patch 8.2.4555: getmousepos() returns the wrong column

Problem:    getmousepos() returns the wrong column. (Ernie Rael)
Solution:   Limit to the text size, not the number of bytes.

src/mouse.c

@@ -3099,17 +3099,14 @@ f_getmousepos(typval_T *argvars UNUSED, typval_T *rettv)
 	    col -= left_off;
 	    if (row >= 0 && row < wp->w_height && col >= 0 && col < wp->w_width)
 	    {
-		char_u	*p;
 		int	count;
 
 		mouse_comp_pos(wp, &row, &col, &line, NULL);
 
-		// limit to text length plus one
-		p = ml_get_buf(wp->w_buffer, line, FALSE);
-		count = (int)STRLEN(p);
+		// limit to text size plus one
+		count = linetabsize(ml_get_buf(wp->w_buffer, line, FALSE));
 		if (col > count)
 		    col = count;
-
 		column = col + 1;
 	    }
 	}

src/testdir/test_functions.vim

@@ -2750,6 +2750,32 @@ func Test_getcurpos_setpos()
   call assert_equal([0, 0, 0, 0, 0], getcurpos(1999))
 endfunc
 
+func Test_getmousepos()
+  enew!
+  call setline(1, "\t\t\t1234")
+  call test_setmouse(1, 25)
+  call assert_equal(#{
+        \ screenrow: 1,
+        \ screencol: 25,
+        \ winid: win_getid(),
+        \ winrow: 1,
+        \ wincol: 25,
+        \ line: 1,
+        \ column: 25,
+        \ }, getmousepos())
+  call test_setmouse(1, 50)
+  call assert_equal(#{
+        \ screenrow: 1,
+        \ screencol: 50,
+        \ winid: win_getid(),
+        \ winrow: 1,
+        \ wincol: 50,
+        \ line: 1,
+        \ column: 29,
+        \ }, getmousepos())
+  bwipe!
+endfunc
+
 " Test for glob()
 func Test_glob()
   call assert_equal('', glob(test_null_string()))

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4555,
 /**/
     4554,
 /**/