fix(options): fix some 'belloff' flags not working properly (#30856)

Problem:  Some 'belloff' flags don't work properly.
Solution: Keep BO_ flags and p_bo_values[] in sync.

src/nvim/optionstr.c

@@ -72,8 +72,8 @@ static char *(p_ambw_values[]) = { "single", "double", NULL };
 static char *(p_bg_values[]) = { "light", "dark", NULL };
 static char *(p_bkc_values[]) = { "yes", "auto", "no", "breaksymlink", "breakhardlink", NULL };
 static char *(p_bo_values[]) = { "all", "backspace", "cursor", "complete", "copy", "ctrlg", "error",
-                                 "esc", "ex", "hangul", "lang", "mess", "showmatch", "operator",
-                                 "register", "shell", "spell", "wildmode", NULL };
+                                 "esc", "ex", "hangul", "insertmode", "lang", "mess", "showmatch",
+                                 "operator", "register", "shell", "spell", "wildmode", NULL };
 // Note: Keep this in sync with briopt_check()
 static char *(p_briopt_values[]) = { "shift:", "min:", "sbr", "list:", "column:", NULL };
 // Note: Keep this in sync with diffopt_changed()

test/functional/options/belloff_spec.lua

@@ -0,0 +1,79 @@
+local t = require('test.testutil')
+local n = require('test.functional.testnvim')()
+local Screen = require('test.functional.ui.screen')
+
+local clear = n.clear
+local command = n.command
+local api = n.api
+local feed = n.feed
+local poke_eventloop = n.poke_eventloop
+local eq = t.eq
+local retry = t.retry
+
+describe("'belloff'", function()
+  local screen
+
+  before_each(function()
+    clear()
+    screen = Screen.new(42, 5)
+    screen:attach()
+    screen:expect([[
+      ^                                          |
+      {1:~                                         }|*3
+                                                |
+    ]])
+  end)
+
+  it('various flags work properly', function()
+    command('set cpoptions+=E')
+
+    local map = {
+      backspace = 'i<BS><Esc>',
+      cursor = 'i<Up><Esc>',
+      copy = 'i<C-Y><Esc>',
+      ctrlg = 'i<C-G><C-G><Esc>',
+      error = 'J',
+      esc = '<Esc>',
+      operator = 'y0',
+      register = 'i<C-R>@<Esc>',
+    }
+
+    local items = {} ---@type string[]
+    local inputs = {} ---@type string[]
+    for item, input in pairs(map) do
+      table.insert(items, item)
+      table.insert(inputs, input)
+    end
+
+    local values = {} ---@type string[]
+    for i, _ in ipairs(items) do
+      -- each tested 'belloff' value enables at most one item
+      local parts = vim.deepcopy(items)
+      table.remove(parts, i)
+      local value = table.concat(parts, ',')
+      table.insert(values, value)
+    end
+    table.insert(values, 'all')
+
+    for i, value in ipairs(values) do
+      api.nvim_set_option_value('belloff', value, {})
+
+      for j, input in ipairs(inputs) do
+        screen.bell = false
+        local beep = value ~= 'all' and i == j
+        -- Nvim avoids beeping more than 3 times in half a second,
+        -- so retry if beeping is expected but not received.
+        retry(not beep and 1 or nil, 1000, function()
+          feed(input)
+          poke_eventloop()
+          screen:expect({
+            condition = function()
+              eq(beep, screen.bell, ('%s with belloff=%s'):format(items[j], value))
+            end,
+            unchanged = not beep,
+          })
+        end)
+      end
+    end
+  end)
+end)