patch 8.1.1959: when using "firstline" in popup window text may jump

Problem:    When using "firstline" in popup window text may jump when
            redrawing it. (Nick Jensen)
Solution:   Set 'scrolloff' to zero in a popup window. (closes #4882)

src/popupwin.c

@@ -1687,11 +1687,12 @@ popup_create(typval_T *argvars, typval_T *rettv, create_type_T type)
 	buf->b_p_swf = FALSE;   // no swap file
 	buf->b_p_bl = FALSE;    // unlisted buffer
 	buf->b_locked = TRUE;
-	wp->w_p_wrap = TRUE;	// 'wrap' is default on
 
 	// Avoid that 'buftype' is reset when this buffer is entered.
 	buf->b_p_initialized = TRUE;
     }
+    wp->w_p_wrap = TRUE;	// 'wrap' is default on
+    wp->w_p_so = 0;		// 'scrolloff' zero
 
     if (tp != NULL)
     {

src/testdir/dumps/Test_popupwin_scroll_5.dump

@@ -1,10 +1,10 @@
 >1+0&#ffffff0| @73
 |2| @73
 |3| @73
-|4| @31|f+0#0000001#ffd7ff255|o|u|r| @3| +0#0000000#ff404010| +0&#ffffff0@32
+|4| @31|t+0#0000001#ffd7ff255|h|r|e@1| @2| +0#0000000#ff404010| +0&#ffffff0@32
-|5| @31|f+0#0000001#ffd7ff255|i|v|e| @3| +0#0000000#4040ff13| +0&#ffffff0@32
+|5| @31|f+0#0000001#ffd7ff255|o|u|r| @3| +0#0000000#4040ff13| +0&#ffffff0@32
-|6| @31|s+0#0000001#ffd7ff255|i|x| @4| +0#0000000#4040ff13| +0&#ffffff0@32
+|6| @31|f+0#0000001#ffd7ff255|i|v|e| @3| +0#0000000#4040ff13| +0&#ffffff0@32
-|7| @31|s+0#0000001#ffd7ff255|e|v|e|n| @2| +0#0000000#ff404010| +0&#ffffff0@32
+|7| @31|s+0#0000001#ffd7ff255|i|x| @4| +0#0000000#ff404010| +0&#ffffff0@32
 |8| @73
 |9| @73
 |:|c|a|l@1| |S|c|r|o|l@1|U|p|(|)| @40|1|,|1| @10|T|o|p| 

src/testdir/dumps/Test_popupwin_scroll_6.dump

@@ -1,10 +1,10 @@
 >1+0&#ffffff0| @73
 |2| @73
 |3| @73
-|4| @31|s+0#0000001#ffd7ff255|i|x| @4| +0#0000000#ff404010| +0&#ffffff0@32
+|4| @31|f+0#0000001#ffd7ff255|i|v|e| @3| +0#0000000#ff404010| +0&#ffffff0@32
-|5| @31|s+0#0000001#ffd7ff255|e|v|e|n| @2| +0#0000000#ff404010| +0&#ffffff0@32
+|5| @31|s+0#0000001#ffd7ff255|i|x| @4| +0#0000000#ff404010| +0&#ffffff0@32
-|6| @31|e+0#0000001#ffd7ff255|i|g|h|t| @2| +0#0000000#4040ff13| +0&#ffffff0@32
+|6| @31|s+0#0000001#ffd7ff255|e|v|e|n| @2| +0#0000000#4040ff13| +0&#ffffff0@32
-|7| @31|n+0#0000001#ffd7ff255|i|n|e| @3| +0#0000000#4040ff13| +0&#ffffff0@32
+|7| @31|e+0#0000001#ffd7ff255|i|g|h|t| @2| +0#0000000#4040ff13| +0&#ffffff0@32
 |8| @73
 |9| @73
 |:|c|a|l@1| |S|c|r|o|l@1|D|o|w|n|(|)| @38|1|,|1| @10|T|o|p| 

src/testdir/test_popupwin.vim

@@ -371,6 +371,24 @@ func Test_popup_firstline()
   call popup_close(winid)
 endfunc
 
+func Test_popup_noscrolloff()
+  set scrolloff=5
+  let winid = popup_create(['xxx']->repeat(50), #{
+	\ maxheight: 5,
+	\ firstline: 11,
+	\ })
+  redraw
+  call assert_equal(11, popup_getoptions(winid).firstline)
+  call assert_equal(11, popup_getpos(winid).firstline)
+
+  call popup_setoptions(winid, #{firstline: 0})
+  call win_execute(winid, "normal! \<c-y>")
+  call assert_equal(0, popup_getoptions(winid).firstline)
+  call assert_equal(10, popup_getpos(winid).firstline)
+
+  call popup_close(winid)
+endfunc
+
 func Test_popup_drag()
   CheckScreendump
 
@@ -1019,14 +1037,18 @@ func Test_popup_option_values()
   " global/buffer-local
   setlocal path=/there
   " global/window-local
-  setlocal scrolloff=9
+  setlocal statusline=2
 
   let winid = popup_create('hello', {})
   call assert_equal(0, getwinvar(winid, '&number'))
   call assert_equal(1, getwinvar(winid, '&wrap'))
   call assert_equal('', getwinvar(winid, '&omnifunc'))
   call assert_equal(&g:path, getwinvar(winid, '&path'))
-  call assert_equal(&g:scrolloff, getwinvar(winid, '&scrolloff'))
+  call assert_equal(&g:statusline, getwinvar(winid, '&statusline'))
+
+  " 'scrolloff' is reset to zero
+  call assert_equal(5, &scrolloff)
+  call assert_equal(0, getwinvar(winid, '&scrolloff'))
 
   call popup_close(winid)
   bwipe
@@ -1713,6 +1735,7 @@ func Test_popup_scrollbar()
   call VerifyScreenDump(buf, 'Test_popupwin_scroll_4', {})
 
   call term_sendkeys(buf, ":call popup_setoptions(winid, #{scrollbarhighlight: 'ScrollBar', thumbhighlight: 'ScrollThumb', firstline: 5})\<CR>")
+  " this scrolls two lines (half the window height)
   call term_sendkeys(buf, ":call ScrollUp()\<CR>")
   call VerifyScreenDump(buf, 'Test_popupwin_scroll_5', {})
 

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1959,
 /**/
     1958,
 /**/