patch 8.2.2324: not easy to get mark en cursor posotion by character count

Problem:    Not easy to get mark en cursor posotion by character count.
Solution:   Add functions that use character index. (Yegappan Lakshmanan,
            closes #7648)

src/eval.c

@@ -5053,6 +5053,61 @@ string2float(
 }
 #endif
 
+/*
+ * Convert the specified byte index of line 'lnum' in buffer 'buf' to a
+ * character index.  Works only for loaded buffers. Returns -1 on failure.
+ * The index of the first character is one.
+ */
+    int
+buf_byteidx_to_charidx(buf_T *buf, int lnum, int byteidx)
+{
+    char_u	*str;
+
+    if (buf == NULL || buf->b_ml.ml_mfp == NULL)
+	return -1;
+
+    if (lnum > buf->b_ml.ml_line_count)
+	lnum = buf->b_ml.ml_line_count;
+
+    str = ml_get_buf(buf, lnum, FALSE);
+    if (str == NULL)
+	return -1;
+
+    if (*str == NUL)
+	return 1;
+
+    return mb_charlen_len(str, byteidx + 1);
+}
+
+/*
+ * Convert the specified character index of line 'lnum' in buffer 'buf' to a
+ * byte index.  Works only for loaded buffers. Returns -1 on failure. The index
+ * of the first byte and the first character is one.
+ */
+    int
+buf_charidx_to_byteidx(buf_T *buf, int lnum, int charidx)
+{
+    char_u	*str;
+    char_u	*t;
+
+    if (buf == NULL || buf->b_ml.ml_mfp == NULL)
+	return -1;
+
+    if (lnum > buf->b_ml.ml_line_count)
+	lnum = buf->b_ml.ml_line_count;
+
+    str = ml_get_buf(buf, lnum, FALSE);
+    if (str == NULL)
+	return -1;
+
+    // Convert the character offset to a byte offset
+    t = str;
+    while (*t != NUL && --charidx > 0)
+	t += mb_ptr2len(t);
+
+    return t - str + 1;
+}
+
 /*
  * Translate a String variable into a position.
  * Returns NULL when there is an error.
@@ -5061,7 +5116,8 @@ string2float(
 var2fpos(
     typval_T	*varp,
     int		dollar_lnum,	// TRUE when $ is last line
-    int		*fnum)		// set to fnum for '0, 'A, etc.
+    int		*fnum,		// set to fnum for '0, 'A, etc.
+    int		charcol)	// return character column
 {
     char_u		*name;
     static pos_T	pos;
@@ -5083,7 +5139,10 @@ var2fpos(
 	pos.lnum = list_find_nr(l, 0L, &error);
 	if (error || pos.lnum <= 0 || pos.lnum > curbuf->b_ml.ml_line_count)
 	    return NULL;	// invalid line number
-	len = (long)STRLEN(ml_get(pos.lnum));
+	if (charcol)
+	    len = (long)mb_charlen(ml_get(pos.lnum));
+	else
+	    len = (long)STRLEN(ml_get(pos.lnum));
 
 	// Get the column number
 	// We accept "$" for the column number: last column.
@@ -5118,18 +5177,29 @@ var2fpos(
     if (name == NULL)
 	return NULL;
     if (name[0] == '.')				// cursor
-	return &curwin->w_cursor;
+    {
+	pos = curwin->w_cursor;
+	if (charcol)
+	    pos.col = buf_byteidx_to_charidx(curbuf, pos.lnum, pos.col) - 1;
+	return &pos;
+    }
     if (name[0] == 'v' && name[1] == NUL)	// Visual start
     {
 	if (VIsual_active)
-	    return &VIsual;
-	return &curwin->w_cursor;
+	    pos = VIsual;
+	else
+	    pos = curwin->w_cursor;
+	if (charcol)
+	    pos.col = buf_byteidx_to_charidx(curbuf, pos.lnum, pos.col) - 1;
+	return &pos;
     }
     if (name[0] == '\'')			// mark
     {
 	pp = getmark_buf_fnum(curbuf, name[1], FALSE, fnum);
 	if (pp == NULL || pp == (pos_T *)-1 || pp->lnum <= 0)
 	    return NULL;
+	if (charcol)
+	    pp->col = buf_byteidx_to_charidx(curbuf, pp->lnum, pp->col) - 1;
 	return pp;
     }
 
@@ -5164,7 +5234,10 @@ var2fpos(
 	else
 	{
 	    pos.lnum = curwin->w_cursor.lnum;
-	    pos.col = (colnr_T)STRLEN(ml_get_curline());
+	    if (charcol)
+		pos.col = (colnr_T)mb_charlen(ml_get_curline());
+	    else
+		pos.col = (colnr_T)STRLEN(ml_get_curline());
 	}
 	return &pos;
     }
@@ -5184,7 +5257,8 @@ list2fpos(
     typval_T	*arg,
     pos_T	*posp,
     int		*fnump,
-    colnr_T	*curswantp)
+    colnr_T	*curswantp,
+    int		charcol)
 {
     list_T	*l = arg->vval.v_list;
     long	i = 0;
@@ -5216,6 +5290,18 @@ list2fpos(
     n = list_find_nr(l, i++, NULL);	// col
     if (n < 0)
 	return FAIL;
+    // If character position is specified, then convert to byte position
+    if (charcol)
+    {
+	buf_T	*buf;
+
+	// Get the text for the specified line in a loaded buffer
+	buf = buflist_findnr(fnump == NULL ? curbuf->b_fnum : *fnump);
+	if (buf == NULL || buf->b_ml.ml_mfp == NULL)
+	    return FAIL;
+
+	n = buf_charidx_to_byteidx(buf, posp->lnum, n);
+    }
     posp->col = n;
 
     n = list_find_nr(l, i, NULL);	// off