terminal: disable 'scrolloff' (fixes flicker)

Besides the special-case in get_scrolloff_value(), it makes sense for
'scrolloff' and 'sidescrolloff' to reflect the correct values (for
plugins, scripts, …).

ref 53d607af9c53accfd634435908fb79061f1212b9
ref #11915
ref #12230

runtime/doc/nvim_terminal_emulator.txt

@@ -50,6 +50,13 @@ mode" in a normal buffer, such as |i| or |:startinsert|. In this mode all keys
 except <C-\><C-N> are sent to the underlying program. Use <C-\><C-N> to return
 to normal-mode. |CTRL-\_CTRL-N|
 
+Terminal-mode forces these local options:
+
+    'nocursorline'
+    'nocursorcolumn'
+    'scrolloff' = 0
+    'sidescrolloff' = 0
+
 Terminal-mode has its own |:tnoremap| namespace for mappings, this can be used
 to automate any terminal interaction.
 

src/nvim/terminal.c

@@ -343,12 +343,16 @@ void terminal_enter(void)
   RedrawingDisabled = false;
 
   // Disable these options in terminal-mode. They are nonsense because cursor is
-  // placed at end of buffer to "follow" output.
+  // placed at end of buffer to "follow" output. #11072
   win_T *save_curwin = curwin;
   int save_w_p_cul = curwin->w_p_cul;
   int save_w_p_cuc = curwin->w_p_cuc;
+  long save_w_p_so = curwin->w_p_so;
+  long save_w_p_siso = curwin->w_p_siso;
   curwin->w_p_cul = false;
   curwin->w_p_cuc = false;
+  curwin->w_p_so = 0;
+  curwin->w_p_siso = 0;
 
   adjust_topline(s->term, buf, 0);  // scroll to end
   // erase the unfocused cursor
@@ -370,6 +374,8 @@ void terminal_enter(void)
   if (save_curwin == curwin) {  // save_curwin may be invalid (window closed)!
     curwin->w_p_cul = save_w_p_cul;
     curwin->w_p_cuc = save_w_p_cuc;
+    curwin->w_p_so = save_w_p_so;
+    curwin->w_p_siso = save_w_p_siso;
   }
 
   // draw the unfocused cursor

test/functional/terminal/buffer_spec.lua

@@ -17,6 +17,18 @@ describe(':terminal buffer', function()
     screen = thelpers.screen_setup()
   end)
 
+  it('terminal-mode forces various options', function()
+    feed([[<C-\><C-N>]])
+    command('setlocal cursorline cursorcolumn scrolloff=4 sidescrolloff=7')
+    eq({ 1, 1, 4, 7 }, eval('[&l:cursorline, &l:cursorcolumn, &l:scrolloff, &l:sidescrolloff]'))
+    eq('n', eval('mode()'))
+
+    -- Enter terminal-mode ("insert" mode in :terminal).
+    feed('i')
+    eq('t', eval('mode()'))
+    eq({ 0, 0, 0, 0 }, eval('[&l:cursorline, &l:cursorcolumn, &l:scrolloff, &l:sidescrolloff]'))
+  end)
+
   describe('when a new file is edited', function()
     before_each(function()
       feed('<c-\\><c-n>:set bufhidden=wipe<cr>:enew<cr>')