'inccommand': rework

- Eliminate/isolate static/global variables
- Remove special-case parameter from buflist_new()
- Remove special-case ECMD_RESERVED_BUFNR
- To determine when u_undo_and_forget() should be done, check
  b_changedtick instead of a heuristic.
- use mb_string2cells() instead of strlen() to measure the :sub patterns
- call ml_close() before buf_clear_file(). Avoids leaks caught by ASan.

Original patch by:
  Robin Elrharbi-Fleury (Robinhola)
  Audrey Rayé (Adrey06)
  Philémon Hullot (DesbyP)
  Aymeric Collange (aym7)
  Clément Guyomard (Clement0)

17 files changed, 335 insertions, 409 deletions

diff --git a/src/nvim/buffer.c b/src/nvim/buffer.c
index 65a42f063a..190c281c76 100644
--- a/src/nvim/buffer.c
+++ b/src/nvim/buffer.c
@@ -268,6 +268,9 @@ open_buffer (
 bool buf_valid(buf_T *buf)
   FUNC_ATTR_PURE FUNC_ATTR_WARN_UNUSED_RESULT
 {
+  if (buf == NULL) {
+    return false;
+  }
   FOR_ALL_BUFFERS(bp) {
     if (bp == buf) {
       return true;
@@ -479,6 +482,18 @@ void buf_clear_file(buf_T *buf)
   buf->b_ml.ml_flags = ML_EMPTY;                /* empty buffer */
 }
 
+/// Clears the current buffer contents.
+void buf_clear(void)
+{
+  linenr_T line_count = curbuf->b_ml.ml_line_count;
+  while (!(curbuf->b_ml.ml_flags & ML_EMPTY)) {
+    ml_delete((linenr_T)1, false);
+  }
+  deleted_lines_mark(1, line_count);  // prepare for display
+  ml_close(curbuf, true);             // free memline_T
+  buf_clear_file(curbuf);
+}
+
 /// buf_freeall() - free all things allocated for a buffer that are related to
 /// the file.  Careful: get here with "curwin" NULL when exiting.
 ///
@@ -678,7 +693,7 @@ void handle_swap_exists(buf_T *old_curbuf)
     swap_exists_did_quit = true;
     close_buffer(curwin, curbuf, DOBUF_UNLOAD, false);
     if (!buf_valid(old_curbuf) || old_curbuf == curbuf) {
-      old_curbuf = buflist_new(NULL, NULL, 1L, BLN_CURBUF | BLN_LISTED, 0);
+      old_curbuf = buflist_new(NULL, NULL, 1L, BLN_CURBUF | BLN_LISTED);
     }
     if (old_curbuf != NULL) {
       enter_buffer(old_curbuf);
@@ -1320,29 +1335,29 @@ void do_autochdir(void)
   }
 }
 
-/*
- * functions for dealing with the buffer list
- */
+//
+// functions for dealing with the buffer list
+//
 
-/*
- * Add a file name to the buffer list.  Return a pointer to the buffer.
- * If the same file name already exists return a pointer to that buffer.
- * If it does not exist, or if fname == NULL, a new entry is created.
- * If (flags & BLN_CURBUF) is TRUE, may use current buffer.
- * If (flags & BLN_LISTED) is TRUE, add new buffer to buffer list.
- * If (flags & BLN_DUMMY) is TRUE, don't count it as a real buffer.
- * This is the ONLY way to create a new buffer.
- */
 static int top_file_num = 1;            /* highest file number */
 
-buf_T *
-buflist_new(
-    char_u *ffname,            // full path of fname or relative
-    char_u *sfname,            // short fname or NULL
-    linenr_T lnum,             // preferred cursor line
-    int flags,                 // BLN_ defines
-    handle_T bufnr
-)
+/// Add a file name to the buffer list.
+/// If the same file name already exists return a pointer to that buffer.
+/// If it does not exist, or if fname == NULL, a new entry is created.
+/// If (flags & BLN_CURBUF) is TRUE, may use current buffer.
+/// If (flags & BLN_LISTED) is TRUE, add new buffer to buffer list.
+/// If (flags & BLN_DUMMY) is TRUE, don't count it as a real buffer.
+/// If (flags & BLN_NEW) is TRUE, don't use an existing buffer.
+/// This is the ONLY way to create a new buffer.
+///
+/// @param ffname full path of fname or relative
+/// @param sfname short fname or NULL
+/// @param lnum   preferred cursor line
+/// @param flags  BLN_ defines
+/// @param bufnr
+///
+/// @return pointer to the buffer
+buf_T * buflist_new(char_u *ffname, char_u *sfname, linenr_T lnum, int flags)
 {
   buf_T       *buf;
 
@@ -1460,9 +1475,7 @@ buflist_new(
     }
     lastbuf = buf;
 
-    // If bufnr is nonzero it is assumed to be a previously
-    // reserved buffer number (handle)
-    buf->handle = bufnr != 0 ? bufnr : top_file_num++;
+    buf->b_fnum = top_file_num++;
     handle_register_buffer(buf);
     if (top_file_num < 0) {  // wrap around (may cause duplicates)
       EMSG(_("W14: Warning: List of file names overflow"));
@@ -2379,7 +2392,7 @@ buf_T *setaltfname(char_u *ffname, char_u *sfname, linenr_T lnum)
   buf_T       *buf;
 
   // Create a buffer.  'buflisted' is not set if it's a new buffer
-  buf = buflist_new(ffname, sfname, lnum, 0, 0);
+  buf = buflist_new(ffname, sfname, lnum, 0);
   if (buf != NULL && !cmdmod.keepalt) {
     curwin->w_alt_fnum = buf->b_fnum;
   }
@@ -2416,7 +2429,7 @@ int buflist_add(char_u *fname, int flags)
 {
   buf_T       *buf;
 
-  buf = buflist_new(fname, NULL, (linenr_T)0, flags, 0);
+  buf = buflist_new(fname, NULL, (linenr_T)0, flags);
   if (buf != NULL) {
     return buf->b_fnum;
   }
@@ -5199,7 +5212,7 @@ bool buf_contents_changed(buf_T *buf)
   bool differ = true;
 
   // Allocate a buffer without putting it in the buffer list.
-  buf_T *newbuf = buflist_new(NULL, NULL, (linenr_T)1, BLN_DUMMY, 0);
+  buf_T *newbuf = buflist_new(NULL, NULL, (linenr_T)1, BLN_DUMMY);
   if (newbuf == NULL) {
     return true;
   }
@@ -5259,3 +5272,15 @@ wipe_buffer (
     unblock_autocmds();
   }
 }
+
+/// Creates or switches to a special-purpose buffer.
+///
+/// @param bufnr     Buffer to switch to, or 0 to create a new buffer.
+void buf_open_special(handle_T bufnr, char *bufname, char *buftype)
+{
+  (void)do_ecmd((int)bufnr, NULL, NULL, NULL, ECMD_ONE, ECMD_HIDE, NULL);
+  (void)setfname(curbuf, (char_u *)bufname, NULL, true);
+  set_option_value((char_u *)"bt", 0L, (char_u *)buftype, OPT_LOCAL);
+  set_option_value((char_u *)"swf", 0L, NULL, OPT_LOCAL);
+  RESET_BINDING(curwin);
+}
diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index 508bdac46d..512555eac1 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -7703,7 +7703,7 @@ static void f_bufnr(typval_T *argvars, typval_T *rettv, FunPtr fptr)
       && !error
       && (name = get_tv_string_chk(&argvars[0])) != NULL
       && !error)
-    buf = buflist_new(name, NULL, (linenr_T)1, 0, 0);
+    buf = buflist_new(name, NULL, (linenr_T)1, 0);
 
   if (buf != NULL)
     rettv->vval.v_number = buf->b_fnum;
diff --git a/src/nvim/ex_cmds.c b/src/nvim/ex_cmds.c
index 97aac76860..9f781c0f8e 100644
--- a/src/nvim/ex_cmds.c
+++ b/src/nvim/ex_cmds.c
@@ -10,6 +10,9 @@
 #include <inttypes.h>
 #include <math.h>
 
+#include "nvim/api/private/defs.h"
+#include "nvim/api/buffer.h"
+#include "nvim/log.h"
 #include "nvim/vim.h"
 #include "nvim/ascii.h"
 #include "nvim/ex_cmds.h"
@@ -65,12 +68,6 @@
  */
 typedef struct sign sign_T;
 
-// boolean to know if inc_sub needs to undo
-static bool inc_sub_did_changes = false;
-
-// reuse the same bufnr for inc_sub
-static handle_T inc_sub_bufnr = 0;
-
 /// Case matching style to use for :substitute
 typedef enum {
   kSubHonorOptions = 0,  ///< Honor the user's 'ignorecase'/'smartcase' options
@@ -90,6 +87,15 @@ typedef struct {
   SubIgnoreType do_ic;  ///< ignore case flag
 } subflags_T;
 
+/// Lines matched during 'incsubstitute'.
+typedef struct {
+  linenr_T lnum;
+  long nmatch;
+  char_u *line;
+  kvec_t(colnr_T) cols;  //< columns of in-line matches
+} MatchedLine;
+typedef kvec_t(MatchedLine) MatchedLineVec;
+
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "ex_cmds.c.generated.h"
 #endif
@@ -1530,7 +1536,7 @@ int rename_buffer(char_u *new_fname)
   }
   curbuf->b_flags |= BF_NOTEDITED;
   if (xfname != NULL && *xfname != NUL) {
-    buf = buflist_new(fname, xfname, curwin->w_cursor.lnum, 0, 0);
+    buf = buflist_new(fname, xfname, curwin->w_cursor.lnum, 0);
     if (buf != NULL && !cmdmod.keepalt) {
       curwin->w_alt_fnum = buf->b_fnum;
     }
@@ -2027,37 +2033,34 @@ theend:
   return retval;
 }
 
-/*
- * start editing a new file
- *
- *     fnum: file number; if zero use ffname/sfname
- *   ffname: the file name
- *		- full path if sfname used,
- *		- any file name if sfname is NULL
- *		- empty string to re-edit with the same file name (but may be
- *		    in a different directory)
- *		- NULL to start an empty buffer
- *   sfname: the short file name (or NULL)
- *	eap: contains the command to be executed after loading the file and
- *	     forced 'ff' and 'fenc'
- *  newlnum: if > 0: put cursor on this line number (if possible)
- *	     if ECMD_LASTL: use last position in loaded file
- *	     if ECMD_LAST: use last position in all files
- *	     if ECMD_ONE: use first line
- *    flags:
- *	   ECMD_HIDE: if TRUE don't free the current buffer
- *     ECMD_SET_HELP: set b_help flag of (new) buffer before opening file
- *	 ECMD_OLDBUF: use existing buffer if it exists
- *	ECMD_FORCEIT: ! used for Ex command
- *	 ECMD_ADDBUF: don't edit, just add to buffer list
- *   oldwin: Should be "curwin" when editing a new buffer in the current
- *	     window, NULL when splitting the window first.  When not NULL info
- *	     of the previous buffer for "oldwin" is stored.
- *
- * return FAIL for failure, OK otherwise
- */
-int 
-do_ecmd (
+/// start editing a new file
+///
+/// @param fnum     file number; if zero use ffname/sfname
+/// @param ffname   the file name
+///                 - full path if sfname used,
+///                 - any file name if sfname is NULL
+///                 - empty string to re-edit with the same file name (but may
+///                   be in a different directory)
+///                 - NULL to start an empty buffer
+/// @param sfname   the short file name (or NULL)
+/// @param eap      contains the command to be executed after loading the file
+///                 and forced 'ff' and 'fenc'
+/// @param newlnum  if > 0: put cursor on this line number (if possible)
+///                 ECMD_LASTL: use last position in loaded file
+///                 ECMD_LAST: use last position in all files
+///                 ECMD_ONE: use first line
+/// @param flags    ECMD_HIDE: if TRUE don't free the current buffer
+///                 ECMD_SET_HELP: set b_help flag of (new) buffer before
+///                 opening file
+///                 ECMD_OLDBUF: use existing buffer if it exists
+///                 ECMD_FORCEIT: ! used for Ex command
+///                 ECMD_ADDBUF: don't edit, just add to buffer list
+/// @param oldwin   Should be "curwin" when editing a new buffer in the current
+///                 window, NULL when splitting the window first.  When not NULL
+///                 info of the previous buffer for "oldwin" is stored.
+///
+/// @return FAIL for failure, OK otherwise
+int do_ecmd (
     int fnum,
     char_u *ffname,
     char_u *sfname,
@@ -2182,9 +2185,10 @@ do_ecmd (
         buflist_altfpos(oldwin);
     }
 
-    if (fnum && !(flags & ECMD_RESERVED_BUFNR)) {
+    if (fnum) {
       buf = buflist_findnr(fnum);
     } else {
+      ILOG("here");
       if (flags & ECMD_ADDBUF) {
         linenr_T tlnum = 1L;
 
@@ -2193,12 +2197,11 @@ do_ecmd (
           if (tlnum <= 0)
             tlnum = 1L;
         }
-        (void)buflist_new(ffname, sfname, tlnum, BLN_LISTED, fnum);
+        (void)buflist_new(ffname, sfname, tlnum, BLN_LISTED);
         goto theend;
       }
       buf = buflist_new(ffname, sfname, 0L,
-                        BLN_CURBUF | ((flags & ECMD_SET_HELP) ? 0 : BLN_LISTED),
-                        fnum);
+                        BLN_CURBUF | ((flags & ECMD_SET_HELP) ? 0 : BLN_LISTED));
       // Autocmds may change curwin and curbuf.
       if (oldwin != NULL) {
         oldwin = curwin;
@@ -3098,16 +3101,17 @@ static char_u *sub_parse_flags(char_u *cmd, subflags_T *subflags,
   return cmd;
 }
 
-/* do_sub()
- *
- * Perform a substitution from line eap->line1 to line eap->line2 using the
- * command pointed to by eap->arg which should be of the form:
- *
- * /pattern/substitution/{flags}
- *
- * The usual escapes are supported as described in the regexp docs.
- */
-void do_sub(exarg_T *eap)
+/// do_sub()
+///
+/// Perform a substitution from line eap->line1 to line eap->line2 using the
+/// command pointed to by eap->arg which should be of the form:
+///
+/// /pattern/substitution/{flags}
+///
+/// The usual escapes are supported as described in the regexp docs.
+///
+/// @return buffer used for 'incsubstitute'
+buf_T *do_sub(exarg_T *eap)
 {
   long i = 0;
   regmmatch_T regmatch;
@@ -3123,24 +3127,22 @@ void do_sub(exarg_T *eap)
   };
   char_u *pat = NULL, *sub = NULL;  // init for GCC
   int delimiter;
+  bool has_second_delim = false;
   int sublen;
   int got_quit = false;
   int got_match = false;
   int which_pat;
   char_u *cmd = eap->arg;
   linenr_T first_line = 0;  // first changed line
-  linenr_T last_line= 0;    // below last changed line AFTER the
-                            // change
+  linenr_T last_line= 0;    // below last changed line AFTER the change
   linenr_T old_line_count = curbuf->b_ml.ml_line_count;
-  char_u      *sub_firstline;  // allocated copy of first sub line
-  bool endcolumn = false;        // cursor in last column when done
+  char_u *sub_firstline;    // allocated copy of first sub line
+  bool endcolumn = false;   // cursor in last column when done
+  MatchedLineVec matched_lines = KV_INITIAL_VALUE;
   pos_T old_cursor = curwin->w_cursor;
   int start_nsubs;
   int save_ma = 0;
 
-  inc_sub_did_changes = false;
-  bool has_second_delim = false;
-
   if (!global_busy) {
     sub_nsubs = 0;
     sub_nlines = 0;
@@ -3158,7 +3160,7 @@ void do_sub(exarg_T *eap)
     /* don't accept alphanumeric for separator */
     if (isalpha(*cmd)) {
       EMSG(_("E146: Regular expressions can't be delimited by letters"));
-      return;
+      return NULL;
     }
     /*
      * undocumented vi feature:
@@ -3169,7 +3171,7 @@ void do_sub(exarg_T *eap)
       ++cmd;
       if (vim_strchr((char_u *)"/?&", *cmd) == NULL) {
         EMSG(_(e_backslash));
-        return;
+        return NULL;
       }
       if (*cmd != '&') {
         which_pat = RE_SEARCH;              // use last '/' pattern
@@ -3217,7 +3219,7 @@ void do_sub(exarg_T *eap)
   } else if (!eap->skip) {    /* use previous pattern and substitution */
     if (old_sub.sub == NULL) {      /* there is no previous command */
       EMSG(_(e_nopresub));
-      return;
+      return NULL;
     }
     pat = NULL;                 /* search_regcomp() will use previous pattern */
     sub = (char_u *) old_sub.sub;
@@ -3228,7 +3230,7 @@ void do_sub(exarg_T *eap)
   }
 
   if (sub_joining_lines(eap, pat, sub, cmd)) {
-    return;
+    return NULL;
   }
 
   cmd = sub_parse_flags(cmd, &subflags, &which_pat);
@@ -3242,7 +3244,7 @@ void do_sub(exarg_T *eap)
     i = getdigits_long(&cmd);
     if (i <= 0 && !eap->skip && subflags.do_error) {
       EMSG(_(e_zerocount));
-      return;
+      return NULL;
     }
     eap->line1 = eap->line2;
     eap->line2 += i - 1;
@@ -3258,17 +3260,17 @@ void do_sub(exarg_T *eap)
     eap->nextcmd = check_nextcmd(cmd);
     if (eap->nextcmd == NULL) {
       EMSG(_(e_trailing));
-      return;
+      return NULL;
     }
   }
 
   if (eap->skip)            /* not executing commands, only parsing */
-    return;
+    return NULL;
 
   if (!subflags.do_count && !MODIFIABLE(curbuf)) {
     // Substitution is not allowed in non-'modifiable' buffer
     EMSG(_(e_modifiable));
-    return;
+    return NULL;
   }
 
   int search_options = eap->is_live ? 0 : SEARCH_HIS;
@@ -3277,7 +3279,7 @@ void do_sub(exarg_T *eap)
     if (subflags.do_error) {
       EMSG(_(e_invcmd));
     }
-    return;
+    return NULL;
   }
 
   // the 'i' or 'I' flag overrules 'ignorecase' and 'smartcase'
@@ -3297,9 +3299,6 @@ void do_sub(exarg_T *eap)
   if (!(sub[0] == '\\' && sub[1] == '='))
     sub = regtilde(sub, p_magic);
 
-  //  list to save matched lines
-  MatchedLineVec lmatch = KV_INITIAL_VALUE;
-
   // Check for a match on each line.
   linenr_T line2 = eap->line2;
   for (linenr_T lnum = eap->line1;
@@ -3368,7 +3367,7 @@ void do_sub(exarg_T *eap)
       copycol = 0;
       matchcol = 0;
       // the current match
-      MatchedLine cmatch = { 0, 0, NULL, KV_INITIAL_VALUE };
+      MatchedLine matched_line = { 0, 0, NULL, KV_INITIAL_VALUE };
 
       /* At first match, remember current cursor position. */
       if (!got_match) {
@@ -3405,9 +3404,9 @@ void do_sub(exarg_T *eap)
         curwin->w_cursor.lnum = lnum;
         do_again = FALSE;
 
-        // increment number of match on the line and store the column
-        cmatch.nmatch++;
-        kv_push(cmatch.start_col, regmatch.startpos[0].col);
+        // Increment the in-line match count and store the column.
+        matched_line.nmatch++;
+        kv_push(matched_line.cols, regmatch.startpos[0].col);
 
         /*
          * 1. Match empty string does not count, except for first
@@ -3627,8 +3626,8 @@ void do_sub(exarg_T *eap)
          * use "\=col("."). */
         curwin->w_cursor.col = regmatch.startpos[0].col;
 
-        // 3. Substitute the string. Don't do this while incsubstitution and
-        //    there's no word to replace by eg : ":%s/pattern"
+        // 3. Substitute the string. During 'incsubstitute' only do this if
+        //    there is a replace pattern.
         if (!eap->is_live || has_second_delim) {
           if (subflags.do_count) {
             // prevent accidentally changing the buffer by a function
@@ -3873,11 +3872,9 @@ skip:
       xfree(sub_firstline);          /* free the copy of the original line */
       sub_firstline = NULL;
 
-      // saving info about the matched line
-      cmatch.lnum = lnum;
-      cmatch.line = vim_strsave(ml_get(lnum));
-
-      kv_push(lmatch, cmatch);
+      matched_line.lnum = lnum;
+      matched_line.line = vim_strsave(ml_get(lnum));
+      kv_push(matched_lines, matched_line);
     }
 
     line_breakcheck();
@@ -3946,78 +3943,65 @@ skip:
   subflags.do_all = save_do_all;
   subflags.do_ask = save_do_ask;
 
-  // inc_sub if sub on the whole file and there are results to display
-  if (lmatch.size != 0) {
-    // we did incsubstitute only if we had no word to replace by
-    // by and no ending slash
-    if (!subflags.do_count && (!eap->is_live || has_second_delim)) {
-      inc_sub_did_changes = true;
-    }
-    if (pat != NULL && *p_ics != NUL && eap->is_live) {
-      bool split = true;
-
-      // p_ics is "", "nosplit" or "split"
-      if (*p_ics == 'n' || eap[0].cmdlinep[0][0] == 's') {
-        split = false;
-      }
-
-      // Place cursor on the first match after the cursor
-      // If all matches are before the cursor, then do_sub did
-      // already place the cursor on the last match
-
-      linenr_T cur_lnum = 0;
-      colnr_T cur_col = -1;
-      MatchedLine current;
-
-      for (size_t j = 0; j < lmatch.size; j++) {
-        current = lmatch.items[j];
-        cur_lnum = current.lnum;
-
-        // 1. Match on line of the cursor, need to iterate over the
-        //    matches on this line to see if there is one on a later
-        //    column
-        if (cur_lnum == old_cursor.lnum) {
-          for (size_t i = 0; i < current.start_col.size; i++) {
-            if (current.start_col.items[i] >= old_cursor.col) {
-              cur_col = current.start_col.items[i];
-              break;
-            }
-          }
-          // match on cursor's line, after the cursor
-          if (cur_col != -1) {
-            curwin->w_cursor.lnum = cur_lnum;
-            curwin->w_cursor.col = cur_col;
+  // Show 'incsubstitute' preview if there are matched lines.
+  buf_T *incsub_buf = NULL;
+  if (matched_lines.size != 0 && pat != NULL && *p_ics != NUL && eap->is_live) {
+    // Place cursor on the first match after the cursor.
+    // If all matches are before the cursor, then do_sub already placed the
+    // cursor on the last match.
+
+    linenr_T cur_lnum = 0;
+    colnr_T cur_col = -1;
+    MatchedLine current;
+
+    for (size_t j = 0; j < matched_lines.size; j++) {
+      current = matched_lines.items[j];
+      cur_lnum = current.lnum;
+
+      // 1. Match on line of the cursor, need to iterate over the
+      //    matches on this line to see if there is one on a later
+      //    column
+      if (cur_lnum == old_cursor.lnum) {
+        for (size_t i = 0; i < current.cols.size; i++) {
+          if (current.cols.items[i] >= old_cursor.col) {
+            cur_col = current.cols.items[i];
             break;
           }
-        // 2. Match on line after cursor, just put cursor on column
-        //    of first match there
-        } else if (cur_lnum > old_cursor.lnum) {
-            cur_col = current.start_col.items[0];
-            curwin->w_cursor.lnum = cur_lnum;
-            curwin->w_cursor.col = cur_col;
-            break;
         }
+        // match on cursor's line, after the cursor
+        if (cur_col != -1) {
+          curwin->w_cursor.lnum = cur_lnum;
+          curwin->w_cursor.col = cur_col;
+          break;
+        }
+      // 2. Match on line after cursor, just put cursor on column
+      //    of first match there
+      } else if (cur_lnum > old_cursor.lnum) {
+          cur_col = current.cols.items[0];
+          curwin->w_cursor.lnum = cur_lnum;
+          curwin->w_cursor.col = cur_col;
+          break;
       }
-
-      inc_sub_display(pat, sub, &lmatch, split);
-    } else if (*p_ics != NUL && eap->is_live) {
-      curwin->w_cursor = old_cursor;
     }
-  } else {
-    curwin->w_cursor = old_cursor;
-  }
-
-  MatchedLine current;
-  for (size_t j = 0; j < lmatch.size; j++) {
-    current = lmatch.items[j];
 
-    if (current.line) { xfree(current.line); }
+    incsub_buf = incsub_display(pat, sub, eap->line1, eap->line2,
+                                &matched_lines);
 
-    kv_destroy(current.start_col);
+  } else if (*p_ics != NUL && eap->is_live) {
+    curwin->w_cursor = old_cursor;  // don't move the cursor
   }
 
+  MatchedLine current;
+  for (size_t j = 0; j < matched_lines.size; j++) {
+    current = matched_lines.items[j];
+    if (current.line) {
+      xfree(current.line);
+    }
+    kv_destroy(current.cols);
+  }
 
-  kv_destroy(lmatch);
+  kv_destroy(matched_lines);
+  return incsub_buf;
 }  // NOLINT(readability/fn_size)
 
 /*
@@ -6058,192 +6042,143 @@ void set_context_in_sign_cmd(expand_T *xp, char_u *arg)
   }
 }
 
-/// Open a window for displaying of the inc_sub mode.
-///
-/// Does not allow editing in the window. Closes the window and restores
-/// the window layout before returning.
-///
-/// @param pat    The pattern word
-/// @param sub    The replacement word
-/// @param lmatch The list containing our data
-static void inc_sub_display(char_u *pat,
-                            char_u *sub,
-                            MatchedLineVec *lmatch,
-                            bool split)
-  FUNC_ATTR_NONNULL_ARG(1, 2, 3)
+/// Shows a preview of :substitute (for 'incsubstitute').
+/// With incsubstitute=split, shows a special buffer in a window, draws the
+/// screen, then restores the layout.
+static buf_T *incsub_display(char_u *pat, char_u *sub,
+                             linenr_T line1, linenr_T line2,
+                             MatchedLineVec *matched_lines)
+  FUNC_ATTR_NONNULL_ALL
 {
-  garray_T winsizes;
-  int save_restart_edit = restart_edit;
-  int save_State = State;
-  int save_exmode = exmode_active;
-  int save_cmdmsg_rl = cmdmsg_rl;
-
-  // Can't do this recursively.  Can't do it when typing a password.
-  if (cmdline_star > 0) {
-    beep_flush();
-    return;
-  }
-
-  // Save current window sizes.
-  win_size_save(&winsizes);
-
-  // Save the current window to restore it later
-  win_T *oldwin = curwin;
-
-  if (split) {
-    // don't use a new tab page
-    cmdmod.tab = 0;
-
-    // Create a window for the command-line buffer.
-    if (win_split((int)p_cwh, WSP_BOT) == FAIL) {
-      beep_flush();
-      return;
-    }
-    cmdwin_type = get_cmdline_type();
-
-    // Create the command-line buffer empty.
-    (void)do_ecmd(inc_sub_bufnr, NULL, NULL, NULL, ECMD_ONE,
-                  ECMD_HIDE | ECMD_RESERVED_BUFNR, NULL);
-    inc_sub_bufnr = curbuf->handle;
-    (void)setfname(curbuf, (char_u *) "[inc_sub]", NULL, true);
-    set_option_value((char_u *) "bt", 0L, (char_u *) "incsub", OPT_LOCAL);
-    set_option_value((char_u *) "swf", 0L, NULL, OPT_LOCAL);
-    curbuf->b_p_ma = false;  // Not Modifiable
+  static handle_T bufnr = 0;  // special buffer, re-used on each visit
+
+  garray_T save_winsizes;
+  win_T *save_curwin = curwin;
+  cmdmod_T save_cmdmod = cmdmod;
+  char_u *save_shm_p = vim_strsave(p_shm);
+  size_t sub_size = mb_string2cells(sub);
+  size_t pat_size = mb_string2cells(pat);
+
+  // We keep a special-purpose buffer around, but don't assume it exists.
+  buf_T *incsub_buf = bufnr ? buflist_findnr(bufnr) : 0;
+  win_size_save(&save_winsizes);  // Save current window sizes.
+  cmdmod.tab = 0;                 // disable :tab modifier
+  cmdmod.noswapfile = true;       // disable swap for 'incsubstitute' buffer
+  // disable file info message
+  set_option_value((char_u *)"shm", 0L, (char_u *)"F", 0);
+
+  bool outside_curline = (line1 != curwin->w_cursor.lnum
+                          || line2 != curwin->w_cursor.lnum);
+  bool split = outside_curline && (*p_ics != 'n') && (sub_size || pat_size);
+  if (incsub_buf == curbuf) {  // Preview buffer cannot preview itself!
+    split = false;
+    incsub_buf = NULL;
+  }
+
+  if (split && win_split((int)p_cwh, WSP_BOT) != FAIL) {
+    buf_open_special(incsub_buf ? bufnr : 0, "[inc_sub]", "incsub");
+    buf_clear();
+    incsub_buf = curbuf;
+    set_option_value((char_u *)"bl", 0L, NULL, OPT_LOCAL);
+    set_option_value((char_u *)"bh", 0L, (char_u *)"hide", OPT_LOCAL);
+    bufnr = incsub_buf->handle;
+    curbuf->b_p_ma = true;
+    curbuf->b_p_ul = -1;
     curwin->w_p_fen = false;
-    curwin->w_p_rl = cmdmsg_rl;
-    cmdmsg_rl = false;
-    RESET_BINDING(curwin);
+    curbuf->b_p_tw = 0;         // Reset 'textwidth' (was set by ftplugin)
 
-    // Showing the prompt may have set need_wait_return, reset it.
-    need_wait_return = false;
-
-    // Reset 'textwidth' after setting 'filetype'
-    // (the Vim filetype plugin sets 'textwidth' to 78).
-    curbuf->b_p_tw = 0;
-
-    // Save the buffer used in the split
-    livebuf = curbuf;
-
-    // Initialize line and highlight variables
-    int line = 0;
-    int src_id_highlight = 0;
-    long sub_size = STRLEN(sub);
-    long pat_size = STRLEN(pat);
-
-    // Get the width of the column which display the number of the line
-    linenr_T highest_num_line = kv_last(*lmatch).lnum;
-
-    // computing the length of the column that will display line number
+    // Width of the "| lnum|..." column which displays the line numbers.
+    linenr_T highest_num_line = kv_last(*matched_lines).lnum;
     int col_width = log10(highest_num_line) + 1 + 3;
 
-    // will be allocated in the loop
     char *str = NULL;
-
     size_t old_line_size = 0;
     size_t line_size;
+    int src_id_highlight = 0;
+    int hl_id = syn_check_group((char_u *)"IncSubstitute", 13);
 
-    // Append the lines to our buffer
-    for (size_t i = 0; i < (*lmatch).size; i++) {
-      MatchedLine mat = (*lmatch).items[i];
-      line_size = STRLEN(mat.line) + col_width + 1;
+    // Dump the lines into the incsub buffer.
+    for (size_t line = 0; line < matched_lines->size; line++) {
+      MatchedLine mat = matched_lines->items[line];
+      line_size = mb_string2cells(mat.line) + col_width + 1;
 
-      // Reallocation if str not long enough
+      // Reallocate if str not long enough
       if (line_size > old_line_size) {
         str = xrealloc(str, line_size * sizeof(char));
         old_line_size = line_size;
       }
 
-      // put ' [ lnum]line' into str and append it to the incsubstitute buffer
+      // put " | lnum|line" into str and append it to the incsubstitute buffer
       snprintf(str, line_size, " [%*ld]%s", col_width - 3, mat.lnum, mat.line);
-      ml_append(line++, (char_u *)str, (colnr_T)line_size, false);
+      ml_append(line, (char_u *)str, (colnr_T)line_size, false);
 
       // highlight the replaced part
       if (sub_size > 0) {
-        int hlgroup_ls = syn_check_group((char_u *)"IncSubstitute", 13);
-
-        for (size_t j = 0; j < mat.start_col.size; j++) {
-          src_id_highlight =
-          bufhl_add_hl(curbuf,
-                       src_id_highlight,
-                       hlgroup_ls,  // id of our highlight
-                       line,
-                       mat.start_col.items[j] + col_width
-                       + j * (sub_size - pat_size) + 1,
-                       mat.start_col.items[j] + col_width
-                       + j * (sub_size - pat_size) + sub_size);
+        for (size_t i = 0; i < mat.cols.size; i++) {
+          colnr_T col_start = mat.cols.items[i] + col_width
+            + i * (sub_size - pat_size) + 1;
+          colnr_T col_end = col_start - 1 + sub_size;
+          src_id_highlight = bufhl_add_hl(curbuf, src_id_highlight, hl_id,
+                                          line + 1, col_start, col_end);
         }
       }
     }
     xfree(str);
-    redraw_later(SOME_VALID);
   }
 
-  // Restore the old window
-  win_enter(oldwin, false);
-  win_size_restore(&winsizes);
-  ga_clear(&winsizes);
-  exmode_active = save_exmode;
-  restart_edit = save_restart_edit;
-  cmdmsg_rl = save_cmdmsg_rl;
-  State = save_State;
+  redraw_later(SOME_VALID);
+
+  win_enter(save_curwin, false);  // Return to original window
+  win_size_restore(&save_winsizes);
+  ga_clear(&save_winsizes);
+
+  set_option_value((char_u *)"shm", 0L, save_shm_p, 0);
+  xfree(save_shm_p);
 
-  cmdwin_type = 0;
+  // Update screen now. Must do this _before_ close_windows().
   int save_rd = RedrawingDisabled;
   RedrawingDisabled = 0;
-  update_screen(0);
+  update_screen(NOT_VALID);
   RedrawingDisabled = save_rd;
 
-  setmouse();
-}
+  cmdmod = save_cmdmod;
 
+  return incsub_buf;
+}
 
-/// :substitute command implementation
+/// :substitute command
 ///
-/// Uses do_sub() to do the actual substitution. Undoes the substitution and
-/// removes it from the undo history unless finishing the command. If
-/// ics is set to "", it just calls do_sub().
-void do_inc_sub(exarg_T *eap)
+/// If 'incsubstitute' is empty, this just calls do_sub().
+/// If 'incsubstitute' is set, substitutes as-you-type ("live").
+/// If the command is cancelled the changes are removed from undo history.
+void ex_substitute(exarg_T *eap)
 {
-  // if incsubstitute disabled, do it the classical way
-  if (*p_ics == NUL || !eap->is_live) {
-    do_sub(eap);
+  if (*p_ics == NUL || !eap->is_live) {  // 'incsubstitute' is disabled
+    (void)do_sub(eap);
     return;
   }
 
-  // Save the state of eap
-  char_u *tmp = eap->arg;
-
+  char_u *save_eap = eap->arg;
   save_search_patterns();
+  int save_changedtick = curbuf->b_changedtick;
+  long save_b_p_ul = curbuf->b_p_ul;
+  curbuf->b_p_ul = LONG_MAX;  // make sure we can undo all changes
+  block_autocmds();   // disable events before incsub opening window/buffer
+  emsg_off++;         // No error messages for live commands
 
-  // save the value of undolevels to the maximum value to avoid losing
-  // history when it is set to a low value
-  long b_p_ul_save = curbuf->b_p_ul;
-  curbuf->b_p_ul = LONG_MAX;
-
-  // Incsub window/buffer is opened in do_sub, so to suppress autocmd
-  // we need to start it before the call
-  block_autocmds();
+  buf_T *incsub_buf = do_sub(eap);
 
-  emsg_off++;  // No error messages for live commands
-  do_sub(eap);
-  emsg_off--;
-  if (inc_sub_did_changes) {
-    if (!u_undo_and_forget(1)) {
-      abort();
-    }
-    inc_sub_did_changes = false;
+  if (save_changedtick != curbuf->b_changedtick
+      && !u_undo_and_forget(1)) {
+    abort();
   }
-
-  // Put back eap in first state
-  eap->arg = tmp;
-  restore_search_patterns();
-  curbuf->b_p_ul = b_p_ul_save;
-
-  update_screen(0);
-  if (livebuf != NULL && buf_valid(livebuf)) {
-    close_windows(livebuf, false);
-    wipe_buffer(livebuf, false);
+  if (buf_valid(incsub_buf)) {
+    // XXX: Must do this *after* u_undo_and_forget(), why?
+    close_windows(incsub_buf, false);
   }
+  curbuf->b_p_ul = save_b_p_ul;
+  eap->arg = save_eap;
+  restore_search_patterns();
+  emsg_off--;
   unblock_autocmds();
-  redraw_later(SOME_VALID);
 }
diff --git a/src/nvim/ex_cmds.h b/src/nvim/ex_cmds.h
index 82848528ce..ccb2202edb 100644
--- a/src/nvim/ex_cmds.h
+++ b/src/nvim/ex_cmds.h
@@ -6,8 +6,6 @@
 #include "nvim/os/time.h"
 #include "nvim/eval_defs.h"
 #include "nvim/pos.h"
-#include "nvim/lib/klist.h"
-#include "nvim/lib/kvec.h"
 
 // flags for do_ecmd()
 #define ECMD_HIDE            0x01    // don't free the current buffer
@@ -18,6 +16,7 @@
 #define ECMD_ADDBUF          0x10    // don't edit, just add to buffer list
 #define ECMD_RESERVED_BUFNR  0x20    // bufnr argument is reserved bufnr
 
+
 /* 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 */
@@ -30,24 +29,6 @@ typedef struct {
   list_T *additional_elements;  ///< Additional data left from ShaDa file.
 } SubReplacementString;
 
-
-// Defs for inc_sub functionality
-
-/// Structure to backup and display matched lines in incsubstitution
-typedef struct {
-  linenr_T lnum;
-  long nmatch;
-  char_u *line;
-  // list of column numbers of matches on this line
-  kvec_t(colnr_T) start_col;
-} MatchedLine;
-
-// List of matched lines
-typedef kvec_t(MatchedLine) MatchedLineVec;
-
-// End defs for inc_sub functionality
-
-
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "ex_cmds.h.generated.h"
 #endif
diff --git a/src/nvim/ex_cmds.lua b/src/nvim/ex_cmds.lua
index 04fc163222..95ede4bdc5 100644
--- a/src/nvim/ex_cmds.lua
+++ b/src/nvim/ex_cmds.lua
@@ -2194,7 +2194,7 @@ return {
     command='substitute',
     flags=bit.bor(RANGE, WHOLEFOLD, EXTRA, CMDWIN),
     addr_type=ADDR_LINES,
-    func='do_inc_sub',
+    func='ex_substitute',
   },
   {
     command='sNext',
@@ -3181,7 +3181,7 @@ return {
     enum='CMD_and',
     flags=bit.bor(RANGE, WHOLEFOLD, EXTRA, CMDWIN, MODIFY),
     addr_type=ADDR_LINES,
-    func='do_sub',
+    func='ex_substitute',
   },
   {
     command='<',
@@ -3222,6 +3222,6 @@ return {
     enum='CMD_tilde',
     flags=bit.bor(RANGE, WHOLEFOLD, EXTRA, CMDWIN, MODIFY),
     addr_type=ADDR_LINES,
-    func='do_sub',
+    func='ex_substitute',
   },
 }
diff --git a/src/nvim/ex_docmd.c b/src/nvim/ex_docmd.c
index d8b92e9ec0..30347cbe85 100644
--- a/src/nvim/ex_docmd.c
+++ b/src/nvim/ex_docmd.c
@@ -1248,7 +1248,7 @@ static char_u * do_one_cmd(char_u **cmdlinep,
   memset(&ea, 0, sizeof(ea));
   ea.line1 = 1;
   ea.line2 = 1;
-  ea.is_live = flags & DOCMD_LIVE_PREVIEW;
+  ea.is_live = flags & DOCMD_LIVE;
   ex_nesting_level++;
 
   /* When the last file has not been edited :q has to be typed twice. */
@@ -9652,25 +9652,22 @@ static void ex_terminal(exarg_T *eap)
 
 /// Check whether commandline starts with a live command
 ///
-/// @param[in] cmd_live Commandline to check. May start with a range.
+/// @param[in] cmd Commandline to check. May start with a range.
 ///
 /// @return True if first command is a live command
-///         Currently :s is the only one
-bool is_live(char_u *cmd_live)
+bool cmd_is_live(char_u *cmd)
 {
-  exarg_T ea;
-  ea.cmd = cmd_live;
+  if (cmd == NULL) {
+    return false;
+  }
 
+  exarg_T ea;
   // parse the command line
-  if (ea.cmd != NULL) {
-    ea.cmd = skip_range(ea.cmd, NULL);
-    if (*ea.cmd == '*') {
-      ea.cmd = skipwhite(ea.cmd + 1);
-    }
-    find_command(&ea, NULL);
-  } else {
-    return false;
+  ea.cmd = skip_range(cmd, NULL);
+  if (*ea.cmd == '*') {
+    ea.cmd = skipwhite(ea.cmd + 1);
   }
+  find_command(&ea, NULL);
 
   return (ea.cmdidx == CMD_substitute);
 }
diff --git a/src/nvim/ex_docmd.h b/src/nvim/ex_docmd.h
index e30ece3e1b..84f1a13a15 100644
--- a/src/nvim/ex_docmd.h
+++ b/src/nvim/ex_docmd.h
@@ -10,8 +10,7 @@
 #define DOCMD_KEYTYPED  0x08      // don't reset KeyTyped
 #define DOCMD_EXCRESET  0x10      // reset exception environment (for debugging
 #define DOCMD_KEEPLINE  0x20      // keep typed line for repeating with "."
-#define DOCMD_LIVE_PREVIEW  0x40  // Command is a live preview like
-                                  // incsubstitution
+#define DOCMD_LIVE      0x40      // show updates as-you-type ("live" command)
 
 /* defines for eval_vars() */
 #define VALID_PATH              1
diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index d1a2ab8bcf..dba7a107e2 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -1591,9 +1591,12 @@ static int command_line_changed(CommandLineState *s)
     msg_starthere();
     redrawcmdline();
     s->did_incsearch = true;
-  } else if (*p_ics != NUL && s->firstc == ':' && is_live(ccline.cmdbuff)) {
-    // compute a live action
-    do_cmdline(ccline.cmdbuff, NULL, NULL, DOCMD_KEEPLINE|DOCMD_LIVE_PREVIEW);
+  } else if (s->firstc == ':'
+             && *p_ics != NUL       // 'incsubstitute' is set
+             && cmdline_star == 0   // not typing a password
+             && cmd_is_live(ccline.cmdbuff)) {
+    // process a "live" command
+    do_cmdline(ccline.cmdbuff, NULL, NULL, DOCMD_KEEPLINE|DOCMD_LIVE);
     redrawcmdline();
   }
 
@@ -5141,16 +5144,12 @@ static int ex_window(void)
   }
   cmdwin_type = get_cmdline_type();
 
-  /* Create the command-line buffer empty. */
-  (void)do_ecmd(0, NULL, NULL, NULL, ECMD_ONE, ECMD_HIDE, NULL);
-  (void)setfname(curbuf, (char_u *)"[Command Line]", NULL, TRUE);
-  set_option_value((char_u *)"bt", 0L, (char_u *)"nofile", OPT_LOCAL);
-  set_option_value((char_u *)"swf", 0L, NULL, OPT_LOCAL);
-  curbuf->b_p_ma = TRUE;
-  curwin->w_p_fen = FALSE;
+  // Create empty command-line buffer.
+  buf_open_special(0, "[Command Line]", "nofile");
   curwin->w_p_rl = cmdmsg_rl;
-  cmdmsg_rl = FALSE;
-  RESET_BINDING(curwin);
+  cmdmsg_rl = false;
+  curbuf->b_p_ma = true;
+  curwin->w_p_fen = false;
 
   /* Do execute autocommands for setting the filetype (load syntax). */
   unblock_autocmds();
diff --git a/src/nvim/fileio.c b/src/nvim/fileio.c
index 7ce2c57420..e83e9f6b01 100644
--- a/src/nvim/fileio.c
+++ b/src/nvim/fileio.c
@@ -5067,7 +5067,7 @@ void buf_reload(buf_T *buf, int orig_mode)
     savebuf = NULL;
   } else {
     // Allocate a buffer without putting it in the buffer list.
-    savebuf = buflist_new(NULL, NULL, (linenr_T)1, BLN_DUMMY, 0);
+    savebuf = buflist_new(NULL, NULL, (linenr_T)1, BLN_DUMMY);
     if (savebuf != NULL && buf == curbuf) {
       /* Open the memline. */
       curbuf = savebuf;
@@ -6409,8 +6409,9 @@ win_found:
           && curbuf != aco->new_curbuf
           && buf_valid(aco->new_curbuf)
           && aco->new_curbuf->b_ml.ml_mfp != NULL) {
-        if (curwin->w_s == &curbuf->b_s)
+        if (curwin->w_s == &curbuf->b_s) {
           curwin->w_s = &aco->new_curbuf->b_s;
+        }
         --curbuf->b_nwindows;
         curbuf = aco->new_curbuf;
         curwin->w_buffer = curbuf;
diff --git a/src/nvim/globals.h b/src/nvim/globals.h
index a5188e98d7..690be70c4d 100644
--- a/src/nvim/globals.h
+++ b/src/nvim/globals.h
@@ -603,7 +603,6 @@ EXTERN int redraw_tabline INIT(= FALSE);           /* need to redraw tabline */
 EXTERN buf_T    *firstbuf INIT(= NULL);  // first buffer
 EXTERN buf_T    *lastbuf INIT(= NULL);   // last buffer
 EXTERN buf_T    *curbuf INIT(= NULL);    // currently active buffer
-EXTERN buf_T    *livebuf INIT(= NULL);   // buffer used for live actions
 
 // Iterates over all buffers in the buffer list.
 # define FOR_ALL_BUFFERS(buf) for (buf_T *buf = firstbuf; buf != NULL; buf = buf->b_next)
diff --git a/src/nvim/mark.c b/src/nvim/mark.c
index 96983a6c3b..6453c41415 100644
--- a/src/nvim/mark.c
+++ b/src/nvim/mark.c
@@ -474,7 +474,7 @@ static void fname2fnum(xfmark_T *fm)
     p = path_shorten_fname(NameBuff, IObuff);
 
     // buflist_new() will call fmarks_check_names()
-    (void)buflist_new(NameBuff, p, (linenr_T)1, 0, 0);
+    (void)buflist_new(NameBuff, p, (linenr_T)1, 0);
   }
 }
 
diff --git a/src/nvim/memline.c b/src/nvim/memline.c
index 5505335769..a9a53ebca7 100644
--- a/src/nvim/memline.c
+++ b/src/nvim/memline.c
@@ -2340,14 +2340,13 @@ int ml_replace(linenr_T lnum, char_u *line, int copy)
   return OK;
 }
 
-/*
- * Delete line 'lnum' in the current buffer.
- *
- * Check: The caller of this function should probably also call
- * deleted_lines() after this.
- *
- * return FAIL for failure, OK otherwise
- */
+/// Delete line `lnum` in the current buffer.
+///
+/// @note The caller of this function should probably also call
+/// deleted_lines() after this.
+///
+/// @param message  Show "--No lines in buffer--" message.
+/// @return FAIL for failure, OK otherwise
 int ml_delete(linenr_T lnum, int message)
 {
   ml_flush_line(curbuf);
diff --git a/src/nvim/quickfix.c b/src/nvim/quickfix.c
index 97172a15ff..f23037613b 100644
--- a/src/nvim/quickfix.c
+++ b/src/nvim/quickfix.c
@@ -3327,7 +3327,7 @@ load_dummy_buffer (
   aco_save_T aco;
 
   // Allocate a buffer without putting it in the buffer list.
-  newbuf = buflist_new(NULL, NULL, (linenr_T)1, BLN_DUMMY, 0);
+  newbuf = buflist_new(NULL, NULL, (linenr_T)1, BLN_DUMMY);
   if (newbuf == NULL) {
     return NULL;
   }
diff --git a/src/nvim/shada.c b/src/nvim/shada.c
index 1cd8f44ea8..01c0807d82 100644
--- a/src/nvim/shada.c
+++ b/src/nvim/shada.c
@@ -1405,7 +1405,7 @@ static void shada_read(ShaDaReadDef *const sd_reader, const int flags)
               cur_entry.data.buffer_list.buffers[i].fname);
           buf_T *const buf = buflist_new(
               cur_entry.data.buffer_list.buffers[i].fname, sfname, 0,
-              BLN_LISTED, 0);
+              BLN_LISTED);
           if (buf != NULL) {
             RESET_FMARK(&buf->b_last_cursor,
                         cur_entry.data.buffer_list.buffers[i].pos, 0);
diff --git a/src/nvim/syntax.c b/src/nvim/syntax.c
index a1c6718b06..68d0e3da0f 100644
--- a/src/nvim/syntax.c
+++ b/src/nvim/syntax.c
@@ -7160,16 +7160,13 @@ int syn_namen2id(char_u *linep, int len)
  */
 int syn_check_group(char_u *pp, int len)
 {
-  int id;
-  char_u  *name;
-
-  name = vim_strnsave(pp, len);
-
-  id = syn_name2id(name);
-  if (id == 0)                          /* doesn't exist yet */
+  char_u  *name = vim_strnsave(pp, len);
+  int id = syn_name2id(name);
+  if (id == 0) {  // doesn't exist yet
     id = syn_add_group(name);
-  else
+  } else {
     xfree(name);
+  }
   return id;
 }
 
diff --git a/src/nvim/undo.c b/src/nvim/undo.c
index a4af45d441..20adf40012 100644
--- a/src/nvim/undo.c
+++ b/src/nvim/undo.c
@@ -1685,7 +1685,7 @@ void u_redo(int count)
   u_doit(count, false);
 }
 
-/// undo and forget.
+/// undo, and remove the undo branch from the undo tree.
 bool u_undo_and_forget(int count)
 {
   if (curbuf->b_u_synced == false) {
@@ -1726,9 +1726,7 @@ bool u_undo_and_forget(int count)
   return true;
 }
 
-/*
- * Undo or redo, depending on 'undo_undoes', 'count' times.
- */
+/// Undo or redo, depending on `undo_undoes`, `count` times.
 static void u_doit(int startcount, bool quiet)
 {
   int count = startcount;
@@ -2342,17 +2340,13 @@ static void u_undoredo(int undo)
 #endif
 }
 
-/*
- * If we deleted or added lines, report the number of less/more lines.
- * Otherwise, report the number of changes (this may be incorrect
- * in some cases, but it's better than nothing).
- */
-static void
-u_undo_end(
-    int did_undo,                   // just did an undo
-    int absolute,                   // used ":undo N"
-    bool quiet
-)
+/// If we deleted or added lines, report the number of less/more lines.
+/// Otherwise, report the number of changes (this may be incorrect
+/// in some cases, but it's better than nothing).
+static void u_undo_end(
+    int did_undo,     //< just did an undo
+    int absolute,     //< used ":undo N"
+    bool quiet)
 {
   char        *msgstr;
   u_header_T  *uhp;
@@ -2361,9 +2355,9 @@ u_undo_end(
   if ((fdo_flags & FDO_UNDO) && KeyTyped)
     foldOpenCursor();
 
-  if (global_busy           // no messages now, wait until global is finished
-      || !messaging()       // 'lazyredraw' set, don't do messages now
-      || quiet) {  // livemode doesn't show messages
+  if (quiet
+      || global_busy        // no messages until global is finished
+      || !messaging()) {    // 'lazyredraw' set, don't do messages now
     return;
   }
 
diff --git a/src/nvim/window.c b/src/nvim/window.c
index 45b52e9454..8512556c0a 100644
--- a/src/nvim/window.c
+++ b/src/nvim/window.c
@@ -2903,7 +2903,7 @@ static int win_alloc_firstwin(win_T *oldwin)
   if (oldwin == NULL) {
     /* Very first window, need to create an empty buffer for it and
      * initialize from scratch. */
-    curbuf = buflist_new(NULL, NULL, 1L, BLN_LISTED, 0);
+    curbuf = buflist_new(NULL, NULL, 1L, BLN_LISTED);
     if (curbuf == NULL) {
       return FAIL;
     }