by the "helpfile" option.
+      if ((helpfd = os_fopen((char *)p_hf, READBIN)) == NULL) {
+        smsg(_("Sorry, help file \"%s\" not found"), p_hf);
+        goto erret;
+      }
+      fclose(helpfd);
+
+      // Split off help window; put it at far top if no position
+      // specified, the current window is vertically split and
+      // narrow.
+      n = WSP_HELP;
+      if (cmdmod.cmod_split == 0 && curwin->w_width != Columns
+          && curwin->w_width < 80) {
+        n |= WSP_TOP;
+      }
+      if (win_split(0, n) == FAIL) {
+        goto erret;
+      }
+
+      if (curwin->w_height < p_hh) {
+        win_setheight((int)p_hh);
+      }
+
+      // Open help file (do_ecmd() will set b_help flag, readfile() will
+      // set b_p_ro flag).
+      // Set the alternate file to the previously edited file.
+      alt_fnum = curbuf->b_fnum;
+      (void)do_ecmd(0, NULL, NULL, NULL, ECMD_LASTL,
+                    ECMD_HIDE + ECMD_SET_HELP,
+                    NULL);  // buffer is still open, don't store info
+
+      if ((cmdmod.cmod_flags & CMOD_KEEPALT) == 0) {
+        curwin->w_alt_fnum = alt_fnum;
+      }
+      empty_fnum = curbuf->b_fnum;
+    }
+  }
+
+  restart_edit = 0;               // don't want insert mode in help file
+
+  // Restore KeyTyped, setting 'filetype=help' may reset it.
+  // It is needed for do_tag top open folds under the cursor.
+  KeyTyped = old_KeyTyped;
+
+  do_tag((char_u *)tag, DT_HELP, 1, false, true);
+
+  // Delete the empty buffer if we're not using it.  Careful: autocommands
+  // may have jumped to another window, check that the buffer is not in a
+  // window.
+  if (empty_fnum != 0 && curbuf->b_fnum != empty_fnum) {
+    buf = buflist_findnr(empty_fnum);
+    if (buf != NULL && buf->b_nwindows == 0) {
+      wipe_buffer(buf, true);
+    }
+  }
+
+  // keep the previous alternate file
+  if (alt_fnum != 0 && curwin->w_alt_fnum == empty_fnum
+      && (cmdmod.cmod_flags & CMOD_KEEPALT) == 0) {
+    curwin->w_alt_fnum = alt_fnum;
+  }
+
+erret:
+  xfree(tag);
+}
+
+/// ":helpclose": Close one help window
+void ex_helpclose(exarg_T *eap)
+{
+  FOR_ALL_WINDOWS_IN_TAB(win, curtab) {
+    if (bt_help(win->w_buffer)) {
+      win_close(win, false, eap->forceit);
+      return;
+    }
+  }
+}
+
+/// In an argument search for a language specifiers in the form "@xx".
+/// Changes the "@" to NUL if found, and returns a pointer to "xx".
+///
+/// @return  NULL if not found.
+char *check_help_lang(char *arg)
+{
+  int len = (int)STRLEN(arg);
+
+  if (len >= 3 && arg[len - 3] == '@' && ASCII_ISALPHA(arg[len - 2])
+      && ASCII_ISALPHA(arg[len - 1])) {
+    arg[len - 3] = NUL;                 // remove the '@'
+    return arg + len - 2;
+  }
+  return NULL;
+}
+
+/// Return a heuristic indicating how well the given string matches.  The
+/// smaller the number, the better the match.  This is the order of priorities,
+/// from best match to worst match:
+///      - Match with least alphanumeric characters is better.
+///      - Match with least total characters is better.
+///      - Match towards the start is better.
+///      - Match starting with "+" is worse (feature instead of command)
+/// Assumption is made that the matched_string passed has already been found to
+/// match some string for which help is requested.  webb.
+///
+/// @param offset      offset for match
+/// @param wrong_case  no matching case
+///
+/// @return  a heuristic indicating how well the given string matches.
+int help_heuristic(char *matched_string, int offset, int wrong_case)
+  FUNC_ATTR_PURE
+{
+  int num_letters;
+  char *p;
+
+  num_letters = 0;
+  for (p = matched_string; *p; p++) {
+    if (ASCII_ISALNUM(*p)) {
+      num_letters++;
+    }
+  }
+
+  // Multiply the number of letters by 100 to give it a much bigger
+  // weighting than the number of characters.
+  // If there only is a match while ignoring case, add 5000.
+  // If the match starts in the middle of a word, add 10000 to put it
+  // somewhere in the last half.
+  // If the match is more than 2 chars from the start, multiply by 200 to
+  // put it after matches at the start.
+  if (offset > 0
+      && ASCII_ISALNUM(matched_string[offset])
+      && ASCII_ISALNUM(matched_string[offset - 1])) {
+    offset += 10000;
+  } else if (offset > 2) {
+    offset *= 200;
+  }
+  if (wrong_case) {
+    offset += 5000;
+  }
+  // Features are less interesting than the subjects themselves, but "+"
+  // alone is not a feature.
+  if (matched_string[0] == '+' && matched_string[1] != NUL) {
+    offset += 100;
+  }
+  return 100 * num_letters + (int)STRLEN(matched_string) + offset;
+}
+
+/// Compare functions for qsort() below, that checks the help heuristics number
+/// that has been put after the tagname by find_tags().
+static int help_compare(const void *s1, const void *s2)
+{
+  char *p1;
+  char *p2;
+
+  p1 = *(char **)s1 + strlen(*(char **)s1) + 1;
+  p2 = *(char **)s2 + strlen(*(char **)s2) + 1;
+
+  // Compare by help heuristic number first.
+  int cmp = strcmp(p1, p2);
+  if (cmp != 0) {
+    return cmp;
+  }
+
+  // Compare by strings as tie-breaker when same heuristic number.
+  return strcmp(*(char **)s1, *(char **)s2);
+}
+
+/// Find all help tags matching "arg", sort them and return in matches[], with
+/// the number of matches in num_matches.
+/// The matches will be sorted with a "best" match algorithm.
+/// When "keep_lang" is true try keeping the language of the current buffer.
+int find_help_tags(const char *arg, int *num_matches, char ***matches, bool keep_lang)
+{
+  int i;
+
+  // Specific tags that either have a specific replacement or won't go
+  // through the generic rules.
+  static char *(except_tbl[][2]) = {
+    { "*",           "star" },
+    { "g*",          "gstar" },
+    { "[*",          "[star" },
+    { "]*",          "]star" },
+    { ":*",          ":star" },
+    { "/*",          "/star" },  // NOLINT
+    { "/\\*",        "/\\\\star" },
+    { "\"*",         "quotestar" },
+    { "**",          "starstar" },
+    { "cpo-*",       "cpo-star" },
+    { "/\\(\\)",     "/\\\\(\\\\)" },
+    { "/\\%(\\)",    "/\\\\%(\\\\)" },
+    { "?",           "?" },
+    { "??",          "??" },
+    { ":?",          ":?" },
+    { "?<CR>",       "?<CR>" },
+    { "g?",          "g?" },
+    { "g?g?",        "g?g?" },
+    { "g??",         "g??" },
+    { "-?",          "-?" },
+    { "q?",          "q?" },
+    { "v_g?",        "v_g?" },
+    { "/\\?",        "/\\\\?" },
+    { "/\\z(\\)",    "/\\\\z(\\\\)" },
+    { "\\=",         "\\\\=" },
+    { ":s\\=",       ":s\\\\=" },
+    { "[count]",     "\\[count]" },
+    { "[quotex]",    "\\[quotex]" },
+    { "[range]",     "\\[range]" },
+    { ":[range]",    ":\\[range]" },
+    { "[pattern]",   "\\[pattern]" },
+    { "\\|",         "\\\\bar" },
+    { "\\%$",        "/\\\\%\\$" },
+    { "s/\\~",       "s/\\\\\\~" },
+    { "s/\\U",       "s/\\\\U" },
+    { "s/\\L",       "s/\\\\L" },
+    { "s/\\1",       "s/\\\\1" },
+    { "s/\\2",       "s/\\\\2" },
+    { "s/\\3",       "s/\\\\3" },
+    { "s/\\9",       "s/\\\\9" },
+    { NULL, NULL }
+  };
+
+  static const char *(expr_table[]) = {
+    "!=?", "!~?", "<=?", "<?", "==?", "=~?",
+    ">=?", ">?", "is?", "isnot?"
+  };
+  char *d = (char *)IObuff;       // assume IObuff is long enough!
+  d[0] = NUL;
+
+  if (STRNICMP(arg, "expr-", 5) == 0) {
+    // When the string starting with "expr-" and containing '?' and matches
+    // the table, it is taken literally (but ~ is escaped).  Otherwise '?'
+    // is recognized as a wildcard.
+    for (i = (int)ARRAY_SIZE(expr_table); --i >= 0;) {
+      if (STRCMP(arg + 5, expr_table[i]) == 0) {
+        for (int si = 0, di = 0;; si++) {
+          if (arg[si] == '~') {
+            d[di++] = '\\';
+          }
+          d[di++] = arg[si];
+          if (arg[si] == NUL) {
+            break;
+          }
+        }
+        break;
+      }
+    }
+  } else {
+    // Recognize a few exceptions to the rule.  Some strings that contain
+    // '*'are changed to "star", otherwise '*' is recognized as a wildcard.
+    for (i = 0; except_tbl[i][0] != NULL; i++) {
+      if (STRCMP(arg, except_tbl[i][0]) == 0) {
+        STRCPY(d, except_tbl[i][1]);
+        break;
+      }
+    }
+  }
+
+  if (d[0] == NUL) {  // no match in table
+    // Replace "\S" with "/\\S", etc.  Otherwise every tag is matched.
+    // Also replace "\%^" and "\%(", they match every tag too.
+    // Also "\zs", "\z1", etc.
+    // Also "\@<", "\@=", "\@<=", etc.
+    // And also "\_$" and "\_^".
+    if (arg[0] == '\\'
+        && ((arg[1] != NUL && arg[2] == NUL)
+            || (vim_strchr("%_z@", arg[1]) != NULL
+                && arg[2] != NUL))) {
+      vim_snprintf(d, IOSIZE, "/\\\\%s", arg + 1);
+      // Check for "/\\_$", should be "/\\_\$"
+      if (d[3] == '_' && d[4] == '$') {
+        STRCPY(d + 4, "\\$");
+      }
+    } else {
+      // Replace:
+      // "[:...:]" with "\[:...:]"
+      // "[++...]" with "\[++...]"
+      // "\{" with "\\{"               -- matching "} \}"
+      if ((arg[0] == '[' && (arg[1] == ':'
+                             || (arg[1] == '+' && arg[2] == '+')))
+          || (arg[0] == '\\' && arg[1] == '{')) {
+        *d++ = '\\';
+      }
+
+      // If tag starts with "('", skip the "(". Fixes CTRL-] on ('option'.
+      if (*arg == '(' && arg[1] == '\'') {
+        arg++;
+      }
+      for (const char *s = arg; *s; s++) {
+        // Replace "|" with "bar" and '"' with "quote" to match the name of
+        // the tags for these commands.
+        // Replace "*" with ".*" and "?" with "." to match command line
+        // completion.
+        // Insert a backslash before '~', '$' and '.' to avoid their
+        // special meaning.
+        if ((char_u *)d - IObuff > IOSIZE - 10) {           // getting too long!?
+          break;
+        }
+        switch (*s) {
+        case '|':
+          STRCPY(d, "bar");
+          d += 3;
+          continue;
+        case '"':
+          STRCPY(d, "quote");
+          d += 5;
+          continue;
+        case '*':
+          *d++ = '.';
+          break;
+        case '?':
+          *d++ = '.';
+          continue;
+        case '$':
+        case '.':
+        case '~':
+          *d++ = '\\';
+          break;
+        }
+
+        // Replace "^x" by "CTRL-X". Don't do this for "^_" to make
+        // ":help i_^_CTRL-D" work.
+        // Insert '-' before and after "CTRL-X" when applicable.
+        if (*s < ' '
+            || (*s == '^' && s[1]
+                && (ASCII_ISALPHA(s[1]) || vim_strchr("?@[\\]^", s[1]) != NULL))) {
+          if ((char_u *)d > IObuff && d[-1] != '_' && d[-1] != '\\') {
+            *d++ = '_';                 // prepend a '_' to make x_CTRL-x
+          }
+          STRCPY(d, "CTRL-");
+          d += 5;
+          if (*s < ' ') {
+            *d++ = (char)(*s + '@');
+            if (d[-1] == '\\') {
+              *d++ = '\\';              // double a backslash
+            }
+          } else {
+            *d++ = *++s;
+          }
+          if (s[1] != NUL && s[1] != '_') {
+            *d++ = '_';                 // append a '_'
+          }
+          continue;
+        } else if (*s == '^') {         // "^" or "CTRL-^" or "^_"
+          *d++ = '\\';
+        } else if (s[0] == '\\' && s[1] != '\\' && *arg == '/' && s == arg + 1) {
+          // Insert a backslash before a backslash after a slash, for search
+          // pattern tags: "/\|" --> "/\\|".
+          *d++ = '\\';
+        }
+
+        // "CTRL-\_" -> "CTRL-\\_" to avoid the special meaning of "\_" in
+        // "CTRL-\_CTRL-N"
+        if (STRNICMP(s, "CTRL-\\_", 7) == 0) {
+          STRCPY(d, "CTRL-\\\\");
+          d += 7;
+          s += 6;
+        }
+
+        *d++ = *s;
+
+        // If tag contains "({" or "([", tag terminates at the "(".
+        // This is for help on functions, e.g.: abs({expr}).
+        if (*s == '(' && (s[1] == '{' || s[1] == '[')) {
+          break;
+        }
+
+        // If tag starts with ', toss everything after a second '. Fixes
+        // CTRL-] on 'option'. (would include the trailing '.').
+        if (*s == '\'' && s > arg && *arg == '\'') {
+          break;
+        }
+        // Also '{' and '}'. Fixes CTRL-] on '{address}'.
+        if (*s == '}' && s > arg && *arg == '{') {
+          break;
+        }
+      }
+      *d = NUL;
+
+      if (*IObuff == '`') {
+        if ((char_u *)d > IObuff + 2 && d[-1] == '`') {
+          // remove the backticks from `command`
+          memmove(IObuff, IObuff + 1, STRLEN(IObuff));
+          d[-2] = NUL;
+        } else if ((char_u *)d > IObuff + 3 && d[-2] == '`' && d[-1] == ',') {
+          // remove the backticks and comma from `command`,
+          memmove(IObuff, IObuff + 1, STRLEN(IObuff));
+          d[-3] = NUL;
+        } else if ((char_u *)d > IObuff + 4 && d[-3] == '`'
+                   && d[-2] == '\\' && d[-1] == '.') {
+          // remove the backticks and dot from `command`\.
+          memmove(IObuff, IObuff + 1, STRLEN(IObuff));
+          d[-4] = NUL;
+        }
+      }
+    }
+  }
+
+  *matches = NULL;
+  *num_matches = 0;
+  int flags = TAG_HELP | TAG_REGEXP | TAG_NAMES | TAG_VERBOSE | TAG_NO_TAGFUNC;
+  if (keep_lang) {
+    flags |= TAG_KEEP_LANG;
+  }
+  if (find_tags(IObuff, num_matches, matches, flags, MAXCOL, NULL) == OK
+      && *num_matches > 0) {
+    // Sort the matches found on the heuristic number that is after the
+    // tag name.
+    qsort((void *)(*matches), (size_t)(*num_matches),
+          sizeof(char_u *), help_compare);
+    // Delete more than TAG_MANY to reduce the size of the listing.
+    while (*num_matches > TAG_MANY) {
+      xfree((*matches)[--*num_matches]);
+    }
+  }
+  return OK;
+}
+
+/// Cleanup matches for help tags:
+/// Remove "@ab" if the top of 'helplang' is "ab" and the language of the first
+/// tag matches it.  Otherwise remove "@en" if "en" is the only language.
+void cleanup_help_tags(int num_file, char **file)
+{
+  char_u buf[4];
+  char_u *p = buf;
+
+  if (p_hlg[0] != NUL && (p_hlg[0] != 'e' || p_hlg[1] != 'n')) {
+    *p++ = '@';
+    *p++ = p_hlg[0];
+    *p++ = p_hlg[1];
+  }
+  *p = NUL;
+
+  for (int i = 0; i < num_file; i++) {
+    int len = (int)STRLEN(file[i]) - 3;
+    if (len <= 0) {
+      continue;
+    }
+    if (STRCMP(file[i] + len, "@en") == 0) {
+      // Sorting on priority means the same item in another language may
+      // be anywhere.  Search all items for a match up to the "@en".
+      int j;
+      for (j = 0; j < num_file; j++) {
+        if (j != i
+            && (int)STRLEN(file[j]) == len + 3
+            && STRNCMP(file[i], file[j], len + 1) == 0) {
+          break;
+        }
+      }
+      if (j == num_file) {
+        // item only exists with @en, remove it
+        file[i][len] = NUL;
+      }
+    }
+  }
+
+  if (*buf != NUL) {
+    for (int i = 0; i < num_file; i++) {
+      int len = (int)STRLEN(file[i]) - 3;
+      if (len <= 0) {
+        continue;
+      }
+      if (STRCMP(file[i] + len, buf) == 0) {
+        // remove the default language
+        file[i][len] = NUL;
+      }
+    }
+  }
+}
+
+/// Called when starting to edit a buffer for a help file.
+void prepare_help_buffer(void)
+{
+  curbuf->b_help = true;
+  set_string_option_direct("buftype", -1, "help", OPT_FREE|OPT_LOCAL, 0);
+
+  // Always set these options after jumping to a help tag, because the
+  // user may have an autocommand that gets in the way.
+  // Accept all ASCII chars for keywords, except ' ', '*', '"', '|', and
+  // latin1 word characters (for translated help files).
+  // Only set it when needed, buf_init_chartab() is some work.
+  char *p = "!-~,^*,^|,^\",192-255";
+  if (STRCMP(curbuf->b_p_isk, p) != 0) {
+    set_string_option_direct("isk", -1, p, OPT_FREE|OPT_LOCAL, 0);
+    check_buf_options(curbuf);
+    (void)buf_init_chartab(curbuf, false);
+  }
+
+  // Don't use the global foldmethod.
+  set_string_option_direct("fdm", -1, "manual", OPT_FREE|OPT_LOCAL, 0);
+
+  curbuf->b_p_ts = 8;         // 'tabstop' is 8.
+  curwin->w_p_list = false;   // No list mode.
+
+  curbuf->b_p_ma = false;     // Not modifiable.
+  curbuf->b_p_bin = false;    // Reset 'bin' before reading file.
+  curwin->w_p_nu = 0;         // No line numbers.
+  curwin->w_p_rnu = 0;        // No relative line numbers.
+  RESET_BINDING(curwin);      // No scroll or cursor binding.
+  curwin->w_p_arab = false;   // No arabic mode.
+  curwin->w_p_rl = false;     // Help window is left-to-right.
+  curwin->w_p_fen = false;    // No folding in the help window.
+  curwin->w_p_diff = false;   // No 'diff'.
+  curwin->w_p_spell = false;  // No spell checking.
+
+  set_buflisted(false);
+}
+
+/// After reading a help file: May cleanup a help buffer when syntax
+/// highlighting is not used.
+void fix_help_buffer(void)
+{
+  linenr_T lnum;
+  char *line;
+  bool in_example = false;
+
+  // Set filetype to "help".
+  if (STRCMP(curbuf->b_p_ft, "help") != 0) {
+    curbuf->b_ro_locked++;
+    set_option_value("ft", 0L, "help", OPT_LOCAL);
+    curbuf->b_ro_locked--;
+  }
+
+  if (!syntax_present(curwin)) {
+    for (lnum = 1; lnum <= curbuf->b_ml.ml_line_count; lnum++) {
+      line = (char *)ml_get_buf(curbuf, lnum, false);
+      const size_t len = STRLEN(line);
+      if (in_example && len > 0 && !ascii_iswhite(line[0])) {
+        // End of example: non-white or '<' in first column.
+        if (line[0] == '<') {
+          // blank-out a '<' in the first column
+          line = (char *)ml_get_buf(curbuf, lnum, true);
+          line[0] = ' ';
+        }
+        in_example = false;
+      }
+      if (!in_example && len > 0) {
+        if (line[len - 1] == '>' && (len == 1 || line[len - 2] == ' ')) {
+          // blank-out a '>' in the last column (start of example)
+          line = (char *)ml_get_buf(curbuf, lnum, true);
+          line[len - 1] = ' ';
+          in_example = true;
+        } else if (line[len - 1] == '~') {
+          // blank-out a '~' at the end of line (header marker)
+          line = (char *)ml_get_buf(curbuf, lnum, true);
+          line[len - 1] = ' ';
+        }
+      }
+    }
+  }
+
+  // In the "help.txt" and "help.abx" file, add the locally added help
+  // files.  This uses the very first line in the help file.
+  char *const fname = path_tail(curbuf->b_fname);
+  if (FNAMECMP(fname, "help.txt") == 0
+      || (FNAMENCMP(fname, "help.", 5) == 0
+          && ASCII_ISALPHA(fname[5])
+          && ASCII_ISALPHA(fname[6])
+          && TOLOWER_ASC(fname[7]) == 'x'
+          && fname[8] == NUL)) {
+    for (lnum = 1; lnum < curbuf->b_ml.ml_line_count; lnum++) {
+      line = (char *)ml_get_buf(curbuf, lnum, false);
+      if (strstr(line, "*local-additions*") == NULL) {
+        continue;
+      }
+
+      // Go through all directories in 'runtimepath', skipping
+      // $VIMRUNTIME.
+      char *p = (char *)p_rtp;
+      while (*p != NUL) {
+        copy_option_part(&p, (char *)NameBuff, MAXPATHL, ",");
+        char *const rt = vim_getenv("VIMRUNTIME");
+        if (rt != NULL
+            && path_full_compare(rt, (char *)NameBuff, false, true) != kEqualFiles) {
+          int fcount;
+          char **fnames;
+          char *s;
+          vimconv_T vc;
+          char *cp;
+
+          // Find all "doc/ *.txt" files in this directory.
+          if (!add_pathsep((char *)NameBuff)
+              || STRLCAT(NameBuff, "doc/*.??[tx]",  // NOLINT
+                         sizeof(NameBuff)) >= MAXPATHL) {
+            emsg(_(e_fnametoolong));
+            continue;
+          }
+
+          // Note: We cannot just do `&NameBuff` because it is a statically sized array
+          //       so `NameBuff == &NameBuff` according to C semantics.
+          char *buff_list[1] = { (char *)NameBuff };
+          if (gen_expand_wildcards(1, buff_list, &fcount,
+                                   &fnames, EW_FILE|EW_SILENT) == OK
+              && fcount > 0) {
+            // If foo.abx is found use it instead of foo.txt in
+            // the same directory.
+            for (int i1 = 0; i1 < fcount; i1++) {
+              for (int i2 = 0; i2 < fcount; i2++) {
+                if (i1 == i2) {
+                  continue;
+                }
+                if (fnames[i1] == NULL || fnames[i2] == NULL) {
+                  continue;
+                }
+                const char *const f1 = fnames[i1];
+                const char *const f2 = fnames[i2];
+                const char *const t1 = path_tail(f1);
+                const char *const t2 = path_tail(f2);
+                const char *const e1 = (char *)STRRCHR(t1, '.');
+                const char *const e2 = (char *)STRRCHR(t2, '.');
+                if (e1 == NULL || e2 == NULL) {
+                  continue;
+                }
+                if (FNAMECMP(e1, ".txt") != 0
+                    && FNAMECMP(e1, fname + 4) != 0) {
+                  // Not .txt and not .abx, remove it.
+                  XFREE_CLEAR(fnames[i1]);
+                  continue;
+                }
+                if (e1 - f1 != e2 - f2
+                    || FNAMENCMP(f1, f2, e1 - f1) != 0) {
+                  continue;
+                }
+                if (FNAMECMP(e1, ".txt") == 0
+                    && FNAMECMP(e2, fname + 4) == 0) {
+                  // use .abx instead of .txt
+                  XFREE_CLEAR(fnames[i1]);
+                }
+              }
+            }
+            for (int fi = 0; fi < fcount; fi++) {
+              if (fnames[fi] == NULL) {
+                continue;
+              }
+
+              FILE *const fd = os_fopen(fnames[fi], "r");
+              if (fd == NULL) {
+                continue;
+              }
+              vim_fgets(IObuff, IOSIZE, fd);
+              if (IObuff[0] == '*'
+                  && (s = vim_strchr((char *)IObuff + 1, '*'))
+                  != NULL) {
+                TriState this_utf = kNone;
+                // Change tag definition to a
+                // reference and remove <CR>/<NL>.
+                IObuff[0] = '|';
+                *s = '|';
+                while (*s != NUL) {
+                  if (*s == '\r' || *s == '\n') {
+                    *s = NUL;
+                  }
+                  // The text is utf-8 when a byte
+                  // above 127 is found and no
+                  // illegal byte sequence is found.
+                  if ((char_u)(*s) >= 0x80 && this_utf != kFalse) {
+                    this_utf = kTrue;
+                    const int l = utf_ptr2len(s);
+                    if (l == 1) {
+                      this_utf = kFalse;
+                    }
+                    s += l - 1;
+                  }
+                  s++;
+                }
+                // The help file is latin1 or utf-8;
+                // conversion to the current
+                // 'encoding' may be required.
+                vc.vc_type = CONV_NONE;
+                convert_setup(&vc,
+                              (char_u *)(this_utf == kTrue ? "utf-8" : "latin1"),
+                              p_enc);
+                if (vc.vc_type == CONV_NONE) {
+                  // No conversion needed.
+                  cp = (char *)IObuff;
+                } else {
+                  // Do the conversion.  If it fails
+                  // use the unconverted text.
+                  cp = (char *)string_convert(&vc, IObuff, NULL);
+                  if (cp == NULL) {
+                    cp = (char *)IObuff;
+                  }
+                }
+                convert_setup(&vc, NULL, NULL);
+
+                ml_append(lnum, cp, (colnr_T)0, false);
+                if ((char_u *)cp != IObuff) {
+                  xfree(cp);
+                }
+                lnum++;
+              }
+              fclose(fd);
+            }
+            FreeWild(fcount, fnames);
+          }
+        }
+        xfree(rt);
+      }
+      break;
+    }
+  }
+}
+
+/// ":exusage"
+void ex_exusage(exarg_T *eap)
+{
+  do_cmdline_cmd("help ex-cmd-index");
+}
+
+/// ":viusage"
+void ex_viusage(exarg_T *eap)
+{
+  do_cmdline_cmd("help normal-index");
+}
+
+/// Generate tags in one help directory
+///
+/// @param dir  Path to the doc directory
+/// @param ext  Suffix of the help files (".txt", ".itx", ".frx", etc.)
+/// @param tagname  Name of the tags file ("tags" for English, "tags-fr" for
+///                 French)
+/// @param add_help_tags  Whether to add the "help-tags" tag
+/// @param ignore_writeerr  ignore write error
+static void helptags_one(char *dir, const char *ext, const char *tagfname, bool add_help_tags,
+                         bool ignore_writeerr)
+  FUNC_ATTR_NONNULL_ALL
+{
+  garray_T ga;
+  int filecount;
+  char **files;
+  char *p1, *p2;
+  char *s;
+  TriState utf8 = kNone;
+  bool mix = false;             // detected mixed encodings
+
+  // Find all *.txt files.
+  size_t dirlen = STRLCPY(NameBuff, dir, sizeof(NameBuff));
+  if (dirlen >= MAXPATHL
+      || STRLCAT(NameBuff, "/**/*", sizeof(NameBuff)) >= MAXPATHL  // NOLINT
+      || STRLCAT(NameBuff, ext, sizeof(NameBuff)) >= MAXPATHL) {
+    emsg(_(e_fnametoolong));
+    return;
+  }
+
+  // Note: We cannot just do `&NameBuff` because it is a statically sized array
+  //       so `NameBuff == &NameBuff` according to C semantics.
+  char *buff_list[1] = { (char *)NameBuff };
+  const int res = gen_expand_wildcards(1, buff_list, &filecount, &files,
+                                       EW_FILE|EW_SILENT);
+  if (res == FAIL || filecount == 0) {
+    if (!got_int) {
+      semsg(_("E151: No match: %s"), NameBuff);
+    }
+    if (res != FAIL) {
+      FreeWild(filecount, files);
+    }
+    return;
+  }
+
+  // Open the tags file for writing.
+  // Do this before scanning through all the files.
+  memcpy(NameBuff, dir, dirlen + 1);
+  if (!add_pathsep((char *)NameBuff)
+      || STRLCAT(NameBuff, tagfname, sizeof(NameBuff)) >= MAXPATHL) {
+    emsg(_(e_fnametoolong));
+    return;
+  }
+
+  FILE *const fd_tags = os_fopen((char *)NameBuff, "w");
+  if (fd_tags == NULL) {
+    if (!ignore_writeerr) {
+      semsg(_("E152: Cannot open %s for writing"), NameBuff);
+    }
+    FreeWild(filecount, files);
+    return;
+  }
+
+  // If using the "++t" argument or generating tags for "$VIMRUNTIME/doc"
+  // add the "help-tags" tag.
+  ga_init(&ga, (int)sizeof(char_u *), 100);
+  if (add_help_tags
+      || path_full_compare("$VIMRUNTIME/doc", dir, false, true) == kEqualFiles) {
+    size_t s_len = 18 + STRLEN(tagfname);
+    s = xmalloc(s_len);
+    snprintf(s, s_len, "help-tags\t%s\t1\n", tagfname);
+    GA_APPEND(char *, &ga, s);
+  }
+
+  // Go over all the files and extract the tags.
+  for (int fi = 0; fi < filecount && !got_int; fi++) {
+    FILE *const fd = os_fopen(files[fi], "r");
+    if (fd == NULL) {
+      semsg(_("E153: Unable to open %s for reading"), files[fi]);
+      continue;
+    }
+    const char *const fname = files[fi] + dirlen + 1;
+
+    bool firstline = true;
+    while (!vim_fgets(IObuff, IOSIZE, fd) && !got_int) {
+      if (firstline) {
+        // Detect utf-8 file by a non-ASCII char in the first line.
+        TriState this_utf8 = kNone;
+        for (s = (char *)IObuff; *s != NUL; s++) {
+          if ((char_u)(*s) >= 0x80) {
+            this_utf8 = kTrue;
+            const int l = utf_ptr2len(s);
+            if (l == 1) {
+              // Illegal UTF-8 byte sequence.
+              this_utf8 = kFalse;
+              break;
+            }
+            s += l - 1;
+          }
+        }
+        if (this_utf8 == kNone) {           // only ASCII characters found
+          this_utf8 = kFalse;
+        }
+        if (utf8 == kNone) {                // first file
+          utf8 = this_utf8;
+        } else if (utf8 != this_utf8) {
+          semsg(_("E670: Mix of help file encodings within a language: %s"),
+                files[fi]);
+          mix = !got_int;
+          got_int = true;
+        }
+        firstline = false;
+      }
+      p1 = vim_strchr((char *)IObuff, '*');       // find first '*'
+      while (p1 != NULL) {
+        p2 = strchr((const char *)p1 + 1, '*');  // Find second '*'.
+        if (p2 != NULL && p2 > p1 + 1) {         // Skip "*" and "**".
+          for (s = p1 + 1; s < p2; s++) {
+            if (*s == ' ' || *s == '\t' || *s == '|') {
+              break;
+            }
+          }
+
+          // Only accept a *tag* when it consists of valid
+          // characters, there is white space before it and is
+          // followed by a white character or end-of-line.
+          if (s == p2
+              && ((char_u *)p1 == IObuff || p1[-1] == ' ' || p1[-1] == '\t')
+              && (vim_strchr(" \t\n\r", s[1]) != NULL
+                  || s[1] == '\0')) {
+            *p2 = '\0';
+            p1++;
+            size_t s_len= (size_t)(p2 - p1) + STRLEN(fname) + 2;
+            s = xmalloc(s_len);
+            GA_APPEND(char *, &ga, s);
+            snprintf(s, s_len, "%s\t%s", p1, fname);
+
+            // find next '*'
+            p2 = vim_strchr(p2 + 1, '*');
+          }
+        }
+        p1 = p2;
+      }
+      line_breakcheck();
+    }
+
+    fclose(fd);
+  }
+
+  FreeWild(filecount, files);
+
+  if (!got_int && ga.ga_data != NULL) {
+    // Sort the tags.
+    sort_strings(ga.ga_data, ga.ga_len);
+
+    // Check for duplicates.
+    for (int i = 1; i < ga.ga_len; i++) {
+      p1 = ((char **)ga.ga_data)[i - 1];
+      p2 = ((char **)ga.ga_data)[i];
+      while (*p1 == *p2) {
+        if (*p2 == '\t') {
+          *p2 = NUL;
+          vim_snprintf((char *)NameBuff, MAXPATHL,
+                       _("E154: Duplicate tag \"%s\" in file %s/%s"),
+                       ((char_u **)ga.ga_data)[i], dir, p2 + 1);
+          emsg((char *)NameBuff);
+          *p2 = '\t';
+          break;
+        }
+        p1++;
+        p2++;
+      }
+    }
+
+    if (utf8 == kTrue) {
+      fprintf(fd_tags, "!_TAG_FILE_ENCODING\tutf-8\t//\n");
+    }
+
+    // Write the tags into the file.
+    for (int i = 0; i < ga.ga_len; i++) {
+      s = ((char **)ga.ga_data)[i];
+      if (STRNCMP(s, "help-tags\t", 10) == 0) {
+        // help-tags entry was added in formatted form
+        fputs(s, fd_tags);
+      } else {
+        fprintf(fd_tags, "%s\t/" "*", s);
+        for (p1 = s; *p1 != '\t'; p1++) {
+          // insert backslash before '\\' and '/'
+          if (*p1 == '\\' || *p1 == '/') {
+            putc('\\', fd_tags);
+          }
+          putc(*p1, fd_tags);
+        }
+        fprintf(fd_tags, "*\n");
+      }
+    }
+  }
+  if (mix) {
+    got_int = false;        // continue with other languages
+  }
+
+  GA_DEEP_CLEAR_PTR(&ga);
+  fclose(fd_tags);          // there is no check for an error...
+}
+
+/// Generate tags in one help directory, taking care of translations.
+static void do_helptags(char *dirname, bool add_help_tags, bool ignore_writeerr)
+  FUNC_ATTR_NONNULL_ALL
+{
+  int len;
+  garray_T ga;
+  char lang[2];
+  char ext[5];
+  char fname[8];
+  int filecount;
+  char **files;
+
+  // Get a list of all files in the help directory and in subdirectories.
+  STRLCPY(NameBuff, dirname, sizeof(NameBuff));
+  if (!add_pathsep((char *)NameBuff)
+      || STRLCAT(NameBuff, "**", sizeof(NameBuff)) >= MAXPATHL) {
+    emsg(_(e_fnametoolong));
+    return;
+  }
+
+  // Note: We cannot just do `&NameBuff` because it is a statically sized array
+  //       so `NameBuff == &NameBuff` according to C semantics.
+  char *buff_list[1] = { (char *)NameBuff };
+  if (gen_expand_wildcards(1, buff_list, &filecount, &files,
+                           EW_FILE|EW_SILENT) == FAIL
+      || filecount == 0) {
+    semsg(_("E151: No match: %s"), NameBuff);
+    return;
+  }
+
+  // Go over all files in the directory to find out what languages are
+  // present.
+  int j;
+  ga_init(&ga, 1, 10);
+  for (int i = 0; i < filecount; i++) {
+    len = (int)STRLEN(files[i]);
+    if (len <= 4) {
+      continue;
+    }
+
+    if (STRICMP(files[i] + len - 4, ".txt") == 0) {
+      // ".txt" -> language "en"
+      lang[0] = 'e';
+      lang[1] = 'n';
+    } else if (files[i][len - 4] == '.'
+               && ASCII_ISALPHA(files[i][len - 3])
+               && ASCII_ISALPHA(files[i][len - 2])
+               && TOLOWER_ASC(files[i][len - 1]) == 'x') {
+      // ".abx" -> language "ab"
+      lang[0] = (char)TOLOWER_ASC(files[i][len - 3]);
+      lang[1] = (char)TOLOWER_ASC(files[i][len - 2]);
+    } else {
+      continue;
+    }
+
+    // Did we find this language already?
+    for (j = 0; j < ga.ga_len; j += 2) {
+      if (STRNCMP(lang, ((char_u *)ga.ga_data) + j, 2) == 0) {
+        break;
+      }
+    }
+    if (j == ga.ga_len) {
+      // New language, add it.
+      ga_grow(&ga, 2);
+      ((char *)ga.ga_data)[ga.ga_len++] = lang[0];
+      ((char *)ga.ga_data)[ga.ga_len++] = lang[1];
+    }
+  }
+
+  // Loop over the found languages to generate a tags file for each one.
+  for (j = 0; j < ga.ga_len; j += 2) {
+    STRCPY(fname, "tags-xx");
+    fname[5] = ((char *)ga.ga_data)[j];
+    fname[6] = ((char *)ga.ga_data)[j + 1];
+    if (fname[5] == 'e' && fname[6] == 'n') {
+      // English is an exception: use ".txt" and "tags".
+      fname[4] = NUL;
+      STRCPY(ext, ".txt");
+    } else {
+      // Language "ab" uses ".abx" and "tags-ab".
+      STRCPY(ext, ".xxx");
+      ext[1] = fname[5];
+      ext[2] = fname[6];
+    }
+    helptags_one(dirname, (char *)ext, (char *)fname, add_help_tags, ignore_writeerr);
+  }
+
+  ga_clear(&ga);
+  FreeWild(filecount, files);
+}
+
+static void helptags_cb(char *fname, void *cookie)
+  FUNC_ATTR_NONNULL_ALL
+{
+  do_helptags(fname, *(bool *)cookie, true);
+}
+
+/// ":helptags"
+void ex_helptags(exarg_T *eap)
+{
+  expand_T xpc;
+  char *dirname;
+  bool add_help_tags = false;
+
+  // Check for ":helptags ++t {dir}".
+  if (STRNCMP(eap->arg, "++t", 3) == 0 && ascii_iswhite(eap->arg[3])) {
+    add_help_tags = true;
+    eap->arg = skipwhite(eap->arg + 3);
+  }
+
+  if (STRCMP(eap->arg, "ALL") == 0) {
+    do_in_path(p_rtp, "doc", DIP_ALL + DIP_DIR, helptags_cb, &add_help_tags);
+  } else {
+    ExpandInit(&xpc);
+    xpc.xp_context = EXPAND_DIRECTORIES;
+    dirname = (char *)ExpandOne(&xpc, (char_u *)eap->arg, NULL,
+                                WILD_LIST_NOTFOUND|WILD_SILENT, WILD_EXPAND_FREE);
+    if (dirname == NULL || !os_isdir((char_u *)dirname)) {
+      semsg(_("E150: Not a directory: %s"), eap->arg);
+    } else {
+      do_helptags(dirname, add_help_tags, false);
+    }
+    xfree(dirname);
+  }
+}
diff --git a/src/nvim/help.h b/src/nvim/help.h
new file mode 100644
index 0000000000..21e11392ee
--- /dev/null
+++ b/src/nvim/help.h
@@ -0,0 +1,11 @@
+#ifndef NVIM_HELP_H
+#define NVIM_HELP_H
+
+#include <stdbool.h>
+
+#include "nvim/ex_cmds_defs.h"
+
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "help.h.generated.h"
+#endif
+#endif  // NVIM_HELP_H
diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index a623c14a8e..75ce1f83ff 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -35,6 +35,7 @@
 #include "nvim/getchar.h"
 #include "nvim/globals.h"
 #include "nvim/grid_defs.h"
+#include "nvim/help.h"
 #include "nvim/indent.h"
 #include "nvim/keycodes.h"
 #include "nvim/log.h"
diff --git a/src/nvim/quickfix.c b/src/nvim/quickfix.c
index d01ee42cbf..94159181d1 100644
--- a/src/nvim/quickfix.c
+++ b/src/nvim/quickfix.c
@@ -23,6 +23,7 @@
 #include "nvim/ex_getln.h"
 #include "nvim/fileio.h"
 #include "nvim/fold.h"
+#include "nvim/help.h"
 #include "nvim/highlight_group.h"
 #include "nvim/mark.h"
 #include "nvim/mbyte.h"
diff --git a/src/nvim/tag.c b/src/nvim/tag.c
index a4b320173c..657ba22926 100644
--- a/src/nvim/tag.c
+++ b/src/nvim/tag.c
@@ -23,6 +23,7 @@
 #include "nvim/fileio.h"
 #include "nvim/fold.h"
 #include "nvim/garray.h"
+#include "nvim/help.h"
 #include "nvim/if_cscope.h"
 #include "nvim/input.h"
 #include "nvim/insexpand.h"