vim-patch:8.2.0674: some source files are too big (#19959)

Problem:    Some source files are too big.
Solution:   Move text formatting functions to a new file. (Yegappan
            Lakshmanan, closes vim/vim#6021)
https://github.com/vim/vim/commit/11abd095210fc84e5dcee87b9baed86061caefe4

Cherry-pick set_can_cindent() from patch 8.1.2062.
Cherry-pick global old_indent from patch 8.2.2127.

11 files changed, 1176 insertions, 1159 deletions

diff --git a/src/nvim/change.c b/src/nvim/change.c
index 9ea970edb5..04dfb20a1b 100644
--- a/src/nvim/change.c
+++ b/src/nvim/change.c
@@ -26,6 +26,7 @@
 #include "nvim/plines.h"
 #include "nvim/search.h"
 #include "nvim/state.h"
+#include "nvim/textformat.h"
 #include "nvim/ui.h"
 #include "nvim/undo.h"
 
diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index 82429d6542..d9aec2fbad 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -56,6 +56,7 @@
 #include "nvim/strings.h"
 #include "nvim/syntax.h"
 #include "nvim/terminal.h"
+#include "nvim/textformat.h"
 #include "nvim/ui.h"
 #include "nvim/undo.h"
 #include "nvim/vim.h"
@@ -108,8 +109,6 @@ static int did_restart_edit;            // "restart_edit" when calling edit()
 
 static bool can_cindent;                // may do cindenting on this line
 
-static int old_indent = 0;              // for ^^D command in insert mode
-
 static int revins_on;                   // reverse insert mode on
 static int revins_chars;                // how much to skip after edit
 static int revins_legal;                // was the last char 'legal'?
@@ -119,8 +118,6 @@ static bool ins_need_undo;              // call u_save() before inserting a
                                         // char.  Set when edit() is called.
                                         // after that arrow_used is used.
 
-static bool did_add_space = false;      // auto_format() added an extra space
-                                        // under the cursor
 static TriState dont_sync_undo = kFalse;  // CTRL-G U prevents syncing undo
                                           // for the next left/right cursor key
 
@@ -1561,7 +1558,7 @@ void display_dollar(colnr_T col)
  * Call this function before moving the cursor from the normal insert position
  * in insert mode.
  */
-static void undisplay_dollar(void)
+void undisplay_dollar(void)
 {
   if (dollar_vcol >= 0) {
     dollar_vcol = -1;
@@ -2012,9 +2009,6 @@ static void insert_special(int c, int allow_modmask, int ctrlv)
  */
 #define ISSPECIAL(c)   ((c) < ' ' || (c) >= DEL || (c) == '0' || (c) == '^')
 
-#define WHITECHAR(cc) (ascii_iswhite(cc) \
-                       && !utf_iscomposing(utf_ptr2char((char *)get_cursor_pos_ptr() + 1)))
-
 ///
 /// "flags": INSCHAR_FORMAT - force formatting
 ///          INSCHAR_CTRLV  - char typed just after CTRL-V
@@ -2213,597 +2207,6 @@ void insertchar(int c, int flags, int second_indent)
   }
 }
 
-/// Format text at the current insert position.
-///
-/// If the INSCHAR_COM_LIST flag is present, then the value of second_indent
-/// will be the comment leader length sent to open_line().
-///
-/// @param c  character to be inserted (can be NUL)
-static void internal_format(int textwidth, int second_indent, int flags, int format_only, int c)
-{
-  int cc;
-  int save_char = NUL;
-  bool haveto_redraw = false;
-  const bool fo_ins_blank = has_format_option(FO_INS_BLANK);
-  const bool fo_multibyte = has_format_option(FO_MBYTE_BREAK);
-  const bool fo_rigor_tw  = has_format_option(FO_RIGOROUS_TW);
-  const bool fo_white_par = has_format_option(FO_WHITE_PAR);
-  bool first_line = true;
-  colnr_T leader_len;
-  bool no_leader = false;
-  int do_comments = (flags & INSCHAR_DO_COM);
-  int has_lbr = curwin->w_p_lbr;
-
-  // make sure win_lbr_chartabsize() counts correctly
-  curwin->w_p_lbr = false;
-
-  /*
-   * When 'ai' is off we don't want a space under the cursor to be
-   * deleted.  Replace it with an 'x' temporarily.
-   */
-  if (!curbuf->b_p_ai
-      && !(State & VREPLACE_FLAG)) {
-    cc = gchar_cursor();
-    if (ascii_iswhite(cc)) {
-      save_char = cc;
-      pchar_cursor('x');
-    }
-  }
-
-  /*
-   * Repeat breaking lines, until the current line is not too long.
-   */
-  while (!got_int) {
-    int startcol;                       // Cursor column at entry
-    int wantcol;                        // column at textwidth border
-    int foundcol;                       // column for start of spaces
-    int end_foundcol = 0;               // column for start of word
-    colnr_T len;
-    colnr_T virtcol;
-    int orig_col = 0;
-    char_u *saved_text = NULL;
-    colnr_T col;
-    colnr_T end_col;
-    bool did_do_comment = false;
-
-    virtcol = get_nolist_virtcol()
-              + char2cells(c != NUL ? c : gchar_cursor());
-    if (virtcol <= (colnr_T)textwidth) {
-      break;
-    }
-
-    if (no_leader) {
-      do_comments = false;
-    } else if (!(flags & INSCHAR_FORMAT)
-               && has_format_option(FO_WRAP_COMS)) {
-      do_comments = true;
-    }
-
-    // Don't break until after the comment leader
-    if (do_comments) {
-      char_u *line = get_cursor_line_ptr();
-      leader_len = get_leader_len((char *)line, NULL, false, true);
-      if (leader_len == 0 && curbuf->b_p_cin) {
-        // Check for a line comment after code.
-        int comment_start = check_linecomment(line);
-        if (comment_start != MAXCOL) {
-          leader_len = get_leader_len((char *)line + comment_start, NULL, false, true);
-          if (leader_len != 0) {
-            leader_len += comment_start;
-          }
-        }
-      }
-    } else {
-      leader_len = 0;
-    }
-
-    // If the line doesn't start with a comment leader, then don't
-    // start one in a following broken line.  Avoids that a %word
-    // moved to the start of the next line causes all following lines
-    // to start with %.
-    if (leader_len == 0) {
-      no_leader = true;
-    }
-    if (!(flags & INSCHAR_FORMAT)
-        && leader_len == 0
-        && !has_format_option(FO_WRAP)) {
-      break;
-    }
-    if ((startcol = curwin->w_cursor.col) == 0) {
-      break;
-    }
-
-    // find column of textwidth border
-    coladvance((colnr_T)textwidth);
-    wantcol = curwin->w_cursor.col;
-
-    curwin->w_cursor.col = startcol;
-    foundcol = 0;
-    int skip_pos = 0;
-
-    /*
-     * Find position to break at.
-     * Stop at first entered white when 'formatoptions' has 'v'
-     */
-    while ((!fo_ins_blank && !has_format_option(FO_INS_VI))
-           || (flags & INSCHAR_FORMAT)
-           || curwin->w_cursor.lnum != Insstart.lnum
-           || curwin->w_cursor.col >= Insstart.col) {
-      if (curwin->w_cursor.col == startcol && c != NUL) {
-        cc = c;
-      } else {
-        cc = gchar_cursor();
-      }
-      if (WHITECHAR(cc)) {
-        // remember position of blank just before text
-        end_col = curwin->w_cursor.col;
-
-        // find start of sequence of blanks
-        int wcc = 0;  // counter for whitespace chars
-        while (curwin->w_cursor.col > 0 && WHITECHAR(cc)) {
-          dec_cursor();
-          cc = gchar_cursor();
-
-          // Increment count of how many whitespace chars in this
-          // group; we only need to know if it's more than one.
-          if (wcc < 2) {
-            wcc++;
-          }
-        }
-        if (curwin->w_cursor.col == 0 && WHITECHAR(cc)) {
-          break;                        // only spaces in front of text
-        }
-
-        // Don't break after a period when 'formatoptions' has 'p' and
-        // there are less than two spaces.
-        if (has_format_option(FO_PERIOD_ABBR) && cc == '.' && wcc < 2) {
-          continue;
-        }
-
-        // Don't break until after the comment leader
-        if (curwin->w_cursor.col < leader_len) {
-          break;
-        }
-
-        if (has_format_option(FO_ONE_LETTER)) {
-          // do not break after one-letter words
-          if (curwin->w_cursor.col == 0) {
-            break;              // one-letter word at begin
-          }
-          // do not break "#a b" when 'tw' is 2
-          if (curwin->w_cursor.col <= leader_len) {
-            break;
-          }
-          col = curwin->w_cursor.col;
-          dec_cursor();
-          cc = gchar_cursor();
-
-          if (WHITECHAR(cc)) {
-            continue;                   // one-letter, continue
-          }
-          curwin->w_cursor.col = col;
-        }
-
-        inc_cursor();
-
-        end_foundcol = end_col + 1;
-        foundcol = curwin->w_cursor.col;
-        if (curwin->w_cursor.col <= (colnr_T)wantcol) {
-          break;
-        }
-      } else if ((cc >= 0x100 || !utf_allow_break_before(cc)) && fo_multibyte) {
-        int ncc;
-        bool allow_break;
-
-        // Break after or before a multi-byte character.
-        if (curwin->w_cursor.col != startcol) {
-          // Don't break until after the comment leader
-          if (curwin->w_cursor.col < leader_len) {
-            break;
-          }
-          col = curwin->w_cursor.col;
-          inc_cursor();
-          ncc = gchar_cursor();
-          allow_break = utf_allow_break(cc, ncc);
-
-          // If we have already checked this position, skip!
-          if (curwin->w_cursor.col != skip_pos && allow_break) {
-            foundcol = curwin->w_cursor.col;
-            end_foundcol = foundcol;
-            if (curwin->w_cursor.col <= (colnr_T)wantcol) {
-              break;
-            }
-          }
-          curwin->w_cursor.col = col;
-        }
-
-        if (curwin->w_cursor.col == 0) {
-          break;
-        }
-
-        ncc = cc;
-        col = curwin->w_cursor.col;
-
-        dec_cursor();
-        cc = gchar_cursor();
-
-        if (WHITECHAR(cc)) {
-          continue;                     // break with space
-        }
-        // Don't break until after the comment leader.
-        if (curwin->w_cursor.col < leader_len) {
-          break;
-        }
-
-        curwin->w_cursor.col = col;
-        skip_pos = curwin->w_cursor.col;
-
-        allow_break = utf_allow_break(cc, ncc);
-
-        // Must handle this to respect line break prohibition.
-        if (allow_break) {
-          foundcol = curwin->w_cursor.col;
-          end_foundcol = foundcol;
-        }
-        if (curwin->w_cursor.col <= (colnr_T)wantcol) {
-          const bool ncc_allow_break = utf_allow_break_before(ncc);
-
-          if (allow_break) {
-            break;
-          }
-          if (!ncc_allow_break && !fo_rigor_tw) {
-            // Enable at most 1 punct hang outside of textwidth.
-            if (curwin->w_cursor.col == startcol) {
-              // We are inserting a non-breakable char, postpone
-              // line break check to next insert.
-              end_foundcol = foundcol = 0;
-              break;
-            }
-
-            // Neither cc nor ncc is NUL if we are here, so
-            // it's safe to inc_cursor.
-            col = curwin->w_cursor.col;
-
-            inc_cursor();
-            cc  = ncc;
-            ncc = gchar_cursor();
-            // handle insert
-            ncc = (ncc != NUL) ? ncc : c;
-
-            allow_break = utf_allow_break(cc, ncc);
-
-            if (allow_break) {
-              // Break only when we are not at end of line.
-              end_foundcol = foundcol = ncc == NUL? 0 : curwin->w_cursor.col;
-              break;
-            }
-            curwin->w_cursor.col = col;
-          }
-        }
-      }
-      if (curwin->w_cursor.col == 0) {
-        break;
-      }
-      dec_cursor();
-    }
-
-    if (foundcol == 0) {                // no spaces, cannot break line
-      curwin->w_cursor.col = startcol;
-      break;
-    }
-
-    // Going to break the line, remove any "$" now.
-    undisplay_dollar();
-
-    // Offset between cursor position and line break is used by replace
-    // stack functions.  MODE_VREPLACE does not use this, and backspaces
-    // over the text instead.
-    if (State & VREPLACE_FLAG) {
-      orig_col = startcol;              // Will start backspacing from here
-    } else {
-      replace_offset = startcol - end_foundcol;
-    }
-
-    /*
-     * adjust startcol for spaces that will be deleted and
-     * characters that will remain on top line
-     */
-    curwin->w_cursor.col = foundcol;
-    while ((cc = gchar_cursor(), WHITECHAR(cc))
-           && (!fo_white_par || curwin->w_cursor.col < startcol)) {
-      inc_cursor();
-    }
-    startcol -= curwin->w_cursor.col;
-    if (startcol < 0) {
-      startcol = 0;
-    }
-
-    if (State & VREPLACE_FLAG) {
-      // In MODE_VREPLACE state, we will backspace over the text to be
-      // wrapped, so save a copy now to put on the next line.
-      saved_text = vim_strsave(get_cursor_pos_ptr());
-      curwin->w_cursor.col = orig_col;
-      saved_text[startcol] = NUL;
-
-      // Backspace over characters that will move to the next line
-      if (!fo_white_par) {
-        backspace_until_column(foundcol);
-      }
-    } else {
-      // put cursor after pos. to break line
-      if (!fo_white_par) {
-        curwin->w_cursor.col = foundcol;
-      }
-    }
-
-    /*
-     * Split the line just before the margin.
-     * Only insert/delete lines, but don't really redraw the window.
-     */
-    open_line(FORWARD, OPENLINE_DELSPACES + OPENLINE_MARKFIX
-              + (fo_white_par ? OPENLINE_KEEPTRAIL : 0)
-              + (do_comments ? OPENLINE_DO_COM : 0)
-              + OPENLINE_FORMAT
-              + ((flags & INSCHAR_COM_LIST) ? OPENLINE_COM_LIST : 0),
-              ((flags & INSCHAR_COM_LIST) ? second_indent : old_indent),
-              &did_do_comment);
-    if (!(flags & INSCHAR_COM_LIST)) {
-      old_indent = 0;
-    }
-
-    // If a comment leader was inserted, may also do this on a following
-    // line.
-    if (did_do_comment) {
-      no_leader = false;
-    }
-
-    replace_offset = 0;
-    if (first_line) {
-      if (!(flags & INSCHAR_COM_LIST)) {
-        // This section is for auto-wrap of numeric lists.  When not
-        // in insert mode (i.e. format_lines()), the INSCHAR_COM_LIST
-        // flag will be set and open_line() will handle it (as seen
-        // above).  The code here (and in get_number_indent()) will
-        // recognize comments if needed...
-        if (second_indent < 0 && has_format_option(FO_Q_NUMBER)) {
-          second_indent = get_number_indent(curwin->w_cursor.lnum - 1);
-        }
-        if (second_indent >= 0) {
-          if (State & VREPLACE_FLAG) {
-            change_indent(INDENT_SET, second_indent, false, NUL, true);
-          } else if (leader_len > 0 && second_indent - leader_len > 0) {
-            int padding = second_indent - leader_len;
-
-            // We started at the first_line of a numbered list
-            // that has a comment.  the open_line() function has
-            // inserted the proper comment leader and positioned
-            // the cursor at the end of the split line.  Now we
-            // add the additional whitespace needed after the
-            // comment leader for the numbered list.
-            for (int i = 0; i < padding; i++) {
-              ins_str((char_u *)" ");
-            }
-            changed_bytes(curwin->w_cursor.lnum, leader_len);
-          } else {
-            (void)set_indent(second_indent, SIN_CHANGED);
-          }
-        }
-      }
-      first_line = false;
-    }
-
-    if (State & VREPLACE_FLAG) {
-      // In MODE_VREPLACE state we have backspaced over the text to be
-      // moved, now we re-insert it into the new line.
-      ins_bytes((char *)saved_text);
-      xfree(saved_text);
-    } else {
-      /*
-       * Check if cursor is not past the NUL off the line, cindent
-       * may have added or removed indent.
-       */
-      curwin->w_cursor.col += startcol;
-      len = (colnr_T)STRLEN(get_cursor_line_ptr());
-      if (curwin->w_cursor.col > len) {
-        curwin->w_cursor.col = len;
-      }
-    }
-
-    haveto_redraw = true;
-    can_cindent = true;
-    // moved the cursor, don't autoindent or cindent now
-    did_ai = false;
-    did_si = false;
-    can_si = false;
-    can_si_back = false;
-    line_breakcheck();
-  }
-
-  if (save_char != NUL) {               // put back space after cursor
-    pchar_cursor((char_u)save_char);
-  }
-
-  curwin->w_p_lbr = has_lbr;
-
-  if (!format_only && haveto_redraw) {
-    update_topline(curwin);
-    redraw_curbuf_later(UPD_VALID);
-  }
-}
-
-/// Called after inserting or deleting text: When 'formatoptions' includes the
-/// 'a' flag format from the current line until the end of the paragraph.
-/// Keep the cursor at the same position relative to the text.
-/// The caller must have saved the cursor line for undo, following ones will be
-/// saved here.
-///
-/// @param trailblank  when true also format with trailing blank
-/// @param prev_line   may start in previous line
-void auto_format(bool trailblank, bool prev_line)
-{
-  pos_T pos;
-  colnr_T len;
-  char_u *old;
-  char_u *new, *pnew;
-  int wasatend;
-  int cc;
-
-  if (!has_format_option(FO_AUTO)) {
-    return;
-  }
-
-  pos = curwin->w_cursor;
-  old = get_cursor_line_ptr();
-
-  // may remove added space
-  check_auto_format(false);
-
-  // Don't format in Insert mode when the cursor is on a trailing blank, the
-  // user might insert normal text next.  Also skip formatting when "1" is
-  // in 'formatoptions' and there is a single character before the cursor.
-  // Otherwise the line would be broken and when typing another non-white
-  // next they are not joined back together.
-  wasatend = (pos.col == (colnr_T)STRLEN(old));
-  if (*old != NUL && !trailblank && wasatend) {
-    dec_cursor();
-    cc = gchar_cursor();
-    if (!WHITECHAR(cc) && curwin->w_cursor.col > 0
-        && has_format_option(FO_ONE_LETTER)) {
-      dec_cursor();
-    }
-    cc = gchar_cursor();
-    if (WHITECHAR(cc)) {
-      curwin->w_cursor = pos;
-      return;
-    }
-    curwin->w_cursor = pos;
-  }
-
-  // With the 'c' flag in 'formatoptions' and 't' missing: only format
-  // comments.
-  if (has_format_option(FO_WRAP_COMS) && !has_format_option(FO_WRAP)
-      && get_leader_len((char *)old, NULL, false, true) == 0) {
-    return;
-  }
-
-  /*
-   * May start formatting in a previous line, so that after "x" a word is
-   * moved to the previous line if it fits there now.  Only when this is not
-   * the start of a paragraph.
-   */
-  if (prev_line && !paragraph_start(curwin->w_cursor.lnum)) {
-    curwin->w_cursor.lnum--;
-    if (u_save_cursor() == FAIL) {
-      return;
-    }
-  }
-
-  /*
-   * Do the formatting and restore the cursor position.  "saved_cursor" will
-   * be adjusted for the text formatting.
-   */
-  saved_cursor = pos;
-  format_lines((linenr_T) - 1, false);
-  curwin->w_cursor = saved_cursor;
-  saved_cursor.lnum = 0;
-
-  if (curwin->w_cursor.lnum > curbuf->b_ml.ml_line_count) {
-    // "cannot happen"
-    curwin->w_cursor.lnum = curbuf->b_ml.ml_line_count;
-    coladvance(MAXCOL);
-  } else {
-    check_cursor_col();
-  }
-
-  // Insert mode: If the cursor is now after the end of the line while it
-  // previously wasn't, the line was broken.  Because of the rule above we
-  // need to add a space when 'w' is in 'formatoptions' to keep a paragraph
-  // formatted.
-  if (!wasatend && has_format_option(FO_WHITE_PAR)) {
-    new = get_cursor_line_ptr();
-    len = (colnr_T)STRLEN(new);
-    if (curwin->w_cursor.col == len) {
-      pnew = vim_strnsave(new, (size_t)len + 2);
-      pnew[len] = ' ';
-      pnew[len + 1] = NUL;
-      ml_replace(curwin->w_cursor.lnum, (char *)pnew, false);
-      // remove the space later
-      did_add_space = true;
-    } else {
-      // may remove added space
-      check_auto_format(false);
-    }
-  }
-
-  check_cursor();
-}
-
-/// When an extra space was added to continue a paragraph for auto-formatting,
-/// delete it now.  The space must be under the cursor, just after the insert
-/// position.
-///
-/// @param end_insert  true when ending Insert mode
-static void check_auto_format(bool end_insert)
-{
-  int c = ' ';
-  int cc;
-
-  if (did_add_space) {
-    cc = gchar_cursor();
-    if (!WHITECHAR(cc)) {
-      // Somehow the space was removed already.
-      did_add_space = false;
-    } else {
-      if (!end_insert) {
-        inc_cursor();
-        c = gchar_cursor();
-        dec_cursor();
-      }
-      if (c != NUL) {
-        // The space is no longer at the end of the line, delete it.
-        del_char(false);
-        did_add_space = false;
-      }
-    }
-  }
-}
-
-/// Find out textwidth to be used for formatting:
-///      if 'textwidth' option is set, use it
-///      else if 'wrapmargin' option is set, use curwin->w_width_inner-'wrapmargin'
-///      if invalid value, use 0.
-///      Set default to window width (maximum 79) for "gq" operator.
-///
-/// @param ff  force formatting (for "gq" command)
-int comp_textwidth(bool ff)
-{
-  int textwidth = (int)curbuf->b_p_tw;
-  if (textwidth == 0 && curbuf->b_p_wm) {
-    // The width is the window width minus 'wrapmargin' minus all the
-    // things that add to the margin.
-    textwidth = curwin->w_width_inner - (int)curbuf->b_p_wm;
-    if (cmdwin_type != 0) {
-      textwidth -= 1;
-    }
-    textwidth -= win_fdccol_count(curwin);
-    textwidth -= win_signcol_count(curwin);
-
-    if (curwin->w_p_nu || curwin->w_p_rnu) {
-      textwidth -= 8;
-    }
-  }
-  if (textwidth < 0) {
-    textwidth = 0;
-  }
-  if (ff && textwidth == 0) {
-    textwidth = curwin->w_width_inner - 1;
-    if (textwidth > 79) {
-      textwidth = 79;
-    }
-  }
-  return textwidth;
-}
-
 /*
  * Put a character in the redo buffer, for when just after a CTRL-V.
  */
@@ -5665,6 +5068,11 @@ bool get_can_cindent(void)
   return can_cindent;
 }
 
+void set_can_cindent(bool val)
+{
+  can_cindent = val;
+}
+
 /// Trigger "event" and take care of fixing undo.
 int ins_apply_autocmds(event_T event)
 {
diff --git a/src/nvim/getchar.c b/src/nvim/getchar.c
index f5f09f1394..c1c5680cb0 100644
--- a/src/nvim/getchar.c
+++ b/src/nvim/getchar.c
@@ -623,6 +623,34 @@ void stuffnumReadbuff(long n)
   add_num_buff(&readbuf1, n);
 }
 
+/// Stuff a string into the typeahead buffer, such that edit() will insert it
+/// literally ("literally" true) or interpret is as typed characters.
+void stuffescaped(const char *arg, bool literally)
+{
+  while (*arg != NUL) {
+    // Stuff a sequence of normal ASCII characters, that's fast.  Also
+    // stuff K_SPECIAL to get the effect of a special key when "literally"
+    // is true.
+    const char *const start = arg;
+    while ((*arg >= ' ' && *arg < DEL) || ((uint8_t)(*arg) == K_SPECIAL
+                                           && !literally)) {
+      arg++;
+    }
+    if (arg > start) {
+      stuffReadbuffLen(start, (arg - start));
+    }
+
+    // stuff a single special character
+    if (*arg != NUL) {
+      const int c = mb_cptr2char_adv((const char_u **)&arg);
+      if (literally && ((c < ' ' && c != TAB) || c == DEL)) {
+        stuffcharReadbuff(Ctrl_V);
+      }
+      stuffcharReadbuff(c);
+    }
+  }
+}
+
 /// Read a character from the redo buffer.  Translates K_SPECIAL and
 /// multibyte characters.
 /// The redo buffer is left as it is.
diff --git a/src/nvim/globals.h b/src/nvim/globals.h
index 6c83e2f3c3..7b93fbc852 100644
--- a/src/nvim/globals.h
+++ b/src/nvim/globals.h
@@ -559,6 +559,8 @@ EXTERN bool can_si INIT(= false);
 // one indent will be removed.
 EXTERN bool can_si_back INIT(= false);
 
+EXTERN int old_indent INIT(= 0);  ///< for ^^D command in insert mode
+
 // w_cursor before formatting text.
 EXTERN pos_T saved_cursor INIT(= { 0, 0, 0 });
 
diff --git a/src/nvim/indent.c b/src/nvim/indent.c
index c44cd06a2f..c4805283c2 100644
--- a/src/nvim/indent.c
+++ b/src/nvim/indent.c
@@ -25,6 +25,7 @@
 #include "nvim/screen.h"
 #include "nvim/search.h"
 #include "nvim/strings.h"
+#include "nvim/textformat.h"
 #include "nvim/undo.h"
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
diff --git a/src/nvim/insexpand.c b/src/nvim/insexpand.c
index a3b5e3df5c..7d17a284e5 100644
--- a/src/nvim/insexpand.c
+++ b/src/nvim/insexpand.c
@@ -43,6 +43,7 @@
 #include "nvim/state.h"
 #include "nvim/strings.h"
 #include "nvim/tag.h"
+#include "nvim/textformat.h"
 #include "nvim/ui.h"
 #include "nvim/undo.h"
 #include "nvim/vim.h"
diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index 1bd780be0f..743297eb9d 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -65,6 +65,7 @@
 #include "nvim/strings.h"
 #include "nvim/syntax.h"
 #include "nvim/tag.h"
+#include "nvim/textformat.h"
 #include "nvim/ui.h"
 #include "nvim/undo.h"
 #include "nvim/vim.h"
diff --git a/src/nvim/ops.c b/src/nvim/ops.c
index a1f4149715..79450acbd6 100644
--- a/src/nvim/ops.c
+++ b/src/nvim/ops.c
@@ -51,6 +51,7 @@
 #include "nvim/state.h"
 #include "nvim/strings.h"
 #include "nvim/terminal.h"
+#include "nvim/textformat.h"
 #include "nvim/ui.h"
 #include "nvim/undo.h"
 #include "nvim/vim.h"
@@ -1311,34 +1312,6 @@ int insert_reg(int regname, bool literally_arg)
   return retval;
 }
 
-/// Stuff a string into the typeahead buffer, such that edit() will insert it
-/// literally ("literally" true) or interpret is as typed characters.
-static void stuffescaped(const char *arg, bool literally)
-{
-  while (*arg != NUL) {
-    // Stuff a sequence of normal ASCII characters, that's fast.  Also
-    // stuff K_SPECIAL to get the effect of a special key when "literally"
-    // is true.
-    const char *const start = arg;
-    while ((*arg >= ' ' && *arg < DEL) || ((uint8_t)(*arg) == K_SPECIAL
-                                           && !literally)) {
-      arg++;
-    }
-    if (arg > start) {
-      stuffReadbuffLen(start, (arg - start));
-    }
-
-    // stuff a single special character
-    if (*arg != NUL) {
-      const int c = mb_cptr2char_adv((const char_u **)&arg);
-      if (literally && ((c < ' ' && c != TAB) || c == DEL)) {
-        stuffcharReadbuff(Ctrl_V);
-      }
-      stuffcharReadbuff(c);
-    }
-  }
-}
-
 /// If "regname" is a special register, return true and store a pointer to its
 /// value in "argp".
 ///
@@ -4218,527 +4191,6 @@ theend:
   return ret;
 }
 
-/// @return  true if the two comment leaders given are the same.
-///
-/// @param lnum  The first line.  White-space is ignored.
-///
-/// @note the whole of 'leader1' must match 'leader2_len' characters from 'leader2'.
-static int same_leader(linenr_T lnum, int leader1_len, char_u *leader1_flags, int leader2_len,
-                       char_u *leader2_flags)
-{
-  int idx1 = 0, idx2 = 0;
-  char_u *p;
-  char_u *line1;
-  char_u *line2;
-
-  if (leader1_len == 0) {
-    return leader2_len == 0;
-  }
-
-  /*
-   * If first leader has 'f' flag, the lines can be joined only if the
-   * second line does not have a leader.
-   * If first leader has 'e' flag, the lines can never be joined.
-   * If first leader has 's' flag, the lines can only be joined if there is
-   * some text after it and the second line has the 'm' flag.
-   */
-  if (leader1_flags != NULL) {
-    for (p = leader1_flags; *p && *p != ':'; p++) {
-      if (*p == COM_FIRST) {
-        return leader2_len == 0;
-      }
-      if (*p == COM_END) {
-        return false;
-      }
-      if (*p == COM_START) {
-        if (*(ml_get(lnum) + leader1_len) == NUL) {
-          return false;
-        }
-        if (leader2_flags == NULL || leader2_len == 0) {
-          return false;
-        }
-        for (p = leader2_flags; *p && *p != ':'; p++) {
-          if (*p == COM_MIDDLE) {
-            return true;
-          }
-        }
-        return false;
-      }
-    }
-  }
-
-  /*
-   * Get current line and next line, compare the leaders.
-   * The first line has to be saved, only one line can be locked at a time.
-   */
-  line1 = vim_strsave(ml_get(lnum));
-  for (idx1 = 0; ascii_iswhite(line1[idx1]); idx1++) {}
-  line2 = ml_get(lnum + 1);
-  for (idx2 = 0; idx2 < leader2_len; idx2++) {
-    if (!ascii_iswhite(line2[idx2])) {
-      if (line1[idx1++] != line2[idx2]) {
-        break;
-      }
-    } else {
-      while (ascii_iswhite(line1[idx1])) {
-        idx1++;
-      }
-    }
-  }
-  xfree(line1);
-
-  return idx2 == leader2_len && idx1 == leader1_len;
-}
-
-/// Implementation of the format operator 'gq'.
-///
-/// @param keep_cursor  keep cursor on same text char
-static void op_format(oparg_T *oap, int keep_cursor)
-{
-  linenr_T old_line_count = curbuf->b_ml.ml_line_count;
-
-  // Place the cursor where the "gq" or "gw" command was given, so that "u"
-  // can put it back there.
-  curwin->w_cursor = oap->cursor_start;
-
-  if (u_save((linenr_T)(oap->start.lnum - 1),
-             (linenr_T)(oap->end.lnum + 1)) == FAIL) {
-    return;
-  }
-  curwin->w_cursor = oap->start;
-
-  if (oap->is_VIsual) {
-    // When there is no change: need to remove the Visual selection
-    redraw_curbuf_later(UPD_INVERTED);
-  }
-
-  if ((cmdmod.cmod_flags & CMOD_LOCKMARKS) == 0) {
-    // Set '[ mark at the start of the formatted area
-    curbuf->b_op_start = oap->start;
-  }
-
-  // For "gw" remember the cursor position and put it back below (adjusted
-  // for joined and split lines).
-  if (keep_cursor) {
-    saved_cursor = oap->cursor_start;
-  }
-
-  format_lines((linenr_T)oap->line_count, keep_cursor);
-
-  /*
-   * Leave the cursor at the first non-blank of the last formatted line.
-   * If the cursor was moved one line back (e.g. with "Q}") go to the next
-   * line, so "." will do the next lines.
-   */
-  if (oap->end_adjusted && curwin->w_cursor.lnum < curbuf->b_ml.ml_line_count) {
-    curwin->w_cursor.lnum++;
-  }
-  beginline(BL_WHITE | BL_FIX);
-  old_line_count = curbuf->b_ml.ml_line_count - old_line_count;
-  msgmore(old_line_count);
-
-  if ((cmdmod.cmod_flags & CMOD_LOCKMARKS) == 0) {
-    // put '] mark on the end of the formatted area
-    curbuf->b_op_end = curwin->w_cursor;
-  }
-
-  if (keep_cursor) {
-    curwin->w_cursor = saved_cursor;
-    saved_cursor.lnum = 0;
-
-    // formatting may have made the cursor position invalid
-    check_cursor();
-  }
-
-  if (oap->is_VIsual) {
-    FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
-      if (wp->w_old_cursor_lnum != 0) {
-        // When lines have been inserted or deleted, adjust the end of
-        // the Visual area to be redrawn.
-        if (wp->w_old_cursor_lnum > wp->w_old_visual_lnum) {
-          wp->w_old_cursor_lnum += old_line_count;
-        } else {
-          wp->w_old_visual_lnum += old_line_count;
-        }
-      }
-    }
-  }
-}
-
-/// Implementation of the format operator 'gq' for when using 'formatexpr'.
-static void op_formatexpr(oparg_T *oap)
-{
-  if (oap->is_VIsual) {
-    // When there is no change: need to remove the Visual selection
-    redraw_curbuf_later(UPD_INVERTED);
-  }
-
-  if (fex_format(oap->start.lnum, oap->line_count, NUL) != 0) {
-    // As documented: when 'formatexpr' returns non-zero fall back to
-    // internal formatting.
-    op_format(oap, false);
-  }
-}
-
-/// @param c  character to be inserted
-int fex_format(linenr_T lnum, long count, int c)
-{
-  int use_sandbox = was_set_insecurely(curwin, "formatexpr", OPT_LOCAL);
-  int r;
-
-  // Set v:lnum to the first line number and v:count to the number of lines.
-  // Set v:char to the character to be inserted (can be NUL).
-  set_vim_var_nr(VV_LNUM, (varnumber_T)lnum);
-  set_vim_var_nr(VV_COUNT, (varnumber_T)count);
-  set_vim_var_char(c);
-
-  // Make a copy, the option could be changed while calling it.
-  char *fex = xstrdup(curbuf->b_p_fex);
-  // Evaluate the function.
-  if (use_sandbox) {
-    sandbox++;
-  }
-  r = (int)eval_to_number(fex);
-  if (use_sandbox) {
-    sandbox--;
-  }
-
-  set_vim_var_string(VV_CHAR, NULL, -1);
-  xfree(fex);
-
-  return r;
-}
-
-/// @param line_count  number of lines to format, starting at the cursor position.
-///                    when negative, format until the end of the paragraph.
-///
-/// Lines after the cursor line are saved for undo, caller must have saved the
-/// first line.
-///
-/// @param avoid_fex  don't use 'formatexpr'
-void format_lines(linenr_T line_count, int avoid_fex)
-{
-  bool is_not_par;                  // current line not part of parag.
-  bool next_is_not_par;             // next line not part of paragraph
-  bool is_end_par;                  // at end of paragraph
-  bool prev_is_end_par = false;     // prev. line not part of parag.
-  bool next_is_start_par = false;
-  int leader_len = 0;               // leader len of current line
-  int next_leader_len;              // leader len of next line
-  char_u *leader_flags = NULL;      // flags for leader of current line
-  char_u *next_leader_flags = NULL;  // flags for leader of next line
-  bool advance = true;
-  int second_indent = -1;           // indent for second line (comment aware)
-  bool first_par_line = true;
-  int smd_save;
-  long count;
-  bool need_set_indent = true;      // set indent of next paragraph
-  linenr_T first_line = curwin->w_cursor.lnum;
-  bool force_format = false;
-  const int old_State = State;
-
-  // length of a line to force formatting: 3 * 'tw'
-  const int max_len = comp_textwidth(true) * 3;
-
-  // check for 'q', '2' and '1' in 'formatoptions'
-  const bool do_comments = has_format_option(FO_Q_COMS);  // format comments
-  int do_comments_list = 0;  // format comments with 'n' or '2'
-  const bool do_second_indent = has_format_option(FO_Q_SECOND);
-  const bool do_number_indent = has_format_option(FO_Q_NUMBER);
-  const bool do_trail_white = has_format_option(FO_WHITE_PAR);
-
-  // Get info about the previous and current line.
-  if (curwin->w_cursor.lnum > 1) {
-    is_not_par = fmt_check_par(curwin->w_cursor.lnum - 1,
-                               &leader_len, &leader_flags, do_comments);
-  } else {
-    is_not_par = true;
-  }
-  next_is_not_par = fmt_check_par(curwin->w_cursor.lnum,
-                                  &next_leader_len, &next_leader_flags, do_comments
-                                  );
-  is_end_par = (is_not_par || next_is_not_par);
-  if (!is_end_par && do_trail_white) {
-    is_end_par = !ends_in_white(curwin->w_cursor.lnum - 1);
-  }
-
-  curwin->w_cursor.lnum--;
-  for (count = line_count; count != 0 && !got_int; count--) {
-    // Advance to next paragraph.
-    if (advance) {
-      curwin->w_cursor.lnum++;
-      prev_is_end_par = is_end_par;
-      is_not_par = next_is_not_par;
-      leader_len = next_leader_len;
-      leader_flags = next_leader_flags;
-    }
-
-    /*
-     * The last line to be formatted.
-     */
-    if (count == 1 || curwin->w_cursor.lnum == curbuf->b_ml.ml_line_count) {
-      next_is_not_par = true;
-      next_leader_len = 0;
-      next_leader_flags = NULL;
-    } else {
-      next_is_not_par = fmt_check_par(curwin->w_cursor.lnum + 1,
-                                      &next_leader_len, &next_leader_flags, do_comments
-                                      );
-      if (do_number_indent) {
-        next_is_start_par =
-          (get_number_indent(curwin->w_cursor.lnum + 1) > 0);
-      }
-    }
-    advance = true;
-    is_end_par = (is_not_par || next_is_not_par || next_is_start_par);
-    if (!is_end_par && do_trail_white) {
-      is_end_par = !ends_in_white(curwin->w_cursor.lnum);
-    }
-
-    /*
-     * Skip lines that are not in a paragraph.
-     */
-    if (is_not_par) {
-      if (line_count < 0) {
-        break;
-      }
-    } else {
-      /*
-       * For the first line of a paragraph, check indent of second line.
-       * Don't do this for comments and empty lines.
-       */
-      if (first_par_line
-          && (do_second_indent || do_number_indent)
-          && prev_is_end_par
-          && curwin->w_cursor.lnum < curbuf->b_ml.ml_line_count) {
-        if (do_second_indent && !LINEEMPTY(curwin->w_cursor.lnum + 1)) {
-          if (leader_len == 0 && next_leader_len == 0) {
-            // no comment found
-            second_indent =
-              get_indent_lnum(curwin->w_cursor.lnum + 1);
-          } else {
-            second_indent = next_leader_len;
-            do_comments_list = 1;
-          }
-        } else if (do_number_indent) {
-          if (leader_len == 0 && next_leader_len == 0) {
-            // no comment found
-            second_indent =
-              get_number_indent(curwin->w_cursor.lnum);
-          } else {
-            // get_number_indent() is now "comment aware"...
-            second_indent =
-              get_number_indent(curwin->w_cursor.lnum);
-            do_comments_list = 1;
-          }
-        }
-      }
-
-      /*
-       * When the comment leader changes, it's the end of the paragraph.
-       */
-      if (curwin->w_cursor.lnum >= curbuf->b_ml.ml_line_count
-          || !same_leader(curwin->w_cursor.lnum,
-                          leader_len, leader_flags,
-                          next_leader_len,
-                          next_leader_flags)) {
-        // Special case: If the next line starts with a line comment
-        // and this line has a line comment after some text, the
-        // paragraph doesn't really end.
-        if (next_leader_flags == NULL
-            || STRNCMP(next_leader_flags, "://", 3) != 0
-            || check_linecomment(get_cursor_line_ptr()) == MAXCOL) {
-          is_end_par = true;
-        }
-      }
-
-      /*
-       * If we have got to the end of a paragraph, or the line is
-       * getting long, format it.
-       */
-      if (is_end_par || force_format) {
-        if (need_set_indent) {
-          int indent = 0;  // amount of indent needed
-
-          // Replace indent in first line of a paragraph with minimal
-          // number of tabs and spaces, according to current options.
-          // For the very first formatted line keep the current
-          // indent.
-          if (curwin->w_cursor.lnum == first_line) {
-            indent = get_indent();
-          } else if (curbuf->b_p_lisp) {
-            indent = get_lisp_indent();
-          } else {
-            if (cindent_on()) {
-              indent = *curbuf->b_p_inde != NUL ? get_expr_indent() : get_c_indent();
-            } else {
-              indent = get_indent();
-            }
-          }
-          (void)set_indent(indent, SIN_CHANGED);
-        }
-
-        // put cursor on last non-space
-        State = MODE_NORMAL;  // don't go past end-of-line
-        coladvance(MAXCOL);
-        while (curwin->w_cursor.col && ascii_isspace(gchar_cursor())) {
-          dec_cursor();
-        }
-
-        // do the formatting, without 'showmode'
-        State = MODE_INSERT;         // for open_line()
-        smd_save = p_smd;
-        p_smd = false;
-        insertchar(NUL, INSCHAR_FORMAT
-                   + (do_comments ? INSCHAR_DO_COM : 0)
-                   + (do_comments && do_comments_list
-               ? INSCHAR_COM_LIST : 0)
-                   + (avoid_fex ? INSCHAR_NO_FEX : 0), second_indent);
-        State = old_State;
-        p_smd = smd_save;
-        second_indent = -1;
-        // at end of par.: need to set indent of next par.
-        need_set_indent = is_end_par;
-        if (is_end_par) {
-          // When called with a negative line count, break at the
-          // end of the paragraph.
-          if (line_count < 0) {
-            break;
-          }
-          first_par_line = true;
-        }
-        force_format = false;
-      }
-
-      /*
-       * When still in same paragraph, join the lines together.  But
-       * first delete the leader from the second line.
-       */
-      if (!is_end_par) {
-        advance = false;
-        curwin->w_cursor.lnum++;
-        curwin->w_cursor.col = 0;
-        if (line_count < 0 && u_save_cursor() == FAIL) {
-          break;
-        }
-        if (next_leader_len > 0) {
-          (void)del_bytes(next_leader_len, false, false);
-          mark_col_adjust(curwin->w_cursor.lnum, (colnr_T)0, 0L,
-                          (long)-next_leader_len, 0);
-        } else if (second_indent > 0) {   // the "leader" for FO_Q_SECOND
-          int indent = (int)getwhitecols_curline();
-
-          if (indent > 0) {
-            (void)del_bytes(indent, false, false);
-            mark_col_adjust(curwin->w_cursor.lnum,
-                            (colnr_T)0, 0L, (long)-indent, 0);
-          }
-        }
-        curwin->w_cursor.lnum--;
-        if (do_join(2, true, false, false, false) == FAIL) {
-          beep_flush();
-          break;
-        }
-        first_par_line = false;
-        // If the line is getting long, format it next time
-        if (STRLEN(get_cursor_line_ptr()) > (size_t)max_len) {
-          force_format = true;
-        } else {
-          force_format = false;
-        }
-      }
-    }
-    line_breakcheck();
-  }
-}
-
-/// @return  true if line "lnum" ends in a white character.
-static int ends_in_white(linenr_T lnum)
-{
-  char_u *s = ml_get(lnum);
-  size_t l;
-
-  if (*s == NUL) {
-    return false;
-  }
-  l = STRLEN(s) - 1;
-  return ascii_iswhite(s[l]);
-}
-
-/// Blank lines, and lines containing only the comment leader, are left
-/// untouched by the formatting.  The function returns true in this
-/// case.  It also returns true when a line starts with the end of a comment
-/// ('e' in comment flags), so that this line is skipped, and not joined to the
-/// previous line.  A new paragraph starts after a blank line, or when the
-/// comment leader changes.
-static int fmt_check_par(linenr_T lnum, int *leader_len, char_u **leader_flags, int do_comments)
-{
-  char_u *flags = NULL;        // init for GCC
-  char_u *ptr;
-
-  ptr = ml_get(lnum);
-  if (do_comments) {
-    *leader_len = get_leader_len((char *)ptr, (char **)leader_flags, false, true);
-  } else {
-    *leader_len = 0;
-  }
-
-  if (*leader_len > 0) {
-    /*
-     * Search for 'e' flag in comment leader flags.
-     */
-    flags = *leader_flags;
-    while (*flags && *flags != ':' && *flags != COM_END) {
-      flags++;
-    }
-  }
-
-  return *skipwhite((char *)ptr + *leader_len) == NUL
-         || (*leader_len > 0 && *flags == COM_END)
-         || startPS(lnum, NUL, false);
-}
-
-/// Used for auto-formatting.
-///
-/// @return  true when a paragraph starts in line "lnum".
-///          false when the previous line is in the same paragraph.
-int paragraph_start(linenr_T lnum)
-{
-  char_u *p;
-  int leader_len = 0;                // leader len of current line
-  char_u *leader_flags = NULL;       // flags for leader of current line
-  int next_leader_len = 0;           // leader len of next line
-  char_u *next_leader_flags = NULL;  // flags for leader of next line
-
-  if (lnum <= 1) {
-    return true;                // start of the file
-  }
-  p = ml_get(lnum - 1);
-  if (*p == NUL) {
-    return true;                // after empty line
-  }
-  const bool do_comments = has_format_option(FO_Q_COMS);  // format comments
-  if (fmt_check_par(lnum - 1, &leader_len, &leader_flags, do_comments)) {
-    return true;  // after non-paragraph line
-  }
-
-  if (fmt_check_par(lnum, &next_leader_len, &next_leader_flags, do_comments)) {
-    return true;  // "lnum" is not a paragraph line
-  }
-
-  if (has_format_option(FO_WHITE_PAR) && !ends_in_white(lnum - 1)) {
-    return true;                // missing trailing space in previous line.
-  }
-  if (has_format_option(FO_Q_NUMBER) && (get_number_indent(lnum) > 0)) {
-    return true;                // numbered item starts in "lnum".
-  }
-  if (!same_leader(lnum - 1, leader_len, leader_flags,
-                   next_leader_len, next_leader_flags)) {
-    return true;                // change of comment leader.
-  }
-  return false;
-}
-
 /// prepare a few things for block mode yank/delete/tilde
 ///
 /// for delete:
diff --git a/src/nvim/option.c b/src/nvim/option.c
index 3f7c200928..95c3ccf71c 100644
--- a/src/nvim/option.c
+++ b/src/nvim/option.c
@@ -5047,17 +5047,6 @@ static int wc_use_keyname(char_u *varp, long *wcp)
   return false;
 }
 
-/// Return true if format option 'x' is in effect.
-/// Take care of no formatting when 'paste' is set.
-bool has_format_option(int x)
-  FUNC_ATTR_PURE FUNC_ATTR_WARN_UNUSED_RESULT
-{
-  if (p_paste) {
-    return false;
-  }
-  return vim_strchr(curbuf->b_p_fo, x) != NULL;
-}
-
 /// @returns true if "x" is present in 'shortmess' option, or
 /// 'shortmess' contains 'a' and "x" is present in SHM_ALL_ABBREVIATIONS.
 bool shortmess(int x)
diff --git a/src/nvim/textformat.c b/src/nvim/textformat.c
new file mode 100644
index 0000000000..43afc08155
--- /dev/null
+++ b/src/nvim/textformat.c
@@ -0,0 +1,1122 @@
+// 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
+
+// textformat.c: text formatting functions
+
+#include <stdbool.h>
+
+#include "nvim/change.h"
+#include "nvim/charset.h"
+#include "nvim/cursor.h"
+#include "nvim/drawscreen.h"
+#include "nvim/edit.h"
+#include "nvim/eval.h"
+#include "nvim/getchar.h"
+#include "nvim/globals.h"
+#include "nvim/indent.h"
+#include "nvim/indent_c.h"
+#include "nvim/memline.h"
+#include "nvim/move.h"
+#include "nvim/ops.h"
+#include "nvim/option.h"
+#include "nvim/os/input.h"
+#include "nvim/search.h"
+#include "nvim/strings.h"
+#include "nvim/textformat.h"
+#include "nvim/undo.h"
+#include "nvim/vim.h"
+#include "nvim/window.h"
+
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "textformat.c.generated.h"
+#endif
+
+static bool did_add_space = false;  ///< auto_format() added an extra space
+                                    ///< under the cursor
+
+#define WHITECHAR(cc) (ascii_iswhite(cc) \
+                       && !utf_iscomposing(utf_ptr2char((char *)get_cursor_pos_ptr() + 1)))
+
+/// Return true if format option 'x' is in effect.
+/// Take care of no formatting when 'paste' is set.
+bool has_format_option(int x)
+  FUNC_ATTR_PURE FUNC_ATTR_WARN_UNUSED_RESULT
+{
+  if (p_paste) {
+    return false;
+  }
+  return vim_strchr(curbuf->b_p_fo, x) != NULL;
+}
+
+/// Format text at the current insert position.
+///
+/// If the INSCHAR_COM_LIST flag is present, then the value of second_indent
+/// will be the comment leader length sent to open_line().
+///
+/// @param c  character to be inserted (can be NUL)
+void internal_format(int textwidth, int second_indent, int flags, bool format_only, int c)
+{
+  int cc;
+  int save_char = NUL;
+  bool haveto_redraw = false;
+  const bool fo_ins_blank = has_format_option(FO_INS_BLANK);
+  const bool fo_multibyte = has_format_option(FO_MBYTE_BREAK);
+  const bool fo_rigor_tw  = has_format_option(FO_RIGOROUS_TW);
+  const bool fo_white_par = has_format_option(FO_WHITE_PAR);
+  bool first_line = true;
+  colnr_T leader_len;
+  bool no_leader = false;
+  int do_comments = (flags & INSCHAR_DO_COM);
+  int has_lbr = curwin->w_p_lbr;
+
+  // make sure win_lbr_chartabsize() counts correctly
+  curwin->w_p_lbr = false;
+
+  // When 'ai' is off we don't want a space under the cursor to be
+  // deleted.  Replace it with an 'x' temporarily.
+  if (!curbuf->b_p_ai
+      && !(State & VREPLACE_FLAG)) {
+    cc = gchar_cursor();
+    if (ascii_iswhite(cc)) {
+      save_char = cc;
+      pchar_cursor('x');
+    }
+  }
+
+  // Repeat breaking lines, until the current line is not too long.
+  while (!got_int) {
+    int startcol;                       // Cursor column at entry
+    int wantcol;                        // column at textwidth border
+    int foundcol;                       // column for start of spaces
+    int end_foundcol = 0;               // column for start of word
+    colnr_T len;
+    colnr_T virtcol;
+    int orig_col = 0;
+    char_u *saved_text = NULL;
+    colnr_T col;
+    colnr_T end_col;
+    bool did_do_comment = false;
+
+    virtcol = get_nolist_virtcol()
+              + char2cells(c != NUL ? c : gchar_cursor());
+    if (virtcol <= (colnr_T)textwidth) {
+      break;
+    }
+
+    if (no_leader) {
+      do_comments = false;
+    } else if (!(flags & INSCHAR_FORMAT)
+               && has_format_option(FO_WRAP_COMS)) {
+      do_comments = true;
+    }
+
+    // Don't break until after the comment leader
+    if (do_comments) {
+      char_u *line = get_cursor_line_ptr();
+      leader_len = get_leader_len((char *)line, NULL, false, true);
+      if (leader_len == 0 && curbuf->b_p_cin) {
+        // Check for a line comment after code.
+        int comment_start = check_linecomment(line);
+        if (comment_start != MAXCOL) {
+          leader_len = get_leader_len((char *)line + comment_start, NULL, false, true);
+          if (leader_len != 0) {
+            leader_len += comment_start;
+          }
+        }
+      }
+    } else {
+      leader_len = 0;
+    }
+
+    // If the line doesn't start with a comment leader, then don't
+    // start one in a following broken line.  Avoids that a %word
+    // moved to the start of the next line causes all following lines
+    // to start with %.
+    if (leader_len == 0) {
+      no_leader = true;
+    }
+    if (!(flags & INSCHAR_FORMAT)
+        && leader_len == 0
+        && !has_format_option(FO_WRAP)) {
+      break;
+    }
+    if ((startcol = curwin->w_cursor.col) == 0) {
+      break;
+    }
+
+    // find column of textwidth border
+    coladvance((colnr_T)textwidth);
+    wantcol = curwin->w_cursor.col;
+
+    curwin->w_cursor.col = startcol;
+    foundcol = 0;
+    int skip_pos = 0;
+
+    // Find position to break at.
+    // Stop at first entered white when 'formatoptions' has 'v'
+    while ((!fo_ins_blank && !has_format_option(FO_INS_VI))
+           || (flags & INSCHAR_FORMAT)
+           || curwin->w_cursor.lnum != Insstart.lnum
+           || curwin->w_cursor.col >= Insstart.col) {
+      if (curwin->w_cursor.col == startcol && c != NUL) {
+        cc = c;
+      } else {
+        cc = gchar_cursor();
+      }
+      if (WHITECHAR(cc)) {
+        // remember position of blank just before text
+        end_col = curwin->w_cursor.col;
+
+        // find start of sequence of blanks
+        int wcc = 0;  // counter for whitespace chars
+        while (curwin->w_cursor.col > 0 && WHITECHAR(cc)) {
+          dec_cursor();
+          cc = gchar_cursor();
+
+          // Increment count of how many whitespace chars in this
+          // group; we only need to know if it's more than one.
+          if (wcc < 2) {
+            wcc++;
+          }
+        }
+        if (curwin->w_cursor.col == 0 && WHITECHAR(cc)) {
+          break;                        // only spaces in front of text
+        }
+
+        // Don't break after a period when 'formatoptions' has 'p' and
+        // there are less than two spaces.
+        if (has_format_option(FO_PERIOD_ABBR) && cc == '.' && wcc < 2) {
+          continue;
+        }
+
+        // Don't break until after the comment leader
+        if (curwin->w_cursor.col < leader_len) {
+          break;
+        }
+
+        if (has_format_option(FO_ONE_LETTER)) {
+          // do not break after one-letter words
+          if (curwin->w_cursor.col == 0) {
+            break;              // one-letter word at begin
+          }
+          // do not break "#a b" when 'tw' is 2
+          if (curwin->w_cursor.col <= leader_len) {
+            break;
+          }
+          col = curwin->w_cursor.col;
+          dec_cursor();
+          cc = gchar_cursor();
+
+          if (WHITECHAR(cc)) {
+            continue;                   // one-letter, continue
+          }
+          curwin->w_cursor.col = col;
+        }
+
+        inc_cursor();
+
+        end_foundcol = end_col + 1;
+        foundcol = curwin->w_cursor.col;
+        if (curwin->w_cursor.col <= (colnr_T)wantcol) {
+          break;
+        }
+      } else if ((cc >= 0x100 || !utf_allow_break_before(cc)) && fo_multibyte) {
+        int ncc;
+        bool allow_break;
+
+        // Break after or before a multi-byte character.
+        if (curwin->w_cursor.col != startcol) {
+          // Don't break until after the comment leader
+          if (curwin->w_cursor.col < leader_len) {
+            break;
+          }
+          col = curwin->w_cursor.col;
+          inc_cursor();
+          ncc = gchar_cursor();
+          allow_break = utf_allow_break(cc, ncc);
+
+          // If we have already checked this position, skip!
+          if (curwin->w_cursor.col != skip_pos && allow_break) {
+            foundcol = curwin->w_cursor.col;
+            end_foundcol = foundcol;
+            if (curwin->w_cursor.col <= (colnr_T)wantcol) {
+              break;
+            }
+          }
+          curwin->w_cursor.col = col;
+        }
+
+        if (curwin->w_cursor.col == 0) {
+          break;
+        }
+
+        ncc = cc;
+        col = curwin->w_cursor.col;
+
+        dec_cursor();
+        cc = gchar_cursor();
+
+        if (WHITECHAR(cc)) {
+          continue;                     // break with space
+        }
+        // Don't break until after the comment leader.
+        if (curwin->w_cursor.col < leader_len) {
+          break;
+        }
+
+        curwin->w_cursor.col = col;
+        skip_pos = curwin->w_cursor.col;
+
+        allow_break = utf_allow_break(cc, ncc);
+
+        // Must handle this to respect line break prohibition.
+        if (allow_break) {
+          foundcol = curwin->w_cursor.col;
+          end_foundcol = foundcol;
+        }
+        if (curwin->w_cursor.col <= (colnr_T)wantcol) {
+          const bool ncc_allow_break = utf_allow_break_before(ncc);
+
+          if (allow_break) {
+            break;
+          }
+          if (!ncc_allow_break && !fo_rigor_tw) {
+            // Enable at most 1 punct hang outside of textwidth.
+            if (curwin->w_cursor.col == startcol) {
+              // We are inserting a non-breakable char, postpone
+              // line break check to next insert.
+              end_foundcol = foundcol = 0;
+              break;
+            }
+
+            // Neither cc nor ncc is NUL if we are here, so
+            // it's safe to inc_cursor.
+            col = curwin->w_cursor.col;
+
+            inc_cursor();
+            cc  = ncc;
+            ncc = gchar_cursor();
+            // handle insert
+            ncc = (ncc != NUL) ? ncc : c;
+
+            allow_break = utf_allow_break(cc, ncc);
+
+            if (allow_break) {
+              // Break only when we are not at end of line.
+              end_foundcol = foundcol = ncc == NUL? 0 : curwin->w_cursor.col;
+              break;
+            }
+            curwin->w_cursor.col = col;
+          }
+        }
+      }
+      if (curwin->w_cursor.col == 0) {
+        break;
+      }
+      dec_cursor();
+    }
+
+    if (foundcol == 0) {                // no spaces, cannot break line
+      curwin->w_cursor.col = startcol;
+      break;
+    }
+
+    // Going to break the line, remove any "$" now.
+    undisplay_dollar();
+
+    // Offset between cursor position and line break is used by replace
+    // stack functions.  MODE_VREPLACE does not use this, and backspaces
+    // over the text instead.
+    if (State & VREPLACE_FLAG) {
+      orig_col = startcol;              // Will start backspacing from here
+    } else {
+      replace_offset = startcol - end_foundcol;
+    }
+
+    // adjust startcol for spaces that will be deleted and
+    // characters that will remain on top line
+    curwin->w_cursor.col = foundcol;
+    while ((cc = gchar_cursor(), WHITECHAR(cc))
+           && (!fo_white_par || curwin->w_cursor.col < startcol)) {
+      inc_cursor();
+    }
+    startcol -= curwin->w_cursor.col;
+    if (startcol < 0) {
+      startcol = 0;
+    }
+
+    if (State & VREPLACE_FLAG) {
+      // In MODE_VREPLACE state, we will backspace over the text to be
+      // wrapped, so save a copy now to put on the next line.
+      saved_text = vim_strsave(get_cursor_pos_ptr());
+      curwin->w_cursor.col = orig_col;
+      saved_text[startcol] = NUL;
+
+      // Backspace over characters that will move to the next line
+      if (!fo_white_par) {
+        backspace_until_column(foundcol);
+      }
+    } else {
+      // put cursor after pos. to break line
+      if (!fo_white_par) {
+        curwin->w_cursor.col = foundcol;
+      }
+    }
+
+    // Split the line just before the margin.
+    // Only insert/delete lines, but don't really redraw the window.
+    open_line(FORWARD, OPENLINE_DELSPACES + OPENLINE_MARKFIX
+              + (fo_white_par ? OPENLINE_KEEPTRAIL : 0)
+              + (do_comments ? OPENLINE_DO_COM : 0)
+              + OPENLINE_FORMAT
+              + ((flags & INSCHAR_COM_LIST) ? OPENLINE_COM_LIST : 0),
+              ((flags & INSCHAR_COM_LIST) ? second_indent : old_indent),
+              &did_do_comment);
+    if (!(flags & INSCHAR_COM_LIST)) {
+      old_indent = 0;
+    }
+
+    // If a comment leader was inserted, may also do this on a following
+    // line.
+    if (did_do_comment) {
+      no_leader = false;
+    }
+
+    replace_offset = 0;
+    if (first_line) {
+      if (!(flags & INSCHAR_COM_LIST)) {
+        // This section is for auto-wrap of numeric lists.  When not
+        // in insert mode (i.e. format_lines()), the INSCHAR_COM_LIST
+        // flag will be set and open_line() will handle it (as seen
+        // above).  The code here (and in get_number_indent()) will
+        // recognize comments if needed...
+        if (second_indent < 0 && has_format_option(FO_Q_NUMBER)) {
+          second_indent = get_number_indent(curwin->w_cursor.lnum - 1);
+        }
+        if (second_indent >= 0) {
+          if (State & VREPLACE_FLAG) {
+            change_indent(INDENT_SET, second_indent, false, NUL, true);
+          } else if (leader_len > 0 && second_indent - leader_len > 0) {
+            int padding = second_indent - leader_len;
+
+            // We started at the first_line of a numbered list
+            // that has a comment.  the open_line() function has
+            // inserted the proper comment leader and positioned
+            // the cursor at the end of the split line.  Now we
+            // add the additional whitespace needed after the
+            // comment leader for the numbered list.
+            for (int i = 0; i < padding; i++) {
+              ins_str((char_u *)" ");
+            }
+            changed_bytes(curwin->w_cursor.lnum, leader_len);
+          } else {
+            (void)set_indent(second_indent, SIN_CHANGED);
+          }
+        }
+      }
+      first_line = false;
+    }
+
+    if (State & VREPLACE_FLAG) {
+      // In MODE_VREPLACE state we have backspaced over the text to be
+      // moved, now we re-insert it into the new line.
+      ins_bytes((char *)saved_text);
+      xfree(saved_text);
+    } else {
+      // Check if cursor is not past the NUL off the line, cindent
+      // may have added or removed indent.
+      curwin->w_cursor.col += startcol;
+      len = (colnr_T)STRLEN(get_cursor_line_ptr());
+      if (curwin->w_cursor.col > len) {
+        curwin->w_cursor.col = len;
+      }
+    }
+
+    haveto_redraw = true;
+    set_can_cindent(true);
+    // moved the cursor, don't autoindent or cindent now
+    did_ai = false;
+    did_si = false;
+    can_si = false;
+    can_si_back = false;
+    line_breakcheck();
+  }
+
+  if (save_char != NUL) {               // put back space after cursor
+    pchar_cursor((char_u)save_char);
+  }
+
+  curwin->w_p_lbr = has_lbr;
+
+  if (!format_only && haveto_redraw) {
+    update_topline(curwin);
+    redraw_curbuf_later(UPD_VALID);
+  }
+}
+
+/// Blank lines, and lines containing only the comment leader, are left
+/// untouched by the formatting.  The function returns true in this
+/// case.  It also returns true when a line starts with the end of a comment
+/// ('e' in comment flags), so that this line is skipped, and not joined to the
+/// previous line.  A new paragraph starts after a blank line, or when the
+/// comment leader changes.
+static int fmt_check_par(linenr_T lnum, int *leader_len, char_u **leader_flags, bool do_comments)
+{
+  char_u *flags = NULL;        // init for GCC
+  char_u *ptr;
+
+  ptr = ml_get(lnum);
+  if (do_comments) {
+    *leader_len = get_leader_len((char *)ptr, (char **)leader_flags, false, true);
+  } else {
+    *leader_len = 0;
+  }
+
+  if (*leader_len > 0) {
+    // Search for 'e' flag in comment leader flags.
+    flags = *leader_flags;
+    while (*flags && *flags != ':' && *flags != COM_END) {
+      flags++;
+    }
+  }
+
+  return *skipwhite((char *)ptr + *leader_len) == NUL
+         || (*leader_len > 0 && *flags == COM_END)
+         || startPS(lnum, NUL, false);
+}
+
+/// @return  true if line "lnum" ends in a white character.
+static bool ends_in_white(linenr_T lnum)
+{
+  char_u *s = ml_get(lnum);
+  size_t l;
+
+  if (*s == NUL) {
+    return false;
+  }
+  l = STRLEN(s) - 1;
+  return ascii_iswhite(s[l]);
+}
+
+/// @return  true if the two comment leaders given are the same.
+///
+/// @param lnum  The first line.  White-space is ignored.
+///
+/// @note the whole of 'leader1' must match 'leader2_len' characters from 'leader2'.
+static bool same_leader(linenr_T lnum, int leader1_len, char_u *leader1_flags, int leader2_len,
+                        char_u *leader2_flags)
+{
+  int idx1 = 0, idx2 = 0;
+  char_u *p;
+  char_u *line1;
+  char_u *line2;
+
+  if (leader1_len == 0) {
+    return leader2_len == 0;
+  }
+
+  // If first leader has 'f' flag, the lines can be joined only if the
+  // second line does not have a leader.
+  // If first leader has 'e' flag, the lines can never be joined.
+  // If first leader has 's' flag, the lines can only be joined if there is
+  // some text after it and the second line has the 'm' flag.
+  if (leader1_flags != NULL) {
+    for (p = leader1_flags; *p && *p != ':'; p++) {
+      if (*p == COM_FIRST) {
+        return leader2_len == 0;
+      }
+      if (*p == COM_END) {
+        return false;
+      }
+      if (*p == COM_START) {
+        if (*(ml_get(lnum) + leader1_len) == NUL) {
+          return false;
+        }
+        if (leader2_flags == NULL || leader2_len == 0) {
+          return false;
+        }
+        for (p = leader2_flags; *p && *p != ':'; p++) {
+          if (*p == COM_MIDDLE) {
+            return true;
+          }
+        }
+        return false;
+      }
+    }
+  }
+
+  // Get current line and next line, compare the leaders.
+  // The first line has to be saved, only one line can be locked at a time.
+  line1 = vim_strsave(ml_get(lnum));
+  for (idx1 = 0; ascii_iswhite(line1[idx1]); idx1++) {}
+  line2 = ml_get(lnum + 1);
+  for (idx2 = 0; idx2 < leader2_len; idx2++) {
+    if (!ascii_iswhite(line2[idx2])) {
+      if (line1[idx1++] != line2[idx2]) {
+        break;
+      }
+    } else {
+      while (ascii_iswhite(line1[idx1])) {
+        idx1++;
+      }
+    }
+  }
+  xfree(line1);
+
+  return idx2 == leader2_len && idx1 == leader1_len;
+}
+
+/// Used for auto-formatting.
+///
+/// @return  true when a paragraph starts in line "lnum".
+///          false when the previous line is in the same paragraph.
+static bool paragraph_start(linenr_T lnum)
+{
+  char_u *p;
+  int leader_len = 0;                // leader len of current line
+  char_u *leader_flags = NULL;       // flags for leader of current line
+  int next_leader_len = 0;           // leader len of next line
+  char_u *next_leader_flags = NULL;  // flags for leader of next line
+
+  if (lnum <= 1) {
+    return true;                // start of the file
+  }
+  p = ml_get(lnum - 1);
+  if (*p == NUL) {
+    return true;                // after empty line
+  }
+  const bool do_comments = has_format_option(FO_Q_COMS);  // format comments
+  if (fmt_check_par(lnum - 1, &leader_len, &leader_flags, do_comments)) {
+    return true;  // after non-paragraph line
+  }
+
+  if (fmt_check_par(lnum, &next_leader_len, &next_leader_flags, do_comments)) {
+    return true;  // "lnum" is not a paragraph line
+  }
+
+  if (has_format_option(FO_WHITE_PAR) && !ends_in_white(lnum - 1)) {
+    return true;                // missing trailing space in previous line.
+  }
+  if (has_format_option(FO_Q_NUMBER) && (get_number_indent(lnum) > 0)) {
+    return true;                // numbered item starts in "lnum".
+  }
+  if (!same_leader(lnum - 1, leader_len, leader_flags,
+                   next_leader_len, next_leader_flags)) {
+    return true;                // change of comment leader.
+  }
+  return false;
+}
+
+/// Called after inserting or deleting text: When 'formatoptions' includes the
+/// 'a' flag format from the current line until the end of the paragraph.
+/// Keep the cursor at the same position relative to the text.
+/// The caller must have saved the cursor line for undo, following ones will be
+/// saved here.
+///
+/// @param trailblank  when true also format with trailing blank
+/// @param prev_line   may start in previous line
+void auto_format(bool trailblank, bool prev_line)
+{
+  pos_T pos;
+  colnr_T len;
+  char_u *old;
+  char_u *new, *pnew;
+  int wasatend;
+  int cc;
+
+  if (!has_format_option(FO_AUTO)) {
+    return;
+  }
+
+  pos = curwin->w_cursor;
+  old = get_cursor_line_ptr();
+
+  // may remove added space
+  check_auto_format(false);
+
+  // Don't format in Insert mode when the cursor is on a trailing blank, the
+  // user might insert normal text next.  Also skip formatting when "1" is
+  // in 'formatoptions' and there is a single character before the cursor.
+  // Otherwise the line would be broken and when typing another non-white
+  // next they are not joined back together.
+  wasatend = (pos.col == (colnr_T)STRLEN(old));
+  if (*old != NUL && !trailblank && wasatend) {
+    dec_cursor();
+    cc = gchar_cursor();
+    if (!WHITECHAR(cc) && curwin->w_cursor.col > 0
+        && has_format_option(FO_ONE_LETTER)) {
+      dec_cursor();
+    }
+    cc = gchar_cursor();
+    if (WHITECHAR(cc)) {
+      curwin->w_cursor = pos;
+      return;
+    }
+    curwin->w_cursor = pos;
+  }
+
+  // With the 'c' flag in 'formatoptions' and 't' missing: only format
+  // comments.
+  if (has_format_option(FO_WRAP_COMS) && !has_format_option(FO_WRAP)
+      && get_leader_len((char *)old, NULL, false, true) == 0) {
+    return;
+  }
+
+  // May start formatting in a previous line, so that after "x" a word is
+  // moved to the previous line if it fits there now.  Only when this is not
+  // the start of a paragraph.
+  if (prev_line && !paragraph_start(curwin->w_cursor.lnum)) {
+    curwin->w_cursor.lnum--;
+    if (u_save_cursor() == FAIL) {
+      return;
+    }
+  }
+
+  // Do the formatting and restore the cursor position.  "saved_cursor" will
+  // be adjusted for the text formatting.
+  saved_cursor = pos;
+  format_lines((linenr_T) - 1, false);
+  curwin->w_cursor = saved_cursor;
+  saved_cursor.lnum = 0;
+
+  if (curwin->w_cursor.lnum > curbuf->b_ml.ml_line_count) {
+    // "cannot happen"
+    curwin->w_cursor.lnum = curbuf->b_ml.ml_line_count;
+    coladvance(MAXCOL);
+  } else {
+    check_cursor_col();
+  }
+
+  // Insert mode: If the cursor is now after the end of the line while it
+  // previously wasn't, the line was broken.  Because of the rule above we
+  // need to add a space when 'w' is in 'formatoptions' to keep a paragraph
+  // formatted.
+  if (!wasatend && has_format_option(FO_WHITE_PAR)) {
+    new = get_cursor_line_ptr();
+    len = (colnr_T)STRLEN(new);
+    if (curwin->w_cursor.col == len) {
+      pnew = vim_strnsave(new, (size_t)len + 2);
+      pnew[len] = ' ';
+      pnew[len + 1] = NUL;
+      ml_replace(curwin->w_cursor.lnum, (char *)pnew, false);
+      // remove the space later
+      did_add_space = true;
+    } else {
+      // may remove added space
+      check_auto_format(false);
+    }
+  }
+
+  check_cursor();
+}
+
+/// When an extra space was added to continue a paragraph for auto-formatting,
+/// delete it now.  The space must be under the cursor, just after the insert
+/// position.
+///
+/// @param end_insert  true when ending Insert mode
+void check_auto_format(bool end_insert)
+{
+  int c = ' ';
+  int cc;
+
+  if (did_add_space) {
+    cc = gchar_cursor();
+    if (!WHITECHAR(cc)) {
+      // Somehow the space was removed already.
+      did_add_space = false;
+    } else {
+      if (!end_insert) {
+        inc_cursor();
+        c = gchar_cursor();
+        dec_cursor();
+      }
+      if (c != NUL) {
+        // The space is no longer at the end of the line, delete it.
+        del_char(false);
+        did_add_space = false;
+      }
+    }
+  }
+}
+
+/// Find out textwidth to be used for formatting:
+///      if 'textwidth' option is set, use it
+///      else if 'wrapmargin' option is set, use curwin->w_width_inner-'wrapmargin'
+///      if invalid value, use 0.
+///      Set default to window width (maximum 79) for "gq" operator.
+///
+/// @param ff  force formatting (for "gq" command)
+int comp_textwidth(bool ff)
+{
+  int textwidth = (int)curbuf->b_p_tw;
+  if (textwidth == 0 && curbuf->b_p_wm) {
+    // The width is the window width minus 'wrapmargin' minus all the
+    // things that add to the margin.
+    textwidth = curwin->w_width_inner - (int)curbuf->b_p_wm;
+    if (cmdwin_type != 0) {
+      textwidth -= 1;
+    }
+    textwidth -= win_fdccol_count(curwin);
+    textwidth -= win_signcol_count(curwin);
+
+    if (curwin->w_p_nu || curwin->w_p_rnu) {
+      textwidth -= 8;
+    }
+  }
+  if (textwidth < 0) {
+    textwidth = 0;
+  }
+  if (ff && textwidth == 0) {
+    textwidth = curwin->w_width_inner - 1;
+    if (textwidth > 79) {
+      textwidth = 79;
+    }
+  }
+  return textwidth;
+}
+
+/// Implementation of the format operator 'gq'.
+///
+/// @param keep_cursor  keep cursor on same text char
+void op_format(oparg_T *oap, bool keep_cursor)
+{
+  linenr_T old_line_count = curbuf->b_ml.ml_line_count;
+
+  // Place the cursor where the "gq" or "gw" command was given, so that "u"
+  // can put it back there.
+  curwin->w_cursor = oap->cursor_start;
+
+  if (u_save((linenr_T)(oap->start.lnum - 1),
+             (linenr_T)(oap->end.lnum + 1)) == FAIL) {
+    return;
+  }
+  curwin->w_cursor = oap->start;
+
+  if (oap->is_VIsual) {
+    // When there is no change: need to remove the Visual selection
+    redraw_curbuf_later(UPD_INVERTED);
+  }
+
+  if ((cmdmod.cmod_flags & CMOD_LOCKMARKS) == 0) {
+    // Set '[ mark at the start of the formatted area
+    curbuf->b_op_start = oap->start;
+  }
+
+  // For "gw" remember the cursor position and put it back below (adjusted
+  // for joined and split lines).
+  if (keep_cursor) {
+    saved_cursor = oap->cursor_start;
+  }
+
+  format_lines((linenr_T)oap->line_count, keep_cursor);
+
+  // Leave the cursor at the first non-blank of the last formatted line.
+  // If the cursor was moved one line back (e.g. with "Q}") go to the next
+  // line, so "." will do the next lines.
+  if (oap->end_adjusted && curwin->w_cursor.lnum < curbuf->b_ml.ml_line_count) {
+    curwin->w_cursor.lnum++;
+  }
+  beginline(BL_WHITE | BL_FIX);
+  old_line_count = curbuf->b_ml.ml_line_count - old_line_count;
+  msgmore(old_line_count);
+
+  if ((cmdmod.cmod_flags & CMOD_LOCKMARKS) == 0) {
+    // put '] mark on the end of the formatted area
+    curbuf->b_op_end = curwin->w_cursor;
+  }
+
+  if (keep_cursor) {
+    curwin->w_cursor = saved_cursor;
+    saved_cursor.lnum = 0;
+
+    // formatting may have made the cursor position invalid
+    check_cursor();
+  }
+
+  if (oap->is_VIsual) {
+    FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
+      if (wp->w_old_cursor_lnum != 0) {
+        // When lines have been inserted or deleted, adjust the end of
+        // the Visual area to be redrawn.
+        if (wp->w_old_cursor_lnum > wp->w_old_visual_lnum) {
+          wp->w_old_cursor_lnum += old_line_count;
+        } else {
+          wp->w_old_visual_lnum += old_line_count;
+        }
+      }
+    }
+  }
+}
+
+/// Implementation of the format operator 'gq' for when using 'formatexpr'.
+void op_formatexpr(oparg_T *oap)
+{
+  if (oap->is_VIsual) {
+    // When there is no change: need to remove the Visual selection
+    redraw_curbuf_later(UPD_INVERTED);
+  }
+
+  if (fex_format(oap->start.lnum, oap->line_count, NUL) != 0) {
+    // As documented: when 'formatexpr' returns non-zero fall back to
+    // internal formatting.
+    op_format(oap, false);
+  }
+}
+
+/// @param c  character to be inserted
+int fex_format(linenr_T lnum, long count, int c)
+{
+  int use_sandbox = was_set_insecurely(curwin, "formatexpr", OPT_LOCAL);
+  int r;
+
+  // Set v:lnum to the first line number and v:count to the number of lines.
+  // Set v:char to the character to be inserted (can be NUL).
+  set_vim_var_nr(VV_LNUM, (varnumber_T)lnum);
+  set_vim_var_nr(VV_COUNT, (varnumber_T)count);
+  set_vim_var_char(c);
+
+  // Make a copy, the option could be changed while calling it.
+  char *fex = xstrdup(curbuf->b_p_fex);
+  // Evaluate the function.
+  if (use_sandbox) {
+    sandbox++;
+  }
+  r = (int)eval_to_number(fex);
+  if (use_sandbox) {
+    sandbox--;
+  }
+
+  set_vim_var_string(VV_CHAR, NULL, -1);
+  xfree(fex);
+
+  return r;
+}
+
+/// @param line_count  number of lines to format, starting at the cursor position.
+///                    when negative, format until the end of the paragraph.
+///
+/// Lines after the cursor line are saved for undo, caller must have saved the
+/// first line.
+///
+/// @param avoid_fex  don't use 'formatexpr'
+void format_lines(linenr_T line_count, bool avoid_fex)
+{
+  bool is_not_par;                  // current line not part of parag.
+  bool next_is_not_par;             // next line not part of paragraph
+  bool is_end_par;                  // at end of paragraph
+  bool prev_is_end_par = false;     // prev. line not part of parag.
+  bool next_is_start_par = false;
+  int leader_len = 0;               // leader len of current line
+  int next_leader_len;              // leader len of next line
+  char_u *leader_flags = NULL;      // flags for leader of current line
+  char_u *next_leader_flags = NULL;  // flags for leader of next line
+  bool advance = true;
+  int second_indent = -1;           // indent for second line (comment aware)
+  bool first_par_line = true;
+  int smd_save;
+  long count;
+  bool need_set_indent = true;      // set indent of next paragraph
+  linenr_T first_line = curwin->w_cursor.lnum;
+  bool force_format = false;
+  const int old_State = State;
+
+  // length of a line to force formatting: 3 * 'tw'
+  const int max_len = comp_textwidth(true) * 3;
+
+  // check for 'q', '2' and '1' in 'formatoptions'
+  const bool do_comments = has_format_option(FO_Q_COMS);  // format comments
+  int do_comments_list = 0;  // format comments with 'n' or '2'
+  const bool do_second_indent = has_format_option(FO_Q_SECOND);
+  const bool do_number_indent = has_format_option(FO_Q_NUMBER);
+  const bool do_trail_white = has_format_option(FO_WHITE_PAR);
+
+  // Get info about the previous and current line.
+  if (curwin->w_cursor.lnum > 1) {
+    is_not_par = fmt_check_par(curwin->w_cursor.lnum - 1,
+                               &leader_len, &leader_flags, do_comments);
+  } else {
+    is_not_par = true;
+  }
+  next_is_not_par = fmt_check_par(curwin->w_cursor.lnum,
+                                  &next_leader_len, &next_leader_flags, do_comments);
+  is_end_par = (is_not_par || next_is_not_par);
+  if (!is_end_par && do_trail_white) {
+    is_end_par = !ends_in_white(curwin->w_cursor.lnum - 1);
+  }
+
+  curwin->w_cursor.lnum--;
+  for (count = line_count; count != 0 && !got_int; count--) {
+    // Advance to next paragraph.
+    if (advance) {
+      curwin->w_cursor.lnum++;
+      prev_is_end_par = is_end_par;
+      is_not_par = next_is_not_par;
+      leader_len = next_leader_len;
+      leader_flags = next_leader_flags;
+    }
+
+    // The last line to be formatted.
+    if (count == 1 || curwin->w_cursor.lnum == curbuf->b_ml.ml_line_count) {
+      next_is_not_par = true;
+      next_leader_len = 0;
+      next_leader_flags = NULL;
+    } else {
+      next_is_not_par = fmt_check_par(curwin->w_cursor.lnum + 1,
+                                      &next_leader_len, &next_leader_flags, do_comments);
+      if (do_number_indent) {
+        next_is_start_par =
+          (get_number_indent(curwin->w_cursor.lnum + 1) > 0);
+      }
+    }
+    advance = true;
+    is_end_par = (is_not_par || next_is_not_par || next_is_start_par);
+    if (!is_end_par && do_trail_white) {
+      is_end_par = !ends_in_white(curwin->w_cursor.lnum);
+    }
+
+    // Skip lines that are not in a paragraph.
+    if (is_not_par) {
+      if (line_count < 0) {
+        break;
+      }
+    } else {
+      // For the first line of a paragraph, check indent of second line.
+      // Don't do this for comments and empty lines.
+      if (first_par_line
+          && (do_second_indent || do_number_indent)
+          && prev_is_end_par
+          && curwin->w_cursor.lnum < curbuf->b_ml.ml_line_count) {
+        if (do_second_indent && !LINEEMPTY(curwin->w_cursor.lnum + 1)) {
+          if (leader_len == 0 && next_leader_len == 0) {
+            // no comment found
+            second_indent =
+              get_indent_lnum(curwin->w_cursor.lnum + 1);
+          } else {
+            second_indent = next_leader_len;
+            do_comments_list = 1;
+          }
+        } else if (do_number_indent) {
+          if (leader_len == 0 && next_leader_len == 0) {
+            // no comment found
+            second_indent =
+              get_number_indent(curwin->w_cursor.lnum);
+          } else {
+            // get_number_indent() is now "comment aware"...
+            second_indent =
+              get_number_indent(curwin->w_cursor.lnum);
+            do_comments_list = 1;
+          }
+        }
+      }
+
+      // When the comment leader changes, it's the end of the paragraph.
+      if (curwin->w_cursor.lnum >= curbuf->b_ml.ml_line_count
+          || !same_leader(curwin->w_cursor.lnum,
+                          leader_len, leader_flags,
+                          next_leader_len,
+                          next_leader_flags)) {
+        // Special case: If the next line starts with a line comment
+        // and this line has a line comment after some text, the
+        // paragraph doesn't really end.
+        if (next_leader_flags == NULL
+            || STRNCMP(next_leader_flags, "://", 3) != 0
+            || check_linecomment(get_cursor_line_ptr()) == MAXCOL) {
+          is_end_par = true;
+        }
+      }
+
+      // If we have got to the end of a paragraph, or the line is
+      // getting long, format it.
+      if (is_end_par || force_format) {
+        if (need_set_indent) {
+          int indent = 0;  // amount of indent needed
+
+          // Replace indent in first line of a paragraph with minimal
+          // number of tabs and spaces, according to current options.
+          // For the very first formatted line keep the current
+          // indent.
+          if (curwin->w_cursor.lnum == first_line) {
+            indent = get_indent();
+          } else if (curbuf->b_p_lisp) {
+            indent = get_lisp_indent();
+          } else {
+            if (cindent_on()) {
+              indent = *curbuf->b_p_inde != NUL ? get_expr_indent() : get_c_indent();
+            } else {
+              indent = get_indent();
+            }
+          }
+          (void)set_indent(indent, SIN_CHANGED);
+        }
+
+        // put cursor on last non-space
+        State = MODE_NORMAL;  // don't go past end-of-line
+        coladvance(MAXCOL);
+        while (curwin->w_cursor.col && ascii_isspace(gchar_cursor())) {
+          dec_cursor();
+        }
+
+        // do the formatting, without 'showmode'
+        State = MODE_INSERT;         // for open_line()
+        smd_save = p_smd;
+        p_smd = false;
+        insertchar(NUL, INSCHAR_FORMAT
+                   + (do_comments ? INSCHAR_DO_COM : 0)
+                   + (do_comments && do_comments_list ? INSCHAR_COM_LIST : 0)
+                   + (avoid_fex ? INSCHAR_NO_FEX : 0), second_indent);
+        State = old_State;
+        p_smd = smd_save;
+        second_indent = -1;
+        // at end of par.: need to set indent of next par.
+        need_set_indent = is_end_par;
+        if (is_end_par) {
+          // When called with a negative line count, break at the
+          // end of the paragraph.
+          if (line_count < 0) {
+            break;
+          }
+          first_par_line = true;
+        }
+        force_format = false;
+      }
+
+      // When still in same paragraph, join the lines together.  But
+      // first delete the leader from the second line.
+      if (!is_end_par) {
+        advance = false;
+        curwin->w_cursor.lnum++;
+        curwin->w_cursor.col = 0;
+        if (line_count < 0 && u_save_cursor() == FAIL) {
+          break;
+        }
+        if (next_leader_len > 0) {
+          (void)del_bytes(next_leader_len, false, false);
+          mark_col_adjust(curwin->w_cursor.lnum, (colnr_T)0, 0L,
+                          (long)-next_leader_len, 0);
+        } else if (second_indent > 0) {   // the "leader" for FO_Q_SECOND
+          int indent = (int)getwhitecols_curline();
+
+          if (indent > 0) {
+            (void)del_bytes(indent, false, false);
+            mark_col_adjust(curwin->w_cursor.lnum,
+                            (colnr_T)0, 0L, (long)-indent, 0);
+          }
+        }
+        curwin->w_cursor.lnum--;
+        if (do_join(2, true, false, false, false) == FAIL) {
+          beep_flush();
+          break;
+        }
+        first_par_line = false;
+        // If the line is getting long, format it next time
+        if (STRLEN(get_cursor_line_ptr()) > (size_t)max_len) {
+          force_format = true;
+        } else {
+          force_format = false;
+        }
+      }
+    }
+    line_breakcheck();
+  }
+}
diff --git a/src/nvim/textformat.h b/src/nvim/textformat.h
new file mode 100644
index 0000000000..9d8327e6eb
--- /dev/null
+++ b/src/nvim/textformat.h
@@ -0,0 +1,12 @@
+#ifndef NVIM_TEXTFORMAT_H
+#define NVIM_TEXTFORMAT_H
+
+#include <stdbool.h>
+
+#include "nvim/normal.h"  // for oparg_T
+#include "nvim/pos.h"  // for linenr_T
+
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "textformat.h.generated.h"
+#endif
+#endif  // NVIM_TEXTFORMAT_H