patch 8.0.1441: using ":undo 0" leaves undo in wrong state

Problem:    Using ":undo 0" leaves undo in wrong state.
Solution:   Instead of searching for state 1 and go above, just use the start.
            (Ozaki Kiichi, closes #2595)

src/testdir/test_undo.vim

@@ -359,3 +359,47 @@ func Test_undo_append()
   norm o
   quit
 endfunc
+
+func Test_undo_0()
+  new
+  set ul=100
+  normal i1
+  undo
+  normal i2
+  undo
+  normal i3
+
+  undo 0
+  let d = undotree()
+  call assert_equal('', getline(1))
+  call assert_equal(0, d.seq_cur)
+
+  redo
+  let d = undotree()
+  call assert_equal('3', getline(1))
+  call assert_equal(3, d.seq_cur)
+
+  undo 2
+  undo 0
+  let d = undotree()
+  call assert_equal('', getline(1))
+  call assert_equal(0, d.seq_cur)
+
+  redo
+  let d = undotree()
+  call assert_equal('2', getline(1))
+  call assert_equal(2, d.seq_cur)
+
+  undo 1
+  undo 0
+  let d = undotree()
+  call assert_equal('', getline(1))
+  call assert_equal(0, d.seq_cur)
+
+  redo
+  let d = undotree()
+  call assert_equal('1', getline(1))
+  call assert_equal(1, d.seq_cur)
+
+  bwipe!
+endfunc

src/undo.c

@@ -2272,7 +2272,7 @@ undo_time(
     long	    closest_start;
     long	    closest_seq = 0;
     long	    val;
-    u_header_T	    *uhp;
+    u_header_T	    *uhp = NULL;
     u_header_T	    *last;
     int		    mark;
     int		    nomark;
@@ -2295,13 +2295,6 @@ undo_time(
      * Init "closest" to a value we can't reach. */
     if (absolute)
     {
-	if (step == 0)
-	{
-	    /* target 0 does not exist, got to 1 and above it. */
-	    target = 1;
-	    above = TRUE;
-	}
-	else
 	target = step;
 	closest = -1;
     }
@@ -2369,6 +2362,10 @@ undo_time(
     closest_start = closest;
     closest_seq = curbuf->b_u_seq_cur;
 
+    /* When "target" is 0; Back to origin. */
+    if (target == 0)
+	goto found;
+
     /*
      * May do this twice:
      * 1. Search for "target", update "closest" to the best match found.
@@ -2494,8 +2491,9 @@ undo_time(
 	    above = TRUE;	/* stop above the header */
     }
 
+found:
     /* If we found it: Follow the path to go to where we want to be. */
-    if (uhp != NULL)
+    if (uhp != NULL || target == 0)
     {
 	/*
 	 * First go up the tree as much as needed.
@@ -2510,14 +2508,18 @@ undo_time(
 		uhp = curbuf->b_u_newhead;
 	    else
 		uhp = uhp->uh_next.ptr;
-	    if (uhp == NULL || uhp->uh_walk != mark
+	    if (uhp == NULL || (target > 0 && uhp->uh_walk != mark)
 					 || (uhp->uh_seq == target && !above))
 		break;
 	    curbuf->b_u_curhead = uhp;
 	    u_undoredo(TRUE);
+	    if (target > 0)
 		uhp->uh_walk = nomark;	/* don't go back down here */
 	}
 
+	/* When back to origin, redo is not needed. */
+	if (target > 0)
+	{
 	    /*
 	     * And now go down the tree (redo), branching off where needed.
 	     */
@@ -2549,7 +2551,8 @@ undo_time(
 		    if (last->uh_alt_next.ptr != NULL)
 			last->uh_alt_next.ptr->uh_alt_prev.ptr =
 							last->uh_alt_prev.ptr;
-		last->uh_alt_prev.ptr->uh_alt_next.ptr = last->uh_alt_next.ptr;
+		    last->uh_alt_prev.ptr->uh_alt_next.ptr =
+							last->uh_alt_next.ptr;
 		    last->uh_alt_prev.ptr = NULL;
 		    last->uh_alt_next.ptr = uhp;
 		    uhp->uh_alt_prev.ptr = last;
@@ -2594,6 +2597,7 @@ undo_time(
 		}
 	    }
 	}
+    }
     u_undo_end(did_undo, absolute);
 }
 

src/version.c

@@ -771,6 +771,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1441,
 /**/
     1440,
 /**/