patch 8.1.0998: getcurpos() unexpectedly changes "curswant"

Problem:    getcurpos() unexpectedly changes "curswant".
Solution:   Save and restore "curswant". (closes #4069)

Author: brammool

src/evalfunc.c

@@ -5474,9 +5474,23 @@ getpos_both(
 							      (varnumber_T)0);
 	if (getcurpos)
 	{
+	    int	    save_set_curswant = curwin->w_set_curswant;
+	    colnr_T save_curswant = curwin->w_curswant;
+	    colnr_T save_virtcol = curwin->w_virtcol;
+
 	    update_curswant();
 	    list_append_number(l, curwin->w_curswant == MAXCOL ?
 		    (varnumber_T)MAXCOL : (varnumber_T)curwin->w_curswant + 1);
+
+	    // Do not change "curswant", as it is unexpected that a get
+	    // function has a side effect.
+	    if (save_set_curswant)
+	    {
+		curwin->w_set_curswant = save_set_curswant;
+		curwin->w_curswant = save_curswant;
+		curwin->w_virtcol = save_virtcol;
+		curwin->w_valid &= ~VALID_VIRTCOL;
+	    }
 	}
     }
     else

src/testdir/test_visual.vim

@@ -1,8 +1,4 @@
 " Tests for various Visual mode.
-if !has('visual')
-  finish
-endif
-
 
 func Test_block_shift_multibyte()
   " Uses double-wide character.
@@ -397,3 +393,14 @@ func Test_Visual_paragraph_textobject()
 
   bwipe!
 endfunc
+
+func Test_curswant_not_changed()
+  new
+  call setline(1, ['one', 'two'])
+  au InsertLeave * call getcurpos()
+  call feedkeys("gg0\<C-V>jI123 \<Esc>j", 'xt')
+  call assert_equal([0, 2, 1, 0, 1], getcurpos())
+
+  bwipe!
+  au! InsertLeave
+endfunc

src/version.c

@@ -779,6 +779,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    998,
 /**/
     997,
 /**/