vim-patch:8.0.1767: with 'incsearch' text may jump up and down

Problem:    With 'incsearch' text may jump up and down. ()
Solution:   Besides w_botline also save and restore w_empty_rows.
            (closes # 2530)
9d34d90210

src/nvim/ex_getln.c

@@ -161,6 +161,8 @@ typedef struct command_line_state {
   int       init_topfill;
   linenr_T  old_botline;
   linenr_T  init_botline;
+  int       old_empty_rows;
+  int       init_empty_rows;
   pos_T     match_start;
   pos_T     match_end;
   int did_incsearch;
@@ -253,6 +255,7 @@ static uint8_t *command_line_enter(int firstc, long count, int indent)
   s->init_topline = curwin->w_topline;
   s->init_topfill = curwin->w_topfill;
   s->init_botline = curwin->w_botline;
+  s->init_empty_rows = curwin->w_empty_rows;
 
   if (s->firstc == -1) {
     s->firstc = NUL;
@@ -275,6 +278,7 @@ static uint8_t *command_line_enter(int firstc, long count, int indent)
   s->old_topline = curwin->w_topline;
   s->old_topfill = curwin->w_topfill;
   s->old_botline = curwin->w_botline;
+  s->old_empty_rows = curwin->w_empty_rows;
 
   assert(indent >= 0);
 
@@ -449,6 +453,7 @@ static uint8_t *command_line_enter(int firstc, long count, int indent)
     curwin->w_topline = s->old_topline;
     curwin->w_topfill = s->old_topfill;
     curwin->w_botline = s->old_botline;
+    curwin->w_empty_rows = s->old_empty_rows;
     highlight_match = false;
     validate_cursor();          // needed for TAB
     redraw_all_later(SOME_VALID);
@@ -1118,6 +1123,7 @@ static void command_line_next_incsearch(CommandLineState *s, bool next_match)
     s->old_topline = curwin->w_topline;
     s->old_topfill = curwin->w_topfill;
     s->old_botline = curwin->w_botline;
+    s->old_empty_rows = curwin->w_empty_rows;
     update_screen(NOT_VALID);
     redrawcmdline();
   } else {
@@ -1243,6 +1249,7 @@ static int command_line_handle_key(CommandLineState *s)
         s->old_topline = s->init_topline;
         s->old_topfill = s->init_topfill;
         s->old_botline = s->init_botline;
+        s->old_empty_rows = s->init_empty_rows;
       }
       redrawcmd();
     } else if (ccline.cmdlen == 0 && s->c != Ctrl_W
@@ -1876,6 +1883,7 @@ static int command_line_changed(CommandLineState *s)
     curwin->w_topline = s->old_topline;
     curwin->w_topfill = s->old_topfill;
     curwin->w_botline = s->old_botline;
+    curwin->w_empty_rows = s->old_empty_rows;
     changed_cline_bef_curs();
     update_topline();
 

src/nvim/testdir/test_search.vim

@@ -1,6 +1,7 @@
 " Test for the search command
 
 source shared.vim
+source screendump.vim
 
 func Test_search_cmdline()
   " See test/functional/legacy/search_spec.lua
@@ -549,6 +550,36 @@ func Test_incsearch_with_change()
   call delete('Xis_change_script')
 endfunc
 
+func Test_incsearch_scrolling()
+  if !CanRunVimInTerminal()
+    return
+  endif
+  call assert_equal(0, &scrolloff)
+  call writefile([
+	\ 'let dots = repeat(".", 120)',
+	\ 'set incsearch cmdheight=2 scrolloff=0',
+	\ 'call setline(1, [dots, dots, dots, "", "target", dots, dots])',
+	\ 'normal gg',
+	\ 'redraw',
+	\ ], 'Xscript')
+  let buf = RunVimInTerminal('-S Xscript', {'rows': 9, 'cols': 70})
+  " Need to send one key at a time to force a redraw
+  call term_sendkeys(buf, '/')
+  sleep 100m
+  call term_sendkeys(buf, 't')
+  sleep 100m
+  call term_sendkeys(buf, 'a')
+  sleep 100m
+  call term_sendkeys(buf, 'r')
+  sleep 100m
+  call term_sendkeys(buf, 'g')
+  call VerifyScreenDump(buf, 'Test_incsearch_scrolling_01', {})
+
+  call term_sendkeys(buf, "\<Esc>")
+  call StopVimInTerminal(buf)
+  call delete('Xscript')
+endfunc
+
 func Test_search_undefined_behaviour()
   if !has("terminal")
     return