Added strdisplaywidth() function.

runtime/doc/eval.txt

@@ -1910,6 +1910,7 @@ sqrt( {expr}			Float	squar root of {expr}
 str2float( {expr})		Float	convert String to Float
 str2nr( {expr} [, {base}])	Number	convert String to Number
 strchars( {expr})		Number	character length of the String {expr}
+strdisplaywidth( {expr} [, {col}]) Number display length of the String {expr}
 strftime( {format}[, {time}])	String	time in specified format
 stridx( {haystack}, {needle}[, {start}])
 				Number	index of {needle} in {haystack}
@@ -5368,7 +5369,17 @@ strchars({expr})					*strchars()*
 		The result is a Number, which is the number of characters
 		String {expr} occupies.  Composing characters are counted
 		separately.
-		Also see |strlen()| and |strwidth()|.
+		Also see |strlen()|, |strdisplaywidth()| and |strwidth()|.
+
+strdisplaywidth({expr}[, {col}])			*strdisplaywidth()*
+		The result is a Number, which is the number of display cells
+		String {expr} occupies on the screen.
+		When {col} is omitted zero is used.  Otherwise it is the
+		screen column where to start.  This matters for Tab
+		characters.
+		When {expr} contains characters with East Asian Width Class
+		Ambiguous, this function's return value depends on 'ambiwidth'.
+		Also see |strlen()|, |strwidth()| and |strchars()|.
 
 strftime({format} [, {time}])				*strftime()*
 		The result is a String, which is a formatted date and time, as
@@ -5432,7 +5443,8 @@ strlen({expr})	The result is a Number, which is the length of the String
 <
 		If the argument is a Number it is first converted to a String.
 		For other types an error is given.
-		Also see |len()|, |strchars()| and |strwidth()|.
+		Also see |len()|, |strchars()|, |strdisplaywidth()| and
+		|strwidth()|.
 
 strpart({src}, {start}[, {len}])			*strpart()*
 		The result is a String, which is part of {src}, starting from
@@ -5478,10 +5490,10 @@ strtrans({expr})					*strtrans()*
 strwidth({expr})					*strwidth()*
 		The result is a Number, which is the number of display cells
 		String {expr} occupies.  A Tab character is counted as one
-		cell (on the screen it depends on the position).
+		cell, alternatively use |strdisplaywidth()|.
 		When {expr} contains characters with East Asian Width Class
 		Ambiguous, this function's return value depends on 'ambiwidth'.
-		Also see |strlen()| and |strchars()|.
+		Also see |strlen()|, |strdisplaywidth()| and |strchars()|.
 
 submatch({nr})						*submatch()*
 		Only for an expression in a |:substitute| command.  Returns

src/charset.c

@@ -839,14 +839,25 @@ win_chartabsize(wp, p, col)
 #endif
 
 /*
- * return the number of characters the string 's' will take on the screen,
- * taking into account the size of a tab
+ * Return the number of characters the string 's' will take on the screen,
+ * taking into account the size of a tab.
  */
     int
 linetabsize(s)
     char_u	*s;
 {
-    colnr_T	col = 0;
+    return linetabsize_col(0, s);
+}
+
+/*
+ * Like linetabsize(), but starting at column "startcol".
+ */
+    int
+linetabsize_col(startcol, s)
+    int		startcol;
+    char_u	*s;
+{
+    colnr_T	col = startcol;
 
     while (*s != NUL)
 	col += lbr_chartabsize_adv(&s, col);

src/eval.c

@@ -710,6 +710,7 @@ static void f_strlen __ARGS((typval_T *argvars, typval_T *rettv));
 static void f_strpart __ARGS((typval_T *argvars, typval_T *rettv));
 static void f_strridx __ARGS((typval_T *argvars, typval_T *rettv));
 static void f_strtrans __ARGS((typval_T *argvars, typval_T *rettv));
+static void f_strdisplaywidth __ARGS((typval_T *argvars, typval_T *rettv));
 static void f_strwidth __ARGS((typval_T *argvars, typval_T *rettv));
 static void f_submatch __ARGS((typval_T *argvars, typval_T *rettv));
 static void f_substitute __ARGS((typval_T *argvars, typval_T *rettv));
@@ -7859,6 +7860,7 @@ static struct fst
 #endif
     {"str2nr",		1, 2, f_str2nr},
     {"strchars",	1, 1, f_strchars},
+    {"strdisplaywidth",	1, 2, f_strdisplaywidth},
 #ifdef HAVE_STRFTIME
     {"strftime",	1, 2, f_strftime},
 #endif
@@ -16804,6 +16806,23 @@ f_strchars(argvars, rettv)
 #endif
 }
 
+/*
+ * "strdisplaywidth()" function
+ */
+    static void
+f_strdisplaywidth(argvars, rettv)
+    typval_T	*argvars;
+    typval_T	*rettv;
+{
+    char_u	*s = get_tv_string(&argvars[0]);
+    int		col = 0;
+
+    if (argvars[1].v_type != VAR_UNKNOWN)
+	col = get_tv_number(&argvars[1]);
+
+    rettv->vval.v_number = (varnumber_T)(linetabsize_col(col, s));
+}
+
 /*
  * "strwidth()" function
  */

src/proto/charset.pro

@@ -15,6 +15,7 @@ int vim_strsize __ARGS((char_u *s));
 int vim_strnsize __ARGS((char_u *s, int len));
 int chartabsize __ARGS((char_u *p, colnr_T col));
 int linetabsize __ARGS((char_u *s));
+int linetabsize_col __ARGS((int startcol, char_u *s));
 int win_linetabsize __ARGS((win_T *wp, char_u *p, colnr_T len));
 int vim_isIDc __ARGS((int c));
 int vim_iswordc __ARGS((int c));