patch 9.0.1610: display is wrong when 'smoothscroll' is setv9.0.1610

Problem:    Display is wrong when 'smoothscroll' is set and scrolling multiple
            lines.
Solution:   Redraw with UPD_NOT_VALID when "skipcol" is or was set.
            (closes #12490, closes #12468)

6 files changed, 26 insertions, 12 deletions

diff --git a/src/move.c b/src/move.c
index e021d71c59..4cd4d1c2bc 100644
--- a/src/move.c
+++ b/src/move.c
@@ -1786,7 +1786,6 @@ scrollup(
 	int	    width1 = curwin->w_width - curwin_col_off();
 	int	    width2 = width1 + curwin_col_off2();
 	int	    size = 0;
-	linenr_T    prev_topline = curwin->w_topline;
 	colnr_T	    prev_skipcol = curwin->w_skipcol;
 
 	if (do_sms)
@@ -1850,10 +1849,9 @@ scrollup(
 	    }
 	}
 
-	// TODO: is comparing w_topline with prev_topline still needed?
-	if (curwin->w_topline == prev_topline
-		|| curwin->w_skipcol != prev_skipcol)
-	    // need to redraw because wl_size of the topline may now be invalid
+	if (prev_skipcol > 0 || curwin->w_skipcol > 0)
+	    // need to redraw more, because wl_size of the (new) topline may
+	    // now be invalid
 	    redraw_later(UPD_NOT_VALID);
     }
     else
diff --git a/src/testdir/dumps/Test_smooth_multi_skipcol_1.dump b/src/testdir/dumps/Test_smooth_multi_skipcol_1.dump
index 80f563b715..f642e9263a 100644
--- a/src/testdir/dumps/Test_smooth_multi_skipcol_1.dump
+++ b/src/testdir/dumps/Test_smooth_multi_skipcol_1.dump
@@ -2,8 +2,8 @@
 | +0&&@39
 |a@39
 @10| @29
-@40
-@40
+|a@39
+@10| @29
 @40
 @40
 |b@2| @36
diff --git a/src/testdir/dumps/Test_smooth_multi_skipcol_2.dump b/src/testdir/dumps/Test_smooth_multi_skipcol_2.dump
index 9ef4aaf789..7431351c78 100644
--- a/src/testdir/dumps/Test_smooth_multi_skipcol_2.dump
+++ b/src/testdir/dumps/Test_smooth_multi_skipcol_2.dump
@@ -1,6 +1,6 @@
 |<+0#4040ff13#ffffff0@2|a+8#0000000&@5>a| @29
-| +0&&@39
-@40
+|a+0&&@39
+@10| @29
 @40
 @40
 |b@2| @36
diff --git a/src/testdir/dumps/Test_smooth_multi_skipcol_3.dump b/src/testdir/dumps/Test_smooth_multi_skipcol_3.dump
new file mode 100644
index 0000000000..a79f3fe633
--- /dev/null
+++ b/src/testdir/dumps/Test_smooth_multi_skipcol_3.dump
@@ -0,0 +1,10 @@
+|<+0#4040ff13#ffffff0@2|a+8#0000000&@5>a| @29
+| +0&&@39
+@40
+|b@2| @36
+|c@2| @36
+|~+0#4040ff13&| @38
+|~| @38
+|~| @38
+|~| @38
+| +0#0000000&@21|4|,|5|0| @9|B|o|t| 
diff --git a/src/testdir/test_scroll_opt.vim b/src/testdir/test_scroll_opt.vim
index 3806486bf6..f8b4b4f09e 100644
--- a/src/testdir/test_scroll_opt.vim
+++ b/src/testdir/test_scroll_opt.vim
@@ -798,10 +798,11 @@ func Test_smoothscroll_multi_skipcol()
 
   let lines =<< trim END
       setlocal cursorline scrolloff=0 smoothscroll
-      call setline(1, repeat([''], 9))
+      call setline(1, repeat([''], 8))
       call setline(3, repeat('a', 50))
-      call setline(8, 'bbb')
-      call setline(9, 'ccc')
+      call setline(4, repeat('a', 50))
+      call setline(7, 'bbb')
+      call setline(8, 'ccc')
       redraw
   END
   call writefile(lines, 'XSmoothMultiSkipcol', 'D')
@@ -811,6 +812,9 @@ func Test_smoothscroll_multi_skipcol()
   call term_sendkeys(buf, "3\<C-E>")
   call VerifyScreenDump(buf, 'Test_smooth_multi_skipcol_2', {})
 
+  call term_sendkeys(buf, "2\<C-E>")
+  call VerifyScreenDump(buf, 'Test_smooth_multi_skipcol_3', {})
+
   call StopVimInTerminal(buf)
 endfunc
 
diff --git a/src/version.c b/src/version.c
index 1288490670..a8f2104698 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@ static char *(features[]) =
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1610,
+/**/
     1609,
 /**/
     1608,